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May 1999
Construction Mechanic
Basic, Volume 2
DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.
Although the words “he,” “him,” and
“his” are used sparingly in this course to
enhance communication, they are not
intended to be gender driven or to affront or
discriminate against anyone.
DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.
By enrolling in this self-study course, you have demonstrated a desire to improve yourself and the Navy.
Remember, however, this self-study course is only one part of the total Navy training program. Practical
experience, schools, selected reading, and your desire to succeed are also necessary to successfully round
out a fully meaningful training program.
THE COURSE: This self-study course is organized into subject matter areas, each containing learning
objectives to help you determine what you should learn along with text and illustrations to help you
understand the information. The subject matter reflects day-to-day requirements and experiences of
personnel in the rating or skill area. It also reflects guidance provided by Enlisted Community Managers
(ECMs) and other senior personnel, technical references, instructions, etc., and either the occupational or
naval standards, which are listed in the Manual of Navy Enlisted Manpower Personnel Classifications
and Occupational Standards, NAVPERS 18068.
THE QUESTIONS: The questions that appear in this course are designed to help you understand the
material in the text.
VALUE: In completing this course, you will improve your military and professional knowledge.
Importantly, it can also help you study for the Navy-wide advancement in rate examination. If you are
studying and discover a reference in the text to another publication for further information, look it up.
1999 Edition Prepared by
CMC(SCW) Charles Lathan
Published by
NAVSUP Logistics Tracking Number
Sailor’s Creed
“I am a United States Sailor.
I will support and defend the
Constitution of the United States of
America and I will obey the orders
of those appointed over me.
I represent the fighting spirit of the
Navy and those who have gone
before me to defend freedom and
democracy around the world.
I proudly serve my country’s Navy
combat team with honor, courage
and commitment.
I am committed to excellence and
the fair treatment of all.”
Basic Automotive Electricity . . . . . . . . . . . . . . . . . . . . 1-1
Automotive Electrical Circuits and Wiring . . . . . . . . . . . . . 2-1
Hydraulic and Pneumatic Systems. . . . . . . . . . . . . . . . . . 3-1
Automotive Clutches, Transmissions, and Transaxles. . . . . . . . 4-1
Drive Lines, Differentials, Drive Axles, and Power Train
Accessories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
Construction Equipment Power Trains . . . . . . . . . . . . . . . 6-1
Brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1
Automotive Chassis and Body . . . . . . . . . . . . . . . . . . . 8-1
Glossary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AI-1
References Used to Develop This TRAMAN . . . . . . . . . . . AII-1
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INDEX-l
The Nonresident Training Course (NRTC) follows the Index
Construction Mechanic Basic, Volume 1, NAVEDTRA 14264, consists of
chapters on Technical Administration; Principles of an Internal Combustion
Engine; Construction of an Internal Combustion Engine; Gasoline Fuel Systems;
Diesel Fuel Systems; and Cooling and Lubricating Systems.
Construction Mechanic Basic, Volume 2, NAVEDTRA 14273, consists of
chapters on Basic Automotive Electricity; Automotive Electrical Circuits and
Wiring; Hydraulic and Pneumatic Systems; Automotive Clutches, Transmissions,
and Transaxles; Drive Lines, Differentials, Drive Axles, and Power Train
Accessories; Construction Equipment Power Trains; Brakes; and Automotive
Chassis and Body.
Safety is a paramount concern for all personnel. Many of the Naval Ship’s
Technical Manuals, manufacturer's technical manuals, and every Planned
Maintenance System (PMS) maintenance requirement card (MRC) include safety
precautions. Additionally, OPNAVINST 5100.19 (series), Naval Occupational
Safety and Health (NAVOSH) Program Manual for Forces Afloat, and
OPNAVINST 5100.23 (series), NAVOSH Program Manual, provide safety and
occupational health information. The safety precautions are for your protection and
to protect equipment. Cautions and warnings of potentially hazardous situations or
conditions are highlighted, where needed, in each chapter of this TRAMAN.
Remember to be safety conscious at all times.
During equipment operation and preventive or corrective maintenance, the
procedures may call for personal protective equipment (PPE), such as goggles,
gloves, safety shoes, hard hats, hearing protection, and respirators. When specified,
use of PPE is mandatory. You must select PPE appropriate for the job since the
equipment is manufactured and approved for different levels of protection. Most
machinery, spaces, and tools requiring you to wear hearing protection are posted
with hazardous noise signs or labels. Eye hazardous areas requiring you to wear
goggles or safety glasses are also posted. In areas where corrosive chemicals are
mixed or used, an emergency eyewash station must be installed. Anytime a
procedure does not specify the PPE, and you are not sure, ask your safety officer.
All lubricating agents, oil, cleaning material, and chemicals used in
maintenance and repair are hazardous materials. Examples of hazardous materials
are gasoline, coal distillates, and asphalt. Gasoline contains a small amount of lead
and other toxic compounds. Ingestion of gasoline can cause lead poisoning. Coal
distillates, such as benzene or naphthalene in benzol, are suspected carcinogens.
Avoid all skin contact and do not inhale the vapors and gases from these distillates.
Asphalt contains components suspected of causing cancer. Anyone handling
asphalt must be trained to handle it in a safe manner.
Hazardous materials require careful handling, storage, and disposal.
OPNAVINST 4110.2 (series), Hazardous Material Control and Management,
contains detailed information on the hazardous material program. Additionally,
PMS documentation provides hazard warnings or refers the maintenance man to the
Hazardous Materials User’s Guide. Material Safety Data Sheets (MSDS) also
provide safety precautions for hazardous materials. All commands are required to
have an MSDS for each hazardous material they have in their inventory; therefore,
additional information is available from your command’s Hazardous Material
Recent legislation and updated Navy directives implemented tighter constraints
on environmental pollution and hazardous waste disposal. OPNAVINST 5090.1
(series), Environmental and Natural Resources Program Manual, provides detailed
information. Your command must comply with federal, state, and local
environmental regulations during any type of construction or demolition. Your
supervisor will provide training on environmental compliance.
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In completing this nonresident training course,
you will demonstrate a knowledge of the subject
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Electricity; Automotive Electrical Circuits and
Wiring; Hydraulic and Pneumatic Systems;
Automotive Clutches, Transmissions, and
Transaxles; Drive Lines, Differentials, Drive
Axles, and Power Train Accessories;
Construction Equipment Power Trains; Brakes;
and Automotive Chassis and Body.
We value your suggestions, questions, and
criticisms on our courses. If you would like to
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Course Title:
Construction Mechanic Basic, Volume 2
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NETPDTC 1550/41 (Rev 4-00)
All matter, regardless of state (solids, liquids, and
gases), is made up of tiny particles, known as atoms.
Atoms combine in small groups of two or more to form
molecules; however, when atoms are divided, smaller
particles are created. These particles have positive or
negative electrical charges.
Learning Objective: Describe the basic principles of
electrical and magnetic theory. Identify the materials,
the devices, and the different types of electrical
circuits. Determine electrical measurements using
Ohm’s law.
The basic principles of automotive electricity are
the essential knowledge required by the mechanic to
understand the operation of all-automotive electrical
systems and components. Unless you have a clear
understanding of these fundamental principles, you
will find it difficult to service the various electrical
components and systems encountered in the Naval
Construction Force (NCF). This understanding will
enable you to make sound decisions in the
troubleshooting process of all electrical systems.
There are over 100 different basic materials in the
universe. These basic materials are called elements.
Iron is one element; copper, aluminum, oxygen,
hydrogen, and mercury are examples of elements. The
basic particles that make up all the elements, and thus
the entire universe, are called protons, electrons, and
neutrons. A proton is the basic particle having a single
positive charge; therefore, a group ofprotons produces a
positive electrical charge. An electron is the basic
particle having a single negative charge; therefore, a
group of electrons produces a negative electrical charge.
A neutron is the basic particle having no charge;
therefore, a group of neutrons would have no charge.
Learning Objective: State the basic principles of
electricity, the theory of electricity, and the composition
of electricity and matter.
The construction of atoms of the various elements
can be examined starting with the simplest of
all—hydrogen. The atom of hydrogen consists of one
proton, around which is circling one electron (fig. 1-1).
There is an attraction between the two particles,
because negative and positive electrical charges
always attract each other. Opposing the attraction
between the two particles, and thus preventing the
All activity that takes place in any type of electrical
circuit depends on the behavior of tiny electrical
charges, called electrons. To understand the behavior
of electrons, we must investigate the composition of
matter. The electron is one of the basic electrical
components of all matter.
Figure 1-1.—Composition of matter.
electrons in that they can be moved readily from their
electron from moving into the proton, is the centrifugal
force on the electron caused by its circular path around
the proton. This same sort of balance is produced if a
ball tied to string was whirled in a circle in the air. The
centrifugal force exerted tries to move the ball out of its
circular path and is balanced by the string (the
attractive force). If the string should break, the
centrifugal force would cause the ball to fly away.
Actually, this is what happens at times with atoms. The
attractive force between the electron and proton
sometimes is not great enough to hold the electron in its
circular path and the electron breaks away.
If a point that has an excess of electrons (negative)
is connected to a point that has a shortage of electrons
(positive), a flow of electrons (electrical current) will
flow through the connector (conductor) until an equal
amount of electrical charge exists between the two
A charge of electricity is formed when numerous
electrons break free of their atoms and gather in one
area. When the electrons begin to move in one
direction (as along a wire, for example), the effect is a
flow of electricity or an electric current. Actually,
electric generators and batteries could be called
electron pumps, because they remove electrons from
one part of an electric circuit and concentrate them in
another part of the circuit. For example, a generator
takes electrons away from the positive terminal and
concentrates them at the negative terminal. Because
the electrons repel each other (like electrical charges
repel), the electrons push out through the circuit and
flow to the positive terminal (unlike electrical charges
attract). Thus we can see that an electric current is
actually a flow of electrons from a negative terminal to
a positive terminal.
In an atom, unlike electrical charges attract and
like electrical charges repel each other. Electrons repel
electrons and protons repel protons, except when
neutrons are present. Though neutrons have no
electrical charge, they do have the ability to cancel out
the repelling forces between protons in an atomic
nucleus and thus hold the nucleus together.
When there are more than two electrons in an
atom, they move about the nucleus in different orbits
(fig. 1-2) which are referred to as shells. The innermost
shells of the atom contain electrons that are not easily
freed and are referred to as bound electrons. The
outermost shell will contain what is referred to as free
electrons. These free electrons differ from bound
Figure 1-2.—Composition of electricity.
keep the electric current from taking a shorter route
instead of going to the intended component. The
electrical properties of a substance depend mainly on
the number of electrons in the outermost shell of each
atom. The maximum number of electrons in an outer
shell is eight. When there are less than four electrons in
the outer shell of an atom, these electrons will tend to
be free. This condition allows the free motion of
electrons, making the substance a conductor (fig. 1-3).
Q1. How many basic materials are in the universe?
What three basic particles make up all elements?
Q3. Electrons that have like charges perform what
Q4. Scientists discovered that electron flow in an
automotive electrical circuit flow in what
Electrical energy is transferred through conductors by means of the movement of free electrons
that migrate from atom to atom within the conductor.
Each electron moves a short distance to the
neighboring atom where it replaces one or more
electrons by forcing them out of their orbits. The
replaced electrons repeat this process in nearby atoms
until the movement is transmitted throughout the entire
length of the conductor, thus creating a current flow.
Copper is an example of a good conductor because it
only has one free electron. This electron is not held
very strongly in its orbit and can break away from the
nucleus very easily. Silver is a better conductor of
electricity but it is too expensive to be used in any great
quantity. Because of this, copper is the conductor used
most widely in automotive applications.
Any material that will allow an electrical current
to flow through it is an electrical conductor. Any
material that blocks electrical current flow is an
electrical insulator. Conductors are used in automotive
equipment to carry electric current to all of the
electrical equipment. Insulators also are necessary to
Whenever there are more than four electrons in the
outer orbits of the atoms of a substance, these electrons
will tend to be bound, causing restriction of free
electron movement, making it an insulator (fig. 1-3).
Common insulating substances in automotive
applications are rubber, plastic, and fiberboard.
Learning Objective: Explain the elements involved in
electrical current flow and describe the material and
devices in use.
It has been proved that electrons (negative
charges) move through a conductor in response to an
electric field. “Electric current” is defined as the
directed flow of electrons and the direction of electron
movement is from a region of negative potential to a
region of positive potential. Therefore, electric current
can be said to flow from negative to positive.
Figure 1-3.—Conductors and insulators.
gives each atom eight electrons in its outer orbit,
making the orbit complete. This makes the material an
insulator because it contains more than four electrons
in its outer orbit. When certain materials, such as
phosphorus, are added to the silicon crystal in highly
controlled amounts, the resultant mixture becomes a
conductor (fig. 1-5). This is because phosphorus,
which has five electrons in forming a covalent bond
with silicon (which has four electrons in its outer
shell), will yield one free electron per molecule, thus
making the material an electrical conductor. The
process of adding impurities to a semiconductor is
called doping. Any semiconductor material that is
doped to yield free electrons is called N-type material.
A semiconductor is an electrical device that acts as
a conductor under certain conditions and as a
nonconductor under other conditions. The most
popular of all semiconductors is silicon. In its pure
state, silicon is neither a good conductor nor insulator.
But by processing silicon in the following ways, its
conductive or insulative properties can be adjusted to
suit just about any need. When a number of silicon
atoms are jammed together in crystalline (glasslike)
form, they form a covalent (sharing) bond. Therefore,
the electrons in the outer ring of one silicon atom join
with the outer ring of other silicon atoms, resulting in a
sharing of outer ring electrons between all of the
atoms. It can be seen in figure 1-4 that covalent sharing
When boron, which has three electrons in its outer
ring, is used to dope the silicon crystal, the resultant
Figure 1-4.—Covalent bonding of silicon.
Figure l-5.-Phosphorus-doped silicon.
When a source voltage, such as a battery, is
connected to N-type material, an electric current will
flow through it, as shown in figure 1-7. The current flow
in the N-type semiconductor consists of the movement
of free electrons, the same as the current flow through a
natural conductor, such as copper. When a current
source of sufficient voltage is connected across a P-type
material, an electric current will also flowthrough it, but
any current flow in a P-type semiconductor is looked
upon as the movement of positively charged holes. The
holes appear to move toward the negative terminal, as
the electrons enter the material at the negative terminal,
fill the holes, and then move from hole to hole toward
the positive terminal. As is the case with the N-type
semiconductors, the movement of electrons through
P-type semiconductors toward the positive terminal is
motivated by the natural attraction of unlike charges.
covalent bonding yields seven electrons in the outer
shell. This leaves an opening for another electron and
is shown in figure 1-6. This space is called a hole and
can be considered a positive charge, just as the extra
electrons that exist in N-type semiconductor material
are considered a negative charge. Materials that have
holes in their outermost electron shells are called
positive or P-type materials. To understand the
behavior of P-type semiconductors, it is necessary to
look upon the hole as a positive current carrier, just as
the free electron in N-type semiconductors are
considered negative current carriers. Just as electrons
move through N-type semiconductors, holes move
from atom to atom in P-type semiconductors.
Movement of holes through P-type semiconductors,
however, is from the positive terminal to the negative
terminal. For this reason, any circuit analysis of solidstate circuitry is done on the basis of positive to
negative (conventional) current flow.
Figure 1-6.—Boron-doped silicone.
Figure 1-7.—Hole movement theory.
increases to 6 volts or more, the diode suddenly will
begin to conduct reverse bias current. This device is
used in control circuits, such as voltage regulators.
A diode (fig. 1-8) is a device that will allow current
to pass through itself in only one direction. A diode can
be thought of as an electrical check valve. Diodes are
constructed by joining N-type material and P-type
material together. The negative electrical terminal is
located on the N-type material and the positive
terminal is located on the P-type material.
A transistor (fig. 1-10) is an electrical device that is
used in circuits to control the flow of current. It
operates by either allowing current to flow or not
allowing it to flow. Transistors operate electronically
and have no moving parts to perform their function.
This design allows for a longer operating life of the
component. The major automotive applications of
transistors are for electronic ignition systems and
voltage regulators.
When a diode is placed in a circuit, the N-material is
connected to the negative side of the circuit and the
positive side of the circuit is connected to the P-material.
In this configuration, which is known as forward bias,
the diode is a good conductor. This is because the
positively charged holes in the P-type material move
toward the junction and fill these holes using them to
move across the P-material. If the connections to the
diodes are reversed, current flow will be blocked. This
design is known as reverse bias. When the diode is
connected backwards, the positively charged holes are
attracted away from the junction to the negative
terminal and the free electrons in the N-material are
attracted away from the junction to the positive
terminal. Without the presence of holes at the junction,
the electrons are not able to cross it.
The PNP transistor (fig. 1-11) is the most common
design in automotive applications. It is manufactured
by sandwiching an N-type semiconductor element
between two P-type semiconductor elements. A
positive charge is applied to one of the P-type
elements. This element is called the emitter. The other
P-type element connects to the electrical component.
This element is called the collector. The third element,
which is in the middle, is made of N-type material and
is called the base. The application of low current
negative charge to the base will allow a heavy current
to flow between the emitter and the collector.
Whenever the current to the base is switched off, the
current flow from the emitter to the collector is
interrupted also.
Zener Diodes
A zener diode (fig. 1-9) is a special type of diode
that conducts current in the reverse direction as long as
the voltage is above a predetermined value that is built
into the device during manufacturing. For instance, a
certain zener diode may not conduct current if the
reverse bias voltage is below 6 volts. As the voltage
The NPN transistor (fig. 1-11) is similar to the PNP
transistor. The difference is that it is used in the
negative side of the circuit. As the term NPN implies,
Figure 1-8.—Diode operation.
Figure 1-9.—Zener diode operation.
Figure 1-10.—Transistor configurations.
Figure 1-11.—Transistor operation.
the makeup of this transistor is two elements of N-type
material (collector and emitter) with an element of
P-type material (base) sandwiched in between. The
NPN transistor will allow a high current negative
charge to flow from the collector to the emitter
whenever a relatively low current positive charge is
applied to the base.
Q 1 . What material allows electric current to flow?
Q2. Name two electrical components that use
Q3. What is the basic difference in operation
between a diode and a transistor?
electrons at the positive terminal), there is a much
stronger repelling force on the electrons; consequently, many more electrons are moving in the
wire. This is exactly the same as saying that the higher
the voltage, the more the electric current will flow in a
circuit, all other things, such as resistance, being equal.
Learning Objective: Determine voltage, amperage,
and resistance. Explain Ohm’s law and describe the
types of electrical circuits used in vehicles.
Electricity is measured in two ways—by the
amount of current (number of electrons) flowing and
by the push, or pressure, that causes current to flow.
The push, or pressure, is caused by actions of the
electrons. They repel each other. When electrons are
concentrated in one place, their negative charges push
against each other. If a path is provided for the
electrons, they will flow away from the area where
they are concentrated.
Current flow, or electron flow, is measured in
amperes. While we normally consider that one ampere is a
rather small current of electricity (approximately what a
100-watt light bulb would draw), it is actually a
tremendous flow of electrons. More than 6 billion
electrons a second are required to make up one ampere.
The pressure to make them move is called voltage.
If there are many electrons concentrated in one spot,
we say that there is high voltage. With high voltage,
many electrons will flow, provided there is a path or
conductor through which they can flow. The more
electrons that flow, the greater the electric current.
Electric current is measured in amperes. Resistance is
the movement of electrons through a substance.
Resistance is a fact of life in electric circuits. We want
resistance in some circuits so that too much current
(too many electrons) will not flow. In other circuits, we
want as little resistance as possible so that high current
can flow.
A copper wire conducts electricity with relative
ease; however, it offers resistance to electron flow.
This resistance is caused by the energy required to free
the outer shell of electrons and the collision between
the atoms of the conductor and the free electrons. It
takes electromotive force (emf) or voltage to
overcome the resistance met by the flowing electrons.
The basic unit of resistance is the ohm. The resistance
of a conductor varies with its length, diameter,
composition, and temperature. A long wire offers more
resistance than a short wire of the same diameter; this is
due to the electrons having farther to travel. Some
materials can lose electrons more readily than others.
Copper loses electrons easily, so there are always
many free electrons in a copper wire. Other materials,
such as iron, do not lose their electrons as easily, so
there are fewer free electrons in an iron wire. However,
fewer electrons can push through an iron wire; that is,
the iron wire has more resistance than the copper wire.
A wire with a small diameter offers more resistance
than a wire with a large diameter. In the small diameter
wire, there are fewer free electrons, and thus fewer
electrons can push through. Most metals show an
increase in resistance with an increase in temperature,
while most nonmetals show a decrease in resistance
with an increase in temperature.
There is a definite relation between current
(electron flow), voltage (current pressure), and
resistance. As the electric pressure goes up, more
electrons flow. Increasing the voltage increases the
amperes ofcurrent. However, increasing the resistance
decreases the amount of current that flows. These
relationships can be summed up in a statement known
as Ohm's law.
Electrons are caused to flow by a difference in
electron balance in a circuit; that is, when there are
more electrons in one part of a circuit than in the other,
the electrons move from the area where they are
concentrated to the area they are lacking. This
difference in electron concentration is called potential
difference, or voltage. The higher the voltage goes, the
greater the electron imbalance becomes. The greater
this electron imbalance, the harder the push on the
electrons (more electrons repelling each other) and the
greater the current of electrons in the circuit. When
there are many electrons concentrated at the negative
terminal of a generator (with a corresponding lack of
Ohm’s law is used to figure out the current (I), the
voltage (E), and the resistance (R) in a circuit. This law
states that voltage is equal to amperage times ohms.
Or, it can be stated as the mathematical formula:
E = I x R. For the purpose of solving problems, the
Ohm’s law formula can be expressed in three ways:
1. To find voltage: E = IR
2. To find amperage: I = E/R
3. To find ohms: R = E/I
The Ohm’s law formula is a useful one to
remember because it helps in understanding the many
things that occur in an electric circuit. For example, if
the voltage remains constant. the current flow goes
down if the resistance goes up. This can be better
explained by using a truck lighting circuit that is going
bad. Suppose the wiring circuit between the battery
and the lights has deteriorated due to connections
becoming poor, strands in the wire breaking, and
switch contacts becoming dirty. All of these conditions
reduce the electron path or, in other words, increase
resistance. This increased resistance decreases the
current flow with the battery voltage constant (for
example, 12 volts). If the resistance of the circuit when
new was 6 ohms, then 2 amperes will flow. To answer
the equation, 12 (volts) must equal 12 (amperes times
ohms). But if the resistance goes up to 8 ohms, only 1.5
amperes can flow. The increased resistance cuts down
the current flow and, consequently, the amount of
If the resistance stays the same but the voltage
increases, the amperage also increases. This is a
condition that might occur if a generator voltage
regulator became defective. In such a case, there would
be nothing to hold the generator voltage within limits,
and the voltage might increase excessively. This
would force excessive amounts of current through
various circuits and cause serious damage. If too much
current went through the light bulb filaments, for
example, the filaments would overheat and burn out.
Also, other electrical devices probably would be
damaged. However, if the voltage is reduced, the
amount of current flowing in a circuit will also be
reduced if the resistance stays the same.
For example with a run-down battery, battery
voltage will drop excessively with a heavy discharge.
When you are trying to start an engine with a run-down
battery, the voltage will drop very low. This voltage is
so low that it cannot push enough current through the
starter for effective starting of the engine.
Automotive circuits (fig. 1-12). The body and
chassis of an automobile are made of steel. This feature
is used to eliminate one of the wires from all of the
automobile circuits. By attaching one of the battery
terminals to the body and chassis, you can connect any
electrical component by hooking up one side, by wire,
to the car battery and the other side to the body. This
design of connecting one side of the battery to the
Figure 1-12.—Typical automotive circuit.
automobile body is called grounding. The majority of
equipment you will encounter in the NCF will have an
electrical system with a negative ground. Vehicles
with positive ground are very uncommon, but it is
always good practice to note what type of grounding
system is used on the equipment you are working on.
others. Important characteristics of parallel circuits are
as follows:
Series circuits (fig. 1-13, view A). A series circuit
consists of two or more electrical components
connected in such a manner that current will flow
through all the components. Important characteristics
of a series circuit are as follows:
The disconnection or burning out of any
individual component in the circuit will not
affect the operation of the others.
The total resistance of the circuit will always be
less than the resistance of any individual
Any break in the circuit (such as a burned-out
light bulb) will render’ the entire circuit
The current will divide itself among the circuit
branches according to the resistance of the
individual devices. The sum of the individual
amperages will be equal to the total circuit
Current (amperage) will be constant throughout
the circuit.
The voltage will be constant throughout the
circuit when measured across the individual
Series-parallel circuits (fig. 1-13, view C). The
series-parallel circuit is a combination of the two
configurations. There must be at least three resistance
units to have a series-parallel circuit. Important
characteristics of series-parallel circuits are as follows:
Total resistance of the circuit is equal to the sum
of each individual resistance.
Total voltage of the circuit is equal to the sum of
the individual voltage drops across each
The total circuit voltage will be equal to the sum
of the total parallel circuit voltage drop plus the
voltage drop of the individual series circuit
Parallel circuits (fig. 1-13, view B). A parallel
circuit consists of two or more electrically operated
components connected by parallel wires. In a parallel
circuit, the current divides, part of it flowing into one
component and part into the others. Practically the
same voltage is applied to each component, and each
component can be turned on or off independently of the
The total circuit resistance will be equal to the
sum of the total parallel circuit resistance plus
the individual resistance of the series circuit
Figure 1-13.—Circuit configurations.
Current flow through the total parallel circuit
will be equal to the current flow through any
individual series circuit component.
The disconnection or the burning out of
series components will completely disable
entire circuit, whereas a failure of any of
parallel circuit components will leave
balance of the circuit still functioning.
Short circuit (fig. 1-14, view B). A short circuit
occurs when copper touches copper, such as when
wiring insulation between two wires fails and the
wiring makes contact.
Q 1 . Voltage is known by what term?
Q2. What are the three basic types of electrical
Open circuit (fig. 1-14, view A). An open circuit is
a break or interruption in the circuit, such as a wire that
has come loose or a slipped connection that is not
making contact. But the expression of an open circuit is
not only used when wire connections are actually
separated as in a switch but also when the resistance in
the wiring circuit is so that no current can flow between
the battery and the unit it operates. A good example of
such a condition is rust and corrosion that forms and
accumulates at a battery cable or terminal.
Q 3 . What type of circuit failure occurs when copper
touches copper?
Learning Objective: Describe the theory ofmagnetism
and the principles of electromagnetism and
electromagnetic induction.
Magnetic field is described as invisible lines of
force which come out of the North Pole and enter the
South Pole. For example, if iron filings were
sprinkled on a piece of glass on top of a bar magnet,
the filings would form themselves in curved lines
Ground circuit. A ground circuit occurs when any
part of the wiring circuit is touching the vehicle frame
inadvertently. A ground involves accidental or
unintentional contact between copper and the iron frame.
Figure 1-14.—(A) Open circuit; (B) Short circuit.
(fig. 1-15). These curved lines, extend from the two
poles of the magnet, follow the magnetic lines of force
surrounding the magnet. Lines of force rules are as
An electric current (flow of electrons) always
creates a magnetic field. In the wire shown in figure
1-18, current flow causes lines of force to circle the
wire. It is thought that these lines of force result from
the movement of the electrons along the wire. As they
move, the electrons send out the lines of force. When
many electrons move, there are many lines of force
(the magnetic field is strong). Few electrons in motion
means a weak magnetic field or few lines of force.
The lines of force (outside the magnet) pass from
the North Pole to the South Pole of the magnet.
The lines of force act somewhat as rubber bands
and try to shorten to minimum length.
The lines of force repel each other along their
entire length and try to push each other apart.
Electron movement as the basis of magnetism in
bar and horseshoe magnets can be explained by
assuming that the atoms of iron are so lined up in the
magnets that the electrons are circling in the same
direction and their individual magnetic lines of force
add to produce the magnetic field.
The rubber band characteristic opposes the
push-apart characteristic.
The lines of force never cross each other.
The magnetic lines of force, taken together, are
referred to as the magnetic field of the magnet.
The magnetic fields of a bar and of a horseshoe
magnet are shown in figure 1-16. In each, note how the
lines of force curve and pass from the North Pole to the
South Pole.
The magnetic field is produced by current flowing
in a single loop of wire (fig. 1-19). The magnetic lines
of force circle the wire, but here they must follow the
Effects between magnetic poles (fig. 1-17). When
two UNLIKE magnetic poles are brought together,
they attract. But when LIKE magnetic poles are
brought together, they repel. These actions can be
explained in terms of the rubber band and the pushapart characteristics. When unlike poles are brought
close to each other, the magnetic lines of force pass
from the North Pole to the South Pole. They try to
shorten (like rubber bands) and, therefore, try to pull
the two poles together. On the other hand, if like poles
are brought close to each other, lines of force going in
the same direction are brought near each other.
Because these lines of force attempt to push apart, a
repelling effect results between the like poles.
Figure 1-16.—Bar and horseshoe magnet.
Figure 1-15.—Magnetic lines of force.
Figure 1-17.—Effects between magnetic poles.
Figure 1-19.—Electromagnetism in a wire loop.
Figure 1-18.—Electromagnetism.
curve of the wire. If two loops are made in the
conductor, the lines of force will circle the two loops.
In the area between the adjacent loops, the magnetic
lines are going in opposite directions. In such a case,
because they are of the same strength (from same
amount of current traveling in both loops), they cancel
each other out. The lines of force, therefore, circle the
two loops almost as though they were a single loop.
However, the magnetic field will be twice as strong
because the lines of force of the two loops combine.
When many loops of wire are formed into a coil, as
shown in figure 1-20, the lines of force of all loops
combine into a pattern that greatly resembles the
magnetic field surrounding a bar magnet. A coil of this
Figure 1-20.—Electromagnetism in a wire coil.
type is known as an electromagnet or a solenoid.
Electromagnets can be in many shapes. The field coils
of generators and starters, the primary winding in an
ignition coil, the coils in electric gauges, even the
windings in a starter armature, can be considered to be
electromagnets. All of these components produce
magnetism by electrical means.
The North Pole of an electromagnet can be
determined, if the direction of current flow (from
negative to positive) is known, by use of the left-hand
rule (fig. 1-21). The left hand is around the coil with the
fingers pointing in the direction of current flow. The
thumb will point to the North Pole of the
electromagnet. This rule is based on current, or
electron, flow from negative to positive.
The left-hand rule also can be used to determine
the direction that the lines of force circle a wirecarrying current if the direction of current is known.
This is done by circling the wire with the left hand with
the thumb pointing in the direction of current flow
(negative to positive). The fingers will then point in the
direction that the magnetic field circles the wire.
The strength of an electromagnet can be increased
greatly by wrapping the loops of wire around an iron
core. The iron core passes the lines of force with much
greater ease than air. This effect of permitting lines of
force to pass through easily is called permeability.
Wrought iron is 3,000 times more permeable than air.
In other words, it allows 3,000 times as many lines of
force to get through. With this great increase in the
number of lines of force, the magnetic strength of the
electromagnet is greatly increased, even though no
more current flows through it. Practically all
electromagnets use an iron core of some type.
Current can be induced to flow in a conductor if it
is moved through a magnetic field. In figure 1-22, the
wire is moved downward through the magnetic field
between the two magnetic poles. As it moves
downward cutting lines of force, current is induced in
it. The reason for this is that the line of force resists
cutting and tends to wrap around the wire as shown.
With lines of force wrapping around the wire, current
is induced. The wire movement through the magnetic
field produces a magnetic whirl around the wire, which
pushes the electrons along the wire.
If the wire is held stationary and the magnetic field
is moved, the effect is the same. All that is required is
that there be relative movement between the conductor
and the magnetic lines of force to produce enough
voltage to move the electrons along the conductor.
Moving the magnet can move the magnetic field
or, if it is a magnetic field from an electromagnet,
starting and stopping the current flow in the
electromagnet can move it. Suppose an electromagnet,
such as the one shown in figure 1-20, has a wire held
close to it. When the electromagnet is connected to a
battery, current will start to flow through it. This
current, as it starts to flow, builds up a magnetic field.
Figure 1-21.—Left-hand rule.
Figure 1-22.—Electromagnetic induction.
past the wire (the principle applied in an ac
A magnetic field forms because of the current flow. This
magnetic field might be considered to expand and move
out from the electromagnet. As the lines of force move
out, the wire will cut them. This wire will therefore have
current induced in it. If the electromagnet is
disconnected from the battery, these lines of force will
disappear and current will stop flowing in the wire.
3. The wire and electromagnet can both be held
stationary and the current turned on and off to
cause the magnetic field to build up and collapse
so the magnetic field moves one way or the other
across the wire (the principle applied in an
ignition coil).
It can be seen now that current can be induced in a
wire by three methods:
1. The wire can be moved through the stationary
magnetic field (the principle applied in a dc
Q1. A magnetic field has what type of lines of force?
2. The wire can be held stationary and the
magnet can be moved so the field is carried
When like magnetic poles are brought together,
what action occurs?
What are two parts of a basic electromagnet?
Q1. Over 100
Q2. Protons, electrons, and neutrons
Q3. Repel each other
From a negative terminal to a positive terminal
Q1. Electrical conductor
Q2. Diodes and transistors
Q3. A diode allows current to pass through but in only one direction; whereas, a
transistor allows current to pass through or stops current flow
Q1. Potential difference
Series, parallel. and series-parallel
Q3. Short circuit
Q1. Invisible lines of force
They repel each other
Q3. A coil of wire wound over a soft iron core
Starting circuit
Ignition circuit
Learning Objective: Identify charging, starting,
ignition, and accessory-circuit components, their
functions, and maintenance procedures. Identify the
basic types of automotive wiring, types of terminals,
and wiring diagrams.
Lighting circuit
Accessory circuit
Electrical power and control signals must be
delivered to electrical devices reliably and safely so
electrical system functions are not impaired or
converted to hazards. This goal is accomplished
through careful circuit design, prudent component
selection, and practical equipment location. By
carefully studying this chapter and the preceding
The electrical systems on equipment used by the
Navy are designed to perform a variety of functions. The
automotive electrical system contains five electrical
circuits. These circuits are as follows (fig. 2-1):
Charging circuit
Figure 2-1.—Electrical circuits.
mechanical (engine) power to produce
chapter, you will understand how these circuits work
and the adjustments and repairs required to maintain
the electrical systems in peak condition.
ALTERNATOR BELT—links the engine
crankshaft pulley with alternator/generator
pulley to drive the alternator/generator.
Learning Objective: Identify charging-circuit
components, their functions, and maintenance
voltmeter, or warning light to inform the
operator of charging system condition.
The charging system performs several functions,
which are as follows:
It recharges the battery after engine cranking or
after the use of electrical accessories with the
engine turned off.
The storage battery is the heart of the charging
circuit (fig. 2-2). It is an electrochemical device for
producing and storing electricity. A vehicle battery
has several important functions, which are as
It supplies all the electricity for the vehicle when
the engine is running.
It must change output to meet different electrical
It must operate the starting motor, ignition
system, electronic fuel injection system, and
other electrical devices for the engine during
engine cranking and starting.
It provides a voltage output that is slightly higher
than battery voltage.
A typical charging circuit consists of the
It must supply ALL of the electrical power for
the vehicle when the engine is not running.
It must help the charging system provide
electricity when current demands are above the
output limit of the charging system.
BATTERY—provides current to energize or
excite the alternator and assists in stabilizing
initial alternator output.
Figure 2-2.—Gross section of a typical storage battery.
Each cell compartment contains two kinds of
chemically active lead plates, known as positive and
negative plates. The battery plates are made of GRID
(stiff mesh framework) coated with porous lead. These
plates are insulated from each other by suitable
separators and are submerged in a sulfuric acid
solution (electrolyte).
It must act as a capacitor (voltage stabilizer) that
smoothes current flow through the electrical
It must store energy (electricity) for extended
The type of battery used in automotive,
construction, and weight-handling equipment is a
lead-acid cell-type battery. This type of battery
produces direct current (dc) electricity that flows in
only one direction. When the battery is discharging
(current flowing out of the battery), it changes
chemical energy into electrical energy, thereby,
releasing stored energy. During charging (current
flowing into the battery from the charging system),
electrical energy is converted into chemical energy.
The battery can then store energy until the vehicle
requires it.
Charged negative plates contain spongy (porous)
lead (Pb) which is gray in color. Charged positive
plates contain lead peroxide (PbO2) which has a
chocolate brown color. These substances are known as
the active materials of the plates. Calcium or antimony
is normally added to the lead to increase battery
performance and to decrease gassing (acid fumes
formed during chemical reaction). Since the lead on
the plates is porous like a sponge, the battery acid
easily penetrates into the material. This aids the
chemical reaction and the production of electricity.
Battery Construction
Lead battery straps or connectors run along the
upper portion of the case to connect the plates. The
battery terminals (post or side terminals) are
constructed as part of one end of each strap.
The lead-acid cell-type storage battery is built to
withstand severe vibration, cold weather, engine heat,
corrosive chemicals, high current discharge, and
prolonged periods without use. To test and service
batteries properly, you must understand battery
construction. The construction of a basic lead-acid
cell-type battery is as follows:
To prevent the plates from touching each other and
causing a short circuit, sheets of insulating material
(microporous rubber, fibrous glass, or plasticimpregnated material), called separators, are inserted
between the plates. These separators are thin and porous
so the electrolyte will flow easily between the plates.
The side of the separator that is placed against the
positive plate is grooved so the gas that forms during
charging will rise to the surface more readily. These
grooves also provide room for any material that flakes
from the plates to drop to the sediment space below.
Battery element
Battery case, cover, and caps
Battery terminals
BATTERY ELEMENT.—The battery element is
made up of negative plates, positive plates, separators,
and straps (fig. 2-3). The element fits into a cell
compartment in the battery case. Most automotive
batteries have six elements.
battery case is made of hard rubber or a high—quality
plastic. The case must withstand extreme vibration,
temperature change, and the corrosive action of the
electrolyte. The dividers in the case form individual
containers for each element. A container with its
element is one cell.
Stiff ridges or ribs are molded in the bottom of the
case to form a support for the plates and a sediment
recess for the flakes of active material that drop off the
plates during the life of the battery. The sediment is
thus kept clear of the plates so it will not cause a short
circuit across them.
The battery cover is made of the same material as
the container and is bonded to and seals the container.
The cover provides openings for the two battery posts
and a cap for each cell.
Figure 2-3.—Battery element.
The specific gravity of an electrolyte is actually the
measure of its density. The electrolyte becomes less
dense as its temperature rises, and a low temperature
means a high specific gravity. The hydrometer that you
use is marked to read specific gravity at 80°F only.
Under normal conditions, the temperature of your
electrolyte will not vary much from this mark.
However, large changes in temperature require a
correction in your reading.
Battery caps either screw or snap into the openings
in the battery cover. The battery caps (vent plugs)
allow gas to escape and prevent the electrolyte from
splashing outside the battery. They also serve as spark
arresters (keep sparks or flames from igniting the gases
inside the battery). The battery is filled through the
vent plug openings. Maintenance-free batteries have a
large cover that is not removed during normal service.
For EVERY 10-degree change in temperature
ABOVE 80°F, you must ADD 0.004 to your specific
gravity reading. For EVERY 10-degree change in
temperature BELOW 80°F, you must SUBTRACT
0.004 from your specific gravity reading. Suppose you
have just taken the gravity reading of a cell. The
hydrometer reads 1.280. A thermometer in the cell
indicates an electrolyte temperature of 60°F. That is a
normal difference of 20 degrees from the normal of
80°F. To get the true gravity reading, you must subtract
0.008 from 1.280. Thus the specific gravity of the cell
is actually 1.272. A hydrometer conversion chart
similar to the one shown in figure 2-4 is usually found
on the hydrometer. From it, you can obtain the specific
gravity correction for temperature changes above or
below 80°F.
Hydrogen gas can collect at the top of a
battery. If this gas is exposed to a flame or
spark, it can explode.
BATTERY TERMINALS.—Battery terminals
provide a means of connecting the battery plates to the
electrical system of the vehicle. Either two round post
or two side terminals can be used.
Battery terminals are round metal posts extending
through the top of the battery cover. They serve as
connections for battery cable ends. Positive post will
be larger than the negative post. It may be marked with
red paint and a positive (+) symbol. Negative post is
smaller, may be marked with black or green paint, and
has a negative (-) symbol on or near it.
Side terminals are electrical connections located
on the side of the battery. They have internal threads
that accept a special bolt on the battery cable end. Side
terminal polarity is identified by positive and negative
symbols marked on the case.
ELECTROLYTE. —The electrolyte solution in a
fully charged battery is a solution of concentrated
sulfuric acid in water. This solution is about 60 percent
water and about 40 percent sulfuric acid.
The electrolyte in the lead-acid storage battery has
a specific gravity of 1.28, which means that it is 1.28
times as heavy as water. The amount of sulfuric acid in
the electrolyte changes with the amount of electrical
charge; also the specific gravity of the electrolyte
changes with the amount of electrical charge. A fully
charged battery will have a specific gravity of 1.28 at
80°F. The figure will go higher with a temperature
decrease and lower with a temperature increase.
As a storage battery discharges, the sulfuric acid is
depleted and the electrolyte is gradually converted into
water. This action provides a guide in determining the
state of discharge of the lead-acid cell. The electrolyte
that is placed in a lead-acid battery has a specific
gravity of 1.280.
Figure 2-4.—Hydrometer conversion chart.
Battery Capacity
capacity will appear on the battery as a time interval
in minutes.
The capacity of a battery is measured in amperehours. The ampere-hour capacity is equal to the
product of the current in amperes and the time in hours
during which the battery is supplying current. The
ampere-hour capacity varies inversely with the
discharge current. The size of a cell is determined
generally by its ampere-hour capacity. The capacity of
a cell depends upon many factors, the most important
of which are as follows:
For example, if a battery is rated at 90 minutes and
the charging system fails, the operator has
approximately 90 minutes (1 1/2 hours) ofdriving time
under minimum electrical load before the battery goes
completely dead.
Battery Charging
Under normal conditions, a hydrometer reading
below 1.240 specific gravity at 80°F is a warning
signal that the battery should be removed and charged.
Except in extremely warm climates, never allow the
specific gravity to drop below 1.225 in tropical
climates. This reading indicates a fully charged
1. The area of the plates in contact with the
2. The quantity and specific gravity of the
3. The type of separators
4. The general condition of the battery (degree of
sulfating, plates buckled, separators warped,
sediment in bottom of cells, etc.)
When a rundown battery is brought into the shop,
you should recharge it immediately. There are several
methods for charging batteries; only direct current is
used with each method. If only alternating current is
available, a rectifier or motor generator must be used to
convert to direct current. The two principal methods of
charging are (1) constant current and (2) constant
voltage (constant potential).
5. The final limiting voltage
Battery Ratings
Battery ratings were developed by the Society of
Automotive Engineers (SAE) and the Battery Council
International (BCI). They are set according to national
test standards for battery performance. They let the
mechanic compare the cranking power of one battery
to another. The two methods of rating lead-acid storage
batteries are the cold-cranking rating and the reserve
capacity rating.
Constant current charging is be used on a single
battery or a number of batteries in series. Constant
voltage charging is used with batteries connected in
parallel. (A parallel circuit has more than one path
between the two source terminals; a series circuit is a
one-path circuit). You should know both methods,
although the latter is most often used.
coldcranking rating determines how much current in
amperes the battery can deliver for thirty seconds
at 0°F while maintaining terminal voltage of 7.2
volts or 1.2 volts per cell. This rating indicates the
ability of the battery to crank a specific engine
(based on starter current draw) at a specified
the constant current method, the battery is connected to
a charging device that supplies a steady flow of
current. The charging device has a rectifier (a gasfilled bulb or a series of chemical disks); thus, the
alternating current is changed into direct current. A
rheostat (resistor for regulating current) of some kind
is usually built into the charger so that you can adjust
the amount of current flow to the battery. Once the
rheostat is set, the amount of current remains constant.
The usual charging rate is 1 amp per positive cell. Thus
a 21-plate battery (which has 10 positive plates per
cell) should have a charging rate no greater than 10
amps. When using this method of charging a battery,
you should check the battery frequently, particularly
near the end of the charging period. When the battery is
gassing freely and the specific gravity remains
constant for 2 hours, you can assume that the battery
will take no more charge.
For example, one manufacturer recommends a
battery with 305 cold-cranking amps for a small fourcylinder engine but a 450 cold-cranking amp battery
for a larger V-8 engine. A more powerful battery is
needed to handle the heavier starter current draw of the
larger engine.
R E S E R V E C A P A C I T Y R A T I N G .—The
reserve capacity rating is the time needed to
lower battery terminal voltage below 10.2 V (1.7 V
per cell) at a discharge rate of 25 amps. This is with
the battery fully charged and at 80°F. Reserve
most cases, slightly larger than the negative
post. Ensure all connections are tight.
The primary disadvantage of constant current
charging is that THE CHARGING CURRENT
CHANGE IT. A battery charged with too high current
rate would overheat and damage the plates, making the
battery useless. Do NOT allow the battery temperature
to exceed 110° while charging.
3. See that the vent holes are clear and open. DO
CHARGING. This prevents acid from spraying
onto the top of the battery and keeps dirt out of
the cells.
Constant voltage charging, also known as constant
potential charging, is usually done with a motor
generator set. The motor drives a generator (similar to
a generator on a vehicle); this generator produces
current to charge the battery. The voltage in this type of
system is usually held constant. With a constant
voltage, the charging rate to a low battery will be high.
But as the battery approaches full charge, the opposing
voltage of the battery goes up so it more strongly
opposes the charging current. This opposition to the
charging current indicates that a smaller charge is
needed. As the battery approaches full charge, the
charging voltage decreases. This condition decreases
the ability to maintain a charging current to the battery.
As a result, the charging current tapers off to a very low
value by the time the battery is fully charged. This
principle of operation is the same as that of the voltage
regulator on a vehicle.
4. Check the electrolyte level before charging
begins and during charging. Add distilled water
if the level of electrolyte is below the top of the
5. Keep the charging room well ventilated. DO
CHARGED. Batteries on charge release
hydrogen gas. A small spark may cause an
6. Take frequent hydrometer readings of each cell
and record them. You can expect the specific
gravity to rise during the charge. If it does not
rise, remove the battery and dispose of it as per
local hazardous material disposal instruction.
7. Keep close watch for excessive gassing,
especially at the very beginning of the charge
when using the constant voltage method.
Reduce the charging current if excessive
gassing occurs. Some gassing is normal and
aids in remixing the electrolyte.
connect the battery to the charger, turn the charging
current on, and, after a normal charging period, turn the
charging current off and remove the battery. Certain
precautions however are necessary both BEFORE and
DURING the charging period. These practices are as
8. Do not remove a battery until it has been
completely charged.
Placing New Batteries in Service
1. Clean and inspect the battery thoroughly before
placing it on charge. Use a solution of baking
soda and water for cleaning; and inspect for
cracks or breaks in the container.
New batteries may come to you full of electrolyte
and fully charged. In this case, all that is necessary is to
install the batteries properly in the piece of equipment.
Most batteries shipped to NCF units are received
charged and dry.
Charged and dry batteries will retain their state of
full charge indefinitely so long as moisture is not
allowed to enter the cells. Therefore, batteries should
be stored in a dry place. Moisture and air entering the
cells will allow the negative plates to oxidize. The
oxidation causes the battery to lose its charge.
Do not permit the soda and water solution
to enter the cells. To do so would neutralize the
acid within the electrolyte.
2. Connect the battery to the charger. Be sure the
battery terminals are connected properly;
connect positive post to positive (+) terminal
and the negative post to negative (-) terminal.
The positive terminals of both battery and
charger are marked; those unmarked are
negative. The positive post of the battery is, in
To activate a dry battery, remove the restrictors
from the vents and remove the vent caps. Then fill all
the cells to the proper level with electrolyte. The best
results are obtained when the temperature of the
battery and electrolyte is within the range of 60°F to
Some gassing will occur while you are filling the
battery due to the release of carbon dioxide that is a
product of the drying process of the hydrogen sulfide
produced by the presence of free sulfur. Therefore, the
filling operations should be in a well-ventilated area.
These gases and odors are normal and are no cause for
Figure 2-5 shows you how much water and acid to
mix for obtaining a certain specific gravity. For
example, mixing 5 parts of water to 2 parts of acid
produces an electrolyte of 1.300, when starting with
1.835 specific gravity acid. If you use 1.400 specific
gravity acid, 2 parts water and 5 parts acid will give the
same results.
Approximately 5 minutes after adding electrolyte,
the battery should be checked for voltage and
electrolyte strength. More than 6 volts or more than 12
volts, depending upon the rated voltage of the battery,
indicates the battery is ready for service. From 5 to 6
volts or from 10 to 12 volts indicate oxidized negative
plates, and the battery should be charged before use.
Less than 5 or less than 10 volts, depending upon the
rated voltage, indicates a bad battery, which should not
be placed in service.
Let the mixed electrolyte cool down to room
temperature before adding it to the battery cells. Hot
electrolyte will eat up the cell plates rapidly. To be on
the safe side, do not add the electrolyte if its
temperature is above 90°F. After filling the battery
cells, let the electrolyte cool again because more heat is
generated by its contact with the battery plates. Next,
take hydrometer readings. The specific gravity of the
electrolyte will correspond quite closely to the values
on the mixing chart if the parts of water and acid are
mixed correctly.
If, before placing the battery in service, the
specific gravity, when corrected to 80°F, is more than
.030 points lower than it was at the time of initial filling
or if one or more cells gas violently after adding the
electrolyte, the battery should be fully charged before
use. If the electrolyte reading fails to rise during
charging, discard the battery.
Battery Maintenance
If a battery is not properly maintained, its service
life will be drastically reduced. Battery maintenance
should be done during every PM cycle. Complete
battery maintenance includes the following:
Most shops receive ready-mixed electrolyte. Some
units may still get concentrated sulfuric acid that must
be mixed with distilled water to get the proper specific
gravity for electrolyte.
Visually checking the battery.
Checking the electrolyte level in cells on
batteries with caps. Adding water if the
electrolyte level is low.
MIXING ELECTROLYTE is a dangerous job.
You have probably seen holes appear in a uniform for
no apparent reason. Later you remembered replacing a
storage battery and having carelessly brushed against
the battery.
Cleaning off corrosion around the battery and
battery terminals.
Using 1.835
Sp. Gr. Acid
Gravity P a r t s
o f
When mixing electrolyte, you are
handling pure sulfuric acid, which can burn
clothing quickly and severely bum your hands
and face. Always wear rubber gloves, an
apron, goggles, and a face shield for protection
against splashes or accidental spilling.
When you are mixing electrolyte, NEVER POUR
INTO WATER. If water is added to concentrated
sulfuric acid, the mixture may explode or splatter and
cause severe burns. Pour the acid into the water slowly,
stirring gently but thoroughly all the time. Large
quantities of acid may require hours of safe dilution.
using 1.400
Sp. Gr. Acid
o f
o f
o f
Figure 2-5.—Electrolyte mixing chart.
Checking the condition of the battery by testing
the state of charge.
Do NOT use a scraper or knife to clean
battery terminals. This action removes too
much metal and can ruin the terminal
BATTERY. —Battery maintenance should always
begin with a thorough visual inspection. Look for signs
of corrosion on or around the battery, signs of leakage,
a cracked case or top, missing caps, and loose or
missing hold-down clamps.
When reinstalling the cables, coat the terminals
with petroleum or white grease. This will keep acid
fumes off the connections and keep them from
corroding again. Tighten the terminals just enough to
secure the connection. Overtightening will strip the
cable bolt threads.
ADDING WATER.—On vent cap batteries, the
electrolyte level can be checked by removing the caps.
Some batteries have a fill ring which indicates the
electrolyte level. The electrolyte should be even with
the fill ring. If there is no fill ring, the electrolyte
should be high enough to cover the tops of the plates.
Some batteries have an electrolyte-level indicator
(Delco Eye). This gives a color code visual indication
of the electrolyte level, with black indicating that the
level is okay and white meaning a low level.
When measuring battery charge, you check the
condition of the electrolyte and the battery plates. As a
battery becomes discharged, its electrolyte has a larger
percentage of water. Thus the electrolyte of a
discharged battery will have a lower specific gravity
number than a fully charged battery. This rise and drop
in specific gravity can be used to check the charge in a
battery. There are several ways to check the state of
charge of a battery.
If the electrolyte level in the battery is low, fill the
cells to the correct level with DISTILLED WATER
(purified water). Distilled water should be used
because it does not contain the impurities found in tap
water. Tap water contains many chemicals that reduce
battery life. The chemicals contaminate the electrolyte
and collect in the bottom of the battery case. If enough
contaminates collect in the bottom of the case, the cell
plates SHORT OUT, ruining the battery.
Nonmaintenance-free batteries can have the state of
charge checked with a hydrometer. The hydrometer tests
specific gravity of the electrolyte. It is fast and simple to
use. There are three types of hydrometers—the float
type, the ball type, and needle type.
and hold the bulb. Then immerse the other end of the
hydrometer in the electrolyte. Then release the bulb.
This action will fill the hydrometer with electrolyte.
Hold the hydrometer even with your line of sight and
compare the numbers on the hydrometer with the top of
the electrolyte.
If water must be added at frequent intervals, the
charging system may be overcharging the battery. A
faulty charging system can force excessive current into
the battery. Battery gassing can then remove water
from the battery.
Maintenance-free batteries do NOT need periodic
electrolyte service under normal conditions. It is
designed to operate for long periods without loss of
Most float type hydrometers are NOT temperature
correcting. However, the new models will have a builtin thermometer and a conversion chart that allow you
to calculate the correct temperature.
TERMINALS.—If the top of the battery is dirty,
using a stiff bristle brush, wash it down with a mixture
of baking soda and water. This action will neutralize
and remove the acid-dirt mixture. Be careful not to
allow cleaning solution to enter the battery.
more popular because you do not have to use a
temperature conversion chart. The balls allow for a
change in temperature when submersed in electrolyte.
This allows for any temperature offset.
To use a ball type hydrometer, draw electrolyte
into the hydrometer with the rubber bulb at the top.
Then note the number of balls floating in the
electrolyte. Instructions on or with the hydrometer will
tell you whether the battery is fully charged or
To clean the terminals, remove the cables and
inspect the terminal posts to see if they are deformed or
broken. Clean the terminal posts and the inside
surfaces of the cable clamps with a cleaning tool before
replacing them on the terminal posts.
same principles as the ball type. When electrolyte is
drawn into the hydrometer, it causes the plastic needle
to register specific gravity.
across the top of the battery. A dirty battery can
discharge when not in use. This condition shortens
battery life and causes starting problems.
To perform a battery leakage test, set a voltmeter
on a low setting. Touch the probes on the battery, as
shown in figure 2-6. If any current is registered on the
voltmeter, the top of the battery needs to be cleaned.
A fully charged battery should have a hydrometer
reading of at least 1.265 or higher. If below 1.265, the
battery needs to be recharged. or it may be defective. A
discharged battery could be caused by the following:
terminal test quickly checks for poor electrical
connection between the terminals and the battery
cables. A voltmeter is used to measure voltage drop
across terminals and cables.
Defective battery
Charging system problems
Starting system problems
Poor cable connections
To perform a battery terminal test (fig. 2-7),
connect the negative voltmeter lead to the battery cable
end. Touch the positive lead to the battery terminal.
With the ignition or injection system disabled so that
the engine will not start, crank the engine while
watching the voltmeter reading.
Engine performance problems requiring
excessive cranking time
Electrical problems drawing current out of the
battery with the ignition OFF
defective battery can be found by using a
hydrometerto check each cell. If the specific gravity in
any cell varies excessively from other cells (25 to 50
points), the battery is bad. Cells with low readings may
be shorted. When all of the cells have equal specific
gravity, even if they are low, the battery can usually be
On maintenance-free batteries a charge indicator
eye shows the battery charge. The charge indicator
changes color with levels of battery charge. For
example, the indicator may be green with the battery
fully charged. It may turn black when discharged or
yellow when the battery needs to be replaced. If there is
no charge indicator eye or when in doubt of its
reliability, a voltmeter and ammeter or a load tester can
also be used to determine battery condition quickly.
Battery Test
Figure 2-6.—Battery leakage test.
As a mechanic you will be expected to test
batteries for proper operation and condition. These
tests are as follows:
Battery leakage test
Battery terminal test
Battery voltage test
Cell voltage test
Battery drain test
Battery load test (battery capacity test)
Quick charge test
leakage test will determine if current is discharging
Figure 2-7.—Battery terminal test.
If the voltmeter reading is .5 volts or above, there
is high resistance at the battery cable connection. This
indicates that the battery connections need to be
cleaned. A good, clean battery will have less than a .5
volt drop.
voltage test is done by measuring total battery voltage
with an accurate voltmeter or a special battery tester
(fig. 2-8). This test determines the general state of
charge and battery condition quickly.
The battery voltage test is used on
maintenance-free batteries because these batteries do
not have caps that can be removed for testing with a
hydrometer. To perform this test, connect the voltmeter
or battery tester across the battery terminals. Turn on
the vehicle headlights or heater blower to provide a
light load. Now read the meter or tester. A well-charged
battery should have over 12 volts. If the meter reads
approximately 11.5 volts, the battery is not charged
adequately, or it may be defective.
CELL VOLTAGE TEST.—The cell voltage test
will let you know if the battery is discharged or
defective. Like a hydrometer cell test, if the voltage
reading on one or more cells is .2 volts or more lower
than the other cells, the battery must be replaced.
Figure 2-9.—Cell voltage test.
To perform a cell voltage test (fig. 2-9), use a low
voltage reading voltmeter with special cadmium (acid
resistant metal) tips. Insert the tips into each cell,
starting at one end of the battery and work your way to
the other. Test each cell carefully. If the cells are low,
but equal, recharging usually will restore the battery. If
cell voltage readings vary more than .2 volts, the
battery is BAD.
BATTERY DRAIN TEST.—A battery drain test
checks for abnormal current draw with the ignition off.
If a battery goes dead without being used, you need to
check for a current drain.
To perform a battery drain test, set up an ammeter,
as shown in figure 2-10. Pull the fuse if the vehicle has
a dash clock. Close all doors and trunk (if applicable).
Then read the ammeter. If everything is off, there
should be a zero reading. Any reading indicates a
problem. To help pinpoint the problem, pull fuses one
at a time until there is a zero reading on the ammeter.
This action isolates the circuit that has the problem.
test, also termed a battery capacity test, is the best
method to check battery condition. The battery load
test measures the current output and performance of
the battery under full current load. It is one of the most
common and informative battery tests used today.
Before load testing a battery, you must calculate
how much current draw should be applied to the
battery. If the ampere-hour rating of the battery is
given, load the battery to three times its amp-hour
rating. For example, if the battery is rated at 60 amphours, test the battery at 180 amps (60 x 3 = 180). The
majority of the batteries are now rated in SAE coldcranking amps, instead of amp-hours. To determine the
load test for these batteries, divide the cold-crank
Figure 2-8.—Battery voltage test performed with a battery
applied. Then turn the load control completely off so
the battery will not be discharged. If the voltmeter
reads 9.5 volts or more at room temperature, the
battery is good. If the battery reads below 9.5 volts at
room temperature, battery performance is poor. This
condition indicates that the battery is not producing
enough current to run the starting motor properly.
Familiarize yourself with proper operating
procedures for the type of tester you have available.
Improper operation of electrical test equipment may
result in serious damage to the test equipment or the
unit being tested.
QUICK CHARGE TEST.—The quick charge
test, also known as 3-minute charge test, determines if
the battery is sulfated. If the results of the battery load
test are poor, fast charge the battery. Charge the battery
for 3 minutes at 30 to 40 amps. Test the voltage while
charging. If the voltage goes ABOVE 15.5 volts, the
battery plates are sulfated and the battery needs to be
Figure 2-10.—Battery drain test setup.
The generator is a machine that applies the
principle of electromagnetic induction to convert
mechanical energy, supplied by the engine, into
electrical energy. The generator restores to the battery
the energy that has been used up in cranking the
engine. Whether the energy required for the rest of the
electrical system is supplied directly by the generator,
by the battery, or by a combination of both depends on
the conditions under which the generator is operating.
rating by two. For example, a battery with 400 coldcranking amps rating should be loaded to 200 amps
(400 ÷ 2 = 200). Connect the battery load tester, as
shown in figure 2-11. Turn the control knob until the
ammeter reads the correct load for your battery.
After checking the battery charge and finding the
amp load value, you are ready to test battery output.
Make sure that the tester is connected properly. Turn
the load control knob until the ammeter reads the
correct load for your battery. Hold the load for 15
seconds. Next, read the voltmeter while the load is
The two types of generators are as follows:
The dc generator supplies electrical energy
directly to the battery and or electrical system
through various regulating devices.
The ac generator (alternator) has the same
function as the dc generator but because only
direct current can be used to charge a battery, a
component, called a rectifier, must be used to
convert from alternating to direct current. The ac
generator (alternator) will be explained in
further detail later in this chapter.
Direct-Current (dc) Generator
The dc generator (fig. 2-12) essentially consists of
an armature, a field frame, field coils, and a
commutator with brushes to establish electrical
contact with the rotating element. The magnetic field
of the generator usually is produced by the
Figure 2-11.—Instrument hookup for battery capacity test.
Figure 2-12.—Sectional view of a dc generator.
induced in the armature coils thus is able to flow to the
external circuits.
electromagnets or poles magnetized by current
flowing through the field coils. Soft iron pole pieces
(or pole shoes) are contained in the field frame that
forms the magnetic circuit between the poles.
Although generators may be designed to have any even
number of poles, two- and four- pole frames are the
most common. The field coils are connected in series.
In the two-pole type frame, the magnetic circuit flows
through only a part of the armature core; therefore. the
armature must be constructed according to the number
of field poles because current is generated when the
coil (winding on the armature) moves across each
magnetic circuit.
There are two types of field circuits, determined by
the point at which the field circuit is grounded, which
are as follows:
One circuit, referred to as the "A" circuit, shunts
the field current from the insulated brushes
through the field winding grounding externally
at the regulator.
In the other, the "B" circuit, the field current is
shunted from the armature series winding in the
regulator to the generator field windings,
grounding internally within the generator.
The current is collected from the armature coils by
brushes (usually made of carbon) that make rubbing
contact with a commutator. The commutator consists
of a series of insulated copper segments mounted on
one end of the armature, each segment connecting to
one or more armature coils. The armature coils are
connected to the external circuits (battery, lights, or
ignition) through the commutator and brushes. Current
The three basic design factors that determine
generator output are (1) the speed of armature rotation,
(2) the number of armature conductors, and (3) the
strength of the magnetic field. Any of these design
factors could be used to control the generator voltage
and current. However, the simplest method is to
determine the strength of the magnetic field and thus
limit the voltage and current output of the generator.
Regulation of Generator Output
The fields of the generator depend upon the current
from the armature of the generator for magnetization.
Because the current developed by the generator
increases in direct proportion to its speed, the fields
become stronger as the speed increases and,
correspondingly, the armature generates more current.
The extreme variations in speed of the automotive
engine make it necessary to regulate output of the
generator to prevent excessive current or voltage
overload. On the average unit of CESE, a charging
current in excess of 12 to 15 amperes is harmful to a
fully charged battery if continued for too long.
Regulators are of two types, functioning to
regulate either voltage or current. The voltage
regulator regulates the voltage in the electric system
and prevents excessive voltage, which can cause
damage to the electric units and overcharge the battery.
The current regulator is a current limiter; it prevents
the generator output from increasing beyond the rated
output of the generator.
Regulation of voltage only might be satisfactory
from the standpoint of the battery; however, if the
battery were badly discharged or if a heavy electrical
load were connected, the heavy current might overload
itself to supply the heavy current demand. Therefore,
both current and voltage controls are used in a charging
In most applications, a regulator assembly consists
of a cutout relay, current regulator, and voltage
regulator (fig. 2-13). Each unit contains a separate
core, coil, and set of contacts. The regulator assembly
provides full control of the shunt-type generator under
all conditions. Either the current regulator or the
voltage regulator may be operating at any one time, but
in no case do they both operate at the same time.
Figure 2-13.—Regulator assembly with cover removed.
parallel into the generator field circuit when the current
regulator points open. This provides a low value of
resistance, which is sufficient to prevent the generator
output from exceeding its safe maximum. When the
voltage regulator contact points open, only one
resistance is inserted into the generator field circuit,
and this provides a higher value of resistance. The
voltage regulator must employ a higher resistance
because it must reduce the generator output as it
operates, and it requires more resistance to reduce the
output than merely to prevent the output from going
beyond the safe maximum of the generator.
For some special applications, you may find a
combined current-voltage regulator. In this case, the
regulators are combined in a single unit. The regulator
assembly will consist of two (regulator and circuit
breaker) instead of three units.
When the electric load requirements are high and
the battery is low, the current regulator will operate to
prevent the generator output from exceeding its safe
maximum. In this case, the voltage is not sufficient to
cause the voltage regulator to operate. But if the load
requirements are reduced or the battery begins to come
up to charge, the line voltage will increase to a value
sufficient to cause the voltage regulator to operate.
When this happens, the generator output is reduced; it
is no longer sufficiently high to cause the current
regulator to operate. All regulation is then dependent
on the voltage regulator. Figure 2-14 shows a
schematic wiring diagram of a typical dc charging
circuit. In this circuit, two resistances are connected in
The regulators just described are known as
electromagnetic vibrating-contact regulators. The
points on the armatures of the regulators may open and
close as many as 300 times in one second to achieve the
desired regulation.
The transistor type regulator is being used in late
model equipment. This regulator has no moving parts.
It consists of transistors, diodes, condensers, and
resistors. Some models have two filter condensers,
while others have only one.
Adjustments are provided on some types of
regulators and should be made only with the use of the
manufacturer’s instructions and the recommended
testing equipment. TRIAL AND ERROR METHOD
Figure 2-14.—Schematic wiring diagram of a typical dc charging circuit.
Generator Maintenance
The dc generator requires periodic cleaning,
lubrication, inspection of brushes and commutator,
and testing of brush spring tension. In addition, the
electrical connections need attention to ensure clean
metal-to-metal contact and tightness.
Some generators have hinged cap oilers. Lubricate
these with a few drops of medium weight oil at each
maintenance cycle. Do not overlubricate, because as
excessive amount of oil can get on the commutator and
prevent the brushes from functioning properly.
Visually and manually inspect the condition of all
cables, clamps, wiring, and terminal connections. See
that the generator drive pulley is tight on the shaft and
that the belt is in good condition and adjusted properly.
Also, ensure that the generator is securely mounted and
has a good ground.
brushes in the brush holder to see that they are free to
operate and have sufficient tension to prevent arcing
and burning of the commutator and brushes. If brushes
are worn down to one half of their original length,
replace them.
Most generators today are not equipped with cover
bands. They may have open slots over the commutator
or be sealed entirely. On those with open slots, the
commutator can be sanded through the slots, but brush
removal can only be accomplished by removing the
commutator end frame. On sealed units, maintenance
can only be performed after disassembly.
Generator Repair
Generators are disassembled only when major
repairs are to be made (fig. 2-15). Other than cleaning
commutators and replacing worn-out brushes during
periodic maintenance, generators require very few
repairs during normal service life. However, if
neglected, generators will develop problems that
cannot be remedied in the field.
Remove the cover band, on generator so equipped,
and inspect the inner surface of the generator cover
band for tiny globules of solder. If any solder is found,
the generator is producing excessive current and has
melted the solder used in connecting the armature
wires to the commutator bars. This condition requires
removal of the generator to repair or replace the
Before removing a generator suspected of being
faulty, you should check the battery, as discussed
earlier, and the generator output. Refer to the
manufacturer’s manual for correct generator output
specifications and proper testing procedures. If the
generator is operating properly and the battery, wiring,
and connections are in operating condition, a defective
voltage regulator is indicated in which, in most cases,
the regulator is removed and replaced. However, if the
generator is not producing the specified amperes at the
specified engine speed, then it must be removed from
the vehicle and either repaired or replaced.
If no solder is found, inspect the commutator,
brushes, and electrical connections. If the commutator
is dirty or slightly rough, using 00 sandpaper can
smooth it. NEVER use emery cloth on the commutator.
Once the commutator has been sanded, blow
compressed air through the interior of the generator to
remove any excess dirt and brush particles. Lift the
Figure 2-15.—Disassembled view of a two-brush generator.
generator field, you must disconnect the grounded
ends from the frame. Place one probe of the test lamp
circuit on the field terminal end of the coils and the
other probe on the grounded end. If the lamp lights, the
field circuit is complete. However, because of the
resistance in the field coil wire, it should not bum with
normal brilliancy. Normal brilliancy of the test light
bulb indicates a possible short circuit between the coils
of the field. If the light does not burn, the field is opencircuited.
A grounded field coil is located by placing one test
probe on the field terminal and the other on the
generator frame (fig. 2-16). If the test lamp lights, the
field is grounded. The ground may be caused by frayed
wires at the coil ends. In most cases, grounds and open
circuits in the field coils cannot be satisfactorily
repaired. The defective field coil must then be
Figure 2-16.—Testing field coils for ground. CMB2F169
field coil ends, the ohmmeter will measure the actual
resistance of the coil. If the specified resistance of a
field coil is given in the manufacturer’s manual, also
obtained by measuring a new coil, you can compare
values obtained through tests. For example, a shortcircuited field coil would have practically no
resistance and the ohmmeter would register near zero;
or the ohmmeter would register excessively high
resistance in testing a coil having an open circuit. By
Test for grounds, shorts, and open circuits in the
field coils can also be made with an ohmmeter. The
ohmmeter has test probes similar to the test lamp
circuit. When these test probes are connected to the
following the manufacturer's instructions in using the
ohmmeter, field coil tests can be made more quickly
and accurately than by using a test lamp circuit.
ARMATURE TEST.—There are two practical
tests for locating shorts, opens, and grounds in
armatures—the growler test and the bar-to-bar test.
To test for short circuits, place the armature on the
V-block of the growler and turn on the current. With a
thin metal strip (hacksaw blade is good) held over the
core, as shown in figure 2-17, rotate the armature
slowly through a complete revolution. If a short is
present, the steel strip will become magnetized and
vibrate. To find out whether the armature coils of the
commutator are short-circuited, clean between the
commutator segments and repeat the test. Should the
thin metal strip still vibrate, the armature is shortcircuited internally and must be replaced.
the contacts and read the milliammeter at the same
time. The readings should be nearly the same for each
pair of adjacent bars. If a coil is short-circuited, the
milliammeter reading will drop to almost zero.
Test the armature for grounds by using the test
light circuit, which is a part of most modern factorybuilt growlers (fig. 2-19). Place the armature on the
V-block and touch one of the test probes to the
Not all armatures can be tested for short circuits by
the method just described. These armatures can be
identified by excessive vibration of the saw blade all
around the armature during the test. With these
armatures, test for short circuits by using the
milliampere contacts on an ac millimeter, as shown in
figure 2-18. In doing so, keep the armature stationary
in the V-block and move the contacts around the
commutator until the highest reading is obtained. Then
turn the armature to bring each pair of segments under
Figure 2-18.—Testing an armature for a short circuit with a
Figure 2-17.—Using an armature growler.
Figure 2-19.—Testing an armature for grounds.
armature core iron. Touch the other probe to each
commutator segment in turn. If the armature is
grounded, the bulb in the base of the growler will light.
In contacting armature surfaces with the test probes, do
not touch the bearing or the brush surfaces of the
commutator. The arc would burn or pit the smooth
finish. Replace the armature if it is grounded.
bars, not on the brush surfaces. If the test lamp does not
light, there is a break some where in the coil. Repeat
this test on every pair of adjacent bars. Do this by
walking the probes from bar to bar. Should you find an
open coil, the fault may be at the commutator
connectors where it is possible to make repairs with a
little solder. If a coil is open-circuited internally, the
armature should be discarded.
In testing individual armature coils for open
circuits, use the test probes, as shown in figure 2-20.
Place them on the riser part of adjacent commutator
The alternator (fig. 2-21) has replaced the dc
generator because of its improved efficiency. It is
smaller, lighter, and more dependable than the dc
generator. The alternator also produces more output
during idle which makes it ideal for late model
The alternator has a spinning magnetic field. The
output windings (stator) are stationary. As the
magnetic field rotates, it induces current in the output
Alternator Construction
Knowledge of the construction of an alternator is
required before you can understand the proper
operation, testing procedures, and repair procedures
applicable to an alternator.
Figure 2-20.—Testing an armature for open circuits.
Figure 2-21.—Typical alternator.
Figure 2-22.—Rotor assembly.
The primary components of an alternator are as
ROTOR ASSEMBLY (rotor shaft, slip rings,
claw poles, and field windings)
STATOR ASSEMBLY (three stator windings
or coils, output wires, and stator core)
RECTIFIER ASSEMBLY (heat sink, diodes,
diode plate, and electrical terminals)
ROTOR ASSEMBLY (fig. 2-22).—The rotor
consists of field windings (wire wound into a coil
placed over an iron core) mounted on the rotor shaft.
Two claw-shaped pole pieces surround the field
windings to increase the magnetic field.
The fingers on one of the claw-shaped pole pieces
produce south (S) poles and the other produces north
(N) poles. As the rotor rotates inside the alternator,
alternating N-S-N-S polarity and ac current is
produced (fig. 2-23). An external source of electricity
is required to excite the magnetic field of the
Figure 2-23.—Simple alternator illustrating reversing
magnetic field and resulting current flow.
Slip rings are mounted on the rotor shaft to provide
current to the rotor windings. Each end of the field coil
connects to the slip rings.
STATOR ASSEMBLY (fig. 2-24).—The stator
produces the electrical output of the alternator. The
stator, which is part of the alternator frame when
assembled, consists of three groups of windings or
coils which produce three separate ac currents. This is
known as three-phase output. One end of the windings
is connected to the stator assembly and the other is
connected to a rectifier assembly. The windings are
Figure 2-24.—Stator assembly.
wrapped around a soft laminated iron core that
concentrates and strengthen the magnetic field
around the stator windings. There are two types of
stators—Y -type stator and delta-type stator.
The Y-type stator (fig. 2-25) has the wire ends
from the stator windings connected to a neutral
junction. The circuit looks like the letter Y. The Y-type
stator provides good current output at low engine
When an alternator is producing current, the
insulated diodes pass only outflowing current to the
battery. The diodes provide a block, preventing reverse
current flow from the alternator. Figure 2-27 shows the
flow of current from the stator to the battery.
The delta-type stator (fig. 2-26) has the stator
wires connected end-to-end. With no neutral junction,
two circuit paths are formed between the diodes. A
delta-type stator is used in high output alternators.
A cross-sectional view of a typical diode is shown
in figure 2-28. Note that the figure also shows the diode
symbol used in wiring diagrams. The arrow in this
symbol indicates the only direction that current will
flow. The diode is sealed to keep moisture out.
assembly, also known as a diode assembly, consists of
six diodes used to convert stator ac output into dc
current. The current flowing from the winding is
allowed to pass through an insulated diode. As the
current reverses direction, it flows to ground through a
grounded diode. The insulated and grounded diodes
prevent the reversal of current from the rest of the
charging system. By this switching action and the
number of pulses created by motion between the
windings of the stator and rotor, a fairly even flow of
current is supplied to the battery terminal of the
Alternator Operation
The operation of an alternator is somewhat
different than the dc generator. An alternator has a
rotating magnet (rotor) which causes the magnetic
lines of force to rotate with it. These lines of force are
cut by the stationary (stator) windings in the alternator
frame, as the rotor turns with the magnet rotating the N
and S poles to keep changing positions. When S is up
and N is down, current flows in one direction, but when
N is up and S is down, current flows in the opposite
direction. This is called alternating current as it
changes direction twice for each complete revolution.
If the rotor speed were increased to 60 revolutions per
second, it would produce 60-cycle alternating current.
The rectifier diodes are mounted in a heat sink
(metal mount for removing excess heat from electronic
parts) or diode bridge. Three positive diodes are pressfit in an insulated frame. Three negative diodes are
mounted into an uninsulated or grounded frame.
Figure 2-25.—Electrical diagram indicating a Y-type stator.
Figure 2-26.—Electrical diagram indicating a delta-type
Figure 2-27.—Current flow from the stator to the battery.
older type. For operation, refer to the "Regulation of
Generator Output" section of this chapter.
The electronic voltage regulators use an electronic
circuit to control rotor field strength and alternator
output. It is a sealed unit and is not repairable. The
electronic circuit must be sealed to prevent damage
from moisture, excessive heat, and vibration. A
rubberlike gel surrounds the circuit for protection.
An integral voltage regulator is mounted inside or
on the rear of the alternator. This is the most common
type used on modern vehicles. It is small, efficient,
dependable, and composed of integrated circuits.
An electronic voltage regulator performs the same
operation as a contact point regulator, except that it
uses transistors, diodes, resistors, and capacitors to
regulate voltage in the system. To increase alternator
output, the electronic voltage regulator allows more
current into the rotor windings, thereby strengthen the
magnetic field around the rotor. More current is then
induced into the stator windings and out of the
Figure 2-28.—Typical diode.
To reduce alternator output, the electronic
regulator increases the resistance between the battery
and the rotor windings. The magnetic field decreases
and less current is induced into the stator windings.
Since the engine speed varies in a vehicle, the
frequency also varies with the change of speed.
Likewise, increasing the number of pairs of magnetic
north and south poles will increase the frequency by
the number pair of poles. A four-pole generator can
generate twice the frequency per revolution of a twopole rotor.
Alternator speed and load determines whether the
regulator increases or decreases charging output. If the
load is high or rotor speed is low (engine at idle), the
regulator senses a drop in system voltage. The
regulator then increases the rotors magnetic field
current until a preset output voltage is obtained. If the
load drops or rotor speed increases, the opposite
Alternator Output Control
A voltage regulator controls alternator output by
changing the amount of current flow through the rotor
windings. Any change in rotor winding current
changes the strength of the magnetic field acting on the
stator windings. In this way, the voltage regulator can
maintain a preset charging voltage. The three basic
types of voltage regulators are as follows:
Alternator Maintenance
Alternator testing and service call for special
precautions since the alternator output terminal is
connected to the battery at all times. Use care to avoid
reversing polarity when performing battery service of
any kind. A surge of current in the opposite direction
could bum the alternator diodes.
Contact point voltage regulator, mounted away
from the alternator in the engine compartment
Do not purposely or accidentally "short" or
"ground" the system when disconnecting wires or
connecting test leads to terminals of the alternator or
regulator. For example, grounding of the field terminal
at either alternator or regulator will damage the
regulator. Grounding of the alternator output terminal
will damage the alternator and possibly other portions
of the charging system.
Electronic voltage regulator, mounted away
from the alternator in the engine compartment
Electronic voltage regulator, mounted on the
back or inside the alternator
The contact point voltage regulator uses a coil, set
of points, and resistors that limits system voltage. The
electronic or solid-state regulators have replaced this
lighting of the test lamp indicates that the rotor
winding is grounded.
Never operate an alternator on an open circuit.
With no battery or electrical load in the circuit,
alternators are capable of building high voltage (50 to
over 110 volts) which may damage diodes and
endanger anyone who touches the alternator output
To check the rotor for shorts and opens, connect
the ohmmeter to both slip rings, as shown in
figure 2-30. An ohmmeter reading below the
manufacturer’s specified resistance value
indicates a short. A reading above the specified
resistance value indicates an open. If a test lamp
does not light when connected to both slip rings,
the winding is open.
Alternator maintenance is minimized by the use of
prelubricated bearings and longer lasting brushes. If a
problem exists in the charging circuit, check for a
complete field circuit by placing a large screwdriver on
the alternator rear-bearing surface. If the field circuit is
complete, there will be a strong magnetic pull on the
blade of the screwdriver, which indicates that the field
is energized. If there is no field current, the alternator
will not charge because it is excited by battery voltage.
STATOR TESTING.—The stator winding can
be tested for opens and grounds after it has been
disconnected from the alternator end frame.
If the ohmmeter reading is low or the test lamp
lights when connected between each pair of stator
leads (fig. 2-31), the stator winding is electrically
Should you suspect troubles within the charging
system after checking the wiring connections and
battery, connect a voltmeter across the battery
terminals. If the voltage reading, with the engine speed
increased, is within the manufacturer’s recommended
specification, the charging system is functioning
properly. Should the alternator tests fail, the alternator
should be removed for repairs or replacement. Do
NOT forget, you must ALWAYS disconnect the
cables from the battery first.
A high ohmmeter reading or failure of the test lamp
to light when connected from any one of the leads to
Alternator Testing
To determine what component(s) has caused the
problem, you will be required to disassemble and test
the alternator.
ROTOR TESTING.—To test the rotor for
grounds, shorts, and opens, perform the following:
Figure 2-30.—Testing the rotor for opens and shorts.
To check for grounds, connect a test lamp or
ohmmeter from one of the slip rings to the rotor
shaft (fig. 2-29). A low ohmmeter reading or the
Figure 2-29.—Testing rotor for grounds.
Figure 2-31 .-Testing a stator for opens.
the stator frame (fig. 2-32) indicates the windings are
not grounded. It is not practical to test the stator for
shorts due to the very low resistance of the winding.
DIODE TESTING.—With the stator windings
disconnected, each diode may be tested with an
ohmmeter or with a test light. To perform the test with
an ohmmeter, proceed as follows:
Connect one ohmmeter test lead to the diode lead
and the other to the diode case (fig. 2-33). Note
the reading. Then reverse the ohmmeters leads to
the diode and again note the reading. If both
readings are very low or very high, the diode is
defective. A good diode will give one low and
one high reading.
Figure 2-34.—Testing diodes with a test lamp.
diode is defective. When a good diode is being
tested, the lamp will light in only one of the two
An alternate method of testing each diode is to use
a test lamp with a 12-volt battery. To perform a test
with a test lamp, proceed as follows:
After completing the required test and making any
necessary repairs or replacement of parts, reassemble
the alternator and install it on the vehicle. After
installation, start the engine and check that the
charging system is functioning properly. NEVER
Attempts to do so serves no purpose and may damage
the diodes, wiring, and other charging circuit
Connect one of the test leads to the diode lead
and the other test lead as shown in figure 2-34.
Then reverse the lead connections. If the lamp
lights in both checks, the diode is defective. Or,
if the lamp fails to light in either direction, the
Charging system tests should be performed when
problems point to low alternator voltage and current.
These tests will quickly determine the operating
condition of the charging system. Common charging
system tests are as follows:
Charging system output test-measures current
and voltage output of the charging system.
Regulator voltage test—measures charging
system voltage under low output, low load
Figure 2-32.—Testing a stator for grounds.
Regulator bypass test—connects full battery
voltage to the alternator field, leaving the
regulator out of the circuit.
Circuit resistance tests—measures resistance in
insulted and grounded circuits of the charging
Charging system tests are performed in two
ways—by using a load tester or by using a volt-ohmmillimeter (VOM/multimeter). The load tester
provides the accurate method for testing a charging
system by measuring both system current and voltage.
Figure 2-33.—Testing diodes with an ohmmeter.
and compare it to the manufacturer’s
Charging System Output Test
The charging system output test measures system
voltage and current under maximum load. To check
output with a load tester, connect tester leads as
described by the manufacturer, as you may have either
an inductive (clip-on) amp pickup type or a noninductive type tester. Testing procedures for an
inductive type tester are as follows:
If the voltmeter reading is steady and within
manufacturer’s specifications, then the regulator
setting is okay. However, if the volt reading is steady
but too high or too low, then the regulator needs
adjustment or replacement. If the reading were not
steady, this would indicate a bad wiring connection, an
alternator problem, or a defective regulator, and
further testing is required.
With the load tester controls set as prescribed by
the manufacturer, turn the ignition switch to the
RUN position. Note the ammeter reading.
Regulator Bypass Test
A regulator bypass test is an easy and quick way of
determining if the alternator, regulator, or circuit is
faulty. Procedures for the regulator bypass test is
similar to the charging system output test, except that
the regulator be taken out of the circuit. Direct battery
voltage (unregulated voltage) is used to excite the rotor
field. This should allow the alternator to produce
maximum voltage output.
Start the engine and adjust the idle speed to test
specifications (approximately 200 rpm).
Adjust the load control on the tester until the
ammeter reads specified current output. Do not
let voltage drop below specifications (about 12
volts). Note the ammeter reading.
Rotate the control knob to the OFF position.
Evaluate the readings.
Depending upon the system there are several ways
to bypass the voltage regulator. The most common
ways are as follows:
To calculate charging system output, add the two
ammeter readings. This will give you total charging
system output in amps. Compare this figure to the
specifications within the manufacturer’s manual.
Sorting a test tab to ground on the rear of the
alternator (if equipped).
Current output specifications will depend on the
size (rating) of the alternator. A vehicle with few
electrical accessories may have an alternator rated at
35 amps, whereas a larger vehicle with more electrical
requirements could have an alternator rated from 40 to
80 amps. Always check the manufacturer’s service
manual for exact values.
Placing a jumper wire across the battery and
field terminals of the alternator.
With a remote regulator, unplug the wire from
the regulator and place a jumper wire across the
battery and field terminals in the wires to the
If the charging system output current tested low,
perform a regulator voltage test and a regulator bypass
test to determine whether the alternator, regulator, or
circuit wiring is at fault.
Follow the manufacturer’s directions to
avoid damaging the circuit. You must NOT
short or connect voltage to the wrong wires or
the diodes or voltage regulator may be ruined.
Regulator Voltage Test
When the regulator bypass test is being performed,
charging voltage and current INCREASE to normal
levels. This indicates a bad regulator. If the charging
voltage and current REMAINS THE SAME, then you
have a bad alternator.
A regulator voltage test checks the calibration of
the voltage regulator and detects a low or high setting.
Most voltage regulators are designed to operate
between 13.5 to 14.5 volt range. This range is stated for
normal temperatures with the battery fully’ charged.
Regulator voltage test procedure is as follows:
Circuit Resistance Test
Set the load tester selector to the correct position
using the manufacturer’s manual. With the load
control OFF, run the engine at 2,000 rpm or
specified test speed. Note the voltmeter reading
A circuit resistance test is used to locate faulty
wiring, loose connections, partially burnt wire,
corroded terminals, or other similar types of problems.
There are two common circuit resistance
tests—insulated resistance test and ground circuit
resistance test.
perform an insulated resistance test, connect the load
tester as described by the manufacturer. A typical
connection setup is shown in figure 2-35. Note how the
voltmeter is connected across the alternator output
terminal and positive battery terminal.
With the vehicle running at a fast idle, rotate the
load control knob to obtain a 20-amp current flow at 15
volts or less. All accessories and lights are to be turned
OFF. Read the voltmeter. The voltmeter should NOT
read over 0.7-volt drop (0.1 volt per electrical
connection) for the circuit to be considered in good
condition. However, if the voltage drop is over 0.7
volt, circuit resistance is high and a poor electrical
connection exists.
TEST.—With the ground circuit resistance test the
voltmeter leads are placed across the negative battery
terminal and alternator housing (fig. 2-36).
The voltmeter should NOT read over 0.1 volt per
electrical connection. If the reading is higher, this
indicates such problems as loose or faulty connections,
burnt plug sockets, or other similar malfunctions.
How many electrical circuits are in a typical
automotive electrical system?
What component of the charging system
produces and stores electricity?
What substance is contained in apositiveplate of
a filly charged battery?
What type of gas collects at the top of a battery?
What is the specific gravity of a fully charged
What are the two methods of rating lead-acid
storage batteries?
Q7. When mixing electrolyte, you should follow what
What battery test will determine if current is
discharging across the top of the battery?
You are performing a battery drain test using an
ammeter. What should the meter read with
everything in the vehicle turned off?
When performing a quick charge test, you should
charge the battery at 30 to 40 amps for what
minimum time period?
What are the two types of field circuits used in dc
What are the three design factors that determine
the output of a dc generator?
What two tests are used for locating shorts in the
armature of a dc generator?
What component of the alternator contains the
heat sink the diodes, the diode plate, and the
electrical terminals?
What type of alternator stator is used in high
output alternators?
Figure 2-35.—Typical insulated resistance test setup.
Q16. How is alternator output reduced using an
electronic voltage regulator?
Figure 2-36.—Typical ground circuit resistance test setup.
What is the most common type of voltage
regulator used on modern vehicles?
What charging system test measures the
charging systems voltage, under low output, low
load conditions?
What two testing devices are used to perform a
charging system test?
Q20. When a regulator bypass test is being performed,
what type of voltage is used to excite the rotor
The starting motor (fig. 2-37) converts electrical
energy from the battery into mechanical or rotating
energy to crank the engine. The main difference
between an electric starting motor and an electric
generator is that in a generator, rotation of the armature
in a magnetic field produces voltage. In a motor,
current is sent through the armature and the field; the
attraction and repulsion between the magnetic poles of
the field and armature coil alternately push and pull the
armature around. This rotation (mechanical energy),
when properly connected to the flywheel of an engine,
causes the engine crankshaft to turn.
Learning Objective: Identify starting-circuit
components, their function, operation, and maintenance
The internal combustion engine is not capable of
self-starting. Automotive engines (both spark-ignition
and diesel) are cranked by a small but powerful electric
motor. This motor is called a cranking motor, starting
motor, or starter.
Starting Motor Construction
The battery sends current to the starter when the
operator turns the ignition switch to start. This causes a
pinion gear in the starter to mesh with the teeth of the
ring gear, thereby rotating the engine crankshaft for
The construction of the all starting motors is very
similar. There are, however, slight design variations.
The main parts of a starting motor are as follows:
core, starter shaft, and commutator assembly
that spin inside a stationary field.
The typical starting circuit consists of the battery,
the starter motor and drive mechanism, the ignition
switch, the starter relay or solenoid, a neutral safety
switch (automatic transmissions), and the wiring to
connect these components.
housing for the brushes, brush springs, and shaft
Figure 2-37.—Typical starting motor.
gear, pinion drive mechanism, and solenoid.
encounter are of three designs—Bendix drive,
overrunning clutch, and Dyer drive.
FIELD FRAME—The center housing that holds
the field coils and pole shoes.
The BENDIX DRIVE (fig. 2-38) relies on the
principle of inertia to cause the pinion gear to mesh
with the ring gear. When the starting motor is not
operating, the pinion gear is out of mesh and entirely
away from the ring gear. When the ignition switch is
engaged, the total battery voltage is applied to the
starting motor, and the armature immediately starts to
rotate at high speed.
DRIVE END FRAME—The end housing
around the pinion gear, which has a bushing for
the armature shaft.
assembly consists of an armature shaft, armature core,
commutator, and armature windings.
The armature shaft supports the armature
assembly as it spins inside the starter housing. The
armature core is made of iron and holds the armature
windings in place. The iron increases the magnetic
field strength of the windings.
The commutator serves as a sliding electrical
connection between the motor windings and the
brushes and is mounted on one end of the armature
shaft. The commutator has many segments that are
insulated from each other. As the windings rotate away
from the pole shoe (piece), the commutator segments
change the electrical connection between the brushes
and the windings. This action reverses the magnetic
field around the windings. The constant changing
electrical connection at the windings keeps the motor
C O M M U T A T O R E N D F R A M E .— The
commutator end frame houses the brushes, the brush
springs, and the armature shaft bushing.
The pinion, being weighted on one side and having
internal screw threads, does not rotate immediately
with the shaft but because of inertia, runs forward on
the revolving threaded sleeve until it engages with the
ring gear. If the teeth of the pinion and ring gear do not
engage, the drive spring allows the pinion to revolve
and forces the pinion to mesh with the ring gear. When
the pinion gear is engaged fully with the ring gear, the
pinion is then driven by the starter through the
compressed drive spring and cranks the engine. The
drive spring acts as a cushion while the engine is being
cranked against compression. It also breaks the
severity of the shock on the teeth when the gears
engage and when the engine kicks back due to ignition.
When the engine starts and runs on its own power, the
ring gear drives the pinion at a higher speed than does
the starter. This action causes the pinion to turn in the
opposite direction on the threaded sleeve and
automatically disengages from the ring gear. This
prevents the engine from driving the starter.
provides positive meshing and demeshing of the starter
motor pinion gear and the ring gear. The starting motor
armature shaft drives the shell and sleeve assembly of
the clutch. The rotor assembly is connected to the
pinion gear which meshes with the engine ring gear.
Spring-loaded steel rollers are located in tapered
notches between the shell and the rotor. The springs
The brushes ride on top of the commutator. They
slide on the commutator to carry battery current to the
spinning windings. The springs force the brushes to
maintain contact with the commutator as it spins,
thereby no power interruptions occurs. The armature
shaft bushing supports the commutator end of the
armature shaft.
drive assembly includes the pinion gear, the pinion
drive mechanism, and solenoid. There are two ways
that a starting motor can engage the pinion
assembly—(1) with a moveable pole shoe that engages
the pinion gear and (2) with a solenoid and shift fork
that engages the pinion gear.
The pinion gear is a small gear on the armature
shaft that engages the ring gear on the flywheel. Most
starter pinion gears are made as part of a pinion drive
mechanism. The pinion drive mechanism slides over
one end of the starter armature shaft. The pinion drive
mechanism found on starting motors that you will
Figure 2-38.—Starting motor with a Bendix drive.
Figure 2-39.—Typical overrunning clutch.
principles of both the Bendix and overrunning clutch
drives and is commonly used on heavy-duty engines.
and plungers hold the rollers in position in the tapered
notches. When the armature shaft turns, the rollers are
jammed between the notched surfaces, forcing the
inner and outer members of the assembly to rotate as a
unit and crank the engine.
A starter solenoid is used to make the electrical
connection between the battery and the starting motor.
The starter solenoid is an electromagnetic switch; it is
similar to other relays but is capable ofhandling higher
current levels. A starter solenoid, depending on the
design of the starting motor, has the following
After the engine is started, the ring gear rotates
faster than the pinion gear, thus tending to work the
rollers back against the plungers, and thereby causing
an overrunning action. This action prevents excessive
speed of the starting motor. When the starting motor is
released, the collar and spring assembly pulls the
pinion out of mesh with the ring gear.
Closes battery-to-starter circuit.
Rushes the starter pinion gear into mesh with the
ring gear.
The DYER DRIVE (fig. 2-40) provides complete
and positive meshing of the drive pinion and ring gear
before the starting motor is energized. It combines
Bypass resistance wire in the ignition circuit.
Figure 2-40.—Dyer drive.
The field coil (winding) is a stationary set of
windings that creates a strong magnetic field around
the motor armature. When current flows through the
winding, the magnetic field between the pole shoes
becomes very large. Acting against the magnetic field
created by the armature, this action spins the motor
with extra power. Field windings vary according to the
application of the starter motor. The most popular
configurations are as follows (fig. 2-41):
The starter solenoid may be located away from or
on the starting motor. When mounted away from the
starter, the solenoid only makes and breaks electrical
connection. When mounted on the starter, it also slides
the pinion gear into the flywheel.
In operation, the solenoid is actuated when the
ignition switch is turned or when the starter button is
depressed. The action causes current to flow through
the solenoid (causing a magnetic attraction of the
plunger) to ground. The movement of the plunger
causes the shift lever to engage the pinion with the ring
gear. After the pinion is engaged, further travel of the
plunger causes the contacts inside the solenoid to close
and directly connects the battery to the starter.
of the two field coils in parallel will increase
their strength because they receive full voltage.
Note that two additional pole shoes are used.
Though they have no windings, their presence
will further strengthen the magnetic field.
If cranking continues after the control circuit is
broken, it is most likely to be caused by either shorted
solenoid windings or by binding of the plunger in the
solenoid. Low voltage from the battery is often the
cause of the starter making a clicking sound. When this
occurs, check all starting circuit connections for
cleanliness and tightness.
The wiring of four field coils in a series-parallel
combination creates a stronger magnetic field
than the two field coil configuration.
four field coils in series provides a large amount
of low-speed torque, which is desirable for
automotive starting motors. However, serieswound motors can build up excessive speed if
FIELD FRAME.—The field frame is the center
housing that holds the field coils and pole shoes.
Figure 2-41.—Field winding configurations.
allowed to run free to the point where they will
destroy themselves.
Three pairs of series-wound field coils provide
the magnetic field for a heavy-duty starter
motor. This configuration uses six brushes.
SHUNT—The use of one filled coil that is
shunted to ground with a series-wound motor
controls motor speed. Because the shunt coil is
not affected by speed, it will draw a steady heavy
current, effectively limiting speed.
Figure 2-42.—Gear reduction starter.
DRIVE END FRAME.—The drive end frame is
designed to protect the drive pinion from damage and
to support the armature shaft. The drive end frame of
the starter contains a bushing to prevent wear between
the armature shaft and drive end frame.
Vehicles equipped with automatic transmissions
require the use of a neutral safety switch. The neutral
safety switch prevents the engine from being started
unless the shift selector of the transmission is in
NEUTRAL or PARK. It disables the starting circuit
when the transmission is in gear. This safety feature
prevents the accidental starting of a vehicle in gear,
which can result in personal injury and vehicle
Types of Starting Motors
There are two types of starting motors that you will
encounter on equipment. These are the direct drive
starter and the double reduction starter. All starters
require the use of gear reduction to provide the
mechanical advantage required to turn the engine
flywheel and crankshaft.
The neutral safety switch is wired into the circuit
going to the starter solenoid. When the transmission is
in forward or reverse gear, the switch is in the OPEN
position (disconnected). This action prevents current
from activating the solenoid and starter when the
ignition switch is turned to the START position. When
the transmission is in neutral or park, the switch is
closed (connected), allowing current to flow to the
starter when the ignition is turned.
starters make use of a pinion gear on the armature shaft
of the starting motor. This gear meshes with teeth on
the ring gear. There are between 10 to 16 teeth on the
ring gear for every one on the pinion gear. Therefore,
the starting motor revolves 10 to 16 times for every
revolution of the ring gear. In operation, the starting
motor armature revolves at a rate of 2,000 to 3,000
revolutions per minute, thus turning the engine
crankshaft at speeds up to 200 revolutions per minute.
A misadjusted or bad neutral safety switch can
keep the engine from cranking. If the vehicle does not
start, you should check the action of the neutral safety
switch by moving the shift lever into various positions
while trying to start the vehicle. If the starter begins to
work, the switch needs to be readjusted.
double reduction starter makes use of gear reduction
within the starter and the reduction between the drive
pinion and the ring gear. The gear reduction drive head
is used on heavy-duty equipment.
To readjust a neutral safety switch, loosen the
fasteners that hold the switch. With the switch
loosened, place the shift lever into park (P). Then,
while holding the ignition switch in the START
position, slide the neutral switch on its mount until the
engine cranks. Without moving the switch, tighten the
fasteners. The engine should now start with the shift
lever in park or neutral. Check for proper operation
after the adjustment.
Figure 2-42 shows a typical gear reduction starter.
The gear on the armature shaft does not mesh directly
with the teeth on the ring gear, but with an intermediate
gear which drives the driving pinion. This action
provides additional breakaway, or starting torque, and
greater cranking power. The armature of a starting
motor with a gear reduction drive head may rotate as
many as 40 revolutions for every revolution of the
engine flywheel.
If by adjusting the switch to normal operation is
not resumed, it may be required to test the switch. All
that is required to test the switch is a 12-volt test light.
The starter circuit voltage drop tests (insulated
circuit resistance test and starter ground test) are
used to locate parts with higher than normal
resistance quickly.
To test the switch, touch the test light to the switch
output wire connection while moving the shift lever.
The light should glow as the shift lever is slid into park
or neutral. The light should not work in any other
position. If the light is not working properly, check the
mechanism that operates the switch. If the problem is
in the switch, replace it.
Starter Current Draw Test
The starter current draw test measures the amount
of amperage used by the starting circuit. It quickly tells
you about the condition of the starting motor and other
circuit components. If the current draw is lower or
higher than the manufacturer’s specifications, there is a
problem in the circuit.
The condition of the starting motor should be
carefully checked at each PM service. This permits you
to take appropriate action, where needed, so equipment
failures caused by a faulty starter can be reduced, if not
To perform a starter current draw test, you may use
either a voltmeter or inductive ammeter or a battery
load tester. These meters are connected to the battery to
measure battery voltage and current flow out of the
battery. For setup procedures, use the manufacturer’s
manual for the type of meter you intend to use.
A visual inspection for clean, tight electrical
connections and secure mounting at the flywheel
housing is the extent of the maintenance check. Then
operate the starter and observe the speed of rotation
and the steadiness of operation. To prevent the starter
from overheating, do NOT operate the starter for more
than 30 seconds.
To keep a gasoline engine from starting during
testing, disconnect the coil supply wire or ground the
coil wire. With a diesel engine, disable the fuel
injection system or unhook the fuel shutoff solenoid.
Check the manufacturer’s service manual for details.
If the starter is not operating properly, remove the
starter, disassemble it, and check the commutator and
brushes. If the commutator is dirty, it may be cleaned
with a piece of No. 00 sandpaper. However, if the
commutator is rough, pitted, or out-of-round or if the
insulation between the commutator bars is high, it
must be reconditioned using an armature lathe.
With the engine ready for testing, crank the engine
and note the voltage and current readings. Check the
manufacturer’s service manual. If they are not within
specifications, there is something wrong with the
starting circuit.
Brushes should be at least half of their original
size. If not, replace them. The brushes should have free
movement in the brush holders and make good, clean
contact with the commutator.
Do NOT crank the engine for more than 30
seconds or starter damage can result. If the
starter is cranked too long, it will overheat.
Allow the starter to cool for a few minutes if
more cranking time is needed.
Once the starter is checked and repaired as needed,
it should be reassembled, making sure that the starter
brushes are seated. Align the housings and install the
bolts securely. Install the starter in the opening in the
flywheel housing and tighten the attaching bolts to the
specified torque. Connect the cable and wire lead
firmly to clean terminals.
Starting Circuit Voltage Drop Tests
A voltage drop test will quickly locate a
component with higher than normal resistance. This
test provides an easy way of checking circuit
condition. You do NOT have to disconnect any wires
and components to check for voltage drops. The two
types of voltage drop tests are the insulated circuit
resistance test and the starter ground circuit test.
There are many ways of testing a starting motor
circuit to determine its operating condition. The most
common tests are as follows:
TEST.—The insulated circuit resistance test checks
ail components between the positive terminal of the
battery and the starting motor for excess resistance.
The starter current draw test is used to measure
the amount of amperage used by the starting
Using a voltmeter, connect the leads to the positive
terminal of the battery and the starting motor output
Learning Objective: Identify ignition-circuit
components, their functions, and maintenance
With the ignition or injection system disabled,
crank the engine. Note the voltmeter reading. It should
not be over 0.5 volts. If voltage drop is greater,
something within the circuit has excessive resistance.
There may be a burned or pitted solenoid contact, loose
electrical connections, or other malfunctions. Each
component is then to be tested individually.
starter ground circuit test checks the circuit between
the starting motor and the negative terminal of the
Using a voltmeter, connect the leads to the
negative terminal of the battery and to the end frame of
the starting motor. Crank the engine and note the
voltmeter reading. If it is higher than 0.5 volts, check
the voltage drop across the negative battery cable. The
engine may not be properly grounded. Clean, tighten,
or replace the battery cable if needed. A battery cable
problem can produce symptoms similar to a dead
battery, bad solenoid, or weak starting motor. If the
cables do NOT allow enough current to flow, the
starter will turn slowly or not at all.
What type of starter uses gear reduction within
the starter and gear reduction between the drive
pinion and the ring gear?
When repairing a starter, you should replace the
brushes if they are one half of their original size.
When a starter is being tested what is the
maximum amount of time the engine should be
cranked before starter damage can occur?
What test is used to check for excessive
resistance in all components between the
positive battery terminal and the starter?
Provide a method of turning the ignition circuit
ON and OFF.
Be capable of operating on various supply
voltages (battery or alternator voltage).
Produce a high voltage arc at the spark plug
electrodes to start combustion.
Distribute high voltage pulses to each spark plug
in the correct sequence.
Vary spark timing with engine speed, load, and
other conditions.
What is the only function of a starter solenoid
when it is mounted away from the starter?
What is the most likely cause of a starter making
a clicking sound?
The functions of an ignition circuit are as follows:
Time the spark so that it occurs as the piston
nears TDC on the compression stroke.
What are the three types of pinion drive
mechanisms used on starting motors?
The ignition circuit supplies high voltage surges
(some as high as 50,000 volts in electronic ignition
circuits) to the spark plugs in the engine cylinders.
These surges produce electric sparks across the spark
plug gaps. The heat from the spark ignites the
compressed air-fuel mixture in the combustion
chambers. When the engine is idling, the spark appears
at the spark plug gap just as the piston nears top dead
center (TDC) on the compression stroke. When the
engine is operating at higher speeds, the spark is
advanced. It is moved ahead and occurs earlier in the
compression stroke. This design gives the compressed
mixture more time to bum and deliver its energy to the
The ignition circuit is actually made of two
separate circuits which work together to cause the
electric spark at the spark plugs. These two circuits are
The primary circuit of the ignition circuit includes
all of the components and wiring operating on low
voltage (battery or alternator voltage). Wiring in the
primary circuit uses conventional wire, similar to the
wire used in other electrical circuits on the vehicle.
The secondary circuit of the ignition circuit is the
high voltage section. It consists of the wire and
components between the coil output and the spark plug
ground. Wiring in the secondary circuit must have a
thicker insulation than that of the primary circuit to
prevent leaking (arcing) of the high voltage.
IGNITION-ON position when the key is released
Various ignition circuit components are designed
to achieve the functions of the ignition circuit. Basic
ignition circuit components are as follows:
Ignition Coil
BATTERY—provides power for the circuit.
(This was discussed earlier in this chapter.)
The ignition coil (fig. 2-44) produces the high
voltage required to make current jump the gap at the
spark plugs. It is a pulse type transformer capable of
producing a short burst of high voltage for starting
IGNITION SWITCH—allows the operator to
turn the circuit and engine ON and OFF.
IGNITION COIL—changes battery voltage to
high ignition voltage (30,000 volts and greater).
ignition voltage to the spark plug. Contains
either mechanical contact points or an electronic
switching circuit.
SPARK PLUG—device that provides an air gap
in the combustion chamber for an electric arc.
Ignition Switch
The ignition switch (fig. 2-43) enables the operator
to turn the ignition on for starting and running the
engine and to turn it off to stop the engine. Most
automotive ignition switches incorporate four
positions, which are as follows:
OFF.—The OFF position shuts off the electrical
system. Systems, such as the headlights, are usually
not wired through the ignition switch and will continue
to operate.
The ignition coil is made of two sets of windings
(primary and secondary), two primary terminals (low
voltage connections), an iron core (long piece of iron
inside the windings), and a high voltage terminal (coil
wire connection).
The primary winding is the outer winding and is
made up of several hundred turns of heavy wire,
wrapped around or near the secondary winding. The
secondary winding is the inner winding and is made up
of several thousand turns of heavy wire located inside
or near the primary winding. The secondary windings
are wound in the opposite direction of the primary, and
the ends are attached internally to the primary
windings and the high voltage terminal. Both windings
are wrapped around an iron core and are housed inside
the coil case.
To obtain the high current required for ignition,
battery current flows through the ignition coil primary
windings producing a strong magnetic field. The
action of the iron core strengthens the magnetic field.
turns on power to the entire vehicle electrical system
with the exception of the ignition circuit.
turns on the entire electrical system including the
ignition circuit.
START.—The START position will energize the
starter solenoid circuit to-crank the engine. The
START position is spring-loaded to return to the
Figure 2-44.—Sectional view of an ignition coil.
Figure 2-43.—Ignition switch and positions.
When the current flowing through the coil is
broken (the primary circuit is opened), the magnetic
field collapses across the secondary windings. As the
magnetic field collapses, a high electrical voltage is
induced into the secondary circuit.
whereas the pickup coil type distributor is used on
many modern vehicles. The ignition distributor has
several functions, which are as follows:
Since both the primary and secondary windings of
the coil are stationary, some means other than
movement of the windings must be found to change the
magnetic field surrounding the coils. In practice, a
switching device in the primary circuit creates this
effect. There are two common methods to break
current flow and fire the coil—mechanical contact
points or an electronic switching device.
It distributes the high voltage surges of the coil to
the spark plugs.
It actuates the ON/OFF cycles of current flow
through the primary windings of the coil.
Ignition Distributor
It causes the spark to occur at each spark plug
earlier in the compression stroke as speed
It changes spark timing with the changes in
engine load. As more load is placed on the
engine, the spark timing must occur later in the
compression stroke to prevent spark knock.
In some cases, the bottom of the distributor shaft
powers the engine oil pump.
An ignition distributor can be a contact point or
pickup coil type, as shown in figure 2-45. A contact
point distributor is commonly found in older vehicles,
In some electronic distributors, the distributors
house the ignition coil and the electronic
switching unit.
DISTRIBUTOR CAP.—The distributor cap is an
insulating plastic component that covers the top of the
distributor housing. Its center terminal transfers
voltage from the coil wire to the rotor. The distributor
cap also has outer terminals that send electric arcs to
the spark plugs. Metal terminals are molded into the
plastic cap to provide electrical connections.
rotor transfers voltage from the coil wire to the spark
plug wires. The rotor is mounted on top of the
distributor shaft. It is an electrical switch that feeds
voltage to each spark plug wire in turn.
A metal terminal on the rotor touches the
distributor cap center terminal. The outer end of the
rotor ALMOST touches the outer cap terminals.
Voltage is high enough that it can jump the air space
between the rotor and cap. Approximately 4,000 volts
are required for the spark to jump this rotor-to-cap gap.
The spark plug consists of a porcelain insulator in
which there is an insulated electrode supported by a
metal shell with a grounded electrode. They have a
simple purpose of supplying a fixed gap in the cylinder
across which the high voltage surges from the coil must
jump after passing through the distributor.
The spark plugs use ignition coil high voltage to
ignite the fuel mixture. Somewhere between 4,000 and
10,000 volts are required to make current jump the gap
Figure 2-45.—Comparison of a (A) contact point distributor
and a (B) pickup coil distributor.
at the plug electrodes. This is much lower than the
output potential of the coil.
prevent overheating and preignition. A cold spark plug
is used in engines operated at high speeds.
Spark plug gap is the distance between the center
and side electrodes. Normal gap specifications range
between .030 to .060 inch. Smaller spark plugs gaps
are used on older vehicles equipped with contact point
ignition systems.
Vehicle manufacturers recommend a specific
spark plug heat range for their engines. The heat range
is coded and given as a number on the spark plug
insulator. The larger the number on the plug, the hotter
the spark plug tip will operate. For example, a 54 plug
would be hotter than a 44 or 34 plug.
Spark plugs are either resistor or non-resistor types
(fig. 2-46). A resistor spark plug has internal resistance
(approximately 10,000 ohms) designed to reduce the
static in radios. Most new vehicles require resistortype
plugs. Non-resistor spark plug has a solid metal rod
forming the center electrode. This type of spark plugs
is NOT commonly used except for racing and off-road
The only time you should change from spark plug
heat range specifications is when abnormal engine or
operating conditions are encountered. For instance, if
the plug runs too cool, sooty carbon will deposit on the
insulator around the center electrode. This deposit
could soon build up enough to short out the plug. Then
high voltage surges would leak across the carbon
instead of producing a spark across the spark plug gap.
Using a hotter plug will bum this carbon deposit away
or prevent it from forming.
Spark Plug Heat Range and Reach
The heat range of the spark plug determines how
hot the plug will get. The length and diameter of the
insulator tip and the ability of the spark plug to transfer
heat into the cooling system determine spark plug heat
Spark plug reach is the distance between the end of
the spark plug threads and the seat or sealing surface of
the plug. Plug reach determines how far the plug
reaches through the cylinder head. If spark plug reach
is too long, the spark plug will protrude too far into the
combustion chamber and the piston at TDC may strike
the electrode. However, if the reach is too short, the
plug electrode may not extend far enough into the
cylinder head and combustion efficiency will be
reduced. A spark plug must reach into the combustion
chamber far enough so that the spark gap will be
properly positioned in the combustion chamber
without interfering with the turbulence of the air-fuel
mixture or reducing combustion action.
A hot spark plug has a long insulator tip that
prevents heat transfer into the waterjackets. It will also
bum off any oil deposits. This provides a self-cleaning
A cold spark plug has a shorter insulator tip and
operates at a cooler temperature. The cooler tip helps
Spark Plug Wires
The spark plug wires carry the high voltage
electric current from the distributor cap side terminals
to the spark plugs. In vehicles with distributorless
ignition, the spark plug wires carry coil voltage
directly to the spark plugs. The two types of spark plug
wires are as follows:
SOLID WIRE—Solid wire spark plug wires are
used on older vehicles. The wire conductor is
simply a strand of metal wire. Solid wires cause
radio interference and are no longer used on
RESISTANCE WIRE—Resistance spark plug
wires consist of carbon-impregnated strands of
rayon braid. They are used on modern vehicle
because they contain internal resistance that
Figure 2-46.—Sectional view of a (A) non-resistor and (B)
resistor spark plug.
prevents radio interference. Also known as radio
interference wires, they have approximately
10,000 ohms per foot. This prevents highvoltage-induced popping or cracking of the radio
Contact Point Ignition System Operation
With the engine running, the distributor shaft and
distributor cam rotate. This action causes the
distributor cam to open and close the contact points.
With the contact points wired to the primary
windings of the ignition coil, the contact points make
and break the ignition coil primary circuit. With the
contact points closed, the magnetic field builds up in
the coil. As the points open, the magnetic field
collapses and voltage is sent to the spark plugs.
On the outer ends of the spark plug wires, boots
protect the metal connectors from corrosion, oil, and
moisture that would permit high voltage to leak across
the terminal to the shell of the spark plug.
Before studying today's electronic ignition
systems, you should have a basic understanding of the
contact point ignition system. The two systems use
many of the same components. These include the
battery, the ignition coil, the ignition distributor, the
spark plugs, and wires and cables that connect them.
Contact Point Ignitions System
With the distributor operating at one half of engine
speed and with only one cam for each engine cylinder,
each spark plug only fires once during a complete
revolution of the distributor cam.
To ensure that the contact points are closed for a set
time, point dwell, also known as cam angle, is set by
using a dwell meter. Point dwell is the amount of time
given in degrees of distributor rotation that the points
remain closed between each opening.
A dwell period is required to assure that the coil
has enough time to build up a strong magnetic field. If
the point dwell is too small, the current will have
insufficient time to pass through the primary windings
of the ignition coil, resulting in a weak spark.
However, if the point dwell is too great, the contact
points will not open far enough, resulting in arcing or
burning of the points.
The internal components of the distributor for a
contact point ignition consist of the following:
DISTRIBUTOR CAM—The distributor cam is
part of, or is attached to, the distributor shaft and
has one lobe for each cylinder. As the cam
rotates with the shaft at one half of engine speed,
the lobes cause the contact points to open and
close the primary circuit.
CONTACT POINTS—The contact points, also
called breaker points, act like spring-loaded
electrical switches in the distributor. Its function
is to cause intermittent current flow in the
primary circuit, thus causing the magnetic field
in the coil to build up and collapse when it
reaches maximum strength. Wires from the
condenser and ignition coil primary circuit
connect to the points.
The basic difference between the contact point and
the electronic ignition system is in the primary circuit.
The primary circuit in a contact point ignition system is
open and closed by contact points. In the electronic
system, the primary circuit is open and closed by the
electronic control unit (ECU).
The secondary circuits are practically the same for
the two systems. The difference is that the distributor,
ignition coil, and wiring are altered to handle the high
voltage produced by the electronic ignition system.
CONDENSER—The condenser, also known as
a capacitor, is wired in parallel with the contact
points and grounded through the distributor
housing. The condenser prevents arcing or
burning at the distributor contact points when the
points are first open. The condenser provides a
place where current can flow until the contact
points are fully open.
One advantage of this higher voltage (up to 60,000
volts) is that spark plugs with wider gaps can be used.
This results in a longer spark, which can ignite leaner
air-fuel mixtures. As a result engines can run on leaner
mixtures for better fuel economy and lower emissions.
magnetic field. Then, when the trigger wheel and
pickup coil turn OFF the ECU, the magnetic field
inside the ignition coil collapses and fires a sparkplug.
Electronic Ignition System Components
The components of an electronic ignition system
regardless of the manufacturer all perform the same
functions. Each manufacturer has it own preferred
terminology and location of the components. The basic
components of an electronic ignition system are as
Hall-Effect Sensor
Some electronic distributors have a magnetic
sensor using the Hall effect. When a steel shutter
moves between the two poles of a magnet, it cuts off
the magnetism between the two poles. The Hall-effect
distributor has a rotor with curved plates, called
shutters. These shutters are curved so they can pass
through the air gap between the two poles of the
magnetic sensor, as the rotor turns. Like the trigger
wheel, there are the same number of shutters as there
are engine cylinders.
TRIGGER WHEEL—The trigger wheel, also
known as a reluctor, pole piece, or armature, is
connected to the upper end of the distributor
shaft. The trigger wheel replaces the distributor
cam. Like the distributor cam lobes, the teeth on
the trigger wheel equal the number of engine
PICKUP COIL—The pickup coil, also known as
a sensor assembly, sensor coil, or magnetic
pickup assembly, produces tiny voltage surges
for the ignition systems electronic control unit.
The pickup coil is a small set of windings
forming a coil.
ELECRTONIC CONTROL UNIT AMPLIFIER—The ignition system electronic
control unit amplifier or control module is an
"electronic switch" that turns the ignition coil
primary current ON and OFF. The ECU
performs the same function as the contact points.
The ignition ECU is a network of transistors,
capacitors, resistors, and other electronic
components sealed in a metal or plastic housing.
The ECU can be located (1) in the engine
compartment, (2) on the side of the distributor,
(3) inside the distributor, or (4) under the vehicle
dash. ECU dwell time (number of degrees the
circuit conducts current to the ignition coil) is
designed into the electronic circuit of the ECU
and is NOT adjustable.
Each time a shutter moves through the air gap
between the two poles of the magnetic sensor, it cuts
off the magnetic field between the poles. This action
provides a signal to the ECU. When a shutter is not in
the way, the magnetic sensor is producing voltage.
This voltage is signaling the ECU to allow current to
flow through the ignition coils primary winding.
However, when the shutter moves to cut off the
magnetic field, the signal voltage drops to zero. The
ECU then cuts off the current to the ignition coils
primary winding. The magnetic field collapses,
causing the coil secondary winding to produce a high
voltage surge. This high voltage surge is sent by the
rotor to the proper spark plug.
Ignition timing refers to how early or late the spark
plugs fire in relation to the position of the engine
pistons. Ignition timing must vary with engine speed,
load, and temperature.
Timing advance happens when the spark plugs fire
sooner than the compression strokes of the engine. The
timing is set several degrees before top dead center
(TDC). More time advance is required at higher speeds
to give combustion enough time to develop pressure on
the power stroke.
Electronic Ignition System Operation
With the engine running, the trigger wheel rotates
inside the distributor. As a tooth of the trigger wheel
passes the pickup coil, the magnetic field strengthens
around the pickup coil. This action changes the output
voltage or current flow through the coil. As a result, an
electrical surge is sent to the electronic control unit, as
the trigger wheel teeth pass the pickup coil.
Timing retard happens when the spark plugs fire
later on the compression strokes. This is the opposite of
timing advance. Spark retard is required at lower
speeds and under high load conditions. Timing retard
prevents the fuel from burning too much on the
compression stroke, which would cause spark knock or
The electronic control unit increases the electrical
surges into ON/OFF cycles for the ignition coil. When
the ECU is ON, current passes through the primary
windings of the ignition coil, thereby developing a
The basic methods to control ignition system
timing are as follows:
of a vacuum diaphragm, link, movable distributor
plate, and a vacuum supply hose.
engine speed)
At idle, the vacuum port from the carburetor or
throttle body to the distributor advance is covered,
thereby NO vacuum is applied to the vacuum
diaphragm, and spark timing is NOT advanced. At part
throttle, the throttle valve uncovers the vacuum port
and the port is exposed to engine vacuum. The vacuum
pulls the diaphragm outward against spring force. The
diaphragm is linked to a movable distributor plate,
which is rotated against distributor shaft rotation and
spark timing is advanced.
VACUUM ADVANCE (controlled by intake
manifold vacuum and engine load)
various sensors—speed, temperature, intake,
vacuum, throttle position, etc.)
Centrifugal Advance
Centrifugal advance makes the ignition coil and
spark plugs fire sooner as engine speed increases,
using spring-loaded weights, centrifugal force, and
lever action to rotate the distributor cam or trigger
wheel. Spark timing is advanced by rotating the
distributor cam or trigger wheel against distributor
shaft rotation. This action helps correct ignition timing
for maximum engine power. Basically the centrifugal
advance consists of two advance weights, two springs,
and a advance lever.
The vacuum advance does not produce any
advance at full throttle. When the throttle valve is wide
open, vacuum is almost zero. Thus vacuum is NOT
applied to the distributor diaphragm and the vacuum
advance does NOT operate.
Computerized Advance
The computerized advance, also known as an
electronic spark advance system, uses various engine
sensors and a computer to control ignition timing. The
engine sensors check various operating conditions and
sends electrical data to the computer. The computer
can change ignition timing for maximum engine
During periods of low engine speed, the springs
hold the advance weights inward towards the
distributor cam or trigger wheel. At this time there is
not enough centrifugal force to push the weights
outward. Timing stays at its normal initial setting.
Ignition system engine sensors include the
As speed increases, centrifugal force on the
weights moves them outwards against spring tension.
This movement causes the distributor cam or trigger
wheel to move ahead. With this design, the higher the
engine speed, the faster the distributor shaft turns, the
farther out the advance weights move, and the farther
ahead the cam or trigger wheel is moved forward or
advanced. At a preset engine speed, the lever strikes a
stop and centrifugal advance reaches maximum.
ENGINE SPEED SENSOR (reports engine
speed to the computer)
piston position)
position of the throttle)
(checks the temperature of the air entering the
The action of the centrifugal advance causes the
contact points to open sooner, or the trigger wheel and
pickup coil turn off the ECU sooner. This causes the
ignition coil to fire with the engine pistons not as far up
in the cylinders.
SENSOR (measures the operating temperature
of the engine)
Vacuum Advance
DETONATION SENSOR (allows the computer
to retard timing when the engine knocks or
The vacuum advance provides additional spark
advance when engine load is low at part throttle
position. It is a method of matching ignition timing
with engine load. The vacuum advance increases
FUEL ECONOMY because it helps maintain idle fuel
spark advance at all times. A vacuum advance consists
engine vacuum, an indicator of load)
The computer receives different current or voltage
levels (input signals) from these sensors. It is
programmed to adjust ignition timing based on engine
conditions. The computer may be mounted on the air
cleaner, under the dash, on a fender panel, or under a
starting. After prolonged use, the spark plug tip can
become coated with ash, oil, and other residue. The
spark plug electrodes can also bum and widen the gap.
This makes it more difficult for the ignition system to
produce an electric arc between the electrodes.
The following is an example of the operation of a
computerized advance. A vehicle is traveling down the
road at 50 mph; the speed sensor detects moderate
engine speed. The throttle position sensor detects part
throttle and the air inlet and coolant temperature
sensors report normal operating temperatures. The
intake vacuum sensor sends high vacuum signals to the
To read spark plugs closely, inspect and analyze
the condition of each spark plug tip and insulator. This
will give you information on the condition of the
engine, the fuel system, and the ignition system. The
conditions commonly encountered with spark plugs
areas follows:
NORMAL OPERATION (fig. 2-47) appears as
brown to grayish-tan deposit with slight
electrode wear. This indicates the correct spark
plug heat range and mixed periods of high- and
low-speed operation. Spark plugs, having this
appearance, may be cleaned, regapped, and
The computer receives all the data and calculates
that the engine requires maximum spark advance. The
timing would occur several degrees before TDC on the
compression stroke. This action assures that high fuel
economy is attained on the road.
If the operator began to pass another vehicle,
intake vacuum sensor detects a vacuum drop to near
zero and a signal is sent to the computer. The throttle
position sensor detects a wide, open throttle and other
sensor outputs say the same. The computer receives
and calculates the data, then, if required, retards
ignition timing to prevent spark knock or ping.
CARBON FOULED (fig. 2-48) appears as dry,
fluffy black carbon, resulting from slow
operating speeds, wrong heat range (too cold),
weak ignition (weak coil, worn ignition cables,
etc.), faulty automatic choke, sticking manifold
control valve, or rich air-fuel mixture. Spark
plugs, having this appearance, may be cleaned,
regapped, and reinstalled.
OIL FOULED (fig. 2-49) appears as wet, oily
deposits with very little electrode wear, resulting
from worn rings, scored cylinder, or leaking
valve seals. Spark plugs, having this appearance,
may be degreased, cleaned, regapped, and
Ignition troubles can result from a myriad of
problems, from faulty components to loose or
damaged wiring. Unless the vehicle stops on the job,
the operator will report trouble indications, and the
equipment is turned into the shop for repairs.
Unless the trouble is known, a systematic
procedure should be followed to locate the cause.
Remember, that electric current will follow the path of
least resistance. Trace ignition wiring while checking
for grounds, shorts, and open circuits. Bare wires,
loose connections, and corrosion are found through
visual inspection.
After checking the system, you must evaluate the
symptoms and narrow down the possible causes. Use
your knowledge of system operation, a service manual
troubleshooting chart, basic testing methods, and
common sense to locate the trouble. Many shops have
specialized equipment that provide the mechanic a
quick and easy means of diagnosing ignition system
Spark Plugs and Spark Plug Wires
Bad spark plugs cause a wide range of problems—
misfiring, lack of power, poor fuel economy, and hard
Figure 2-47.—Normal operation.
Figure 2-50.—Ash fouled.
Figure 2-48.—Carbon fouled.
electrodes, resulting from over-advanced timing, lowoctane fuel, wrong spark plug heat range (too high), or a
lean air-fuel mixture. Spark plugs, having this
condition, are to be replaced with ones having the
recommended heat range.
When a spark plug is removed for cleaning or
inspection, it should be regapped by the engine
manufacturer’s specifications. New spark plugs are
also to be regapped before installation, as they may
have been dropped or mishandled and are not within
A wire type feeler gauge should be used to measure
spark plug gap. Slide the feeler gauge between the
electrodes. If needed, bend the side electrode until the
feeler gauge fits snugly. The gauge should drag
Figure 2-49.—Oil fouled.
ASH FOULED (fig. 2-50) appears as red, brown,
yellow, or white colored deposits which accumulate on
the insulator, resulting from poor fuel quality or oil
entering the cylinder. Most ash deposits have no
adverse effect on the operation of the spark plug as long
as they remain in a powdery state. However, under
certain conditions these deposits melt and form a shiny
glaze on the insulator which, when hot, acts as a good
electrical conductor. This allows current to follow the
deposit instead ofjumping the gap, thus shorting out the
spark plug. Spark plugs, having a powdery condition,
may be cleaned, regapped, and replaced. Those having a
glazed deposit are to be replaced.
PREIGNITON DAMAGE (fig. 2-5 1) appears as
burned or blistered insulator tips and badly worn
Figure 2-51.—Preignition damage.
problems point to possible distributor cap or rotor
troubles, remove and inspect them. The distributor cap
should be carefully checked to see that sparks have not
been arcing from point to point. Both interior and
exterior must be clean. The firing points should not be
eroded, and the interior of the towers must be clean.
slightly, as it is pulled in and out of the gap. Spark plug
gaps vary from 0.30 inch on contact point ignitions to
over 0.60 inch on electronic ignition systems.
When the spark plugs are being reinstalled, tighten
them to the manufacturer’s recommendation. Some
manufacturers give spark plug torque, while others
recommend bottoming the plugs on the seat and then
turning an additional one-quarter to one-half turn. Refer
to the manufacturer’s service manual for exact
The rotor tip, from which the high-tension spark
jumps to each distributor cap terminal, should not be
worn. It also should be checked for excessive burning,
carbon trace, looseness, or other damage. Any wear or
irregularity will result in excessive resistance to the
high-tension spark. Make sure that the rotor fits snugly
on the distributor shaft.
A faulty spark wire can either have a burned or
broken conductor, or it could have deteriorated
insulation. Most spark plugs wires have a resistance
conductor that can be easily separated. If the conductor
is broken, voltage and current cannot reach the spark
plug. If the insulation is faulty, sparks may leak
through to ground or to another wire instead of
reaching the spark plugs. To test the wires for proper
operation, you can perform the following:
A common problem arises when a CARBON
TRACE (small line of carbonlike substance that
conducts electricity) forms on the inside of the
distributor cap or outer edge of the rotor. The carbon
trace will short coil voltage to ground or to a wrong
terminal lug in the distributor cap. A carbon trace will
cause the spark plugs to either fire poorly or not at all.
will check the spark plug conductor or coil wire
conductor. To perform a wire resistance test, connect an
ohmmeter across each end of the wire. The meter will
read internal wire resistance in ohms. Typically
resistance should NOT be over 5,000 ohms per inch or
100.000 ohms total. Since specifications vary, compare
your readings to the manufacturer’s specifications.
Using a droplight, check the inside of the
distributor cap for cracks and carbon trace. Carbon
trace is black which makes it hard to see on a blackcolored distributor cap. If carbon trace or a crack is
found, replace the distributor cap or rotor.
SERVICE. —In a contact point distributor, there are
two areas of concern—the contact points and the
checks for sparks arcing through the insulation to
ground. To perform an insulation test with the hood up,
block out as much light as possible, start the engine, and
move a grounded screwdriver next to the insulation. If a
spark jumps through the insulation to the screwdriver,
the wire is bad. Spark plug leakage is a condition in
which electric arcs pass through the wire insulation.
Bad contact points cause a variety of engine
performance problems. These problems include highspeed missing, no-start problem, and many other
ignition troubles. Visually inspect the surfaces of the
contact points to determine their condition. Points with
burned and pitted contacts or with a worn rubbing
block must be replaced. However, if the points look
good, point resistance should be measured. Turn the
engine over until the points are closed and then use an
ohmmeter to connect the meter to the primary point
lead and to ground. If resistance reading is too high, the
points are burned and must be replaced.
Installing new spark plug wire is a simply task,
especially when one wire at a time is replaced. Wire
replacement is more complicated if all of the wires
have been removed. Then you must use engine firing
order and cylinder numbers to route each wire
correctly. Service manuals can be used to trace the
wires from each distributor cap tower to the correct
spark plug.
A faulty condenser may leak (allow some dc
current to flow to ground), be shorted (direct electrical
connection to ground), or be opened (broken lead wire
to the condenser foils). If the condenser is leaking or
open, it will cause point arcing and burning. If the
condenser is shorted, primary current will flow to
ground and the engine will NOT start. To test a
condenser using an ohmmeter, connect the meter to the
Distributor Service
The distributor is critical to the proper operation of
the ignition system. The distributor senses engine
speed, alters ignition timing, and distributes high
voltage to the spark plugs. If any part of the distributor
is faulty, engine performance suffers.
condenser and to ground. The meter should register
slightly and then return to infinity (maximum
resistance). Any continuous reading other than infinity
indicates that the condenser is leaking and must be
Ensure the feeler gauge is clean before
inserting it between the points. Oil and grease
will reduce the service life of the points.
Installing contact points is a relatively simple
procedure but must be done with precision and care in
order to achieve good engine performance and
economy. Make sure the points are clean and free of
any foreign material.
To use a dwell meter for adjusting contact points,
connect the red lead of the dwell meter to the
distributor side of the ignition coil (wire going to the
contact points). Connect the black lead to ground.
Proper alignment of the contact points is extremely
important (fig. 2-52). If the faces of the contact points
do not touch each other fully, heat generated by the
primary current cannot be dissipated and rapid burning
takes place. The contacts are aligned by bending the
stationary contact bracket only. NEVER BEND THE
MOVABLE CONTACT ARM. Ensure the contact
arm-rubbing block rests flush against the distributor
cam. A small amount of an approved lubricate should
be placed on the distributor cam to reduce friction
between the cam and rubbing block. Once the points
are installed, they can be adjusted using either a feeler
gauge or dwell meter.
If the distributor cap has an adjustment window,
the points should be set with the engine running. With
the meter controls set properly, adjust the points
through the window of the distributor cap using a Allen
wrench or a special screwdriver. Turn the point
adjustment screw until the dwell meter reads within
manufacturer’s specification. However, if the
distributor cap does not have an adjustment window,
remove the distributor cap and ground the ignition coil
wire. Then crank the engine; this action will simulate
engine operation and allow point adjustment with the
dwell meter.
To use a feeler gauge to set the contact points, turn
the engine over until the points are FULLY OPEN. The
rubbing block should be on top of a distributor cam
lobe. With the points open, slide the specified
thickness feeler gauge between them. Adjust the
points so that there is a slight drag on the blade of the
feeler gauge. Depending upon point design, use a
screwdriver or Allen wrench to open and close the
points. Tighten the hold-down screws and recheck the
point gap. Typically point gap settings average around
.015 inch for eight-cylinder engines and .025 inch for
six- and four-cylinder engines. For the gap set of the
engine you are working on, consult the manufacturer’s
service manual.
Dwell specifications vary with the number of
cylinders. An eight-cylinder engine requires 30
degrees of dwell. An engine with few cylinders
requires more dwell time. Always consult the
manufacturer’s service manual for exact dwell values.
Dwell should remain constant as engine speed
increases or decreases. However, if the distributor is
worn, you can have a change in the dwell meter
reading. This is known as DWELL VARIATION. If
dwell varies more than 3 degrees, the distributor
should either be replaced or rebuilt. Also, a change in
the point gap or dwell will change ignition timing. For
this reason, the points should always be adjusted
before ignition timing.
SERVICE.—Most electronic ignition distributors use
a pickup coil to sense trigger wheel rotation and speed.
The pickup coil sends small electrical impulses to the
ECU. If the distributor fails to produce these electrical
impulses properly, the ignition system can quit
A faulty pickup coil will produce a wide range of
engine troubles, such as stalling, loss of power, or not
starting at all. If the small windings in the pickup coil
break, they will cause problems only under certain
conditions. It is important to know how to test a pickup
coil for proper operation.
Figure 2-52.—Contact point alignment.
actual pickup resistance with the manufacturer’s
specifications. If the resistance is too high or low, the
pickup coil is faulty. To perform this test, connect the
ohmmeter across the output leads of the pickup coil.
Wiggle the wire to the pickup coil and observe the
meterreading. This will assist in locating any breaks in
the wires to the pickup. Also, using a screwdriver,
lightly tap the coil. This action will uncover any break
in the coil windings.
Pickup coil resistance varies between 250 and
1,500 ohms, and you should refer to the service manual
for exact specifications. Any change in the readings
during the pickup coil resistance test indicates the coil
should be replaced. Refer to the manufacturer’s service
manual for instructions for the removal and
replacement of the pickup coil.
Figure 2-53.—Determining the direction of rotor rotation.
sluggish during acceleration. If extremely retarded,
combustion flames blowing out of the open exhaust
valve can overheat the engine and crack the exhaust
Once the pickup coil has been replaced, it will be
necessary to set the PICKUP COIL AIR GAP. The air
gap is the space between the pickup coil and the trigger
wheel tooth. To obtain an accurate reading, use a NONMAGNETIC FEELER GAUGE (plastic or brass).
A timing light is used to measure ignition timing. It
normally has three leads—two small leads that connect
to the battery-and one larger lead that connects to the
NUMBER ONE spark plug wire. Depending on the
type of timing light, the large lead may clip around the
plug wire (inductive type), or it may need to be
connected directly to the metal terminal of the plug
wire (conventional type).
With one tooth of the trigger wheel pointing at the
pickup coil, slide the correct thickness non-magnetic
feeler gauge between the trigger wheel and the pickup
coil. Move the pickup coil in or out until the correct air
gap is set. Tighten the pickup coil screws and doublecheck the air gap setting.
Ignition Timing
Draw a chalk line over the correct timing mark.
This will make it easier to see. The timing marks may
be either on the front cover in harmonic balance of the
engine, or they may be on the engine flywheel.
The ignition system must be timed so the sparks
jump across the spark plug gaps at exactly the right
time. Adjusting the distributor on the engine so that the
spark occurs at this correct time is called setting the
ignition timing. The ignition timing is normally set at
idle or a speed specified by the engine manufacturer.
Before measuring engine timing, disconnect and plug
the vacuum advance hose going to the distributor. This
action prevents the vacuum advance from functioning
and upsetting the readings. Adjustment is made by
loosening the distributor hold-down screw and turning
the distributor in its mounting.
With the engine running, aim the flashing timing
light at the timing mark and reference pointer. The
flashing timing light will make the mark appear to
stand still. If the timing mark and the pointer do not line
up, turn the distributor in its mounting until the timing
mark and pointer are aligned. Tighten the distributor
hold-down screw.
Turning the distributor housing against the
distributor shaft rotation ADVANCES THE TIMING.
Turning the distributor housing with shaft rotation
RETARDS THE TIMING. Refer to figure 2-53.
Keep your hands and the timing light leads
from the engine fan and belts. The spinning fan
and belts can damage the light or cause serious
personal injury.
When the ignition timing is TOO ADVANCED,
the engine may suffer from spark knock or ping. When
ignition timing is TOO RETARDED, the engine will
have poor fuel economy and power and will be very
After the initial ignition timing, you should check
to see if the automatic advance mechanism is working.
This can be done by keeping the timing light flashes
aimed at the timing mark and gradually increasing
speed. If the advance mechanism is operating, the
timing mark should move away from the pointer. If the
timing mark fails to move as the speed increases or it
hesitates and then suddenly jumps, the advance
mechanism is faulty and should either be repaired or
Replace the distributor vacuum line and see if
timing still conforms to the manufacturer’s
specifications. If the timing is NOT advanced when the
vacuum line is connected and the throttle is opened
slightly, the vacuum advance unit or tubing is
Most computer-controlled ignition systems have
no provision for timing adjustment. A few, however,
have a tiny screw or lever on the computer for small
ignition timing changes.
A computer-controlled ignition system has what is
known as BASE TIMING. Base timing is the ignition
timing without computer-controlled advance. Base
timing is checked by disconnecting a wire connector in
the computer wiring harness. This wire connector may
be found on or near the engine or sometimes next to the
distributor. When in the base timing mode, a
conventional timing light can be used to measure
ignition timing. If ignition timing is not correct, you
can rotate the distributor, in some cases, or move the
mounting for the engine speed or crank position
sensor. If base timing cannot be adjusted, the
electronic control unit or other components will have
to be replaced. Always refer to the manufacturer’s
service manual when timing a computer-controlled
ignition system.
Q1. Of the two circuits within the ignition circuit,
which one uses conventional wiring?
What component of the ignition circuit acts as a
pulse type transformer for producing a short
burst of high voltage?
What are the two type of sparkplugs?
What factors determine the heat range of a spark
Q7. In an electronic ignition system, the trigger
wheel replaces what contact point ignition
Q8. In a computerized advance, which sensor allows
the computer to retard timing when the engine
knocks or pings?
Q9. The condition that exists when an electric arc
passes through the insulation of a spark plug
wire is known by what term?
What number of degrees can dwell vary before a
distributor is either rebuilt or replaced?
What tool is used to set the air gap of the pickup
What ignition timing condition adversely affects
engine fuel economy and power?
Q13. In a computer-controlled ignition system, the
ignition timing without the computer-controlled
advance is known by what term?
Learning Objective: Identify lighting-circuit
components, their functions, and maintenance
The lighting circuit (fig. 2-54) includes the battery,
vehicle frame, all the lights, and various switches that
control their use. The lighting circuit is known as a
single-wire system since it uses the vehicle frame for
the return.
The complete lighting circuit of a vehicle can be
broken down into individual circuits, each having one
or more lights and switches. In each separate circuit,
the lights are connected in parallel, and the controlling
switch is in series between the group of lights and the
The marker lights, for example, are connected in
parallel and are controlled by a single switch. In some
installations, one switch controls the connections to the
battery, while a selector switch determines which of two
circuits is energized. The headlights, with their high and
low beams, are an example of this type of circuit.
In some instances, such as the courtesy lights,
several switches may be connected in parallel so that
any switch may be used to turn on the light.
Q5. The smaller the number designator for a spark
plug, the hotter the sparkplug. (T/F)
When a wiring diagram is being studied, all light
circuits can be traced from the battery through the
ammeter to the switch (or switches) to the individual
Q6. The amount of time in degrees that the contact
points remain closed between each opening is
known by what term?
Figure 2-55.—Lamp construction and configurations.
small one-half-candlepower bulbs to large 50candlepower bulbs. The greater the candlepower
of the lamp, the more current it requires when
lighted. Lamps are identified by a number on the
Small gas-filled incandescent lamps with tungsten
filaments are used on automotive and construction
equipment (fig. 2-55). The filaments supply the light
when sufficient current is flowing through them. They
are designed to operate on a low voltage current of 12
or 24 volts, depending upon the voltage of the
electrical system used.
When you replace a lamp in a vehicle, be sure the
new lamp is of the proper rating. The lamps within
the vehicle will be of the single- or double-contact
types with nibs to fit bayonet sockets, as shown in
figure 2-56.
Lamps are rated as to size by the candlepower
(luminous intensity) they produce. They range from
Figure 2-58.—Dash-mounted headlight switch.
Figure 2-56.—(A) Single-contact bulb; (B) Double-contact
lamp is also whiter than a conventional lamp, which
increases lighting ability.
Headlight Switch
The headlights are sealed beam lamps (fig. 2-57)
that illuminate the road during nighttime operation.
Headlights consist of a lens, one or two elements, and a
integral reflector. When current flows through the
element, the element gets white hot and glows. The
reflector and lens direct the light forward.
The headlight switch is an ON/OFF switch and
rheostat (variable resistor) in the dash panel (fig. 2-58)
or on the steering column (fig. 2-59). The headlight
switch controls current flow to the lamps of the
headlight system. The rheostat is for adjusting the
brightness of the instrument panel lights.
Many modern passenger vehicles use halogen
headlights. A halogen headlight contains a small, inner
halogen lamp surrounded by a conventional sealed
housing. A halogen headlamp increases light output by
25 percent with no increase in current. The halogen
Military vehicles that are used in tactical situations
are equipped with a headlight switch that is integrated
with the blackout lighting switch (fig. 2-60). An
important feature of this switch is that it reduces the
possibility of accidentally turning on the lights in a
Figure 2-57.—A typical sealed beam headlight assembly.
positions. But it will give parking lights only when the
main switch is in service drive (to the extreme right).
When the main switch is off, the auxiliary switch
should not be moved from the OFF position.
Dimmer Switch
The dimmer switch controls the high and low
headlamp beam function and is normally mounted
on the floorboard (fig. 2-61) or steering column (fig.
2-62). When the operator activates the dimmer switch,
it changes the electrical connection to the headlights.
Figure 2-59.—Steering column mounted headlight switch.
Figure 2-61.—Floor-mounted dimmer switch.
Figure 2-60.—Blackout light/headlight switch.
blackout. With no lights on, the main switch can be
turned to the left without operating the mechanical
switch to get blackout marker lights (including
blackout taillights and stoplights) and blackout driving
lights. But for stoplights for daylight driving or
headlights for ordinary night driving, you must first lift
the mechanical switch lever and then turn the main
switch to the right. The auxiliary switch gives panel
lights when the main switch is in any of its ON
Figure 2-62.—Steering column mounted dimmer switch.
In one position, the high beams are turned on, and, in
the other position, the dimmer changes them to low
should be no more than 12 inches from the floor. To
comply with regulations of most localities, you should
place the screen 25 feet ahead of the vehicle.
Aiming Headlights
The accepted driving beam pattern for passenger
vehicles will show the high intensity portion
(hotspot) of the light rays centered on a horizontal line
that is 2 inches below the center or horizontal
reference line on the screen (fig. 2-63). This means
that there will be a 2-inch drop of the light beam for
every 25 feet of distance from the headlight.
The headlights can be aimed using a mechanical
aimer or a wall screen. Either method assures that the
headlight beams point in the direction specified by the
vehicle manufacturer. Headlights that are aimed too
high can blind oncoming vehicles. Headlights that are
aimed too low or to one side will reduce the operator’s
Headlights on large trucks present a special
problem because of the effect of a heavy load. At the
same 25 feet, truck headlights should be aimed so that
none of the high intensity portion of the light will
project higher than a level of 5 inches below the center
on the headlight being tested. This is necessary to
compensate for the variations in loading.
To ensure that the headlights are properly aimed,
you should have a half a tank of fuel, the correct tire
pressure, and only the spare tire and jack in the vehicle.
Some manufacturers recommend that someone sit in
the operator and passenger seats while aiming the
HEADLIGHT AIMERS are a device for pointing
the vehicle headlights in a specified position. They
may be permanently installed on a track or may be
portable. Some require a level floor, and others have
internal leveling mechanisms to allow for uneven shop
floors. To use the aimer, follow the instructions for the
specific type of equipment.
When using a screen for aiming the headlights on a
vehicle that uses a four-headlight system, adjust the
hotspots of the No. 1 (inboard) lights so that they are
centered on the vertical lines 2 inches below the
horizontal line (fig. 2-64). The low beam of the No. 2
(outboard) lights is aimed so that the hotspot does not
extend to the left of straight ahead or extend more than
6 inches to the right of straight ahead. The top of the
hotspot of the No. 2 lights is aimed at the horizontal
line. When the No. 2 lights are properly adjusted, the
high beam will be correct.
of measured lines marked on a shop wall or on a framed
easel for aiming the headlights of a vehicle. The screen
should be no less than 10 feet wide and 42 inches high.
When it is mounted on an easel with casters, the screen
Figure 2-63.—Accepted beam pattern for aiming passenger vehicle headlights.
top of the low beam is directed not less than 2
degrees below the horizon. The beam
distribution on a level road at 100 feet from the
light is 30 feet wide.
Figure 2-64.—Accepted beam pattern
MARKER LIGHT (fig. 2-66) are designed to be
visible at a horizontal distance of 800 feet and
not visible beyond 1,200 feet. The lights also
must be invisible from the air above 400 feet
with the vehicle on upgrades and downgrades of
20 percent. The horizontal beam cutoff for the
lights is 60 degrees right and left of the beams
center line at 100 feet.
for a four-headlight
The COMPOSITE LIGHT (fig. 2-67) is
currently the standard light unit that is used on
the rear of tactical military vehicles. The
composite light combines service stop, tail, and
turn signals with blackout stop and taillighting.
Blackout lighting is a requirement for certain
combat operations. The purposes of blackout lighting
are as follows:
To provide the vehicle operator with sufficient
light to operate the vehicle in total darkness
To provide minimum lighting to show vehicle
position to a leading or trailing vehicle when
illumination must be restricted to a level not
visible to a distant enemy
The three types of blackout lighting are as follows:
is designed to provide a white light of 25 to 50
candlepower at a distance of 10 feet directly in
front of the light. The light is shielded so that the
Figure 2-66.—Blackout stop/taillight and marker light.
Figure 2-67.—Military composite light.
Figure 2-65.—Blackout driving light.
A wiring diagram for a typical turn-signal system
is shown in figure 2-69. A common design for a turnsignal system is to use the same rear light for both the
stop and turn signals. This somewhat complicates the
design of the switch in that the stoplight circuit must
pass through the turn-signal switch. When the turnsignal switch is turned off, it must pass stoplight
current to the rear lights. As a left or right turn signal is
selected, the stoplight circuit is open and the turnsignal circuit is closed to the respective rear light.
Blackout lighting control switches are designed to
prevent the service lighting from being turned on
accidentally. Their operation is described in the
"Headlight Switch" section of this TRAMAN.
Vehicles that operate on any public road must be
equipped with turn signals. These signals indicate a
left or right turn by providing a flashing light signal at
the rear and front of the vehicle.
The turn-signal switch is located on the steering
column (fig. 2-68). It is designed to shut off
automatically after the turn is completed by the action
of the canceling cam.
The turn signal flasher unit (fig. 2-70) creates the
flashing of the turn signal lights. It consists basically of
a bimetallic (two dissimilar metals bonded together)
strip wrapped in a wire coil. The bimetallic strip serves
as one of the contact points.
When the turn signals are actuated, current flows
into the flasher—first through the heating coil to the
bimetallic strip, then through the contact points, then
out of the flasher, where the circuit is completed
through the turn-signal light. This sequence of events
will repeat a few times a second, causing a steady
flashing of the turn signals.
The backup light system provides visibility to the
rear of the vehicle at night and a warning to the
Figure 2-68.—Typical turn-signal switch.
Figure 2-69.—Typical turn-signal wiring diagram.
equipped vehicles is combined with the neutral
safety switch.
All vehicles that are used on public highways must
be equipped with a stoplight system. The stoplight
system consists of a fuse, brake light switch (fig. 2-71),
two rear warning lights, and related wiring.
The brake light switch on most automotive
equipment is mounted on the brake pedal. When the
brake pedal is pressed, it closes the switch and turns on
the rear brake lights. On construction and tactical
equipment, you may find a pressure light switch. This
type of switch uses either air or hydraulic pressure,
depending on the equipment. It is mounted on the
master cylinder of the hydraulic brake system or is
attached to the brake valve on an air brake system. As
the brakes are depressed, either air or hydraulic
pressure builds on a diaphragm inside the switch. The
diaphragm closes allowing electrical current to turn on
the rear brake lights.
Figure 2-70.—Turn signal flasher.
pedestrians, whenever the vehicle is shifted into
reverse. The backup light system has a fuse, gearshiftor transmission-mounted switch, two backup lights,
and wiring to connect these components.
The backup light switch closes the light circuit
when the transmission is shifted into reverse. The most
common backup light switch configurations are as
The backup light switch mounted on the
transmission and operated by the shift lever.
The emergency light system, also termed hazard
warning system, is designed to signal oncoming traffic
that a vehicle has stopped, stalled, or has pulled up to
the side of the road. The system consists of a switch,
flasher unit, four turn signal lights, and related wiring.
The switch is normally a push-pull switch and is
mounted on the steering column.
When the switch is closed, current flows through
the emergency flasher. Like a turn signal flasher, the
emergency flasher opens and closes the circuit to the
lights. This causes all four turn signals to flash.
The backup light switch mounted on the steering
column and operated by the gearshift linkage.
The transmission- or gearshift-mounted backup
light switch on many automatic transmission-
Figure 2-71.—Brake light switches.
Fuses are safety devices placed in electrical circuits
to protect wires and electrical units from a heavy flow of
current. Each circuit, or at least each individual
electrical system, is provided with a fuse that has an
ampere rating for the maximum current required to
operate the units. The fuse element is made from metal
with a low-melting point and forms the weakest point of
the electrical circuit. In case of a short circuit or other
trouble, the fuse will be burned out first and open the
circuit just as a switch would do. Examination of a
burnt-out fuse usually gives an indication of the
problem. A discolored sight glass indicates the circuit
has a short either in the wiring or in one of its
components. If the glass is clear, the problem is an
overloaded circuit. Be sure when replacing a fuse that it
has a rating equal to the one burned out. Ensure that the
trouble of the failure has been found and repaired.
A circuit breaker performs the same function as a
fuse. It disconnects the power source from the circuit
when current becomes too high. The circuit breaker
will remain open until the trouble is corrected. Once
the trouble is corrected, a circuit breaker will
automatically reset itself when current returns to
normal levels. The fuses and circuit breakers can
usually be found behind the instrument panel on a fuse
block (fig. 2-72).
Q1. By what percentage is light output increased
when using halogen headlights?
Q3. When using a headlight-aiming screen, you
place the screen at what distance in front of the
Q4. On a 20 percent downgrade, blackout taillights
should be invisible from the air at what distance?
Q5. On most automotive vehicles, the brake light
switch is mounted at what location?
Learning Objective: Identify instrument, gauges, and
accessories, their functions, and maintenance
The instrument panel is placed so that the
instruments and gauges can easily be read by the
operator. They inform the operator of the vehicle
speed, engine temperature, oil pressure, rate of charge
or discharge of the battery, amount of fuel in the fuel
tank, and distance traveled. Vehicle accessories, such
as windshield wipers and horns, provide the operator
with much needed safety devices.
The battery condition gauge is one of the most
important gauges on the vehicle. If the gauge is
interpreted properly, it can be used to troubleshoot or
prevent breakdowns. The following are the three basic
configurations of battery condition gauges—ammeter,
voltmeter, and indicator lamp.
The AMMETER is used to indicate the amount
of current flowing to and from the battery. It does NOT
give an indication of total charging output because of
other units in the electrical system. If the ammeter
shows a 10-ampere discharge, it indicates that a 100
ampere-hour battery would be discharged in 10 hours,
as long as the discharge rate remained the same. Current
flowing from the battery to the starting motor is never
sent through the ammeter, because the great quantities
of amperes used (200 to 600 amperes) cannot be
measured due to its limited capacity. In a typical
ammeter (fig. 2-73), all the current flowing to and from
the battery, except for starting, actually is sent through a
coil to produce a magnetic field that deflects the
ammeter needle in proportion to the amount of current.
The coil is matched to the maximum current output of
the charging unit, and this varies with different
Q2. What component of the headlight switch allows
for adjusting the brightness of the instrument
panel lights?
The VOLTMETER (fig. 2-74) provides a more
accurate indication of the condition of the electrical
Figure 2-72.—Fuse block.
to 14.5 volts for a 12-volt electrical system. As long as
the system voltage remains in this range, the operator
can assume that no problem exists. This contrasts with
an ammeter, which gives the operator no indication of
problems, such as an improperly calibrated voltage
regulator, which could allow the battery to be drained
by regulating system voltage to a level below normal.
The INDICATOR LAMP has gained popularity
as an electrical system condition gauge over the years.
Although it does not provide as detailed analysis of the
electrical system condition as a gauge, it is considered
more useful to the average vehicle operator. This is
because it is highly visible when a malfunction occurs,
whereas a gauge usually is ignored because the average
vehicle operator does not know how to interpret its
readings. The indicator lamp can be used in two
different ways to indicate an electrical malfunction,
which are as follows:
Figure 2-73.—Ammeter schematic.
2-75) is set up to warn the operator
whenever the electrical system voltage has
dropped below the normal operational
2. NO-CHARGE INDICATOR (fig. 2-76) is
set up to indicate whenever the alternator is
not producing current.
Most fuel gauges are operated electrically and are
composed of two units—the gauge, mounted on the
instrument panel; and the sending unit, mounted in the
fuel tank. The ignition switch is included in the fuel
gauge circuit, so the gauge operates only when the
ignition switch is in the ON position. Operation of the
electrical gauge depends on either coil action or
Figure 2-74.—Voltmeter schematic.
system and is easier to interpret by the operator. During
vehicle operation, the voltage indicated on the
voltmeter is considered to be normal in a range of 13.2
Figure 2-75.—Low voltage warning lamp schematic.
Figure 2-76.—No-charge indiutor schematic.
thermostatic action. The four types of fuel gauges are
as follows:
the float arm. The power supply to the gauge is kept
constant through the use of a voltage limiter. The
voltage limiter consists of a set of contact points that are
controlled by an electrically heated bimetallic arm.
The THERMOSTATIC FUEL GAUGE, SELFREGULATING (fig. 2-77), contains an electrically
heated bimetallic strip that is linked to a pointer. A
bimetallic strip consists of two dissimilar metals that,
when heated, expand at different rates, causing it to
deflect or bend. In the case of this gauge, the deflection
of the bimetallic strip results in the movement of the
pointer, causing the gauge to give a reading. The
sending unit consists of a hinged arm with a float on the
end. The movement of the arm controls a grounded
point that makes contact with another point which is
attached to an electrically heated bimetallic strip. The
heating coils in the tank and the gauge are connected to
each other in series.
DIFFERENTIAL TYPE (fig. 2-79), is similar to the
other type of thermostatic fuel gauges, except that it
uses two electrically heated bimetallic strips that share
equally in operating and supporting the gauge pointer.
The pointer position is obtained by dividing the
available voltage between the two strips (differential).
The tank unit is a rheostat type similar to that already
described; however, it contains a wire-wound resistor
that is connected between external terminals of one of
the gauges of the bimetallic strip. The float arm moves a
grounded brush that raises resistance progressively to
one terminal, while lowering resistance to the other.
This action causes the voltage division and resulting
heat differential to the gauge strips formulating the
gauge reading.
EXTERNALLY REGULATED (fig. 2-78), differs
from a self-regulating system in the use of a variable
resistance fuel tank sending unit and an external
voltage-limiting device. The sending unit controls the
gauge through the use of a rheostat (wire wound
resistance unit whose value varies with its effective
length). Theeffective length of the rheostat is controlled
in the sending unit by a sliding brush that is operated by
consists of a pointer mounted on an armature.
Depending upon the design, the armature may contain
one or two poles. The gauge is motivated by a magnetic
field that is created by two separate magnetic coils that
Figure 2-77.—Thermostatic fuel gauge, self-regulating.
Figure 2-79.—Thermostatic fuel gauge, differential type.
are contained in the gauge. One of these coils is
connected directly to the battery, producing a constant
magnetic field. The other coil produces a variable field,
whose strength is determined by a rheostat-type tank
unit. The coils are placed 90 degrees apart.
A pressure gauge is used widely in automotive and
construction applications to keep track of such things
as oil pressure, fuel line pressure, air brake system
Figure 2-78.—Thermostatic fuel gauge, externally regulated.
2. The sending unit that is used with the
magnetic-type gauge also translates pressure into the
flexing of a diaphragm. In the case of the magnetic
gauge sending unit, however, the diaphragm operates a
The INDICATOR LAMP (warning light) is used
in place of a gauge on many vehicles. The warning light,
although not an accurate indicator, is valuable because
of its high visibility in the event of a low-pressure
condition. The warning light receives battery power
through the ignition switch. The circuit to ground is
completed through a sending unit. The sending unit
consists of a pressure-sensitive diaphragm that operates
a set of contact points that are calibrated to turn on the
warning light whenever pressure drops below a set
Figure 2-80.—Magnetic fuel gauge.
pressure, and the pressure in the hydraulic systems.
Depending on the equipment, a mechanical gauge, an
electrical gauge, or an indicator lamp may be used.
The MECHANICAL GAUGE (fig. 2-81) uses a
thin tube to carry an actual pressure sample directly to
the gauge. The gauge basically consists of a hollow,
flexible C-shaped tube, called a bourbon tube. As air or
fluid pressure is applied to the bourbon tube, it will tend
to straighten out. As it straightens, the attached pointer
will move, giving a reading.
The temperature gauge is a very important
indicator in construction and automotive equipment.
The most common uses are to indicate engine
coolant, transmission, differential oil, and hydraulic
system temperature. Depending on the type of
equipment, the gauge may be mechanical, electric,
or a warning light.
The ELECTRIC GAUGE may be of the
thermostatic or magnetic type as previous discussed.
The sending unit (fig. 2-82) that is used with each gauge
type varies as follows:
1. The sending unit that is used with the
thermostatic pressure gauge uses a flexible diaphragm
that moves a grounded contact. The contact that mates
with the grounded contact is attached to a bimetallic
strip. The flexing of the diaphragm, which is done with
pressure changes, varies the point tension. The different
positions of the diaphragm produce gauge readings.
The ELECTRIC GAUGE may be the
thermostatic or magnetic type, as described previously.
The sending unit (fig. 2-83) that is used varies,
depending upon application.
1. The sending unit that is used with the
thermostatic gauge consists of two bimetallic strips,
each having a contact point. One bimetallic strip is
heated electrically. The other strip bends to increase the
tension of the contact points. The different positions of
the bimetallic strip create the gauge readings.
2. The sending unit that is used with the
magnetic gauge contains a device called a thermistor. A
thermistor is an electronic device whose resistance
decreases proportionally with an increase in
The MAGNETIC GAUGE contains a bourbon
tube and operates by the same principles as the
mechanical pressure gauge.
The INDICATOR LAMP (warning light)
operates by the same principle as the indicator light
previously discussed.
Figure 2-81.—Mechanical pressure gauge.
Figure 2-82.—Types of sending units for pressure gauges.
Figure 2-83.—Types of temperature gauge sending units.
Speedometers and tachometers in some form are
used in virtually all types of self-propelled equipment.
Speedometers are used to indicate vehicle speed in
miles per hour (mph) or kilometers per hour (kph). In
most cases, the speedometer also contains the
odometer which keeps a record of the amount of
mileage (in miles or kilometers depending on
application) that a vehicle has accumulated. Some
speedometers also contain a resetable trip odometer so
those individual trips can be measured.
A tachometer is a device that is used to measure
engine speed in revolutions per minute (rpm). The
tachometer may also contain an engine-hour gauge
which is installed on equipment that uses no odometer
to keep a record of engine use. Speedometers and
tachometers may be driven either mechanically,
electrically, or electronically.
Mechanical Speedometers and Tachometers
Both the mechanical speedometer and the
tachometer consist of a permanent magnet that is
trip odometers do not record tenths, thereby contain
only five digits. When the odometer reaches its highest
value, it will automatically reset to zero. Newer
vehicles incorporate a small dye pad in the odometer to
color the drum of its highest digit to indicate the total
mileage is in excess of the capability of the odometer.
rotated by a flexible shaft. Surrounding the rotating
magnet is a metal cup that is attached to the indicating
needle. The revolving magnetic field exerts a pull on
the cup that forces it to rotate. The rotation of the cup is
countered by a calibrated hairspring. The influence of
the hairspring and the rotating magnetic field on the
cup produces accurate readings by the attached needle.
The flexible shaft consists of a flexible outer casing
that is made of either steel or plastic and an inner drive
core that is made of wire-wound spring steel. Both
ends of the core are molded square, so they can fit into
the driving member at one end and the driven member
at the other end and can transmit torque.
Electric Speedometers and Tachometers
The electric speedometer and tachometer use a
mechanically driven permanent magnet generator to
supply power to a small electric motor (fig. 2-84). The
electric motor then is used to rotate the input shaft of
the speedometer or tachometer. The voltage from the
generator will increase proportionally with speed, and
speed will likewise increase proportionally with
voltage enabling the gauges to indicate speed.
Gears on the transmission output shaft turn the
flexible shaft that drives the speedometer. This shaft is
referred to as the speedometer cable. A gear on the
ignition distributor shaft turns the flexible shaft that
drives the tachometer. This shaft is referred to as the
tachometer cable.
The signal generator for the speedometer is usually
driven by the transmission output shaft through gears.
The signal generator for the tachometer usually is
driven by the distributor through a power takeoff on
gasoline engines. When the tachometer is used with a
diesel engine, a special power takeoff provision is
made, usually on the camshaft drive.
The odometer of the mechanical speedometer is
driven by a series of gears that originate at a spiral gear
on the input shaft. The odometer consists of a series of
drums with digits printed on the outer circumference
that range from zero to nine. The drums are geared to
each other so that each time the one furthest to the right
makes one revolution, it will cause the one to its
immediate left to advance one digit. The second to the
right then will advance the drum to its immediate left
one digit for every revolution it makes. This sequence
continues to the left through the entire series of drums.
The odometer usually contains six digits to record
99,999.9 miles or kilometers. However, models with
Electronic Speedometers and Tachometers
Electronic speedometers and tachometers are selfcontained units that use an electric signal from the
engine or transmission. They differ from the electric
unit in that they use a generated signal as the driving
force. The gauge is transistorized and will supply
information through either a magnetic analog (dial) or
light-emitting diode (LED) digital gauge display. The
Figure 2-84.—Electric speedometer and tachometer operation.
gauge unit derives its input signal in the following
another cause of horn problems. The contacts inside
the relay may be burned or stuck together.
An electronic tachometer obtains a pulse signal
from the ignition distributor, as it switches the coil on
and off. The pulse speed at this point will change
proportionally with engine speed. This is the most
popular signal source for a tachometer that is used on a
gasoline engine.
The windshield wiper system is one of the most
important safety factors on any piece of equipment. A
typical electric windshield wiper system consists of a
switch, motor assembly, wiper linkage and arms, and wiper
blades. The description of the components is as follows:
A tachometer that is used with a diesel engine
uses the alternating current generated by the stator
terminal of the alternator as a signal. The frequency of
the ac current will change proportionally with engine
multiposition switch, which may contain a rheostat.
Each switch position provides for different wiping
speeds. The rheostat, if provided, operates the delay
mode for a slow wiping action. This permits the
operator to select a delayed wipe from every 3 to 20
seconds. A relay is frequently used to complete the
circuit between the battery voltage and the wiper motor.
An electronic speedometer derives its signal
from a magnetic pickup coil that has its field interrupted
by a rotating pole piece. The signal units operation is the
same as the operation of the reluctor and pickup coil
described earlier in this TRAMAN. The pickup coil is
located strategically in the transmission case to interact
with the reluctor teeth on the input shaft.
one, two, or three speeds. The motor (fig. 2-85) has a
worm gear on the armature shaft that drives one or two
gears, and, in turn, operates the linkage to the wiper
arms. The motor is a small, shunt wound dc motor.
Resistors are placed in the control circuit from the
switch to reduce the current and provide different
operating speeds.
The horn currently used on automotive vehicles is
the electric vibrating type. The electric vibrating horn
system typically consists of a fuse, horn button switch,
relay, horn assembly, and related wiring. When the
operator presses the horn button, it closes the horn
switch and activates the horn relay. This completes the
circuit, and current is allowed through the relay circuit
and to the horn.
The WIPER LINKAGE and ARMS transfers
motion from the wiper motor transmission to the wiper
blades. The rubber wiper blades fit on the wiper arms.
The WIPER BLADE is a flexible rubber
squeegee-type device. It may be steel or plastic backed
and is designed to maintain total contact with the
windshield throughout the stroke. Wiper blades should
be inspected periodically. If they are hardened, cut, or
split, they are to be replaced.
Most horns have a diaphragm that vibrates by
means of an electromagnetic. When the horn is
energized, the electromagnet pulls on the horn
diaphragm. This movement opens a set ofcontact points
inside the horn. This action allows the diaphragm to flex
back towards its normal position. This cycle is repeated
rapidly. The vibrations of the diaphragm within the air
column produce the note of the horn.
When electrical problems occur in the windshield
wiper system, use the service manual and its wiring
diagram of the circuit. First check the fuses, electrical
connections, and all grounds. Then proceed with
checking the components.
Tone and volume adjustments are made by
loosening the adjusting locknut and turning the
adjusting nut. This very sensitive adjustment controls
the current consumed by the horn. Increasing the
current increases the volume. However, too much
current will make the horn sputter and may lock the
Which type of battery condition gauge provides
the most accurate indication of the condition of
the electrical system?
Q2. How ispointerposition obtained in a differential
type thermostatic fuel gauge?
When a electric horn will not produce sound, check
the fuse, the connections, and test for voltage at the horn
terminal. If the horn sounds continuously, a faulty horn
switch is the most probable cause. A faulty horn relay is
Q3. The signal generator for an electric tachometer
used on a gasoline engine is driven by what
Figure 2-85.—Wiper motor assembly.
lead to all parts of the equipment, the ground return
system saves installation time and eliminates the need
for an additional wiring to complete the circuit. The
all-metal construction of the automotive equipment
makes it possible to use this system.
Q4. What is the most probable cause of a horn
sounding continuously?
Learning Objective: Identify the basic types of
automotive wiring, types of terminals, and wiring
The TWO-WIRE CIRCUIT requires two wires to
complete the electrical circuit—one wire from the
source of electrical energy to the unit it will operate,
and another wire to complete the circuit from the unit
back to the source of the electrical power.
Electrical power and control signals must be
delivered to electrical devices reliably and safely so
that the electrical system functions are not impaired or
converted to hazards. To fulfill power distribution
military vehicles, use one- and two-wire circuits,
wiring harnesses, and terminal connections.
Two-wire circuits provide positive connection for
light and electrical brakes on some trailers. The
coupling between the trailer and the equipment,
although made of metal and a conductor of electricity,
has to be jointed to move freely. The rather loose joint
or coupling does not provide the positive and
continuous connection required to use a ground return
system between two vehicles. The two-wire circuit is
commonly used on equipment subject to frequent or
heavy vibrations. Tracked equipment, off-road
vehicles (tactical), and many types of construction
equipment are wired in this manner.
Among your many duties will be the job of
maintaining and repairing automotive electrical
systems. All vehicles are not wired in exactly the same
manner; however, once you understand the circuit of
one vehicle, you should be able to trace an electrical
circuit of any vehicle using wiring diagrams and color
Tracing wiring circuits, particularly those
connecting lights or warning and signal devices, is no
simple task. By studying the diagram in figure 2-72,
you will see that the branch circuits making up the
individual systems have one wire to conduct electricity
from the battery to the unit requiring it and ground
connections at the battery and the unit to complete the
circuit. These are called ONE-WIRE CIRCUITS or
branches of a GROUND RETURN SYSTEM. In
automotive electrical systems with branch circuits that
Wiring assemblies consist of wires and cables of
definitely prescribed length, assembled together to
form a subassembly that will interconnect specific
electrical components and/or equipment. The two
basic types of wiring assemblies are as follows:
The CABLE ASSEMBLY consists of a stranded
conductor with insulation or a combination of insulated
conductors enclosed in a covering or jacket from end to
end. Terminating connections seal around the outer
jacket so that the inner conductors are isolated
completely from the environment. Cable assemblies
may have two or more ends.
WIRING HARNESS assemblies (fig. 2-86)
serve two purposes. They prevent chafing and
loosening of terminals and connections caused by
vibration and road shock while keeping the wires in a
neat condition away from moving parts of the vehicle.
Wiring harnesses contain two or more individual
conductors laid parallel or twisted together and
wrapped with binding material, such as tape, lacing
cord, and wire ties. The binding materials do not isolate
the conductors from the environment completely, and
conductor terminations may or may not be sealed.
Wiring harnesses also may have two or more ends.
Wires in the electrical system should be identified
by a number, color, or code to facilitate tracing circuits
during assembly, troubleshooting, or rewiring
operations. This identification should appear on wiring
schematics and diagrams and whenever practical on
the individual wire. The assigned identification for a
continuous electrical connection should be retained on
a schematic diagram until the circuit characteristic is
altered by a switching point or active component.
Figure 2-86.—A typical wiring harness.
Wiring color codes are used by manufacturers to
assist the mechanics in identifying the wires used in
many circuits and making repairs in a minimum of
time. No color code is common to all manufacturers.
For this reason, the manufacturer’s service manual is a
must for speedy troubleshooting and repairs.
codes, are used to identify the wiring illustrated by
diagrams in the technical manuals. These tags are
securely fastened near the end of individual wires.
Wiring diagrams (fig. 2-88) are drawings that
show the relationship of the electrical components and
wires in a circuit. They seldom show the routing of the
wires within the electrical system of the vehicle.
Wiring found on tactical equipment (M-series) has
no color. All the wires used on these vehicles are black.
Small metal tags (fig. 2-87), stamped with numbers or
Often you will find ELECTRICAL SYMBOLS
used in wiring diagrams to simulate individual
components. Figure 2-89 shows some of the symbols
you may encounter when tracing individual circuits in
a wiring diagram.
Wire terminals are divided into two major
classes—the solder type and the solderless type, which
is also known as the pressure or crimp type. The solder
Figure 2-87.—Metal tag wire identification.
Figure 2-88.—Wiring diagram of a passenger vehicle showing standard equipment and color code for wires.
Figure 2-89.—Wiring diagram symbols.
type has a cup in which the wire is held by solder
permanently. The solderless type is connected to the
wire by special tools. These tools deform the barrel of
the terminal and exert pressure on the wire to form a
strong mechanical bond and electrical connection.
Solderless type terminals are gradually replacing
solder type terminals in military equipment.
Wire passing through holes in the metal members
of the frame or body should be protected by rubber
grommets. If rubber grommets are not available, use a
piece of rubber hose the size of the hole to protect the
wiring from chafing or cutting on sharp edges.
Wire in the electrical system should be supported
by clamps or fastened by wire ties at various points
about the vehicle. When installing new wiring, be sure
to keep it away from any heat-producing component
that would scorch or bum the insulation.
What type of wire circuit is commonly used on
equipment that is subject to heavy vibrations?
What are the two types of wiring assemblies?
Q3. On tactical equipment that has no color-coded
wiring, how are the wires identified?
Q1. Five
Q2. Battery
Q3. Lead peroxide
Q4. Hydrogen
Q5. 1.28
Q6. Cold-cranking rating and reserve capacity rating
Q7. Always pour acid into water
Q8. Battery leakage test
Q9. Zero
Q10. 3 minutes
Q11. A and B circuits
Q12. Speed of armature rotation, number of armature conductors, and the
strength of the magnetic field
Q13. Growler test and bar-to-bar test
Q14. Rectifier assembly
Q15. Delta type
Q16. The regulator increases resistance between the battery and the rotor
windings of the alternator
Q17. Integral regulator
Q18. Regulator voltage test
Q19. Load tester and volt-ohm-millimeter (multimeter)
Q20. Direct battery voltage
Q1. Bendix drive, overrunning clutch, and Dyer drive
Q2. Makes and break-s the electrical connection
Q3. Low battery voltage
Q4. Double reduction starter
Q5. False
Q6. 30 seconds
Q7. Insulated circuit resistance test
Q1. Primary circuit
Q2. Ignition coil
Q3. Resistor and non-resistor types
Q4. The length and diameter of the insulator tip and the ability of the sparkplug
to transfer heat to the cooling system
Q5. False
Q6. Point dwell
Q7. Distributor cam
Q8. Detonation sensor
Q9. Sparkplug leakage
Q10. More than 3 degrees
Q11. Non-magnetic feeler gauge
Q12. Timing is too retarded
Q13. Base timing
Q1. 25 percent
Q2. Rheostat
Q3. 25 feet
Q4. 400 feet
Q5. On the brake pedal
Q1. Voltmeter
Q2. By dividing the available voltage between two electrically heated bimetallic
Q3. Distributor
Q4. Faulty horn switch
Q1. Two-wire circuit
Q2. Cables and harnesses
Q3. Small metal tags with numbers
If the system is well-adapted to the work it is
required to perform and not misused, it can provide
smooth, flexible, uniform action without vibration and
is unaffected by variation of load. Hydraulic systems
can provide widely variable motions in both rotary and
straight-line transmission of power. The need for
control by hand can be minimized. In addition, they are
economical to operate.
Learning Objective: Explain the operating principles
of hydraulic and pneumatic systems. Identify the
components, component functions, and maintenance
procedures of hydraulic and pneumatic systems.
In automotive and construction equipment, the
terms hydraulic and pneumatic describe a method of
transmitting power from one place to another through
the use of a liquid or a gas. Certain physical laws or
principles apply to all liquids and gases. You should be
familiar with the following terms, as they are
associated with hydraulic and pneumatic systems.
The basic principles of hydraulics are few and
simple and are as follows:
Liquids have no shape of their own.
HYDRAULICS is a branch of science that deals
with the study and use of liquids as related to the
mechanical aspects of physics.
Liquids will NOT compress.
Liquids transmit applied pressure in all
PNEUMATICS is a branch of science that deals
with the study and use of air and other gases as
related to the mechanical aspects of physics.
Liquids provide great increase in work force.
The chapter covers the basic principles associated
with hydraulics and pneumatics, followed by coverage
of various system components. The purpose of this
information is to give you an analytical understanding
of the interrelationships of principles and the
components in an operating system.
Pressure and Force
The terms force and pressure are used extensively
in the study of fluid power. It is essential that we
distinguish between these terms. Force means a total
push or pull. It is push or pull exerted against the total
area of a particular surface and is expressed in pounds
or grams. Pressure means the amount of push or pull
(force) applied to each unit area of the surface and is
expressed in pounds per square inch (lb/in2) or grams
per square centimeter (gm/cm2). Pressure may be
exerted in one direction, in several directions, or in all
Learning Objective: Identify operational
characteristics, component functions, and maintenance
procedures of a hydraulic system.
The extensive use of hydraulics to transmit
power is due to the fact that a properly constructed
hydraulic system possesses a number of favorable
characteristics. These are as follows:
Computing Force, Pressure, and Area
A formula is used in computing force, pressure,
and area in hydraulic systems. In this formula, P refers
to pressure, F indicates force, and A represents area.
Eliminates the need for complicated systems
using gears, cams, and levers.
Motion can be transmitted without the slack
inherent in the use of solid machine parts.
Force equals pressure times area. Thus, the
formula is written F = P x A
The fluids used are not subject to breakage as are
mechanical parts.
Pressure equals force divided by area. By
rearranging the above formula, this state may be
condensed into the following: P = F divided by A.
Hydraulic system mechanisms are not subjected
to great wear.
Since area equals force divided by pressure, the
formula for area is written as follows: A = F divided
by P
Figure 3-1 shows a memory device for recalling
the different variations of the formula. Any letter in the
triangle may be expressed as the product or quotient of
the other two, depending on its position within the
Incompressibility and Expansion
of Liquids
For all practical purposes, fluids are incompressible. Under extremely high pressures: the volume
of a fluid can be decreased somewhat, though the
decrease is so slight that it is considered to be
negligible except by design engineers.
Liquids expand and contract because of
temperature changes. When liquid in a closed
container is subjected to high temperatures, it expands
and this exerts pressure on the walls of the container;
therefore, it is necessary that pressure-relief
mechanisms and expansion chambers be incorporated
into hydraulic systems. Without these precautionary
measures, the expanding fluid could exert enough
pressure to rupture the system.
Transmission of Forces through Liquids
Figure 3-2.—Transmission of force: (A) Solid; (B) Fluid.
When a force is applied to the end of a column of
confined liquid (fig. 3-2, view B), it is transmitted
straight through the other end and also undiminished in
every direction throughout the column—forward,
backward, and sideways—so that the containing
vessel is literally tilled with pressure.
An example of this distribution of force is shown in
figure 3-3. The flat hose takes on a circular cross
section when it is filled with water under pressure. The
outward push of the water is equal in every direction.
When the end of a solid bar is struck, the main
force of the blow is carried straight through the bar to
the other end (fig. 3-2, view A). This happens because
the bar is rigid. The direction of the blow almost
entirely determines the direction of the transmitted
force. The more rigid the bar, the less force is lost
inside the bar or transmitted outward at right angles to
the direction of the blow.
Pascal’s Law
The foundation of modern hydraulics was
established when Blaise Pascal, a French scientist,
Figure 3-1.—Device for determining the arrangement of the
force, pressure, and area formula.
Figure 3-3.—Distribution of force.
discovered the fundamental law for the science of
hydraulics. Pascal’s law tells us that pressure on a
confined fluid is transmitted undiminished in every
direction, and acts with equal force on equal areas,
throughout the confining vessel or system.
According to Pascal’s law, any force applied to a
confined fluid is transmitted in all directions
throughout the fluid regardless of the shape of the
container. Consider the effect of this in the systems
shown in views A and B of figure 3-4. If there is
resistance on the output piston (view A, piston 2) and
the input piston is pushed downward, a pressure is
created through the fluid which acts equally at right
angles to surfaces in all parts of the container.
If the force 1 is 100 pounds and the area of input
piston 1 is 10 square inches, then pressure in the fluid is
10 psi ( 100 ÷ 10). It must be emphasized that this fluid
pressure cannot be created without resistance to flow,
which, in this case, is provided by the 100-pound force
acting against the top of the output piston 2. This
pressure acts on piston 2, so for each square inch of its
area, it is pushed upward with the force of 10 pounds.
In this case, a fluid column of a uniform cross section is
considered so the area of output piston 2 is the same as
input piston 1, or 10 square inches; therefore, the
upward force on output piston 2 is 100 pounds—the
same as was applied to input piston 1. All that has been
accomplished in this system was to transmit the 100pound force around a bend; however, this principle
underlies practically all-mechanical applications of
fluid power.
Figure 3-4.—Force transmitted from piston to piston.
the pressure is the same because the force is
concentrated on a relatively small area.
This pressure of 10 psi acts on all parts of the fluid
container, including the bottom of output piston 2;
therefore, the upward force on output piston 2 is 10
pounds for each of its 20 square inches of area, or 200
pounds (10 x 20). In this case, the original force has
been multiplied tenfold while using the same pressure
in the fluid as before. In any system with these
dimensions, the ratio of output force to input force is
always 10 to 1 regardless of the applied force; for
example, if the applied force of input piston 1 is 50
pounds, the pressure in the system is increased to 25
psi. This will support a resistant force of 500 pounds on
output piston 2.
At this point, it should be noted that since Pascal’s
law is independent of the shape of the container, it is
not necessary that the’ tubing connecting the two
pistons should be the full area of the pistons. A
connection of any size, shape, or length will do so long
as an unobstructed passage is provided. Therefore, the
system shown in view B of figure 3-4 (a relatively
small, bent pipe connects the two cylinders) will act the
same as that shown in view A.
Multiplication of Forces
Some hydraulic systems are used to multiply
force. In figure 3-5, notice that piston 1 is smaller than
piston 2. Assume that the area of the input piston 1 is 2
square inches. With a resistant force on piston 2, a
downward force of 20 pounds acting on piston 1
creates 10 psi (20 ÷ 2) in the fluid. Although this force
is much smaller than the applied forces in figure 3-4,
Figure 3-5.—Multiplication of force in a hydraulic system.
The system works the same in reverse. Consider
piston 2 as the input and piston 1 as the output; then the
output force will always be one tenth of the input force.
petroleum-based, synthetic fire-resistant, and waterbased fire-resistant.
Therefore, the first basic rule for two pistons used
in a fluid power system is the force acting on each is
directly proportional to its area, and the magnitude
of each force is the product of the pressure and its
area is totally applicable.
Petroleum-Based Fluids
The most common hydraulic fluids used in
hydraulic systems are the petroleum-based oils. These
fluids contain additives to protect the fluid from
oxidation, to protect the metals from corrosion, to
reduce the tendency of the fluid to foam, and to
improve the viscosity.
Volume and Distance Factors
In the systems shown in views A and B of figure
3-4, the pistons have areas of 10 square inches. Since
the areas of the input and output pistons are equal, a
force of 100 pounds on the input piston will support a
resistant force of 100 pounds on the output piston. At
this point the pressure of the fluid is 10 psi. A slight
force in excess of 100 pounds on the input piston will
increase the pressure of the fluid, which, in turn,
overcomes the resistance force. Assume that the output
piston is forced downward 1 inch. This action
displaces 10 cubic inches of fluid (1 in. x 10 sq. in. = 10
cubic inches). Since liquid is practically
incompressible, this volume must go some place. This
volume of fluid moves the output piston. Since the area
of the output piston is likewise 10 square inches, it
moves 1 inch upward to accommodate the 10 cubic
inches of fluid. The pistons are of equal areas;
therefore, they will move the same distance, though in
opposite directions.
Applying this reasoning to the system in figure
3-5, it is obvious that if the input piston 1 is pushed
down 1 inch, only 2 cubic inches of fluid is displaced.
The output piston 2 will move only one tenth of an inch
to accommodate these 2 cubic inches of fluid, because
its area is 10 times that of input piston 1. This leads to
the second basic rule for two pistons in the same fluid
power system. which is the distances moved are
inversely proportional to their areas.
Synthetic Fire-Resistant Fluids
Petroleum-based oils contain most of the desired
traits of a hydraulic fluid. However, they are
flammable under normal conditions and can become
explosive when subjected to high pressures and a
source of flame or high temperatures. Nonflammable
synthetic liquids have been developed for use in
hydraulic systems where fire hazards exist. These
synthetic fire-resistant fluids are phosphate ester fireresistant fluid, silicone synthetic fire-resistant fluid.
and the lightweight synthetic fire-resistant fluid.
Water-Based Fire-Resistant Fluids
The most widely used water-based hydraulic
fluids may be classified as water-glycol mixtures and
water-synthetic base mixtures. The water-glycol
mixture contains additives to protect it from oxidation,
corrosion, and biological growth and to enhance its
load-carrying capacity.
Fire resistance of the water mixture depends on the
vaporization and smothering effect of steam generated
from the water. The water in water-based fluids is
constantly being driven off while the system is
operating. Therefore, frequent checks are required to
maintain the correct ratio of water to base mixture.
An arrangement of interconnected components is
required to transmit and control power through
pressurized fluid. Such an arrangement is commonly
referred to as a system. The number and arrangement
of the components vary from system to system,
depending on application. In many applications, one
main system supplies power to several subsystems,
which are commonly referred to as circuits. The
complete system may be a small compact unit; more
often, however, the components are located at widely
separated points for convenient control.
While the terms and principles mentioned above
are not all that apply to the physics of fluids, they are
sufficient to allow further discussion in this training
manual (TRAMAN). The TRAMAN, Fluid Power,
NAVEDTRA 12964, should be obtained and studied
for more comprehensive coverage of this subject.
There have been many liquids tested for use in
hydraulic systems. Currently liquids being tested
include mineral oil, water, phosphate ester, waterbased ethylene glycol compounds, and silicone fluids.
The three most common types of hydraulic fluids are
The basic components of a fluid power system are
essentially the same, regardless of whether the system
uses hydraulic or pneumatic medium. The basic
components are as follows:
2. Separating air from the oil, and
3. Settling out contamination in the oil.
Ideally, the reservoir should be high and narrow,
rather than shallow and broad. The oil level should be
as high as possible above the opening to the pump
suction line. This condition prevents the vacuum at the
line opening from causing a vortex or whirlpool effect.
Anytime you see a whirlpool at the suction line
opening, the system is taking in air.
Strainers and filters
Control valves (directional and relief)
Actuating devices (cylinders)
As a rule of thumb, the reservoir level should be
two to three times the pump output per minute. By this
rule which works well for stationary machinery, a 20gpm system would require a 40- or 60-gpm reservoir.
However, this is not possible for mobile equipment.
You are more likely to find a 20- or 30-gallon tank to
support a 100-gpm system. This is possible because
mobile systems operate intermittently, rather than all
the time. The largest reservoirs are on mobile
equipment. These reservoirs may have a 40- or 50gallon capacity, capable of handling more than 200gpm output.
Lines (pipe, tubing, or flexible hose)
Connectors and fittings
Sealing materials and devices
Several applications of fluid power require only a
simple system; that is, a system which uses only a few
components in addition to the basic components.
A properly constructed reservoir (fig. 3-6) is more
than just a tank to hold oil until the system demands
fluid. Is should also be capable of the following:
The reservoir must be sized to ensure there is a
reserve of oil with all the cylinders in the system fully
extended. The reserve must be high enough to prevent
a whirlpool at the suction line opening. Also, there
1. Dissipating heat from the fluid,
Figure 3-6.—Typical hydraulic reservoir.
create system pressure, since only a resistance to the
flow can create pressure. As the pump provides flow, it
transmits a force to the fluid. As the fluid flow
encounters resistance, this force is changed into
pressure. Resistance to flow is the result of a resistance
or obstruction in the path of flow. This restriction is
normally the work accomplished by the hydraulic
system, but can also be restrictions of lines, fittings,
and valves within the system. Thus the load imposed
on the system or action of a pressure-regulating device
controls the pressure.
must be enough space to hold all the oil when the
cylinders retract with some space to spare for
expansion of hot oil.
An air vent allows the air to be drawn in and
pushed out of the reservoir by the ever-changing fluid
level. An air filter is attached to the air vent to prevent
drawing atmospheric dust into the system by the everchanging fluid level. A firmly secured filling strainer
of fine mesh wire is always placed below the filler cap.
The sight gauge is provided so the normal fluid
level can always be seen, as it is essential that the fluid
in the reservoir be at the correct level. The baffle plate
segregates the outlet fluid from the inlet fluid.
Although not a total segregation, it does allow time to
dissipate the air bubbles, lessen the fluid turbulence
(contaminants settle out of nonturbulent fluid), and
cool the return fluid somewhat before it is picked up by
the pump.
Pumps are rated according to their volumetric
output and displacement. Volumetric output is the
amount of fluid a pump can deliver to its outlet port in a
certain period of time at a given speed. Volumetric
output is usually expressed in gallons per minute
(gpm). Since changes in pump speed affect volumetric
output, some pumps are rated by their displacement.
Pump displacement is the amount of fluid the pump
can deliver per cycle. Since most pumps use a rotary
drive, displacement is usually expressed in terms of
cubic inches per revolution.
Reservoirs used on CESE may vary considerably
from that shown in figure 3-6; however, manufacturers
retain many of the noted features as possible
depending on design limits and use.
Many different methods are used to classify
pumps. Terms, such as nonpositive displacement,
positive displacement, fixed displacement, variable
displacement, fixed delivery, variable delivery,
constant volume, and others are used to describe
pumps. The first two of these terms describe the
fundamental division of pumps because all pumps are
either nonpositive displacement or positive
displacement. Basically pumps that discharge liquid in
a continuous flow are referred to as nonpositive
displacement, and those that discharge volumes
separated by a period of no discharge are referred to as
positive displacement.
Strainers and Filters
Strainers are constructed of fine mesh wire screens
or of screening elements, consisting of specially
processed wire of varying thickness wrapped around
metal frames. They do NOT provide as fine a
screening action as filters, but they offer less resistance
to flow and are used in pump suction lines where
pressure drop must be kept to a minimum. If one
strainer is not large enough to handle the supply of the
pump. two or more strainers can be used in parallel.
The most common device installed in hydraulic
systems to prevent foreign particles and contamination
from remaining in the system are called filters. They
may be located in the reservoir, in the return line, in the
pressure line, or any other location in the system where
the designer of the system decides they are needed to
safeguard the system against impurities.
Pumps may also be classified according to the
specific design used to create the flow of fluid.
Practically all-hydraulic pumps fall within three
designs classifications—centrifugal, rotary, and
reciprocating. Since the use of centrifugal pumps is
limited, we will only discuss rotary and reciprocating.
Filters are classified as full flow and partial flow.
In the full-flow filter, all fluid that enters the unit
passes through the filtering element, while in the
partial-flow filter. only a portion of the fluid passes
through the element.
ROTARY PUMPS.—All rotary pumps have
rotating parts that trap the fluid at the inlet (suction) port
and force it through the discharge port into the system.
Gears (figs. 3-7, 3-8, and 3-9), screws (fig. 3-10), lobes
(fig. 3-11), and vanes (fig. 3-12) are commonly used to
move the fluid. Rotary pumps are positive
displacement of the fixed displacement type.
The purpose of a hydraulic pump is to supply a
flow of fluid to a hydraulic system. The pump does not
Rotary pumps are designed with very small
clearances between rotating parts and stationary parts
Figure 3-7.—Gear-type rotary pump.
to minimize slippage from the discharge side back to
the suction side. They are designed to operate at
relatively moderate speeds. Operating at high speeds
causes erosion and excessive wear which results in
increased clearances.
provides flow during every other stroke, while the
double-action provides flow during each stroke.
Single-action pumps are frequently used in hydraulic
There are numerous types of rotary pumps and
various methods of classification. They may be
classified by shaft position—either vertically or
horizontally mounted; the type of drive—electric
motor, gasoline engine, and so forth; their
manufacturer’s name; or service application. However,
classification of rotary pumps is generally made
according to the type of rotating element.
Several types of power-operated hydraulic pumps,
such as the radial piston (fig. 3-14) and axial piston
(figs. 3-15 and 3-16), are classified as reciprocating
pumps. These pumps are sometimes classified as
rotary pumps, because a rotary motion is imparted to
the pumps by the source of power. However, the actual
pumping is performed by sets of pistons reciprocating
inside sets of cylinders.
reciprocating is defined as back-and-forth motion. In a
reciprocating pump, it is the back-and-forth motion of
pistons inside of cylinders that provides the flow of
fluid. Reciprocating pumps, like rotary pumps, operate
on the positive principle; that is, each stroke delivers a
definite volume of liquid to the system.
Control Valves
It is all but impossible to design a practical fluid
power system without some means of controlling the
volume and pressure of the fluid and directing the flow
of fluid to the operating units. This is accomplished by
incorporating different types of valves. A valve is
defined as any device by which the flow of fluid may
be started, stopped, or regulated by a movable part that
opens or obstructs passage.
The most common type of reciprocating pump is
the hand pump (fig. 3-13). There are two types of
manually operated reciprocating pumps—single
action and double action. The single-action pump
Figure 3-8.—Herringbone gear pump.
Valves may be controlled manually, electrically,
pneumatically, mechanically, hydraulically, or by
combinations of two or more methods. Factors that
determine the method of control include the purpose of
the valve, the design and purpose of the system, the
location of the valve within the system, and the
availability of the source of power.
Valves must be accurate in the control of fluid flow
and pressure and the sequence of operation. Leakage
between the valve element and the valve seat is
reduced to a negligible quantity by precisionmachined surfaces, resulting in carefully controlled
clearances. This is one of the very important reasons
for minimizing contamination in the system.
Contamination causes valves to stick, plugs small
orifices, and causes abrasions of the valve seating
surfaces which will result in leakage between the valve
element and valve seat when the valve is closed. Any of
these can result in inefficient operation or complete
stoppage of the equipment.
Valves are classified according to their use: flow
control, pressure control, and directional control.
Some of these valves have multiple functions that fall
into more than one classification.
Figure 3-9.—Helical gear pump.
Figure 3-10.—Screw pump.
Figure 3-11.—Lobe pump.
Figure 3-14.—Nine-piston radial piston pump.
of controlling pressure. There are many types of
automatic pressure control valves. Some of them
merely provide an escape for pressure that exceeds a
set pressure, some only reduce the pressure to a lower
pressure system or subsystem, and some keep the
pressure in a system within a required range. The most
common pressure control valves are relief valves (fig.
3-21), pressure regulators (fig. 3-22), pressurereducing valves (fig. 3-23), and counterbalance valves
(fig. 3-24).
Figure 3-12.—Vane pump.
Directional control valves are designed to direct the
flow of fluid, at the desired time, to the point in a fluid
power system where it will do work; for example,
using a directional control valve to drive a ram back
and forth in its cylinder. Various other terms are used
to identity directional control valves, such as selector
valve, transfer valve, and control valve.
Figure 3-13.—Hydraulic hand pump.
Directional control valves for hydraulic and
pneumatic systems are similar in design and operation.
However, there is one major difference. The return
port of a hydraulic valve is ported through a return line
to the reservoir, while the similar port in a pneumatic
valve, commonly referred to as an exhaust port, is
usually vented to the atmosphere.
valves are used to regulate the flow of fluid in a fluidpower system. Control of flow in fluid-power systems
is important because the rate of movement of fluidpowered mechanisms depends on the rate of flow of
the pressurized fluid. Some of the most commonly
used flow control valves are ball valves (fig. 3-17),
gate valves (fig. 3-18), globe valves (fig. 3-19), and
needle valves (fig. 3-20).
Directional control valves may be operated by
differences in pressure acting on opposite sides of the
valving element, or they may be positioned manually,
mechanically, or electrically. Often two or more
methods of operating the same valve will be used in
different phases or its action.
and efficient operation of hydraulic systems, systems
components, and related equipment requires a means
Figure 3-15.—In-line axial piston pump.
Figure 3-16.—Bent-axis axial piston pump.
Figure 3-18.—Rising stem gate valve.
Directional control valves may be classified in
several ways. Some of the different ways are by the
type of control, the number of ports in the valve
housing, and the specific function of the valve. The
most common method is by the type of valving element
used in the construction of the valve. The most
common types of valving elements used in a hydraulic
Figure 3-17.—Typical ball valve.
1. Adjusting screw
2. Adjusting screwcap
3. Spring
Figure 3-19.—Globe valve.
4. Return port
5. Ball
6. Pressure port
Figure 3-21.—Typical relief valve.
system are the poppet (fig. 3-25), rotary spool (fig.
3-26), and sliding spool valves (fig. 3-27).
An actuating cylinder is a device that converts
fluid power to linear motion, or straight-line force and
motion. Since linear motion is a back-and-forth motion
along a straight line, this type of actuator is sometimes
referred to as a reciprocating. The cylinder consists of a
ram or piston operating within a cylindrical bore.
Actuating cylinders may be installed so that the
cylinder is anchored to a stationary structure and the
ram or piston is attached to the mechanism to be
operated, or the piston or ram may be anchored to the
stationary structure and the cylinder attached to the
mechanism to be operated.
and piston are often used interchangeably. However, a
ram-type cylinder is usually considered one in which
the cross-sectional area of the piston is more than one
halfofthe cross-sectional area of the movable element.
In most actuating cylinders of this type, the rod and the
Figure 3-20.—Cross-sectional view of a needle valve.
Figure 3-22.—Hydraulic pressure regulator.
Figure 3-23.—Spring-loaded pressure-reducing valve.
movable element have equal areas. This type of
movable element is frequently referred to as a plunger.
The most common ram-type cylinders are the single(fig. 3-28) and double-acting (fig. 3-29).
6. Pilot passage
Adjustment screw
7. Check valve
Internal drain
8. Discharge outlet
or reverse free
flow inlet
Pressure inlet or
9. Piston
reverse free flow
Figure 3-24.—Counterbalance valve.
flat surface on the external part of the ram for pushing
or lifting the unit to be operated. Other applications
require some mechanical means of attachment, such as
a clevis or eyebolt. The design of ram-type cylinders
varies in many other respects to satisfy the
requirements of different applications.
The ram-type actuator is primarily used to push,
rather than pull. Some applications require simply a
Figure 3-25.—The basic operation of a simple poppet valve.
cylinder in which the cross-sectional area of the piston
is less than one half of the cross-sectional area of the
movable element is referred to as a piston-type
cylinder. This type of cylinder is normally used for
applications that require both push and pull functions.
The piston-type cylinder is the most common type
used in fluid power systems.
Figure 3-26.—Operation of a rotary spool valve.
The piston rod may extend through either or both
ends of the cylinder. The extended end of the rod is
normally threaded so that some type of mechanical
connector, such as an eyebolt or clevis, and locknut can
be attached. This threaded connection provides for
adjustment between the rod and the unit to be actuated.
After the correct adjustment is made, the locknut is
tightened against the connector to prevent the
connector from turning. The other end of the connector
is attached to, either directly or through additional
mechanical linkage, the unit to be actuated.
The essential parts of a piston-type cylinder are a
cylindrical barrel, a piston and rod, end caps, and
suitable seals. The end caps are attached to the end of
the barrel. These end caps usually contain fluid ports.
The end cap on the rod end contains a hole for the
piston rod to pass through. Suitable seals are used
between the hole and the piston rod to keep fluid from
leaking out and to keep dirt and other contaminants
from entering the barrel. The opposite end cap of most
cylinders is provided with a fitting for securing the
actuating cylinder to some structure. This end cap is
referred to as the anchor end cap.
To satisfy the many requirements of fluid power
systems, piston-type cylinders are available in various
designs with the most common being the single- (fig.
3-30, view A) and double-acting (fig. 3-30, view B).
Figure 3-28.—Single-acting ram-type actuating cylinder.
Figure 3-29.—Double-acting ram-type actuating cylinder.
oil during slack periods and feeds it back into the system
during peak periods of oil usage.
2. Absorb shocks. Accumulators that absorb
shocks take in excess oil during peak pressures and let it
out again after the surge is past. This action reduces
vibrations and noise in the system. It also smoothes
operation during pressure delays, such as when a
variable displacement pump goes into stroke.
Figure 3-27.—Operation of a sliding spool valve.
which hydraulic fluid is stored under pressure from an
external source. Accumulators have four major uses:
3. Build pressure gradually. Accumulators that
build pressure gradually are used to soften the working
stroke of a piston against a fixed load as in a hydraulic
1. Store energy. Accumulators that store energy
are often used as boosters for systems with fixed
displacement pumps. The accumulator stores pressure
4. Maintain constant pressure. Accumulators
that maintain constant pressure are always weightloaded types that place a fixed force on the oil in a closed
An accumulator is a pressure storage reservoir in
Figure 3-30.—(A) Single- and (B) double-acting piston-type cylinders.
4. Maintain constant pressure. Accumulators
that maintain constant pressure are always
weight-loaded types that place a fixed force on the oil in
a closed circuit. Whether the volume of oil changes
from leakage or from heat expansion or contraction, this
accumulator keeps the same gravity pressure on the
While most accumulators can do any of these
things, their use in a system is limited to only one. The
major types of accumulators are as follows: pneumatic
(gas-loaded), weight-loaded, spring-loaded.
pneumatic accumulators. gas and oil occupy the same
container. When the oil pressure rises, incoming oil
compresses the gas. When oil pressure drops, the gas
expands, forcing oil out.
In most cases, the gas is separated from the oil by a
piston (fig. 3-31), a bladder (fig. 3-32), or a diaphragm
(fig. 3-33). This prevents mixing of gas and oil,
keeping gas out of the hydraulic system.
The weight-loaded accumulator uses a piston and
cylinder along with heavy weights on the piston for
loading or charging the oil. It is loaded by gravity and
operation is very basic. The pressure oil in the
hydraulic circuit is pushed into the lower section of the
cylinder, raising the piston and weights. The
accumulator is now charged and ready for work. When
oil is needed, pressure drops in the system and gravity
Figure 3-31 .—Floating piston-type accumulator.
Figure 3-33.—Diaphragm accumulator.
disadvantage is its bulky size and heavy weight which
renders it not practical for mobile equipment.
The spring-loaded accumulator (fig. 3-34) is very
Figure 3-32 .—Bladder-type accumulator.
Tubing, Piping, and Hose
The three types of lines used in fluid power
systems are tubing (semirigid), pipe (rigid), and hose
(flexible). A number of factors are considered when
the type of line is selected for a particular system.
These factors include the type of fluid, the required
system pressure, and the location of the system. For
example, heavy pipe might be used for a large
stationary system, but comparatively lightweight steel
tubing is used in the automotive brake system. Flexible
hose is requires in installations where units must be
free to move relative to each other.
PIPING AND TUBING.—The choice between
pipe and tubing depends on system pressure and flow.
The advantages of tubing include easier bending and
flaring, fewer fittings, better appearance, better
reusability, and less leakage. However, pipe is cheaper
and will handle large volumes under high pressures.
Pipe is also used where straight-line hookups are
required and for more permanent installations.
Figure 3-34.—Spring-loaded accumulator.
similar to the weight-loaded accumulator except that
springs do the loading. In operation, pressure oil loads
the piston by compressing the spring. When pressure
drops, the spring forces oil into the system.
In either case, the hydraulic lines must be
compatible with the entire system. Pressure loss in the
line must be kept to a minimum for an efficient system.
Pipes for hydraulic systems should be made of
seamless cold-drawn mild steel. Galvanized pipe
should NOT be used because the zinc coating could
flake or scale, causing damage to the valves and
A hydraulic motor is a device that converts fluid
power energy to rotary motion and force. The function
of a motor is opposite that of a pump. However, the
design and operation of motors are very similar to
Tubing used in fluid power systems is commonly
made from steel, copper, aluminum, and, in some
instances, plastic. Each of these materials has its own
distinct advantages or disadvantages in certain
Motors have many uses in fluid power systems. In
hydraulic power drives, pumps and motors are
combined with suitable lines and valves to form
hydraulic transmissions.
Copper. —The use of copper is limited to lowpressure hydraulic systems where vibration is limited.
Copper has high resistance to corrosion and is easily
drawn or bent. However, it is unsatisfactory for high
temperatures and has a tendency to harden and break
due to stress and vibration.
Fluid motors may either be fixed- or variabledisplacement. Fixed-displacement motors provide
constant torque and variable speed. Controlling the
amount of input flow varies the speed. Variabledisplacement motors are constructed so that the
working relationship of the internal parts can be varied
to change displacement. The majority of the motors
used in fluid power systems are the fixed-displacement
Steel.—Tubing constructed of cold-drawn steel is
the accepted standard in hydraulics where high
pressures are encountered. Steel is used because of its
strength, stability for bending and flanging, and
adaptability to high pressures and temperatures. Its
chief disadvantage is its comparatively low resistance
to corrosion. There are two types of steel tubing—
seamless and electric welded.
Fluid motors are usually classified according to the
type of internal element that is directly actuated by the
flow. The most common element are the gear (fig. 3-7),
the vane (fig. 3-12), and the piston (fig. 3-15).
Aluminum .—Aluminum is limited to lowpressure use, yet it has good flaring and bending
operating pump would ultimately cause rigid tubing to
Flexible hose is designated by a dash number,
which is the ID of the hose expressed in 16ths of an
inch and is stenciled on the side of the hose. For
example, the inside of a -16 hose is 1 inch. For a few
hose styles, this is approximate and is not a true ID.
Plastic .—Plastic tubing lines are made from a
variety of materials; nylon is the most suitable for use in
low-pressure hydraulic applications ONLY.
There are three important dimensions of any tubular
product—outside diameter (OD), inside diameter
(ID), and wall thickness. Sizes of pipe are listed by the
nominal (or approximate) ID and wall thickness. Sizes of
tubing are listed by the actual OD and the wall thickness.
Rubber hose is designed for specific fluid,
temperature, and pressure ranges and is provided in
various specifications. Flexible hydraulic hose is
composed of three basic parts (fig. 3-36):
Inner Tube.—The inner tube is a synthetic rubber
layer that is oil-resistant. It must be smooth, flexible,
and able to resist heat and corrosion.
The material, the inside diameter, and the wall
thickness are the three primary considerations in the
selection of lines for the circulatory system of a particular
fluid power system.
Reinforcement Layers.—The reinforcement layers
vary with the type of hose. These layers (or plies) are
constructed of natural or synthetic fibers, braided wire, or
a combination of these. The strength of this layer depends
upon the pressure requirement of the system.
The manufacturers of tubing and pipe usually supply
charts, graphs, or tables which aid in the selection of
proper lines for fluid power systems. These tables and
charts use different methods for deriving the correct sizes
of pipe and tubing.
Line should normally be kept as short and free of
bends as possible. However, tubing should NOT be
assembled in a straight line, because a bend tends to
eliminate strain by absorbing vibration and compensates
for thermal expansion and contraction. Bends are
preferred to elbows, because bends cause less of a power
loss. A few of the incorrect and correct methods of
installing tubing are shown in figure 3-35.
FLEXIBLE HOSE.—Hose is used in fluid power
systems where there is a need for flexibility, such as
connection to units that move while in operation or to
units attached to a hinged portion of the equipment. It
is also used in locations that are subjected to severe
vibration. Flexible hose is usually used to connect the
pump to the system. The vibration that is set up by the
Figure 3-36.—Flexible rubber hose construction.
Figure 3-35.—Correct and incorrect methods of installing tubing.
Outer Cover.—The outer cover protects the
reinforcement layers. A special rubber is most commonly
used for the outer layer because it resists abrasion and
exposure to weather, oil, and dirt.
Flexible hose is provided in four-pressure ranges.
Low pressure is used in a low-pressure system and for the
exhaust lines of high-pressure systems. Mediumpressure hose is used in systems with pressures up to
1,200 psi; high-pressure hose is used with pressures up to
3,000 psi; and extra-high-pressure hose is used in
systems with pressures up to 5,000 psi. High- and extrahigh-pressure hoses normally come as complete
assemblies with factory installed end fittings. Mediumand low-pressure hose are available in bulk and are
usually fabricated locally.
Flexible hose must NOT be twisted on installation,
since this reduces the life of the hose considerably and
may cause fittings to loosen as well. You can determine
whether or not a hose is twisted by looking at the lay line
that runs along the length of the hose. This lay line should
not tend to spiral around the hose (fig. 3-37).
Figure 3-37.—Correct and incorrect installation of
flexible hose.
Hose should be installed so that it will be subjected to
a minimum of flexing during operation. Support clamps
are not necessary with short installations, but with hoses
of considerable length (48 inches for example), clamps
should be placed not more than 24 inches apart. Closer
supports are desirable and, in some cases, needed.
Hose must NEVER be stretched tight between two
fittings. About 5 to 8 percent of the total length must be
allowed as slack to provide freedom of movement under
pressure. When flexible hose is under pressure, it
contracts in length and expands in diameter. Examples of
correct and incorrect installations of flexible hose are
shown in figure 3-37.
Connectors and Fittings
There are many types of connectors and fittings
required for a fluid power system. The type of
connector or fitting depends upon the type of
circulatory system (pipe, tubing, or flexible hose), the
fluid medium, and the maximum operating pressure of
the system. Some of the most common connectors and
fittings are described in the following paragraphs.
T H R E A D E D C O N N E C T O R S .—Threaded
connectors (fig. 3-38) are used in low-pressure pipe
systems. The connectors are made with standard pipe
threads cut on the inside surface of the connector. The
end of the pipe is threaded on the outside for
connecting with the connector. Standard pipe threads
are tapered slightly to ensure a tight connection.
Figure 3-38.—Threaded pipe connectors.
To prevent seizing, you can apply a suitable pipe
thread compound to the threads. When a compound is
applied to the threads, the two end threads are to be kept
free of the compound so that it will not contaminate the
fluid. Pipe compound, when improperly applied, may get
inside lines and harm pumps and control equipment.
Because of this reason many manufacturers forbid the
use of such compounds when fabricating the piping for a
Flareless-tube connectors are available in many of
the same shapes and threaded combinations as flaredtube connectors (fig. 3-40). The fitting has a counterbore
shoulder for the end of the tubing to rest against. The
angle of the counterbore causes the cutting edge of the
sleeve or ferrule to cut into the outside surface of the tube
when the two are assembled.
The nut presses on the bevel of the sleeve and causes
it to clamp tightly to the tube. Resistance to vibration is
concentrated at this point, rather than at the sleeve cut.
When fully tightened, the sleeve or ferrule is bowed
Another material used on pipe thread is sealant
tape, made by TEFLON TM. This tape is made of
polytetraflouroethylene (PTFE), which provides an
effective means of sealing pipe connections and
eliminates the need of having to torque connections to
excessively high values to prevent leakage. It also
provides for ease in maintenance whenever it is necessary
to disconnect pipe joints.
connectors are commonly used in circulatory systems
consisting of lines made of tubing. These connectors
provide safe, strong, dependable connections without the
necessity of threading, welding, or soldering the tubing.
The connector consists of a fitting, a sleeve, and a nut (fig.
Figure 3-39.—Flared-tube connector.
The fittings are made of steel, aluminum alloy, or
bronze. The fitting used in a connection should be
made of the same material as that of the sleeve, the nut,
and the tubing. For example, use steel connectors with
steel tubing and aluminum alloy connectors with
aluminum alloy tubing. Fittings are made in union, 45degree and 90-degree elbows, tees and various other
shapes (fig. 3-40).
Tubing used with flare connectors must be flared
before assembly. The nut fits over the sleeve, and when
tightened, draw the sleeve and tubing flare tightly against
the male fitting to form a seal.
The male fitting has a cone-shaped surface with the
same angle as the inside of the flare. The sleeve supports
the tube so vibration does not concentrate at the edge of
the flare and distributes the shearing action over a wider
area for added strength. Correct and incorrect methods
of installing flared-tube connectors are shown in figure
3-41. Tubing nuts should be tightened with a torque
wrench to the value specified in applicable technical
flareless-tube connector eliminates all tube flaring, yet
provides a safe, strong, and dependable tube connection.
This connector consists of a fitting, a sleeve or ferrule,
and a nut (fig. 3-42).
Figure 3-40.—Flared-tube fittings.
Figure 3-41.—Correct and incorrect methods of installing flared fittings.
When tube-type fittings are being tightened,
observe the following:
Tighten only until snug. NEVER overtighten. More
damage has been done to tube fittings by overtightening
than from any other cause.
If a fitting starts to leak and appears loose, retighten
only until leak stops.
Where necessary, use two wrenches on fittings to
avoid twisting the lines.
hose connectors are designed to be either permanent or
reusable and are made of forged steel. There are various
types of end fittings for both the piping connection side
and the hose connection side of hose fittings (fig. 3-43).
Figure 3-42.—Flareless-tube connector.
slightly at the midsection and acts as a spring. This action
of the sleeve or ferrule maintains a constant tension
between the body and the nut, thereby preventing the nut
from loosening.
Permanent hose fittings are discarded with the hose
when the hose is damaged or defective. They are either
crimped or swedged onto the hose. A crimping machine
that may be found in most shops does crimping of the
fitting. The crimping machine is either powered by hand.
an air pump, or a hydraulic pump.
Before the installation of a new flareless-tube
connector, the end of the tubing must be square,
concentric, and free from burrs. For the connection to
be effective, the cutting edge of the sleeve or ferrule
must bite into the external surface of the tube.
Figure 3-43.—End fittings and hose fittings.
However, dust plugs must be used when the coupler is
Reusable hose fittings are pushed on, screwed on, or
clamped onto the hose. When the hose wears out, the
fittings can be removed and used on a new hose that is cut
from stock. Many fittings can be converted to another
thread type by changing the nipple in the socket.
Sealing Materials and Devices
No hydraulic circuit can operate without the proper
seals to hold the fluid under pressure in the system. Seals
also keep dirt and other foreign materials out of the
If hoses and fittings are matched
incorrectly, the results can be pinhole leaks,
ruptures, heat build ups, pressure drops,
cavitation, and other failures.
Hydraulic seals appear to be simple objects when
held in the hand but, in use, they are highly complex;
precision parts must be treated carefully if they are to
do their job properly.
disconnect couplers are used where oil lines must be
connected or disconnected frequently. They are selfsealing devices and do the work of two shutoff valves and
a tube coupler.
Hydraulic seals are used in the following two main
1. Static seals are used to seal fixed parts. Static
seals are usually gaskets, but also may be Orings or packings.
These couplers are fast, easy to use, and keep oil loss
at aminimum. More importantly, there is no need to drain
or bleed the system every time a hookup is required.
be tanned and treated to make it useful as a sealing
material. The tanning processes are those normally used in
the leather industry. It is generally resistant to abrasion
regardless of whether the grain side or flesh side is exposed
to abrasive action. Leather remains flexible at low
temperatures and can be forced with comparative ease into
contact with metal flanges. When leather is properly
impregnated, it is impermeable to most liquids and some
gases. Leather is capable of withstanding the effects of
temperatures ranging from -70°F to +220°F.
2. Dynamic seals are used to seal moving parts.
Dynamic seals include shaft and rod seals and
compression packings. A slight leakage in these
seals is acceptable for seal lubrication.
SEALING MATERIALS.—There have been many
different materials used in the development of sealing
devices. The material used for a particular application
depends on several factors: fluid compatibility;
resistance to heat, pressure, and wear resistance;
hardness; and type of motion.
Metal.—One of the most common metal seals used
in Navy equipment is copper. Flat copper rings are
sometimes used as gaskets under adjusting screws to
provide a fluid seal. Copper is easily bent and requires
careful handling. In addition, copper becomes hard when
used over a long period of time and when subjected to
compression. It is advised that when a component is
disassembled, the copper sealing rings should be
The selection of the correct packings and gaskets
and their proper installations are important factors in
maintaining an efficient fluid power system. The types
of seals to be used in a particular piece of equipment
are specified by the equipment manufacturer.
Seals are made of materials that have been
carefully chosen or developed for specific
applications. These materials include polytetraflouroethylene (PTFE), commonly called TEFLONTM,
synthetic rubber, cork, leather, metal, and asbestos.
The most common types of materials are discussed in
the following paragraphs.
In some fluid power actuating cylinders, metallic
piston rings are used as packing. These rings are similar
in design to the piston rings used in engines.
TYPES OF SEALS.—Fluid power seals are
usually typed according to their shape or design. These
types include T-seals, O-rings, quad-rings, and U-cups,
and so on. Some of the most commonly used seals are
discussed in the following paragraphs.
Cork.—The physical properties of cork make it
ideally suited as a sealing material in certain applications.
The compressibility of cork seals makes them well-suited
for confined applications in which little or no spread of
the material is allowed. The compressibility of cork also
makes a good seal that can be used under various
pressures and allows the gasket to be cut to any desired
thickness to fit any surface, while still forming an
excellent seal. Cork is generally recommended for use
where sustained temperatures do not exceed 275°F.
T-Seals. —The T-seal has an elastomeric
bidirectional sealing element resembling an inverted
letter T. This sealing element is always paired with two
special extrusion-resisting backup rings, one on each side
of the T. The basic T-seal configuration is shown in figure
3-44, view A. The backup rings are single turn, bias cut,
and are usually made of TEFLONTM, nylon, or a
combination of TEFLON and nylon. Nylon is widely
used for T-seal backup rings because it provides excellent
resistance to extrusion and has low friction
Synthetic Rubber.— The materials used in synthetic
rubber seals are either neoprene or nitrile-butadiene base.
These seals are available in a wide range of density,
tensile strength, and elongations. Many factors
contribute to make synthetic rubber ideal for seals. The
elasticity of the material makes it easier in many
applications. Since synthetic rubber seals are virtually
impermeable in their compressed state, they require less
sealing load than many other types of gaskets. Synthetic
rubber seals are used in a variety of applications and
are capable of functioning in temperature ranges as
wide as -65°F to +300°F.
The special T-ring configuration adds stability to the
seal, eliminating spiraling and rolling. T-seals are used in
applications where large clearances could occur as a
result of expansion.
O-Rings. —An O-ring is doughnut-shaped. O-rings
are usually molded from rubber compounds; however,
they can be molded or machined from plastic materials.
The O-ring is usually fitted into a rectangular groove that
is machined into the item to be sealed.
Leather. —Leather is a closely-knit material that is
generally tough, pliable, and relatively resistant to
abrasion, wear, stress, and the effects of temperature
changes. Because it is porous, it is able to absorb
lubricating fluids. This porosity makes it necessary to
impregnate leather for most uses. In general, leather must
An O-ring sealing system is often one of the first
sealing systems considered when fluid closure is
Figure 3-44.—T-seals.
designed because of the following advantages of such
a system:
Low cost
Ease of installation
Ease in maintenance
No adjustment required
No critical torque in clamping
Low distortion structure
Figure 3-45.—Quad-ring.
Small space requirement
Effectiveness over wide pressure and temperature
O-rings are used in both static (as gaskets) and
dynamic (as packing) applications. An O-ring has always
been the most satisfactory choice of seals in static
applications when the fluids, temperatures, pressure, and
geometry permit.
Quad-Rings. —The quad-ring is very similar to the
O-ring, the major difference being that the quad-ring has
a modified square type of cross section, as shown in
figure 3-45. Quad-rings are molded and trimmed to
extremely close tolerances in cross-sectional area, inside
diameter, and outside diameter. Quad-rings are ideally
suited for both low pressures and extremely high
Figure 3-46.—Typical U-cup seal.
Maintenance of a hydraulic system that is properly
operated and cared for is a routine task. Maintenance
usually consists of changing or cleaning filters and
strainers, and occasionally adding or changing the fluid
in the system. However, overheating, excessive pressure,
and contamination can damage an improperly operated
U-CUPS.—The U-cup (fig. 3-46) is a popular
packing due to its ease of installation and low friction.
U-cups are used primarily for pressures below 1,500 psi;
but, they can be used for higher pressures with the use of
backup rings. When more than one U-cup is installed,
they are installed back to back or heel to heel. This backto-back installation is necessary to prevent a pressure trap
(hydraulic lock) between two packings.
Proper maintenance reduces your hydraulic troubles.
By caring for the system using a regular maintenance
program, you can eliminate common problems and
anticipate special ones. These problems can be corrected
before a breakdown occurs.
When a hydraulic system is worked on, cleanliness is
No. 1. Dirt and metal particles can score valves, seize
pumps, clog orifices, resulting in major repair work.
3. Operate the equipment to cycle the flushing oil
through the system. Ensure that all valves are
operated so that the new oil goes through the lines.
Oil and Filter Changes
The time necessary to clean the system
will vary, depending on the condition of the
equipment. Usually from 4 to 48 hours is
sufficient for most systems.
Despite all the precautions you take when working
on the hydraulic system, some contaminates will get into
the system anyway. Good hydraulic oils will hold
contaminates in suspension and the filters will collect
them as oil passes through. A good hydraulic oil contains
additives that work to keep contaminants from damaging
or plugging the system. However, these additives lose
their effectiveness after an extended period of time;
therefore, oil changes at the recommended intervals can
ensure that contamination is held to a minimum. By
changing the oil at its recommended interval ensures that
the additives will do their job.
(Drain out the flushing oil, replace the filters, and
refill the system with clean hydraulic oil of the
recommended type.)
If gums or lacquer has formed on working parts and
the parts are sticking, remove the affected parts and clean
them thoroughly. Consult the manufacturer’s manual
before removing and cleaning any parts for proper
Regular filter changes ensure solid particles are
removed from the system. They should be changed
more often under adverse operating conditions. When
filters are changed, thoroughly clean the filter housing
before installing a new filter. Remember to add enough
fluid to compensate for any fluid lost in filter
Preventing Leaks
Leaking hydraulic connections are frequent reasons
for maintenance. Some leaks are external, being evident
on the outside of components. Others are internal, which
does not result in actual loss of oil, but it does reduce the
efficiency of the system.
Cleaning and Flushing the System
INTERNAL LEAKAGE.—A small amount of
internal leakage is allowed to provide lubrication of
moving parts. This leakage is normal and does not result
in faulty operation. On the other hand, an excess of
internal leakage results in slow operation, loss of power,
and overheating of the hydraulic fluid. The cylinders may
creep or drift and, if the leak is bad enough, the control
valves may not function properly.
Cleaning and flushing the system should be
performed based on the manufacturer’s recommendation
or when the system is known to be contaminated. The
nature and amount of deposits in a particular system may
vary widely. Inspection of the system may show any
condition between a sticky, oily film and a hard, solid
deposit (gum or lacquer formation) which completely
chokes off the system. If the system is drained
periodically according to the manufacturer’s recommendations, the formation of gum and lacquer will be
greatly reduced.
Internal leaks are caused by wear of the seals and
mating parts during normal operation. Leakage is
accelerated by using oil that has too low a viscosity
because the oil thins faster at higher temperatures. High
pressures also force more oil out of leaking points in the
system. This is why excessive pressures can actually
reduce the efficiency of the hydraulic system.
If there is no gum or lacquer formation suspected,
clean the system as follows:
1. Drain the system completely.
Internal leaks are hard to detect. Usually, all you can
do is observe the operation of the system for signs of
sluggishness, creeping, and drifting. When these signs
appear, it is time to test the system and pinpoint the
2. After draining, clean any sediment from the
reservoir, and replace the filter elements.
If flushing is required because the oil is badly
contaminated, clean and flush the system as follows:
EXTERNAL LEAKAGE.—External leaks not
only look bad but make it hazardous for the operators of
the equipment. A leak that allows floor plates to become
slippery may cause the operator to fall on or off the
1. Drain the system completely.
2. Refill the system with the recommended hydraulic
oil for the system involved.
the hose as pressure changes. Angled fittings
should be used instead of loops.
equipment and get injured. A leak that drips on hot engine
parts may start a fire that could result in the loss of the
Do not twist a hose; twisting causes the hoses to
Every joint in a hydraulic system is a potential point
of leakage. This is why the number of connections in a
system must be kept to a minimum. Leaks often arise
from hoses that deteriorate and rupture under pressure.
Such a leak is usually first noticed when equipment has
remained idle for a period of time and hydraulic fluid is
found underneath. Figures 3-47 and 3-48 show the proper
procedures for repairing hoses with reusable fittings. You
can remove a medium- or high-pressure hose from its
fittings by unscrewing the nipple from the socket and
then the socket from the hose.
Use clamps or brackets to keep a hose away from
moving parts or to prevent chafing when the hose
Keep hoses away from hot surfaces, such as
manifold and exhaust systems. If you are unable to
do so, install a heat shield to protect the hose.
Route hoses so there are no sharp bends. This is
critical with high-pressure hoses.
Here are some hints that will help reduce hose
leakage and maintenance:
Leave a little slack in the hose between
connections to allow for swelling when pressure is
applied. A taut hose is likely to pull out of its
Do not loop a hose unless the manufacturer
requires it. This causes unnecessary flexing of
Sometimes you can stop leaks at fittings by
tightening the hose connections. Tighten them only
enough to stop the leakage. If you cannot stop a leak by
tightening, secure the equipment and remove the
connection. Inspect the threaded and mating parts of the
connector. Look for cracks in the flared ends of the
tubing. If O rings are used, examine them for cuts or tears.
Any damaged or defective items should be replaced.
Figure 3-47.—Replacing low-pressure hose on a reusable fitting.
results in rapid failure of the packing and causes scoring
of the rod. If you find an internal seal instead of packing,
the cylinder must be removed and disassembled to stop
the leak. Components can leak, but care in assembly and
use of new seals, packings, and gaskets during overhaul
will reduce this problem.
Preventing Overheating
Heat causes hydraulic fluid to break down faster and
lose its effectiveness. In many systems, heat is dissipated
through the lines, the components, and the reservoir to
keep the fluid fairly cool. On high-pressure, high-speed
systems, oil coolers are used to dissipate the extra heat.
The following maintenance tips will help prevent
Ensure oil is at the proper level.
Remove dirt and mud from lines, reservoir, and
Repair dented and kinked lines.
Keep relief valves adjusted properly.
Do not overspeed or overload the system.
Never hold control valves in the power position
too long.
If the system still overheats, refer to the
manufacturer's manuals for charts that list the causes and
remedies for overheating.
Q1. If a force of 20 pounds is placed on an input
piston with an area of 4 square inches, what is
the pressure within the fluid?
Q2. If an input piston that is 3 square inches is
pushed down 2 inches, how far will the displaced
fluid raise an output piston that is 4 square
What type of hydraulic fluid contains additives to
reduce the foaming action?
Figure 3-48.—Replacement procedures for medium- and
high-pressure hose reusable fittings.
A properly constructed hydraulic reservoir
should be capable of what three functions?
Cylinders may leak around piston rods or rams.
You can repair some leaks by tightening the packing
located in the cylinder end cap. Tighten the end cap
evenly until only a light film of oil is noticeable on the
rod when it is extended. DO NOT overtighten; this
That device is installed in a hydraulic system to
prevent foreign particles from remaining in the
What component of a hydraulic system supplies
a flow of fluid to the system?
Q7. What type of valve is used to regulate the flow of
hydraulic fluid?
Compressibility and Expansion of Gases
Gases can be readily compressed and are assumed
to be perfectly elastic. This combination of properties
gives gas the ability to yield to a force and return
promptly to its original condition when the force is
removed. These are the properties of air that is used in
pneumatic tires, tennis balls, and other deformable
objects whose shapes are maintained by compressed
What are the three dimensions of any tubular
What are the three basic parts of a flexible hose?
What type of connector is used in a low-pressure
pipe system?
When tubing nuts are tightened what tool should
you use?
What type of seal application allows for a slight
leakage for seal lubrication?
What is the most common metal seal used in
Navy equipment?
What type of seal is ideally suited for both lowpressure and high-pressure applications?
What kind of leakage is caused by the wearing of
seals and mated parts?
Kinetic Theory of Gases
In an attempt to explain the compressibility of gases,
consider the container shown in figure 3-49 as containing
a gas. At any given time, some molecules are moving in
one direction, some are travelling in other directions, and
some may be in a state of rest. The average effect of the
molecules bombarding each container wall corresponds
to the pressure of the gas. As more gas is pumped into the
container, more molecules are available to bombard the
walls, thus the pressure in the container increases.
Increasing the speed with which the molecules hit the
walls can also increase the gas pressure in a container. If
the temperature of the gas is raised, the molecules move
faster, causing an increase in pressure. This can be shown
by considering the automobile tire. When you take a long
drive on a hot day, the pressure in the tires increases and a
tire that appeared to be soft in cool morning temperature
may appear normal at a higher midday temperature.
Learning Objective: Explain the operating principles of a
pneumatic system. Identify operational characteristics and
service procedures applicable to heavy-duty compressors.
The word pneumatics is a derivative of the Greek
word pneuma, which means air, wind, or breath.
Pneumatics can be defined as that branch of engineering
science that pertains to gaseous pressure and flow. As
used in this manual, pneumatics is the portion of fluid
power in which compressed air, or other gas, is used to
transmit and control power to actuating mechanisms.
Boyle's Law
When the automotive tire is initially inflated, air that
normally occupies a specific volume is compressed into a
smaller volume inside the tire. This increases the pressure
on the inside of the tire.
This section discusses the basic principles of
pneumatics, characteristics of gases, heavy-duty air
compressors, and air compressor maintenance. It also
discusses the hazards of pneumatics, methods of
controlling contamination, and safety precautions
associated with compressed gases.
Gases differ from liquids in that they have no definite
volume; that is, regardless of size or shape of the vessel, a
gas will completely fill it. Gases are highly compressible,
while liquids are only slightly so. Also, gases are lighter
than equal volumes of liquids, making gases less dense
than liquids.
Figure 3-49.—Molecular bombardment creating pressure.
Charles Boyle, an English scientist, was among the
first to experiment with the pressure-volume
relationship of gas. During an experiment when he
compressed a volume of air, he found that the volume
decreased as pressure increased, and by doubling the
force exerted on the air, he could decrease the volume
of the air by half (fig. 3-50).
Temperature is a dominant factor affecting the
physical properties of gases. It is of particular concern in
calculating changes in the state of gases. Therefore, the
experiment must be performed at a constant temperature.
The relationship between pressure and volume is known
as Boyle's law. Boyle's law states when the temperature
of a gas is constant, the volume of an enclosed gas
varies inversely with pressure.
The ideal fluid medium for a pneumatic system must
be a readily available gas that is nonpoisonous,
chemically stable, free from any acids that can cause
corrosion of system components, and nonflammable. It
should be a gas that will not support combustion of other
Gases that have these desired qualities may not
have the required lubricating power. Therefore,
lubrication of the components must be arranged by
other means. For example, some air compressors are
provided with a lubricating system, some components
are lubricated upon installation or, in some cases,
lubrication is introduced into the air supply line (inline oilers).
Boyle's law assumes conditions of constant
temperature. In actual situations this is rarely the case.
Temperature changes continually and affects the volume
of a given mass of gas.
Two gases meeting these qualities and most
commonly used in pneumatic systems are compressed air
and nitrogen. Since nitrogen is used very little except in
gas-charged accumulators, we will only discuss
compressed air.
Charles's Law
Compressed Air
Jacques Charles, a French physicist, provided much
of the foundation for modem kinetic theory of gases.
Through experiments, he found that all gases expand and
contract proportionally to the change in absolute
temperature, providing the pressure remains constant.
The relationship between volume and temperature is
known as Charles's law. Charles's law states that the
volume of a gas is proportional to its absolute
temperature if constant pressure is maintained.
Compressed air is a mixture of all gases contained in
the atmosphere. However, in this manual it is referred to
as one of the gases used as a fluid medium for pneumatic
The unlimited supply of air and the ease of
compression make compressed air the most widely
used fluid for pneumatic systems. Although moisture
and solid particles must be removed from the air, it
does not require the extensive distillation or separation
process required in the production of other gases.
Gases serve the same purpose in pneumatic systems
as liquids serve in hydraulic systems. Therefore, many of
the same qualities that are considered when selecting a
liquid for a hydraulic system must be considered when
selecting a gas for a pneumatic system.
Compressed air has most of the desired characteristics of a gas for pneumatic systems. It is
nonpoisonous and nonflammable but does contain
oxygen which supports combustion. The most
undesirable quality of compressed air as a fluid
medium for a pneumatic system is moisture content.
The atmosphere contains varying amounts of moisture
in vapor form. Changes in the temperature of
compressed air will cause condensation of moisture in
the system. This condensed moisture can be very
harmful to the system and may freeze the line and
components during cold weather. Moisture separators
and air dryers are installed in the lines to minimize or
eliminate moisture in systems where moisture would
deteriorate system performance.
An air compressor provides the supply of
compressed air at the required volume and pressure. In
Figure 3-50.—Gas compressed to half its original volume by a
doubled force.
most systems the compressor is part of the system with
distribution lines leading from the compressor to the
devices to be operated.
Compressors are used in pneumatic systems to
provide requirements similar to those required by pumps
in hydraulic systems. They furnish compressed air as
required to operate the units of the pneumatic systems.
Compressed air systems are categorized by their
operating pressure as follows:
High-pressure (HP)—3,000 to 5,000 psi
Even though manufactured by different
companies, most compressors are quite similar. They
are governed by a pressure control system that can be
adjusted to compress air to the maximum pressure.
Medium-pressure (MP )—151 to 1,000 psi
Low-pressure (LP)—150 psi and below
Compressor Design
The compressor unit may be of the reciprocating,
rotary, or screw design.
The reciprocating compressor is similar to that of
an automotive engine. They may be air- or liquidcooled. As the pistons move up and down, air flows into
the cylinder through the intake valve. As the piston
moves upward, the intake valve closes and traps air in
the cylinder. The trapped air is compressed until it
exceeds the pressure within the collecting manifold, at
which time the discharge valve opens and the
compressed air is forced into the air manifold (fig. 351). The reciprocating compressor is normally
connected to the engine through a direct coupling or a
clutch. The engine and compressor are separate units.
The rotary compressor has a number of vanes held
in captive in slots in the rotor. These vanes slide in and out
of the slots, as the rotor rotates. Figure 3-52 shows an end
Figure 3-51.—Intake and compression strokes in a
reciprocating compressor.
Figure 3-52.—Compression cycle in a rotary compressor.
view of the vanes in the slots. The rotor revolves about the
center of the shaft that is offset from the center of the
pumping casing. Centrifugal force acting on the rotating
vanes maintains contact between the edge of the vanes
and the pump casing. This feature causes the vanes to
slide in and out of the slots, as the rotor turns.
Notice in figure 3-52 the variation in the clearance
between the vanes and the bottom of the slots, as the rotor
revolves. The vanes divide the crescent-shaped space
between the offset rotor and the pump casing into
compartments that increase in size, and then decrease in
size, as the rotor rotates. Free air enters each
compartment as successive vanes pass across the air
intake. This air is carried around in each compartment
and is discharged at a higher pressure due to the
decreasing compartment size (volume) of the moving
compartments as they progress from one end to the other
of the crescent-shaped space.
The compressor is lubricated by oil circulating
throughout the unit. All oil is removed from the air by an
oil separator before the compressed air leaves the service
The screw compressors used in the NCF are directdrive, two-stage machines with two precisely matched
spiral-grooved rotors (fig. 3-53). The rotors provide
positive-displacement internal compression smoothly
and without surging. Oil is injected into the compressor
unit and mixes directly with the air, as the rotors turn
compressing the air. The oil has three primary functions:
1. As a coolant, it controls the rise in air
temperature normally associated with the heat
of compression.
2. It seals the leakage paths between the rotors and
the stator and also between the rotors themselves.
Figure 3-53.—Compression cycle in a screw compressor.
3. It acts as lubricating film between the rotors
allowing one rotor to directly drive the other,
which is an idler.
2. The engine coolant rises above a predetermined
3. The compressor discharge rises above a certain
After the air/oil mixture is discharged from the
compressor unit, the oil is separated from the air. The oil
that mixes with the air during compression passes into the
receiver-separator where it is removed and returned to the
oil cooler in preparation for re-injection.
4. Any of the protective safety circuits develop a
Other features that may be observed in the
operation of the air compressors is a governor system
whereby the engine speed is reduced when less than
full air delivery is used. An engine and compression
control system prevents excessive buildup in the
All large volume compressors have protection
devices that shut them down automatically when any
of the following conditions develop:
1. The engine oil pressure drops below a certain
Pressure-Control System
When air is compressed, heat is generated. This heat
causes the air to expand, thus requiring an increase in
power for further compression. If this heat is successfully
removed between stages of compression, the total power
required for additional compression may be reduced by
as much as 15 percent. In multistage reciprocating
compressors, this heat is removed by means of
intercoolers that are heat exchangers placed between
each compression stage. Rotary air compressors are
cooled by oil and do not use intercoolers.
All portable air compressors are governed by a
pressure-control system. The control system is
designed to balance the compressor's air delivery and
engine speed with varied demands for compressed air.
It is obvious that the presence of water or moisture
in an air line is not desirable. The water is carried along
through the line into the tool where the water washes
away the lubricating oil, causing the tool to run
sluggishly and increases maintenance. The effect is
particularly pronounced in the case of high-speed tools
where the wearing surfaces are limited in size and
excessive wear reduces efficiency by creating internal
air leakage.
In a reciprocating compressor the pressure-control
system causes the engine to idle and the suction valves
to remain open when the pressure reaches a set
maximum, thus making the compressor unit
inoperative. When the air pressure drops below a set
minimum, the pressure-control unit causes the engine
to increase speed and the suction valves to close,
thereby resuming the com pression cycle.
The rotary compressor output is governed by
varying the engine speed. The engine will operate at
the speed required to compress enough air to supply the
demand at a fairly constant pressure. When the engine
has slowed to idling speed as a result of low demand, a
valve controls the amount of free air that may enter the
Further problems may result from the decrease in
temperature caused by the sudden expansion of air at the
tool. This low temperature creates condensation that
freezes around the valves, ports, and outlets. This
condition obviously impairs the operational efficiency of
the tool and cannot be allowed.
A screw compressor output is governed by automatic
control that provides smooth, stepless capacity
regulation from full load to no load in response to the
demand for air. From a full load down to no load is
accomplished by a floating-speed engine control in
combination with the variable-inlet compressor.
The most satisfactory means of minimizing these
conditions is the removal of the moisture from the air
immediately after compression and before the air enters
the distribution system. This may be accomplished in
reciprocating compressors through the use of an
aftercooler that is an air radiator that transfers heat from
the compressed air to the atmosphere. The aftercooler
reduces the temperature of the compressed air to the
condensation point where most of the moisture is
removed. Cooling the air not only eliminates the
difficulties which moisture causes at points where air is
used but also ensures better distribution.
A number of built-in features that make portable
compressors easy to maintain include:
an automatic blowdown valve for releasing air
pressure when the engine is stopped,
a valve for draining moisture that accumulates in
the receiver tank,
a drain cock at the bottom of the piping at the
bottom of the oil storage tank,
Receiver Tank
an air filter service indicator to show when the filter
needs servicing, and
The receiver tank is of welded steel construction and
is installed on the discharge side of the compressor. It acts
as a surge tank as well as a condensation chamber for the
removal of oil and water vapors. It stores enough air
during operation to actuate the pressure control system
and is fitted with at least one service valve, a drain or
blow-by valve, and a safety valve.
a demister, or special filter, that separates
lubricating oil from compressed air.
Remember a good maintenance program is the key
to a long machine life. So it is up to both the operator
and the mechanic to ensure that the maintenance is
performed on time every time.
Inspect all gaskets and gasket contact surfaces of
the housing. Should faulty gaskets be evident.
replace them immediately.
Air Cleaner Servicing
The air cleaner contains a primary and secondary dry
filter element (fig. 3-54). An air filter restriction indicator
is located at the rear of the air filter housing to alert the
operator of the need to service the filters. When a red band
appears in the air filter restriction indicator, secure the
compressor and service the filters.
After the element has been installed, inspect and
tighten all air inlet connections before resuming
The primary element is cleanable by using
compressed air. When the element is cleaned, never let
the air pressure exceed 30 psi. The secondary filter is not
cleanable and should be replaced when necessary.
Reverse flush the primary element by directing
compressed air up from the inside out. Continue reverse
flushing until all dust is removed. Should any oil or
greasy dirt remain on the filter surface, the element
should be replaced. When the element is satisfactorily
cleaned, inspect it thoroughly before installation.
Inspection procedures are as follows:
Do not strike the element against any hard
surface to dislodge dust. This will damage the
sealing surfaces and possibly rupture the
Main Oil Filter Servicing
The main oil filter is a replaceable cartridge. The
servicing of the filter is required as indicated by the
maintenance indicator on the filter or each time the
compressor oil is changed. Under normal operating
conditions. the oil is changed at approximately 500
operating hours. Under severe conditions. more frequent
servicing is required.
Place a bright light inside the element to inspect it
for damage. Concentrated light will shine through
the element and disclose any holes. A damaged
element is to be replaced.
Figure 3-54.—Air filter.
Demister or Separator Element
The demister, or separator element, is located
inside the receiver tank (fig. 3-55). Replacement of the
demister is indicated by the maintenance indicator
(usually mounted on the receiver tank but also can be
remote-mounted) or any sign of oil in the air at the
service valves. You can reach the demister after
removing the plate on the end of the receiver tank.
As in hydraulic systems, fluid contamination is the
leading cause of malfunctions in pneumatic systems. In
addition to the solid particles of foreign matter that find
their way to enter the system, there is also the problem of
moisture. Most systems are equipped with one or more
devices to remove contamination. These include filters,
water separators, air dehydrators, and chemical dryers.
Most systems contain drain valves at critical low points in
the system. These valves are opened periodically to allow
the escaping gas to purge a large percentage of the
contaminants, both solids and moisture, from the system.
In some systems these valves are automatic, while in
others they must be operated manually.
Removing lines from various components throughout
the system and then attempting to pressurize the system,
causing a high rate of air flow through the system, does
complete purging. The air flow will cause the foreign
matter to be dislodged and blown from the system.
Figure 3-55.—Demister (separator element).
If an excessive amount of foreign matter,
particularly oil, is blown from any one system,
the lines and components should be removed
and cleaned or, in some cases, replaced.
All compressed gases are hazardous. Compressed air
and nitrogen are neither poisonous nor flammable, but
should be handled with care. Some pneumatic systems
operate at pressures exceeding 3,000 psi. Lines and
fittings have exploded, injuring personnel and property.
Literally thousands of careless workers have blown dust
or other harmful particles into their eyes by careless
handling of compressed air outlets.
In addition to monitoring the devices installed to
remove contamination, it is your responsibility as a
mechanic to control the contamination. You can do this
by using the following maintenance practices:
Keep all tools and the work area in a clean, dirt-free
If you ever have to handle nitrogen gas, remember
that it will not support life, and when released in a
confined space, it will cause asphyxia (the loss of
consciousness as a result of too little oxygen and too
much carbon dioxide in the blood). Although compressed
air and nitrogen seem safe in comparison with other
gases, do not let overconfidence lead to personal injury.
Cap or plug all lines and fittings immediately after
disconnecting them.
Replace all packing and gaskets during
assembly procedures.
Connect all parts with care to avoid stripping
metal slivers from threaded areas. Install and
torque all fittings and lines according to
applicable technical manuals.
To minimize personal injury and equipment
damage when using compressed gases, observe all
Do NOT subject compressed gas cylinders to
temperatures greater than 130°F. Remember, any
pressurized system can be hazardous to your health if it is
not maintained and operated carefully and safely.
To minimize personal injury and equipment
damage when using compressed gases, observe all
practical operating safety precautions, including the
Do NOT use compressed air to clean parts of your
body or clothing or to perform general space cleanup
instead of sweeping.
NEVER attempt to stop or repair a leak while the
leaking portion is still under pressure. Always isolate.
depressurize. and tag out the portion of the system to be
Avoid the application of heat to the air piping
system or components, and avoid striking a sharp,
heavy blow on any pressurized part of the piping
Avoid rapid operation of manual valves. The
heat of compression caused by a sudden high-pressure
flow into an empty line or vessel can cause an explosion
if oil is present. Valves should be slowly cracked open
until air flow is noted and should be kept in this position
until pressures on both sides of the valve have
equalized. The rate of pressure rise should be kept under
200 psi per second, if possible. Valves may then be
opened fully.
What two properties allow gas the ability to yield
to force and return to its original condition when
the force is removed?
What law states that when the temperature of a
gas is constant, the volume of enclosed gas
varies inversely with pressure?
What four qualities should the ideal gas have for
apneumatic system?
What is the most undesirable quality of
compressed air when used as a fluid medium for
a pneumatic system?
Q5. A pneumatic system with an operating
pressure of 500 psi is known as what type of
What are the three designs of air compressors?
What device in a rotary air compressor removes
oil from the compressed air before the air leaves
the service valves?
Q1. 5 psi
Q2. 1 inch
Q3. Petroleum-based fluids
Q4. Dissipating heat, separating air, settling out contamination
Q5. Filters
Q6. Pump
Q7. Flow-control valve
Q8. Inside diameter, outside diameter, wall thickness
Q9. Inner tube, reinforcement layers, outer cover
Q10. Threaded connectors
Q11. Torque wrench
Q12. Dynamic seal
Q13. Copper
Q14. Quad-ring
Q15. Internal leakage
Q1. Compressibility and elasticity
Q2. Boyle's law
Q3. Nonpoisonous, chemical stable, free from corrosive acids, and nonflammable
Q4. Moisture content
Q5. Medium-pressure system
Q6. Reciprocating, rotary, and screw
Q7. Oil separator
Learning Objective: State the operating principles and
identify the components and the maintenance for a clutch,
a manual transmission, an automatic transmission, and a
Learning Objective: State the operating principles and
identify the components and maintenance requirements
for an automotive clutch.
An automotive clutch is used to connect and
disconnect the engine and manual (hand-shifted)
transmission or transaxle. The clutch is located
between the back of the engine and the front of the
In a vehicle, the mechanism that transmits the
power developed by the engine to the wheels and/or
tracks and accessory equipment is called the power
train. In a simple application, such as a stationary
engine-powered hoist, a set of gears or a chain and
sprocket could perform this task. However, automotive and construction equipment are not designed
for such simple operating conditions. They are
designed to provide pulling power, to move at high
speeds, to travel in reverse as well as forward, and to
operate on rough terrain as well as smooth roads. To
meet these varying conditions, vehicle power trains
are equipped with a variety of components. This
chapter discusses the basic automotive clutch,
transmissions (manual and automatic), and transaxles
(manual and automatic).
With a few exceptions, the clutches common to the
Naval Construction Force (NCF) equipment are the
single-, double-, and multiple-disc types. The clutch
that you will encounter the most is the single-disc type,
as shown in figure 4-1. The double-disc clutch (fig. 4-2)
is substantially the same as the single disc, except that
another driven disc and an intermediate driving plate are
added. This clutch is used in heavy-duty vehicles and
construction equipment. The multiple-disc clutch is
used in the automatic transmission and for the steering
clutch used in tracked equipment.
Figure 4-1.—Single-disc clutch.
Figure 4-2.—Double-disc clutch, exploded view.
Figure 4-3.—Clutch linkage mechanism.
The operating principles, component functions,
and maintenance requirements are essentially the same
for each of the three clutches mentioned. This being the
case, the single-disc clutch will be used to acquaint you
with the fundamentals of the clutch.
hydraulic circuit, and the clutch fork. Some manufacturers include the release bearing as part of the
clutch release mechanism.
A clutch linkage mechanism uses levers and rods
to transfer motion from the clutch pedal to the clutch
fork. One configuration is shown in figure 4-3. When
the pedal is pressed, a pushrod shoves on the bell crank
and the bell crank reverses the forward movement of
the clutch pedal. The other end of the bell crank is
connected to the release rod. The release rod transfers
bell crank movement to the clutch fork. It also provides
a method of adjustment for the clutch.
The clutch is the first drive train component
powered by the engine crankshaft. The clutch lets the
driver control power flow between the engine and the
transmission or transaxle. Before understanding the
operation of a clutch, you must first become familiar
with the parts and their function. This information is
very useful when learning to diagnose and repair the
clutch assembly.
The clutch cable mechanism uses a steel cable
inside a flexible housing to transfer pedal movement to
the clutch fork. As shown in figure 4-4, the cable is
usually fastened to the upper end of the clutch pedal,
with the other end of the cable connecting to the clutch
fork. The cable housing is mounted in a stationary
position. This allows the cable to slide inside the
housing whenever the clutch pedal is moved. One end
of the clutch cable housing has a threaded sleeve for
clutch adjustment.
Clutch Release Mechanism
A clutch release mechanism allows the operator to
operate the clutch. Generally, it consists of the clutch
pedal assembly, either mechanical linkage, cable, or
Figure 4-4.—Clutch cable mechanism.
A hydraulic clutch release mechanism (fig. 4-5)
uses a simple hydraulic circuit to transfer clutch pedal
action to the clutch fork. It has three basic
parts—master cylinder, hydraulic lines, and a slave
Movement of the clutch pedal creates hydraulic
pressure in the master cylinder, which actuates the
slave cylinder. The slave cylinder then moves the
clutch fork.
assembly, with the manual transmission bolted to the
back of the housing. The lower front of the housing has
a metal cover that can be removed for fly-wheel ring
gear inspection or when the engine must be separated
from the clutch assembly. A hole is provided in the side
of the housing for the clutch fork. It can be made of
aluminum, magnesium, or cast iron.
Release Bearing
The release bearing, also called the throw-out
bearing, is a ball bearing and collar assembly. It
reduces friction between the pressure plate levers and
the release fork. The release bearing is a sealed unit
pack with a lubricant. It slides on a hub sleeve
extending out from the front of the manual
transmission or transaxle.
Clutch Fork
The clutch fork, also called a clutch arm or release
arm, transfers motion from the release mechanism to
the release bearing and pressure plate. The clutch fork
sticks through a square hole in the bell housing and
mounts on a pivot. When the clutch fork is moved by
the release mechanism, it PRIES on the release bearing
to disengage the clutch.
The release bearing snaps over the end of the
clutch fork. Small spring clips hold the bearing on the
fork. Then fork movement in either direction slides the
release bearing along the transmission hub sleeve.
A rubber boot fits over the clutch fork. This boot is
designed to keep road dirt, rocks, oil, water, and other
debris from entering the clutch housing.
Pressure Plate
Clutch Housing
The pressure plate is a spring-loaded device that
can either engage or disengage the clutch disc and the
flywheel. It bolts to the flywheel. The clutch disc fits
The clutch housing is also called the bell housing.
It bolts to the rear of the engine, enclosing the clutch
Figure 4-5.—Hydraulic clutch release mechanism.
between the flywheel and the pressure plate. There are
two types of pressure plates—the coil spring type and
the diaphragm type.
cover fits over the springs, the release levers, and the
pressure plate face. Its main purpose is to hold the
assembly together. Holes around the outer edge of the
cover are for bolting the pressure plate to the flywheel.
Coil spring pressure plate uses small coil springs
similar to valve springs (fig. 4-6). The face of the
pressure plate is a large, flat ring that contacts the
clutch disc during clutch engagement. The backside of
the pressure plate has pockets for the coil springs and
brackets for hinging the release levers. During clutch
action, the pressure plate moves back and forth inside
the clutch cover. The release levers are hinged inside
the pressure plate to pry on and move the pressure plate
face away from the clutch disc and flywheel. Small
clip-type springs fit around the release levers to keep
them rattling when fully released. The pressure plate
Diaphragm pressure plate (fig. 4-7) uses a single
diaphragm spring instead of coil springs. This type of
pressure plate functions similar to that of the coil
spring type. The diaphragm spring is a large, round
disc of spring steel. The spring is bent or dished and has
pie-shaped segments running from the outer edge to
the center. The diaphragm spring is mounted in the
pressure plate with the outer edge touching the back of
the pressure plate face. The outer rim of the diaphragm
is secured to the pressure plate and is pivoted on rings
(pivot rings) approximately 1 inch from the outer edge.
Figure 4-6.—Coil spring pressure plate.
Figure 4-7.—Diaphragm pressure plate operation.
Application of pressure at the inner section of the
diaphragm will cause the outer rim to move away from
the flywheel and draw the pressure plate away from the
clutch disc, disengaging the clutch.
The flywheel is the mounting surface for the
clutch. The pressure plate bolts to the flywheel face.
The clutch disc is clamped and held against the
flywheel by the spring action of the pressure plate. The
face of the flywheel is precision machined to a smooth
surface. The face of the flywheel that touches the
clutch disc is made of iron. Even if the flywheel were
aluminum, the face is iron because it wears well and
dissipates heat better.
Clutch Disc
The clutch disc, also called friction lining, consists
of a splined hub and a round metal plate covered with
friction material (lining). The splines in the center of
the clutch disc mesh with the splines on the input shaft
of the manual transmission. This makes the input shaft
and disc turn together. However, the disc is free to slide
back and forth on the shaft.
Pilot Bearing
The pilot bearing or bushing is pressed into the end
of the crankshaft to support the end of the transmission
input shaft. The pilot bearing is a solid bronze bushing,
but it also may be a roller or ball bearing.
Clutch disc torsion springs, also termed damping
springs, absorb some of the vibration and shock
produced by clutch engagement. They are small coil
springs located between the clutch disc splined hub
and the friction disc assembly. When the clutch is
engaged, the pressure plate jams the stationary disc
against the spinning flywheel. The torsion springs
compress and soften, as the disc first begins to turn
with the flywheel.
The end of the transmission input shaft has a small
journal machined on its end. This journal slides inside
the pilot bearing. The pilot bearing prevents the
transmission shaft and clutch disc from wobbling up
and down when the clutch is released. It also assists the
input shaft center the disc on the flywheel.
Clutch disc facing springs, also called the
cushioning springs, are flat metal springs located
under the friction lining of the disc. These springs have
a slight wave or curve, allowing the lining to flex
inward slightly during initial engagement. This also
allows for smooth engagement.
When the operator presses the clutch pedal, the
clutch release mechanism pulls or pushes on the clutch
release lever or fork (fig. 4-8). The fork moves the
release bearing into the center of the pressure plate,
causing the pressure plate to pull away from the clutch
disc releasing the disc from the flywheel. The engine
crankshaft can then turn without turning the clutch disc
and transmission input shaft.
The clutch disc friction material, also called disc
lining or facing, is made of heat-resistant asbestos,
cotton fibers, and copper wires woven or molded
together. Grooves are cut into the friction material to
aid cooling and release of the clutch disc. Rivets are
used to bond the friction material to both sides of the
metal body of the disc.
When the operator releases the clutch pedal, spring
pressure inside the pressure plate pushes forward on
the clutch disc (fig. 4-8). This action locks the
Figure 4-8.—Clutch operation.
flywheel, the clutch disc, the pressure plate, and the
transmission input shaft together. The engine again
rotates the transmission input shaft, the transmission
gears, the drive train, and the wheels of the vehicle.
drag during clutch disengagement. Too little free play
causes clutch slippage. It is important for you to know
how to adjust the three types of clutch release
Clutch Linkage Adjustment
Many of the newer vehicles incorporate a clutch
start switch into the starting system. The clutch start
switch is mounted on the clutch pedal assembly. The
clutch start switch prevents the engine from cranking
unless the clutch pedal is depressed fully. This serves
as a safety device that keeps the engine from possibly
starting while in gear. Wires from the ignition switch
feeds starter solenoid current through the switch.
Unless the switch is closed (clutch pedal depressed),
the switch prevents current from reaching the starter
solenoid. With the transmission in neutral, the clutch
start switch is bypassed so the engine will crank and
Mechanical clutch linkage is adjusted at the
release rod going to the release fork (fig. 4-9). One end
of the release rod is threaded. The effective length of
the rod can be increased to raise the clutch pedal
(decrease free travel). It can also be shortened to lower
the clutch pedal (increase free travel).
Like the mechanical linkage, a clutch cable
adjustment may be required to maintain the correct
pedal height and free travel. Typically the clutch cable
will have an adjusting nut. When the nut is turned, the
length of the cable housing increases or decreases. To
increase clutch pedal free travel, turn the clutch cable
housing nut to shorten the housing, and, to decrease
To change the clutch adjustment, loosen the
release rod nuts. Turn the release rod nuts on the
threaded rod until you have reached the desired free
pedal travel.
Clutch Cable Adjustment
Clutch adjustments are made to compensate for
wear of the clutch disc lining and linkage between the
clutch pedal and the clutch release lever. This involves
setting the correct amount of free play in the release
mechanism. Too much free play causes the clutch to
Figure 4-9.—Clutch pedal and linkage.
allows 1 1/2 inches of clutch pedal free travel
will allow adequate clutch operation until the
vehicle reaches the shop and manuals are
clutch pedal free travel, turn the nut to lengthen the
Hydraulic Clutch Adjustment
The hydraulically operated clutch shown in figure
4-10 is adjusted by changing the length of the slave
cylinder pushrod. To adjust a hydraulic clutch, simply
turn the nut or nuts on the pushrod as needed.
An automotive clutch normally provides dependable service for thousands of miles. However, stop and
go traffic will wear out a clutch quicker than highway
driving. Everytime a clutch is engaged, the clutch disc
and other components are subjected to considerable
heat, friction, and wear.
When a clutch adjustment is made, refer to
the manufacturer's service manual for the
correct method of adjustment and clearance. If
no manuals are available, an adjustment that
Operator abuse commonly causes premature
clutch troubles. For instance, "riding the clutch"
Figure 4-10.—Master cylinder, slave cylinder, and connections for a typical hydraulic clutch.
Binding linkage prevents the pressure plate from
exerting its full pressure against the disc, allowing it to
slip. Inspect the release mechanism for rusted, bent,
misaligned, sticking, or damaged components. Wiggle
the release fork to check for free play. These problems
result in slippage.
(overslipping clutch upon acceleration), resting your
foot on the clutch pedal while driving, and other
driving errors can cause early clutch failure.
When a vehicle enters the shop for clutch troubles,
you should test-drive the vehicle. While the vehicle is
being test-driven, you should
A broken motor mount (engine mount) can cause
clutch slippage by allowing the engine to move,
binding the clutch linkage. Under load, the engine can
lift up in the engine compartment, shifting the clutch
linkage and pushing on the release fork.
check the action of the clutch pedal,
listen for unusual noises, and
feel for clutch pedal vibrations.
Grease and oil on the disc will also cause slippage.
When this occurs, locate and stop any leakage,
thoroughly clean the clutch components, and replace
the clutch disc. This is the only remedy.
Gather as much information as you can on the
operation of the clutch. Use this information, your
knowledge of clutch principles, and a service manualtroubleshooting chart to determine which components
are faulty.
If clutch slippage is NOT caused by a problem
with the clutch release mechanism, then the trouble is
normally inside the clutch. You have to remove the
transmission and clutch components for further
inspection. Internal clutch problems, such as weak
springs and bent or improperly adjusted release levers,
will prevent the pressure plate from applying even
pressure. This condition allows the disc to slip.
There are five types of clutch problems—slipping,
grabbing, dragging, abnormal noises, and vibration. It
is important to know the symptoms produced by these
problems and the parts that might be the cause.
Slipping occurs when the driven disc fails to rotate
at the same speed as the driving members when the
clutch is fully engaged. This condition results
whenever the clutch pressure plate fails to hold the disc
tight against the face of the flywheel. If clutch slippage
is severe, the engine speed will rise rapidly on
acceleration, while the vehicle gradually increases in
speed. Slight but continuous slippage may go
unnoticed until the clutch facings are ruined by
excessive temperature caused by friction.
To test the clutch for slippage, set the emergency
brake and start the engine. Place the transmission or
transaxle in high gear. Then try to drive the vehicle
forward by slowly releasing the clutch pedal. A clutch
in good condition should lock up and immediately kill
the engine. A badly slipping clutch may allow the
engine to run, even with the clutch pedal fully released.
Partial clutch slippage could let the engine run
momentarily before stalling.
Normal wear of the clutch lining causes the free
travel of the clutch linkage to decrease, creating the
need for adjustment. Improper clutch adjustment can
cause slippage by keeping the release bearing in
contact with the pressure plate in the released position.
Even with your foot off the pedal, the release
mechanism will act on the clutch fork and release
Never let a clutch slip for more than a
second or two. The extreme heat generated by
slippage will damage the flywheel and pressure
plate faces.
A grabbing or chattering clutch will produce a very
severe vibration or jerking motion when the vehicle is
accelerated from a standstill. Even when the operator
slowly releases the clutch pedal, it will seem like the
clutch pedal is being pumped rapidly up and down. A
loud bang or chattering may be heard, as the vehicle
body vibrates.
Some clutch linkages are designed to allow only
enough adjustment to compensate for the lining to
wear close to the rivet heads. This prevents damage to
the flywheel and pressure plate by the rivets wearing
grooves in their smooth surfaces.
Other linkages will allow for adjustment after the
disc is worn out. When in doubt whether the disc is
worn excessively, remove the inspection cover on the
clutch housing and visually inspect the disc.
Clutch grabbing and chatter is caused by problems
with components inside the clutch housing (friction
clutch release mechanism. With the engine off, pump
the pedal and listen for the sound. Once the source of
the sound is located, you should clean, lubricate, or
replace the parts as required.
disc, flywheel, or pressure plate). Other reasons for a
grabbing clutch could be due to oil or grease on the disc
facings, glazing, or loose disc facings. Broken parts in
the clutch, such as broken disc facings, broken facing
springs, or a broken pressure plate, will also cause
Sounds produced from the clutch, when the clutch
is initially ENGAGED, are generally due to friction
disc problems, such as a worn clutch disc facing, which
causes a metal-to-metal grinding sound. A rattling or a
knocking sound may be produced by weak or broken
clutch disc torsion springs. These sounds indicate
problems that require the removal of the transmission
and clutch assembly for repair.
There are several things outside of the clutch that
will cause a clutch to grab or chatter when it is being
engaged. Loose spring shackles or U-bolts, loose
transmission mounts, and worn engine mounts are
among the items to be checked. If the clutch linkage
binds, it may release suddenly to throw the clutch into
quick engagement, resulting in a heavy jerk. However,
if all these items are checked and found to be in good
condition, the trouble is inside the clutch itself and will
have to be removed for repair.
If clutch noises are noticeable when the clutch is
DISENGAGED, the trouble is most likely the clutch
release bearing. The bearing is probably either worn,
binding, or, in some cases, loses its lubricant. Most
clutch release bearings are factory lubricated;
however, on some larger trucks and construction
equipment, the bearing requires periodic lubrication.
A worn pilot bearing may also produce noises when the
clutch is disengaged. The worn pilot bearing can let the
transmission input shaft and clutch disc vibrate up and
down, causing an unusual noise.
A dragging clutch will make the transmission or
transaxle grind when trying to engage or shift gears.
This condition results when the clutch disc does not
completely disengage from the flywheel or pressure
plate when the clutch pedal is depressed. As a result,
the clutch disc tends to continue turning with the
engine and attempts to drive the transmission.
Sounds heard in NEUTRAL, that disappear when
the clutch pedal is pushed, are caused by problems
inside the transmission. Many of these sounds are due
to worn bearings. However, always refer to the
troubleshooting chart in the manufacturer's manual.
The most common cause of a dragging clutch is too
much clutch pedal free travel. With excessive free
travel, the pressure plate will not fully release when the
clutch pedal is pushed to the floor. Always check the
clutch adjustments first. If adjustment of the linkage
does not correct the trouble, the problem is in the
clutch, which must be removed for repair.
Pedal Pulsation
A pulsating clutch pedal is caused by the runout
(wobble or vibration) of one of the rotating members of
the clutch assembly. A series of slight movements can
be felt on the clutch pedal. These pulsations are
noticeable when light foot pressure is applied. This is
an indication of trouble that could result in serious
damage if not corrected immediately. There are
several conditions that can cause these pulsations. One
possible cause is misalignment of the transmission and
On the inside of the clutch housing, you will
generally find a warped disc or pressure plate, oil or
grease on the friction surface, rusted or damaged
transmission input shaft, or improper adjustment of the
pressure plate release levers causing the problem.
Abnormal Noises
Faulty clutch parts can make various noises. When
an operator reports that a clutch is making noise, find
out when the noise is heard. Does the sound occur
when the pedal is moved, when in neutral, when in
gear, or when the pedal is held to the floor? This will
assist you in determining which parts are producing
these noises.
If the transmission and engine are not in line,
detach the transmission and remove the clutch
assembly. Check the clutch housing alignment with
the engine and crankshaft. At the same time, the
flywheel can be checked for runout, since a bent
flywheel or crankshaft flange will produce clutch
pedal pulsation. If the flywheel does not seat on the
crankshaft flange, remove the flywheel. After cleaning
the crankshaft flange and flywheel, replace the
flywheel, making sure a positive seat is obtained
An operator reports hearing a scraping, clunking,
or squeaking sound when the clutch pedal is moved up
or down. This is a good sign of a worn or unlubricated
between the flywheel and the flange. If the flange is
bent, the crankshaft must be replaced.
war-page of the pressure plate. Using a dial indicator,
measure the runout of the flywheel. The pressure plate
release levers should show very limited or no signs of
wear from contact with the release bearing. If
excessive wear, cracks, or warpage is noted on the
flywheel and/or pressure plate, the assembly should be
replaced. This is also a good time to inspect the ring
gear teeth on the flywheel. If they are worn or chipped,
a new ring gear should be installed.
Other causes of clutch pedal pulsation include bent
or maladjusted pressure plate release levers, warped
pressure plate, or warped clutch disc. If either the
clutch disc or pressure plate is warped, they must be
When adjustment or repair of the linkage fails to
remedy problems with the clutch, the clutch must be
removed for inspection. Any faulty parts should be
discarded and replaced with new or rebuilt
components. If replacement parts are not readily
available, a decision to use the old components should
be based on the manufacturer’s recommendations and
the maintenance supervisor.
Transmission or transaxle removal is required to
service the clutch. Always follow the detailed
directions in the service manual. To remove the clutch
in a rear-wheel drive vehicle, remove the drive shaft,
the clutch fork, the clutch release mechanism, and the
transmission. With a front-wheel drive vehicle, the
axle shafts (drive axles), the transaxle, and, in some
cases, the engine must be removed for clutch repairs.
When the transmission or transaxle is
removed, support the weight of the engine.
Never let the engine, the transmission, or the
transaxle be unsupported. The transmission
input shaft, clutch fork, engine mounts, and
other associated parts could be damaged.
Be careful how you clean the parts of the
clutch. Avoid using compressed air to blow
clutch dust from the parts. A clutch disc contains asbestos—a cancer-causing substance.
While inspecting the flywheel, you should check
the pilot bearing in the end of the crankshaft. A worn
pilot bearing will allow the transmission input shaft and
clutch disc to wobble up and down. Using a telescoping
gauge and a micrometer, measure the amount of wear in
the bushing. For wear measurements of the pilot
bearing, refer to the service manual. If a roller bearing
is used, rotate them. They should turn freely and show
no signs of rough movement. If replacement of the
pilot bearing is required, the use of a slide hammer
puller will drive the bearing out of the crankshaft end.
Before installing a new pilot bearing, check the fit by
sliding it over the input shaft of the transmission. Then
drive the new bearing into the end of the crankshaft.
Inspect the disc for wear; inspect the depth of the
rivet holes, loose rivets, and worn or broken torsion
springs. Check the splines in the clutch disc hub for a
"like new" condition. The clutch shaft splines
should be inspected by placing the disc on the clutch
shaft and sliding it over the splines. The disk should
move relatively free back and forth without any
unusual tightness or binding. Normally, the clutch
disc is replaced anytime the clutch is tom down for
After removal of the transmission or transaxle,
remove the clutch housing from the rear of the engine.
Support the housing as you remove the last bolt. Be
careful not to drop the clutch housing as you pull it
away from the dowel pins.
Another area to inspect is the release bearing. The
release bearing and sleeve is usually sealed and factory
packed (lubricated). A bad release bearing will
produce a grinding noise whenever the clutch pedal is
pushed down. To check the action of the release
bearing, insert your fingers into the bearing; then turn
the bearing while pushing on it. Try to detect any
roughness; it should rotate smoothly. Also, inspect the
spring clip on the release bearing or fork. If bent, worn,
or fatigued, the bearing or fork must be replaced.
Using a hammer and a center punch, mark the
pressure plate and flywheel. These marks are needed
when reinstalling the same pressure plate to assure
correct balancing of the clutch.
With the clutch removed, all components are to be
cleaned and inspected for wear and damage. After
cleaning, you should inspect the flywheel and pressure
plate for signs of unusual wear, such as scoring or
cracks. A straightedge should be used to check for
The last area to check before reassembly is the
clutch fork. If it is bent or worn, the fork can prevent
the clutch from releasing properly. Inspect both ends
of the fork closely. Also, inspect the clutch fork pivot
point in the clutch housing; the pivot ball or bracket
should be undamaged and tight.
When a new pressure plate is installed, do not
forget to check the plate for proper adjustments. These
adjustments will ensure proper operation of the
pressure plate. The first adjustment ensures proper
movement of the pressure plate in relation to the cover.
With the use of a straightedge and a scale as shown in
figure 4-11, begin turning the adjusting screws until
you obtain the proper clearance between the
straight-edge and the plate as shown. For exact
measurements, refer to the manufacturer’s service
The second adjustment positions the release levers
and allows the release bearing to contact the levers
simultaneously while maintaining adequate clearance
of the levers and disc or pressure plate cover. This
adjustment is known as finger height. To adjust the
pressure plate, place the assembly on a flat surface and
measure the height of the levers, as shown in figure
4-12. Adjust it by loosening the locknut and turning.
After the proper height has been set, make sure the
locknuts are locked and staked with a punch to keep
them from coming loose during operations. Exact
release lever height can be found in the manufacturer’s
service manual.
Reassemble the clutch in the reverse order of
disassembly. Mount the clutch disc and pressure plate
on the flywheel. Make sure the disc is facing in the
right direction. Usually, the disc's offset center (hub
and torsion springs) fit into the pressure plate.
Figure 4-12.—Pressure plate release lever adjustment.
If reinstalling, the old pressure plate lines up the
alignment marks made before disassembly. Start all of
the pressure plates bolts by hand. Never replace a
clutch pressure plate bolt with a weaker bolt. Always
install the special case-hardened bolt recommended by
the manufacturer.
Use a clutch alignment tool to center the clutch
disc on the flywheel. If an alignment tool is
unavailable, an old clutch shaft from the same type of
vehicle may be used. Tighten each pressure plate bolt a
little at a time in a crisscross pattern. This will apply
equal pressure on each bolt, as the pressure plate
spring(s) are compressed. When the bolts are snugly in
place, torque them to the manufacturer’s specifications
found in the service manual. Once the pressure plates
bolts are torqued to specs, slide out the alignment tool.
Without the clutch disc being centered, it is almost
impossible to install the transmission or transaxle.
Next install the clutch fork and release bearing in
the clutch housing. Fit the clutch housing over the rear
of the engine. Dowels are provided to align the housing
on the engine. Install and tighten the bolts in a
crisscross manner.
Install the transmission and drive shaft or the
transaxle and axle shafts. Reconnect the linkages, the
cables, any wiring, the battery, and any other parts
required for disassembly. After all parts have been
installed, adjust the clutch pedal free travel as
prescribed by the manufacturer and test-drive the
vehicle for proper operation.
Figure 4-11.—Pressure plate adjustment.
What is the function of the automotive clutch?
What component(s) allow(s) the operator to
operate the clutch?
What component(s) transfer(s) motion from the
release mechanism to the release bearing and
pressure plate?
Operate quietly with minimum power loss.
What component(s) within the clutch disc
absorb(s) vibration and shock produced by
clutch engagement?
What component prevents the engine starting
unless the clutch pedal is fully depressed?
Before understanding the operation and power
flow through a manual transmission, you first must
understand the construction of the transmission. This
is necessary for you to be able to diagnose and repair
damaged transmissions properly.
Transmission Case
The transmission case provides support for the
bearings and shafts, as well as an enclosure for
lubricating oil. A manual transmission case is cast
from either iron or aluminum. Because they are lighter
in weight, aluminum cases are preferred.
Q6. If no service manual is available and an
adjustment of the clutch is required, what
amount of clutch pedal free travel will allow
adequate clutch operation?
A drain plug and fill plug are provided for
servicing. The drain plug is located on the bottom of
the case, whereas the fill plug is located on the side.
Learning Objective: State the operating principles,
identify the components, and maintenance of a manual
Extension Housing
Also known as the tail shaft, the extension
housing bolts to the rear of the transmission case. It
encloses and holds the transmission output shaft and
rear oil seal. A gasket is used to seal the mating
surfaces between the transmission case and the
extension housing. On the bottom of the extension
housing is a flange that provides a base for the
transmission mount.
A manual transmission is designed with two
purposes in mind. One purpose of the transmission is
providing the operator with the option of maneuvering
the vehicle in either the forward or reverse direction.
This is a basic requirement of all automotive vehicles.
Almost all vehicles have multiple forward gear ratios,
but, in most cases, only one ratio is provided for
Front Bearing Hub
Another purpose of the transmission is to provide
the operator with a selection of gear ratios between
engine and wheel so that the vehicle can operate at the
best efficiency under a variety of operating conditions
and loads. If in proper operating condition, a manual
transmission should do the following:
Sometimes called the front bearing cap, the
bearing hub covers the front transmission bearing and
acts as a sleeve for the clutch release bearing. It bolts to
the transmission case and a gasket fits between the
front hub and the case to prevent oil leakage.
Be able to increase torque going to the drive
wheel for quick acceleration.
Transmission Shafts
Supply different gear ratios to match different
engine load conditions.
A manual transmission has four steel shafts
mounted inside the transmission case. These shafts are
the input shaft, the countershaft, the reverse idler shaft,
and the main shaft.
Have a reverse gear for moving the vehicle
INPUT SHAFT.—The input shaft, also known as
the clutch shaft, transfers rotation from the clutch disc
Provide the operator with an easy means of
shifting transmission gears.
to the countershaft gears (fig. 4-13). The outer end of
the shaft is splined except the hub of the clutch disc.
The inner end has a machined gear that meshes with the
countershaft. A bearing in the transmission case
supports the input shaft in the case. Anytime the clutch
disc turns, the input shaft gear and gears on the
countershaft turn.
COUNTERSHAFT. —The countershaft, also
known as the cluster gear shaft, holds the countershaft
gear into mesh with the input shaft gear and other gears
in the transmission (fig. 4-14). It is located slightly
below and to one side of the clutch shaft. The
countershaft does not turn in the case. It is locked in
place by either a steel pin, force fit, or locknuts.
REVERSE IDLER SHAFT.—The reverse idler
shaft is a short shaft that supports the reverse idle gear
(fig. 4-15). It mounts stationary in the transmission
case about halfway between the countershaft and
output shaft, allowing the reverse idle gear to mesh
with both shafts.
MAIN SHAFT.—The main shaft, also called the
output shaft, holds the output gears and synchronizers
(fig. 4-16). The rear of the shaft extends to the rear of
the extension housing where it connects to the drive
shaft to turn the wheel of the vehicle. Gears on the shaft
are free to rotate, but the synchronizers are locked on
the shaft by splines. The synchronizers will only turn
when the shaft itself turns.
Transmission Gears
Transmission gears can be classified into four
groups—input gear, countershaft gears, main shaft
gears, and the reverse idler gear. The input gear turns
Figure 4-13.—Transmission input shaft and bearing.
Figure 4-14.—Transmission countershaft assembly—exploded view.
Figure 4-15.—Reverse idler shaft and gear assembly-exploded view.
Figure 4-16.—Transmission main shaft assembly-exploded view.
the countershaft gears, the countershaft gears turns the
main shaft gears, and, when engaged, the reverse idler
In low gear, a small gear on the countershaft drives a
larger gear on the main shaft, providing for a high gear
ratio for accelerating. Then, in high gear, a larger
countershaft gear turns a small main shaft gear or a gear
of equal size, resulting in a low gear ratio, allowing the
vehicle to move faster. When reverse is engaged, power
flows from the countershaft gear, to the reverse idler
gear, and to the engaged main shaft gear. This action
reverses main shaft rotation.
The synchronizer is a drum or sleeve that slides back
and forth on the splined main shaft by means of the
shifting fork. Generally, it has a bronze cone on each side
that engages with a tapered mating cone on the secondand high-speed gears. A transmission synchronizer (fig.
4-17) has two functions, which are as follows:
1. Lock the main shaft gear to the main shaft.
2. Prevent the gear from clashing or grinding
during shifting.
When the synchronizer is moved along the main
shaft, the cones act as a clutch. Upon touching the
gear that is to be engaged, the main shaft is accelerated or slowed down until the speeds of the main
shaft and gear are synchronized. This action occurs
during partial movement of the shift lever. Completion of lever movement then slides the sleeve and
gear into complete engagement. This action can be
readily understood by remembering that the hub of
the sleeve slides on the splines of the main shaft to
engage the cones; then the sleeve slides on the hub to
engage the gears. As the synchronizer is slid against
a gear, the gear is locked to the synchronizer and to
the main shaft. Power can then be sent out of the
transmission to the wheels.
Shift Forks
Shift forks fit around the synchronizer sleeves to
transfer movement to the sleeves from the shift
Figure 4-17.—Synchronizers.
whereas column-mounted shift levers are generally
linkage. The shift fork sets in a groove cut into the
synchronizer sleeve. The linkage rod or shifting rail
connects the shift fork to the operator’s shift lever. As
the lever moves, the linkage or rail moves the shift fork
and synchronizer sleeve to engage the correct
transmission gear.
used with an external rod linkage.
Manual transmissions are of three major types:
1. Sliding gear
Shift Linkage and Levers
2. Constant mesh
There are two types of shift linkages used on
manual transmissions. They are the EXTERNAL ROD
and the INTERNAL SHIFT RAIL. They both perform
the same function. They connect the shift lever with the
shift fork mechanism.
3. Synchromesh
A quick overview of the three types is as follows:
The sliding gear transmission has two or more
shafts mounted in parallel or in line, with sliding spur
gears arranged to mesh with each other and provide a
change in speed or direction.
The transmission shift lever assembly can be
moved to cause movement of the shift linkage, shift
forks, and synchronizers. The shift lever may be either
floor mounted or column mounted, depending upon
the manufacturer. Floor-mounted shift levers are
generally used with an internal shift rail linkage,
The constant mesh transmission has parallel
shafts with gears in constant mesh. Shifting is done by
locking free-running gears to their shaft by using sliding
The synchromesh transmission also has gears in
constant mesh. However, gears can be selected without
clashing or grinding by synchronizing the speeds of the
mating part before they engage.
The sliding gear transmission is generally used in
farm and industrial machines; therefore, we will only
look closely at the constant mesh and synchromesh
Constant Mesh Transmission
To eliminate the noise developed by the spur-tooth
gears used in the sliding gear transmission, automotive
manufacturers developed the constant mesh transmission, also known as the collar shift transmission
(fig. 4-18). The constant mesh transmission has
parallel shafts with gears in constant mesh. In neutral,
Figure 4-18.—Constant mesh transmission assembly.
the gears are free running but, when shifted, they are
locked to their shafts by sliding collars.
the synchronizing clutch mechanisms lock the gears
The following is an example of the operation of a
constant mesh transmission: When the shift lever is
moved to THIRD, the THIRD and FOURTH shifter
fork moves the sliding collar toward the THIRD speed
gear. This engages the external teeth of the sliding
collar with the internal teeth of the THIRD speed gear.
Since the THIRD speed gear is meshed and rotating
with the countershaft, the sliding collar must also
rotate. The sliding collar is splined to the main shaft,
and therefore, the main shaft rotates with the sliding
collar. This principle is carried out when the shift lever
moves from one speed to the next.
The synchronizer accelerates or slows down the
rotation of the shaft and gear, until both are rotating at
the same speed and can be locked together without a
gear clash. Since the vehicle is normally standing still
when it is shifted into reverse gear, a synchronizer is
not ordinarily used on the reverse gear.
Now that you understand the basic parts and
construction of a manual transmission, we will cover
the flow of power through a five-speed synchromesh
transmission. In this example neither first gear nor
reverse gear are synchronized.
Constant mesh gears are seldom used for all
speeds. Common practice is to use such gears for the
higher gears, with sliding gears for FIRST and
REVERSE, or for REVERSE only.
Reverse Gear
Synchromesh Transmission
In passing from neutral to reverse, the first-reverse
main shaft gear is shifted rearward to mesh with the
reverse idler gear (fig. 4-20, view A). The sole function
of this gear is to make the main shaft rotate in the
opposite direction to the input shaft; it does not affect
gear ratio.
The construction of the synchromesh transmission
is the same as that of the constant mesh transmission
with the exception that a synchronizer has been added
(fig. 4-19). The addition of synchronizers allows the
gears to be constant mesh when the cluster gears and
Figure 4-19.—Synchromesh transmission.
First Gear
meshing the gear with the countershaft first-speed
gear. The countershaft first-speed gear and main shaft
first-reverse speed gear transmits power to the main
shaft (fig. 4-20, view B). Gear ratio is approximately
7.55 to 1.
To get the vehicle moving from a standstill, the
operator moves the gearshift lever into first. The main
shaft first-reverse speed gear is slid into position,
Figure 4-20.—Power flow of a five-speed transmission.
Second Gear
To shift into second, the operator depresses the
clutch and moves the shift lever into second gear. The
second-third-speed synchronizer has been moved to
the right so its internal teeth engage the external teeth
of the main shaft second-speed gear. Power is
transmitted by the countershaft second-speed gear to
the main shaft second-speed gear, which is coupled to
the main shaft by the second-third-gear synchronizer,
and to the main shaft (fig. 4-20, view C). Gear ratio is
approximately 4.18 to 1.
Third Gear
To shift into third, the operator depresses the
clutch and moves the shift lever disengaging the
second-third synchronizer from the main shaft secondspeed gear. The second-third-speed synchronizer has
been moved to the left so its internal teeth engage the
external teeth of the main shaft third-speed gear.
Power is transmitted by the countershaft third-speed
gear to the main shaft third-speed gear, which is
coupled to the main shaft by the second-third
synchronizer and through the main shaft (fig. 4-20,
view D). Gear ratio is approximately 2.45 to 1.
speed synchronizer has been moved to the right so its
internal teeth engage the external teeth of the main
shaft fourth-speed gear. Power is transmitted by the
countershaft fourth-speed gear through the main shaft
fourth-speed gear, which is coupled to the main shaft
by the fourth-fifth-speed synchronizer, and through
the main shaft (fig. 4-20, view E). Gear ratio is
approximately 1.45 to 1.
Fifth Gear
The operator depresses the clutch and moves the
shift lever disengaging the fourth-fifth-speed
synchronizer from the main shaft fourth-speed gear.
The fourth-fifth-speed synchronizer is moved to the
left so its internal teeth engage the external teeth of the
input gear. Power is transmitted by the input gear,
which is coupled to the main shaft by the fourth-fifthspeed synchronizer. Since the interlocking action of
the synchronizer, in effect, makes one continuous shaft
of the input shaft and the main shaft, the drive is direct
(fig. 4-20, view F). Gear ratio is 1.00 to 1.
The auxiliary transmission (fig. 4-21) is used to
provide additional gear ratios in the power train. This
transmission is installed behind the main transmission
and power flows directly to it from the main
transmission, when of the integral type, or by a short
propeller shaft (jack shaft) and universal joints.
Fourth Gear
The operator depresses the clutch and moves the
shift lever disengaging the second-third synchronizer
from the main shaft third-speed gear. The fourth-fifth-
Figure 4-21.—Auxiliary transmission with power takeoff used for driving winch.
In this constant mesh auxiliary transmission, the
main gear is part of the input shaft, and it is in constant
mesh with the countershaft drive gear. A pilot bearing
aligns the main shaft output shaft with the input shaft.
The low-speed main shaft gear runs free on the main
shaft when direct drive is being used and is in constant
mesh with the countershaft low-speed gear. A geartype dog clutch, splined to the main shaft, slides
forward or backward when you shaft the auxiliary
transmission into high or low gear position.
Support and alignment are provided by a frame
cross member. Rubber-mounting brackets are used to
isolate vibration and noise from the chassis. A lever
that extends into the operator's compartment
accomplishes shifting. Like the main transmission, the
auxiliary transmission may have either constant mesh
gears or synchronizers to allow for easier shifting.
This transmission, when of the two-speed design,
has a low range and direct drive. Three- and four-speed
auxiliary transmissions commonly have at least one
overdrive gear ratio. The OVERDRIVE position
causes increased speed of the output shaft in relation to
the input shaft. Overdrive is common on heavy-duty
trucks used to carry heavy loads and travel at highway
In HIGH GEAR, when direct drive from the main
transmission is being used, the dog clutch is forward
and makes a direct connection between the input shaft
and the main shaft. When in LOW GEAR, the dog
clutch is meshed with the low-speed, main shaft gear
and is disengaged from the main drive gear.
The auxiliary transmission shown in figure 4-22
provides two-speed ratios. When it is in the DIRECT
DRIVE position, power flows directly through the
transmission and is controlled only by the main
transmission. When the auxiliary transmission is
shifted into LOW RANGE, vehicle speed is reduced
and torque is increased. When the low range is used
with the lowest speed of the main transmission, the
engine drives the wheels very slowly and with less
engine horsepower.
Transmissions are designed to last for the life of the
vehicle when lubricated and operated properly. The
most common cause of failure results from shifting
when the vehicle is not completely stopped or without
waiting long enough to allow the gears to stop spinning
after depressing the clutch pedal. This slight clashing
Figure 4-22.—Sectional view of an auxiliary transmission showing gear arrangement.
of gears may not seem significant at the time, but each
time this occurs, small particles of the gears will be
ground off and carried with the lubricate through the
transmission. These small metal particles may become
embedded in the soft metal used in synchronizers,
reducing the frictional quality of the clutch. At the
same time, these particles damage the bearings and
their races by causing pitting, rough movement, and
noise. Soon transmission failure will result. When this
happens, you will have to remove the transmission and
replace either damaged parts or the transmission unit.
As a mechanic, the first step toward repairing a
transmission is the diagnosis of the problem. To begin
diagnosis, gather as much information as possible.
Determine in which gears the transmission acts
up—first, second, third, fourth, or in all forward gears
when shifting. Does it happen at specific speeds? This
information will assist you in determining which parts
are faulty. Refer to a diagnosis chart in the manufacturer’s service manual when a problem is difficult
to locate. It will be written for the exact type of
Corrective Actions
Possible Cause
Transmission noise in neutral
Transmission not aligned with
Bearings dry, badly worn, or broken Lubricate or replace
Low oil level
Gears worn, scuffed, or broken
Transmission noisy in gear
Hard to shift
Countershaft badly worn
Excessive end play of countershaft
All causes noted above
Same as above
Main shaft rear bearing worn or
Gear teeth worn
Engine vibration damper defective
Speedometer drive gears worn
Clutch disc defective
Gears loose on main shaft
Replace worn parts
Clutch not releasing
Sliding gear tight on shaft splines
Shift linkage out of adjustment
Clean splines or replace shaft or gear
Main shaft splines distorted
Clean or replace
Synchronizer damaged
Sliding gear teeth damaged
Gears clash or grind when shifting Clutch not releasing
Synchronizer defective
Transmission sticks in gear
Gears sticking on main shaft
Free up gears or replace defective
Clutch not releasing
Detent balls stuck.
Free up the balls
Shift linkage out of adjustment
Possible Cause
Corrective Action
Transmission sticks in gear—
Sliding gears tight on shaft splines
Clean splines or replace shaft or
Slips out of gear
Shift linkage out of adjustment
Gear loose on shaft
Replace shaft or gear
Gear teeth worn
Excessive end play in gears
Lack of spring tension on shift lever Install new spring
Badly worn transmission bearings
Transmission leaks oil
Oil level too high
Drain to proper level
Install new gaskets
Damaged gaskets
Oil seal damaged or installed
Install new seals
Oil throw rings damaged,
improperly installed, or missing
Install new oil throw rings properly
6. Remove any cross members or supports.
Many problems that seem to be caused by the
transmission are caused by clutch, linkage, or drive
line problems. Keep this in mind before removing and
disassembling a transmission.
7. Support the transmission and engine with jacks.
Operate the jack on the engine to take the weight
off the transmission. Be careful not to crush the
oil pan.
Because of the variations in construction of
transmissions, always refer to the manufacturer’s
service manual for proper procedures in the removal,
disassembly, repair, assembly, and installation. These
operations vary from 6 to 8 hours, depending on
transmission type and vehicle manufacturer.
Never let the engine hang suspended by
only the front motor mounts.
8. Depending upon what is recommended by the
service manual, either remove the transmissionto-clutch cover bolts or the bolts going into the
engine from the clutch cover.
The basic removal procedures are as follows:
1. Unscrew the transmission drain plug and drain
the oil.
9. Slide the transmission straight back, holding it
in alignment with the engine. You may have to
wiggle the transmission slightly to free it from
the engine.
2. Remove the drive shaft and install a plastic cap
over the end of the transmission shaft.
Once the transmission has been removed from the
engine, clean the outside and place it on your
workbench. Teardown procedures will vary from one
transmission to another. Always consult the service
manual for the type of transmission you are working
on. If improper disassembly methods are used, major
part damage could possibly result.
3. Disconnect the transmission linkage at the
4. Unbolt and remove the speedometer cable from
the extension housing.
5. Remove all electrical wires leading to switches
on the transmission.
Before disassembly, remove the inspection cover.
This will allow you to observe transmission action.
Shift the transmission into each gear, and, at the same
time, rotate the input shaft while inspecting the
conditions of the gears and synchronizers.
use measuring tools and gauges to determine their
Any worn or damaged parts in the transmission
must be replaced. This is why your inspection is very
critical. If any trouble is NOT corrected, the transmission overhaul may fail. You would have to complete
the job a second time, wasting man-hours and
materials, as well as unnecessary equipment downtime.
The basic disassembly procedures are as follows:
1. Unbolt and remove the rear extension housing.
It may be necessary to tap the housing off with a
soft face mallet or bronze hammer.
Always replace all gaskets and seals in the
transmission. Even though the seal or gasket may have
not been leaking before disassembly, it may start to
leak after assembly.
2. Unbolt and remove the front extension housing
and any snap rings.
3. Carefully pry the input shaft and gear forward
far enough to free the main shaft.
4. Using a brass driftpin, push the reverse idler
shaft and countershaft out of the transmission
When replacing a main shaft gear either due to
wear or damage, you should also replace the matching
gear on the countershaft. If a new gear is meshed with
an old gear, transmission gear noise will occur.
5. Remove the input shaft and output shaft
assemblies. Slide the output shaft and gears out
of the back of the transmission as a unit. Be
careful not to damage any of the gears.
If new bolts are needed, make sure it is the correct
thread type and length. Some transmission use metric
bolts. Remember mixing threads will cause part
After the transmission is disassembled, clean all
the parts thoroughly and individually. Clean all the
parts of hardened oil, lacquer deposits, and dirt. Pay
particular attention to the small holes in the gears and
to the shifter ball bores in the shifter shaft housing.
Remove all gasket material using a putty knife or other
suitable tool. Ensure that the metal surfaces are not
gouged or scratched. Also, clean the transmission
bearings and blow-dry them using low-pressure
compressed air.
All parts must be lightly coated with a mediumgrade lubricating oil. This is done immediately after
the inspection or repair. Oiling the parts give them a
necessary rust-preventive coating and facilitates the
assembly process.
After obtaining new parts to replace the worn or
damaged parts, you are ready for transmission
assembly. To assemble the transmission, use the
reverse order of disassembly. Again refer to the service
manual for exact directions, as well as proper
clearances and wear limits of the parts. The service
manual will have an exploded view of the transmission. It will show how each part is located in
relation to the others. Step-by-step direction will
accompany the illustrations.
Always use protective eyewear when you
are blowing the bearing dry with compressed
air. Do NOT allow the bearing to spin. Air
pressure can make the bearing spin at
tremendously high rpm, possibly causing the
bearing to explode and fly apart.
Certain key areas of the transmission should be
given extra attention during assembly. One area is the
needle bearings. To hold the needle bearings into the
countershaft or other shafts, you coat the bearings with
HEAVY GREASE. The grease will hold the bearing in
place as you slide the countershaft into the gears. Also,
measure the end play or clearance of the gears and
synchronizers and the countershaft and case as
directed by the service manual.
After all parts of the transmission have been
cleaned, inspect everything closely to determine
whether they can be reused or have to be replaced. The
wear or damage to some of the parts will be evident to
the eye. If brass-colored particles are found, one or
more of the synchronizers or thrust washers are
damaged. These are normally the only transmission
parts made of this material. If iron chips are found,
main drive gears are probably damaged. To check for
damage or wear on other parts, it may be necessary to
Before installing, ensure the transmission shifts
properly. This will save you from having to remove the
transmission if there is still problems. Also, since the
transmission is already out, this is an ideal time to
inspect the condition of the clutch.
If you notice foaming in the oil, drain the
transmission and refill it with clean oil. Foaming is
evidence that water or some other lubricant that will
not mix with the recommended transmission oil is
Before installation, place a small amount of grease
in the pilot bearing and on the release bearing inner
surface. Now, the transmission is ready to be installed.
Basic transmission installation is as follows:
When it becomes necessary to change the transmission oil, the following procedure should be used:
1. Before you drain the oil, clean around the drain
and fill plugs thoroughly. Both drain and fill
plugs should be removed to allow the oil to
DO NOT place any lubricant on the end of
the clutch shaft input splines or pressure plate
release levers. Grease in these locations can
spray onto the clutch disc, causing clutch
slippage and failure.
2. Drain the transmission immediately after the
vehicle has been operated. The oil will then be
warm and will readily drain, taking along the
suspended contaminants as it drains.
1. Place the transmission on the transmissionjack.
2. Position the transmission behind the engine.
Ensure that the release bearing is in place on the
clutch fork.
3. Check the drained oil for any uncommon
foreign matter, such as large metal particles
(steel or brass). This is a good sign of internal
damage to the gears, bearings, or synchronizers.
If large particles are found, notify your shop
supervisor for further instructions.
3. Carefully align the transmission and engine,
ensuring that the input and output shaft lines up
perfectly with the center line of the engine
crankshaft. If the transmission is slightly tilted,
it will not fit into place.
4. Once the transmission has drained completely
and no large metal particles are found, you
replace the drain plug and refill the transmission
with the proper grade of oil until it reaches the
bottom of the fill plug. You then replace the till
4. With the transmission in high gear, slowly push
the transmission into the clutch housing. You
may need to raise or lower the transmission
slightly to keep it aligned.
5. When the transmission is almost in place,
wiggle the extension housing in a circular
motion while pushing toward the engine. This
will help start the input shaft in the pilot bearing.
The transmission will then slide into position.
Other than the periodic check required on the
transmission fluid, drain and refill are performed as
prescribed by the manufacturer. You should check the
bolts for tightness and inspect the case for damage each
scheduled PM.
6. With the transmission bolted to the clutch cover,
install the rear support or cross member and
transmission mount. Reinstall the clutch
linkage, the transmission linkage, and any other
What material is most commonly used in casting
a transmission case?
With the transmission installed and the clutch
adjusted, test-drive the vehicle for proper operation. If
the transmission is noisy, extremely loose, or binds, it
must be removed and disassembled for further
inspection and corrective action.
What four shafts are located in a manual
What are the two functions of the synchronizer?
What are the two types of shift linkages used on
manual transmissions?
What type of equipment uses a sliding gear
The manual transmission should have the oil level
checked at each PM. Recurrent low oil level indicates
that there is leakage around the oil seals.
Q6. If first gear ratio is 7.55 to 1, what is the gear
ratio when the transmission is shifted into
7. Adjust the clutch.
effect of the fluid coupling within the torque converter
is desirable.
Learning Objective: State the operating principles,
identify the components, and maintenance procedures
of an automatic transmission.
Because the automatic transmission shifts gear
ratios independent of the operator, it must do so
without the operator releasing the throttle. The
automatic transmission does this by using planetary
gearsets whose elements are locked and released in
various combinations that produce the required
forward and reverse gear ratios. The locking of the
planetary gearset elements is done through the use of
hydraulically actuated multiple-disc clutches and
brake bands. The valve body controls the hydraulic
pressure that actuates these locking devices. The valve
body can be thought of as a hydraulic computer that
receives signals that indicate vehicle speed, throttle
position, and gearset lever position. Based on this
information, the valve body sends hydraulic pressure
to the correct locking devices.
The automatic transmission (fig. 4-23), like the
manual transmission, is designed to match the load
requirements of the vehicle to the power and speed
range of the engine. The automatic transmission,
however, does this automatically depending on throttle
position, vehicle speed, and the position of the control
lever. Automatic transmissions are built in models that
have two-, three-, or four-forward speeds and in some
that are equipped with overdrive. Operator control is
limited to the selection of the gear range by moving a
control lever.
The automatic transmission is coupled to the
engine through a torque converter. The torque
converter is used with an automatic transmission,
because it does not have to be manually disengaged by
the operator each time the vehicle is stopped. Because
the automatic transmission shifts without any interruption of engine torque application, the cushioning
The parts of the automatic transmission are as
Torque converter—fluid coupling that connects
and disconnects the engine and transmission.
Figure 4-23.—Automatic transmission cross-sectional view.
Input shaft—transfers power from the torque
converter to internal drive members and
Oil pump—produces pressure to operate
hydraulic components in the transmission.
Valve body—operated by shift lever and
sensors; controls oil flow to pistons and servos.
The torque converter is a fluid clutch that performs
the same basic function as a manual transmission dry
friction clutch (fig. 4-24). It provides a means of
uncoupling the engine for stopping the vehicle in gear.
It also provides a means of coupling the engine for
A torque converter has four basic parts:
Pistons and servos—actuates the bands and
1. Outer housing—normally made of two pieces of
steel welded together in a doughnut shape,
housing the impeller, stator, and turbine. The
housing is filled with transmission fluid.
Bands and clutches—applies clamping or
driving pressure on different parts of gearsets to
operate them.
2. Impeller—driving member that produces oil
movement inside the converter whenever the
engine is running. The impeller is also called the
converter pump.
Planetary gears—provides different gear ratios
and reverse gear.
Output shaft—transfers engine torque from the
gearsets to the drive shaft and rear wheels.
3. Turbine—a driven fan splined to the input shaft
of the automatic transmission. Placed in front of
Figure 4-24.—Torque converter, partial cutaway view.
the stator and impeller in the housing. The
turbine is not fastened to the impeller but is free
to turn independently. Oil is the only connection
between the two.
4. Stator—designed to improve oil circulation
inside the torque converter. Increases efficiency
and torque by causing the oil to swirl around the
inside of the housing.
At cruising speeds, the impeller and turbine spin at
almost the same speed with very little slippage. When
the impeller is spun fast enough, centrifugal force
throws oil out hard enough to almost lock the impeller
and turbine. After the oil has imparted its force to the
turbine, the oil follows the contour of the turbine shell
and blades so that it leaves the center section of the
turbine spinning counterclockwise.
Because the turbine has absorbed the force
required to reverse the direction of the clockwise
spinning of the oil, it now has greater force than is
being delivered by the engine. The process of
multiplying engine torque has begun,
The primary action of the torque converter results
from the action of the impeller passing oil at an angle
into the blades of the turbine. The oil pushes against the
faces of the turbine vanes, causing the turbine to rotate
in the same direction as the impeller (fig. 4-25). With
the engine idling, the impeller spins slowly. Only a
small amount of oil is thrown into the stator and
turbine. Not enough force is developed inside the
torque converter to spin the turbine. The vehicle
remains stationary with the transmission in gear.
Torque multiplication refers to the ability of a
torque converter to increase the amount of engine
torque applied to the transmission input shaft. Torque
multiplication occurs when the impeller is spinning
faster than the turbine (fig. 4-26). For example, if the
engine is accelerated quickly, the engine and impeller
rpm might increase rapidly while the turbine is almost
During acceleration, the engine crankshaft, the
converter housing, and the impeller begin to move
faster. More oil is thrown out by centrifugal force,
turning the turbine. As a result, the transmission input
shaft and vehicle starts to move, but with some
stationary. This is known as stall speed. Stall speed of a
torque converter occurs when the impeller is at
maximum speed without rotation of the turbine. This
condition causes the transmission fluid to be thrown
Figure 4-25.—Torque converter in fluid coupling stage.
Figure 4-26.—Torque converter in torque multiplication
that allows it to rotate clockwise but not counterclockwise. The purpose of the stator is to redirect the
oil returning from the turbine and change its rotation
back to that of the impeller. Stator action is only
needed when the impeller and turbine are turning at
different speeds. The one-way clutch locks the stator
when the impeller is turning faster than the turbine.
This causes the stator to route oil flow over the impeller
vanes properly. Then, when turbine speed almost
equals impeller speed, the stator can freewheel on its
shaft so not to obstruct flow.
Even at normal highway speeds, there is a certain
amount of slippage in the torque converter. Another
type of torque converter that is common on modern
vehicles is the lockup torque converter (fig. 4-28). The
lockup torque converter provides increased fuel
economy and increased transmission life through the
elimination of heat caused by torque converter
slippage. A typical lockup mechanism consists of a
hydraulic piston, torsion springs, and clutch friction
Figure 4-27.—Stator assembly.
off the stator vanes at tremendous speeds. The greatest
torque multiplication occurs at stall speed.
When the turbine speed nears impeller speed,
torque multiplication drops off. Torque is increased in
the converter by sacrificing motion. The turbine spins
slower than the impeller during torque multiplication.
In lower gears, the converter clutch is released.
The torque converter operates normally, allowing
slippage and torque multiplication. However, when
shifted into high or direct drive, transmission fluid is
channeled to the converter piston. The converter piston
pushes the friction discs together, locking the turbine
and impeller. The crankshaft is able to drive the
transmission input shaft directly, without slippage.
The torsion springs assist to dampen engine power
pulses entering the drive train.
If the counterclockwise oil were allowed to
continue to the center section of the impeller, the oil
would strike the blades of the pump in a direction that
would hinder its rotation and cancel any gains in
torque. To prevent this, you can add a stator assembly.
The stator (fig. 4-27) is located between the pump
and the turbine and is mounted on a one-way clutch
Figure 4-28.—Torque converter with lockup clutch.
Figure 4-29.—Planetary gearset.
gears rotate on their axis and turn the ring gear. Should
the brake be engaged on the ring gear, the sun gear
causes the planetary gears to walk around the inside of
the ring gear and force the planet carrier to rotate in the
same direction as the sun gear, but at a slower speed
(low gear). To provide additional speed ranges or a
reverse, you must add other planetary gearsets to this
A planetary gearset (fig. 4-29) consists of three
members-sun gear, ring gear, and planetary carrier
which holds the planetary gears in proper relation with
the sun and ring gear. The planetary gears are free to
rotate on their own axis while they "walk" around the
sun gear or inside the ring gear.
By holding or releasing the components of a
planetary gearset, it is possible to do the following:
A compound planetary gearset combines two
planetary units into one housing or ring gear. It may
have two sun gears or a long sun gear to operate two
Reduce output speed and increase torque (gear
Increase output speed while reducing torque
Reverse output direction (reverse gear).
Serve as a solid unit to transfer power (one to one
Freewheel to stop power flow (park or neutral).
Figure 4-30 shows the simplest application of
planetary gears in a transmission. With the application
shown, two forward speeds and neutral are possible.
High gear or direct drive is shown. The clutch is
holding the planet carrier to the input shaft, causing the
carrier and sun gear to rotate as a single unit. With the
clutch released, all gears are free to rotate and no power
is transmitted to the output shaft. In neutral, the
planetary carrier remains stationary while the pinion
Figure 4-30.—Simple planetary gear application.
sets of planetary gears. A compound planetary gearset
is used to provide more forward gear ratios than a
simple planetary gearset.
Automatic transmission clutches and bands are
friction devices that drive or lock planetary gearsets
members. They are used to cause the gearset to transfer
Multiple-Disc Clutch
clutch is made up of the following components (fig.
DISCS AND PLATES.—The active components
of the multiple-disc clutch are the discs and the plates.
The discs are made of steel and are faced with a friction
material. They have teeth cut into their inner
circumference to key them positively to the clutch hub.
The plates are made of steel with no lining. They have
teeth cut into their outer circumference to key them
positively with the inside of a clutch drum or to the
inside of the transmission case. By alternately stacking
the discs and plates, they are locked together or
released by simply squeezing them.
The multiple-disc clutch is used to transmit
torque by locking elements of the planetary gearsets to
rotating members within the transmission. In some
cases, the multiple-disc clutch is also used to lock a
planetary gearset element to the transmission case so it
can act as a reactionary member. The multiple-disc
CLUTCH DRUM AND HUB.—The clutch drum
holds the stack of discs and plates and is attached to the
planetary gearset element that is being driven. The
clutch hub attaches to the driving member and fits
inside the clutch discs and plates.
Figure 4-31.—Multiple-disc clutch.
clutch discs and plates are free to rotate within each
other. The result is that the clutch hub rotates freely and
does not drive the clutch drum.
PRESSURE PLATE.—The pressure plates are
thick clutch plates that are placed on either end of the
stack. Their purpose is to distribute the application
pressure equally on the surfaces of the clutch discs and
APPLIED—When the clutch is applied, hydraulic
pressure is applied to the clutch piston that, in turn,
applies pressure to the clutch discs and plates, causing
them to lock together. The result is that the clutch hub
drives the clutch drum through the clutch.
CLUTCH PISTON.—The clutch piston uses
hydraulic pressure to apply the clutch. Hydraulic
pressure is supplied to the clutch piston through the
center of the rotating member.
Overrunning Clutch
CLUTCH PISTON SEALS.—The clutch piston
seals serve to prevent the leakage of hydraulic pressure
around the inner and outer circumferences of the clutch
An overrunning clutch is used in automatic
transmissions to lock a planetary gearset to the
transmission case so that it can act as a reactionary
member. The overrunning clutch for the planetary
gears is similar to the one in a torque converter stator or
an electric starting motor drive gear. A planetary
gearset overrunning clutch consists of an inner race,
set of springs, rollers, and an outer race.
ensure rapid release of the clutch when hydraulic
pressure to the clutch piston is released. The clutch
springs may be in the form of several coil springs
equally spaced around the piston or one large coil
spring that fits in the center of the clutch drum. Some
models use a diaphragm-type clutch spring.
Operation of the overrunning clutch is very simple
to understand. When driven in one direction, rollers
lock between ramps on the inner and outer race,
allowing both races to turn. This action can be used to
stop movement of the planetary member, for example.
When turned in the other direction, rollers walk off the
ramps, and the races are free to turn independently.
The operation of the multiple-disc clutch is as
follows (fig. 4-32):
RELEASED—When the clutch is released, there
is no hydraulic pressure on the clutch piston and the
Figure 4-32.—Multiple-disc clutch operation.
Figure 4-33.—Brake band.
Brake Band
release of the band. Some servos use hydraulic
pressure on both sides of their pistons so that they use
hydraulic pressure for both the release and the
application of the band.
The brake band is used to lock a planetary gearset
element to the transmission case so that the element
can act as a reactionary member. The brake band is
made up of the following elements (fig. 4-33):
The operation of the brake band is as follows (fig.
BAND.—The brake band is a circular piece of
spring steel that is rectangular in cross section. Its
inside circumference is lined with a friction material.
The brake band has bosses on each end so that it can be
held and compressed.
Released—When the brake band is released,
there is no hydraulic pressure applied to the servo, and
the drum is free to rotate within the band.
Applied—When the brake band is applied,
hydraulic pressure is applied to the servo that, in turn,
tightens the band around the drum. The result is that the
drum is locked in a stationary position, causing an
output change from the planetary gearset.
DRUM.—The drum fits inside of the band and
attaches to the planetary gear-set element and is to be
locked by the band. Its outer surface is machined
smoothly to interact with the friction surface of the
brake band. By pulling the open ends of the band
together, the rotation of the drum stops.
In the applied circuit of a clutch or band, an
accumulator is used to cushion initial application (fig.
4-35). It temporarily absorbs some of the hydraulic
pressure to cause slower movement of the applied
ANCHOR.—The anchor firmly attaches one end
of the brake band to the transmission case. A provision
for adjusting the clearance between the band and the
drum is usually provided on the anchor.
SERVO.—The servo uses hydraulic pressure to
squeeze the band around the drum. The servo piston is
acted on by hydraulic pressure from the valve body that
is fed through an internal passage through the case. The
servo piston has a seal around it to prevent leakage of
hydraulic pressure and is spring loaded to allow quick
The hydraulic system of an automatic transmission
serves four basic purposes:
1. Actuates clutches and brake bands by hydraulic
pressure from the hydraulic slave circuits.
Figure 4-34.—Brake band operation.
Figure 4-35.—Operation of the accumulator.
2. Controls the shifting pattern ofthetransmission.
This is done by switching hydraulic pressure to
programmed combinations of clutches and
brake bands based on vehicle speed and engine
transmission fluid is drawn into the pump from the
transmission pan. The pump compresses the oil and
forces it to the pressure regulator. The pump has
several basic functions:
Produces pressure to operate the clutches, the
bands, and the gearsets.
3. Circulates the transmission fluid through a
remote cooler to remove excess heat that is
generated in the transmission and torque
Lubricates the moving parts in the transmission.
Keeps the torque converter filled with transmission fluid for proper operation.
4. Provides a constant fresh supply of oil to all
critical wearing surfaces of the transmission.
Circulates transmission fluid through the transmission and cooling tank (radiator) to transfer
The hydraulic system for an automatic transmission typically consists of the following.
Operates hydraulic valves in the transmission.
Pressure Regulator
The typical hydraulic pump (fig. 4-36) is an
internal-external rotor or gear-type pump. Located in
the front of the transmission case, it is keyed to the
torque converter hub so that it is driven by the engine.
As the torque converter spins the oil pump,
The pressure regulator limits the maximum
amount of oil pressure developed by the oil pump. It is
a spring-loaded valve that routes excess pump pressure
out of the hydraulic system, assuring proper
transmission operation.
Figure 4-36.—Typical transmission hydraulic pump.
Manual Valve
Vacuum Modulator Valve
A manual valve (fig. 4-37), operated by the shift
mechanism, allows the operator to select park, neutral,
reverse, or different drive ranges. A manual valve is
basically a multiport spool valve that switches line
pressure to selected passages, as it is moved through its
operating positions.
The vacuum modulator valve (fig. 4-38) is a
diaphragm device that uses engine manifold vacuum to
indicate engine load to the shift valve. As engine
vacuum (load) rises and falls, it moves the diaphragm
inside the modulator. This, in turn, moves the rod and
hydraulic valve to change throttle control pressure in
Figure 4-37.—Manual valve operation.
Figure 4-38.—Vacuum modulator valve.
meshed with a gear on the transmission output shaft.
Whenever the vehicle and output shaft are moving, the
centrifugal weights rotate. When the output shaft and
weights are spinning slowly, the weights are held in by
the governor springs, causing low-pressure output and
the transmission remains in low gear. As the engine
speeds increases, the weights are thrown out further
and governor pressure increases, moving the shift
valve and causing the transmission to shift into higher
the transmission. In this way, the vacuum modulator
can match transmission shift points to engine loads.
Governor Valve
The governor valve (fig. 4-39) senses engine speed
(transmission output shaft speed) to help control gear
shifting. The vacuum modulator and governor work
together to determine shift points. The governor gear is
Figure 4-39.—Operation of the governor.
Figure 4-40.—Shift valve.
to a lever on the transmission. When the operator
depresses the throttle, the lever moves the kickdown
valve. This action causes hydraulic pressure to override normal shift control pressure and the transmission
Shift Valves
The shift valves (fig. 4-40) are simple balancetype spool valves that select between low and high gear
when the manual valve is in drive. Using control
pressure (oil pressure from the regulator, governor,
vacuum modulator, and manual valves), they operate
the bands, servos, and gearsets. Oil pressure from the
other transmission valves acts on each end of the shift
valve. In this way, the shift valve is sensitive to engine
load (vacuum modulator valve oil pressure), engine
speed (governor valve oil pressure), and gearshift
position (manual valve oil pressure). These valves
move according to the forces and keep the transmission shifted into the correct gear ratio for the
driving conditions.
Valve Body
The valve body contains many of the hydraulic
valves, such as the pressure regulator, shift valves,
manual valve, and others used in an automatic
transmission. The valve body bolts to the bottom of the
transmission case and is housed in the transmission
pan. A filter or screen is attached to the bottom of the
valve body. Passages in the valve body route fluid from
the pump to the valves and then into the transmission
case. Passages in the transmission case carry fluid to
other hydraulic components.
Kickdown Valve
To get an idea of how complicated the hydraulic
system really is, a schematic view of an actual
hydraulic system for an automatic transmission is
shown is figure 4-41.
The kickdown valve causes the transmission to
shift into a lower gear during fast acceleration. A rod or
cable links the carburetor or fuel injection throttle body
Figure 4-41.—Hydraulic schematic of a typical three-speed automatic transmission.
Automatic transmission service can be easily
divided into the following areas: preventive maintenance, troubleshooting, and major overhaul. Before
you perform maintenance or repair on an automatic
transmission, consult the maintenance manual for
instructions and proper specifications. As a floor
mechanic, however, your area of greatest concern is
preventive maintenance. Preventive maintenance
includes the following:
Checking the transmission fluid daily
Adjusting the shifting and kickdown linkages
to be in the transmission in place of fluid and, in turn,
cause slow application and burning of clutch plates and
facings. Slippage occurs, heat results, and failure of the
transmission follows.
Another possible, but remote, problem is water,
indicated by the fluid having a "milky" appearance. A
damaged fluid cooling tube in the radiator (automotive) or a damaged oil cooler (construction) could
be the problem. The remedy is simple. Pressure-test
the suspected components and perform any required
repairs. After repairs have been performed, flush and
refill the transmission with clean, fresh fluid.
Linkage and Band Adjustment
Adjusting lockup bands
The types of linkages found on an automatic
transmission are gearshift selection and throttle kickdown. The system can be a cable or a series of rod and
levers. These systems do not normally present a
problem, and preventive maintenance usually involves
only a visual inspection and lubrication of the pivot
points of linkages or the cable. When adjusting these
linkages, you should strictly adhere to the manufacturer’s specifications.
Changing the transmission fluid and filter at
recommended service intervals
Checking the Fluid
The operator is responsible for first echelon
(operator’s) maintenance. The operator should not only
be trained to know to look for the proper fluid level but
also know how to look for discoloration of the fluid and
debris on the dipstick.
If an automatic transmission is being used in
severe service, the manufacturer may suggest periodic
band adjustment. Lockup bands are always adjusted to
the manufacturer’s specifications. Bands are adjusted
by loosening the locknut and tightening down the
adjusting screw to a specified value. The band
adjusting screw is backed off a specified amount of
turns and the locking nut tightened down. NOT ALL
BANDS ARE ADJUSTABLE. Always check the
manufacturer’s service manual before any servicing of
the transmission.
Fluid levels in automatic transmissions are almost
always checked at operating temperature. This is
important to know since the level of the fluid may vary
as much as three quarters of an inch between hot and
The fluid should be either reddish or clear. The
color varies due to the type of fluid. (For example:
construction equipment using OE-10 will be clear). A
burnt smell or brown coloration of the fluid is a sign of
overheated oil from extra heavy use or slipping bands
or clutch packs. The vehicle should be sent to the shop
for further inspection.
Fluid Replacement
Fluid replacement is to be performed according to
the manufacturer’s recommendations. These recommendations vary considerably for different makes and
models. When you change automatic transmission
fluid, always read the service manual first.
Not all transmission fluids are the same.
Before you add fluid, check the manufacturer’s
recommendations first. The use of the wrong
fluid will lead to early internal parts failure and
costly overhaul.
Service intervals depend on the type of use the
vehicle receives. In the NCF, because of the operating
environment, more than a few of the vehicles are
subjected to severe service. Severe service includes the
following: hot and dusty conditions, constant stop and
go driving (taxi service), trailer towing, constant heavy
hauling, and around the clock operations (contingency). Any CESE operating in these conditions
Overfilling the transmission can result in the fluid
foaming and the fluid being driven out through the vent
tube. The air that is trapped in the fluid is drawn into the
hydraulic system by the pump and distributed to all
parts of the transmission. This situation will cause air
should have its automatic transmission fluid and filter
changed on a regular schedule, based on the
manufacturer's specifications for severe service.
Ensure the vehicle is on level ground or a lift and let the
oil drain into a proper catchment device.
for a couple of minutes. Move the gear selectorthrough
all gear ranges several times, allowing the fluid to flow
through the entire hydraulic system to release any
trapped air. Return the selector lever to park or neutral
and recheck the fluid level. Bring the fluid to the proper
level. Run the vehicle until operating temperature is
reached, checking for leaks. Also, recheck the fluid
and adjust the level as necessary.
The draining of the transmission can be
accomplished in one of the following three ways:
1. Removing the drain plug
2. Loosening the dipstick tube
Overfilling an automatic transmission will
cause foaming of the fluid. This condition
prevents the internal working parts from being
properly lubricated, causing slow actuation of
the clutches and bands. Eventual burning of the
3. Removing the oil pan
Oil drained from automatic transmissions
contains heavy metals and is considered
hazardous waste and should be disposed of
according to local naval station instructions.
Once the oil is drained, remove the pan completely
for cleaning by paying close attention to any debris in
the bottom of the pan. The presenceofa high amount of
metal particles may indicate serious internal problems.
Clean the pan; set it aside.
All automatic transmissions have a filter or screen
attached to the valve body. The screen is cleanable,
whereas the filter is a disposable type and should
always be replaced when removed. These are retained
in different ways: retaining screws, metal retaining
clamps, or O rings made of neoprene. Clean the screen
with solvent and use low-pressure air to blow-dry it.
Do not use rags to wipe the screen dry, as it tends to
leave lint behind that will be ingested into the
hydraulic system of the transmission. If the screen is
damaged or is abnormally hard to clean, replace it.
Draining the oil from the pan of the transmission
does not remove all of the oil—draining the oil from
the torque converter completes the process. To do this,
remove the torque converter cover and remove the
drain plug, if so equipped. For a torque converter
with-out a drain plug, special draining instructions
may be found in the manufacturer’s service manual.
Before performing this operation, clear it with your
shop supervisor.
In a vehicle equipped with an automatic
transmission, operator control is limited to the
selection of the gear range by moving a control
lever. (T/F)
In a torque converter, when does torque
multiplication occur?
What is the purpose of the stator in the torque
What are the three members of a planetary
What is thepurpose of the multiple-disc clutch in
an automatic transmission?
Where is the hydraulic pump of an automatic
transmission located?
Learning Objective: Identify components of the
manual and automatic transaxles. State the differences
between transmissions and transaxles.
A transaxle is a transmission and differential
combination in a single assembly. Transaxles are used
in front-wheel drive vehicles. A transaxle allows the
wheels next to the engine to propel the vehicle. Short
drive axles are used to connect the transaxle output to
the hubs and drive wheels.
Refilling the Transmission
Reinstall the transmission oil pan, the oil plug, and
the fill tube. Fill the transmission with the fluid
prescribed by the manufacturer to the proper level.
With the brakes applied, start the engine and let it idle
Vehicle manufacturers claim that a transaxle and
front-wheel drive has several advantages over a
Transaxle Synchronizers—splined hub assemblies that can lock freewheeling gears to their
shafts for engagement.
vehicle with rear-wheel drive. A few of these advantages are the following:
Improved efficiency and reduced drive train
Improved traction on slippery surfaces because
of increased weight on the drive wheels
Transaxle Differential—transfers gearbox
torque to the driving axle and allows the axles to
turn at different speeds.
Increased passenger compartment space (no
hump in floorboard for rear drive shaft)
Transaxle Case—aluminum housing that
encloses and supports parts of the transaxle.
Less unsprung weight (weight that must move
with suspension action), thereby providing a
smoother ride
The manual transaxle can be broken up into two
separate units—a manual transaxle transmission and a
transaxle differential. A manual transaxle transmission provides several (usually four or five) forward
gears and reverse. You will find that the names of
shafts, gears, and other parts in the transaxle vary,
depending on the location and function of the
components. For example, the input shaft may also be
called the main shaft, and the output shaft is called the
pinion shaft because it drives the ring and pinion gear
in the differential. The output, or pinion, shaft has a
gear or sprocket for driving the differential ring gear.
Quieter operation since engine and drive train
noise is centrally located in the engine compartment
Improved safety because of the increased mass
in front of the passengers
Most transaxles are designed so that the engine can
be transverse (sideways) mounted in the engine compartment. The transaxle bolts to the rear of the engine.
This produces a very compact unit. Engine torque
enters the transaxle transmission. The transmission
transfers power to the differential. Then the differential turns the drive axles that rotate the front wheels.
The clutch used on the manual transaxle transmission is almost identical to the manual transmission
clutch for rear-wheel drive vehicles. It uses a friction
disc and spring-loaded pressure plate bolted to the
flywheel. Some transaxles used a conventional clutch
release mechanism (release bearing and fork); others
use a long pushrod passing through the input shaft.
Both manual and automatic transaxles are
available. Manual transaxle uses a friction clutch and a
standard transmission-type gearbox. An automatic
transaxle uses a torque converter and a hydraulic
system to control gear engagement.
The transaxle differential, like a rear axle differential, transfers power to the axles and wheels while
allowing one wheel to turn at a different speed than the
other. A small pinion gear on the gearbox output shaft
or countershaft turns the differential ring gear. The
ring gear is fastened to the differential case. The case
holds the spider gears (pinion gears and axle side
gears) and a pinion shaft. The axle shafts are splined to
the differ-ential side gears.
A manual transaxle uses a standard clutch and
transmission. A foot-operated clutch engages and
disengages the engine and transaxle. A hand-operated
shift lever allows the operator to charge gear ratios.
The basic parts relating to a manual transaxle are as
Transaxle Input Shaft—main shaft splined to the
clutch disc turns the gear in the transaxle.
An automatic transaxle is a combination automatic
transmission and differential combined into a single
assembly. The basic parts of an automatic transaxle are
as follows:
Transaxle Input Gears—either freewheeling or
fixed gears on the input shaft and meshes with
the output gears.
Transaxle Torque Converter—(fluid-type clutch
that slips at low speed but locks up and transfers
engine power at a predetermined speed; couples
and uncouples engine crankshaft to transmission
input shaft and gear train).
Transaxle Output Gears—either fixed or freewheeling gears driven by the input gears.
Transaxle Output Shaft—transfers torque to the
ring gear, pinion gears, and differential.
Transaxle Oil Pump—(produces hydraulic
pressure to operate, lubricate, and cool the
automatic transaxle; its pressure activates the
pistons and servos).
Transaxle Planetary Gearsets—(provides
different gear ratios and reverse in the automatic
Transaxle Valve Body—(controls the flow of
the fluid to the pistons and servos in the
transaxle; it contains hydraulic valves operated
by the operators shift linkage and by engine
speed and load-sensing components).
Transaxle Pistons and Servos—(operates the
clutches and bands when activated by fluid
pressure from the valve body).
Transaxle Differential—(transfers powers from
the transmission components to the axle shafts).
Many of the components used in the automatic
transaxle are also found in the automatic transmission.
Operating principles of these components are the same
as the automatic transmission. The differential of the
automatic transaxle is similar to that used on the
manual transaxle.
Transaxle Clutches and Bands—(applies
planetary gears in the transaxle; different bands
and clutches are activated to operate different
units in the gear-sets).
What is the purpose of the output shaft of a
manual transaxle?
Q2. In an automatic transaxle, what component(s)
operate(s) the clutches and bands?
Connects anddisconnects the engine and manual transmission or transaxle
Clutch release mechanism
Clutch fork
Torsion spring
Clutch start switch
1 1/2 inch
Q1. Aluminum
Q2. Input shaft, countershaft, reverse idler shaft, and main shaft
Locks the main shaft gear to the main shaft and prevents the gears from
clashing during shifting
External rod and internal shift rail
Industrial and farm equipment
7.55 to 1
When the impeller is spinning faster than the turbine
Redirects oil returning from the turbine and changes its rotation back to that of
the impeller
Sun gear, ring gear, and planetary carrier
To transmit torque by locking elements of the planetary gearset to rotating
members within the transmission
Located in the front of the transmission case and keyed to the torque converter
Transfer torque to the ring gear, the pinion gears, and the differential
Transaxle pistons and servos
shaft that extends from the transmission or transfer
case to a center support bearing and a drive shaft that
extends from the center support bearing to the rear
Learning Objective: Identify the components and
explain the functions and the maintenance procedures
for a drive line assembly, differentials, drive axles, a
transfer case, and a power takeoff unit. Describe the
different types of universal and constant velocity joints.
Explain the adjustments and measurements of the ring
and pinion gears. Describe the procedures for removing
and replacing axle bearings and seals.
The drive line assembly (fig. 5-1) consists of the
SLIP YOKE—connects the transmission output
shaft to the front universal joint.
connection that fastens the slip yoke to the drive
One important function of the power train is to
transmit the power of the engine to the wheels. In a
simple situation, a set of gears or a chain could perform
this task, but automotive vehicles usually are not
designed for such simple operating conditions. They
are designed to have great pulling power, move at
different speeds, operate forward and reverse, and
travel on rough as well as smooth surfaces. To meet
these widely varying conditions, a number of units
have been added. In this chapter we will discuss drive
lines, differentials, drive axles (rear and front drive),
and power train accessories (transfer cases and power
DRIVE SHAFT—a hollow metal tube that
transfers turning power from the front universal
joint to the rear universal joint.
REAR UNIVERSAL JOINT—a flex joint that
connects the drive shaft to the differential yoke.
REAR YOKE—holds the rear universal joint
and transfers torque to the gears in the rear axle
The type of transmission (manual or automatic)
determines how the slip joint is connected to the drive
shaft. On a manual transmission, the slip yoke is
splined to the drive shaft with the yoke for the universal
joint directly behind the transmission or transfer case,
whereas, with the automatic transmission, the slip
yoke is splined to the output shaft. Either way they
serve the same purpose—to provide the necessary
telescopic action for the drive shaft. As the axle
housing moves forward and backward, the slip joint
gives freedom of movement in a horizontal direction
and yet is capable of transmitting rotary motion.
Learning Objective: Identify the parts and the
functions of different types of drive lines. Describe the
different types of universal joints.
The drive line assembly has several important
functions. It must perform the following:
Send turning power from the transmission to the
rear axle assembly.
Flex and allow up-and-down movement of the
rear axle assembly.
The slip yoke used with an automatic transmission
has the outer diameter machined smooth. This smooth
surface provides a bearing surface for the bushing and
rear oil seal in the transmission. The transmission rear
oil seal rides on the slip yoke and prevents fluid
leakage out of the rear of the transmission. The seal
also keeps dirt out of the transmission and off the slip
Provide a sliding action to adjust for changes in
drive line length.
Provide a smooth power transfer.
The assembly provides a path through which
power is transmitted from the transmission to the drive
axle assemblies or auxiliary equipment. Vehicles,
having a long wheelbase, are equipped with a drive
Figure 5-1.—Drive line assembly.
The drive shaft, also called a propeller shaft, is
commonly a hollow steel tube with yoke(s) welded on
the end. The tubular design makes the drive shaft
strong and light. Most vehicles use a single, one-piece
drive shaft. However, many trucks have a two-piece
drive shaft. This cuts the length of each shaft to avoid
drive line vibration.
Since a drive shaft spins at full engine t-pm in high
gear, it must be straight and perfectly balanced (weight
evenly distributed around center line of shaft). If NOT
balanced, the shaft can vibrate violently. To prevent
this vibration, drive shaft balancing weights are
welded to the shaft at the factory. Small metal weights
are attached to the light side to counteract the heavy
side for smooth operation.
Figure 5-2.—Hotchkiss drive.
The drive shaft can be either open or enclosed,
depending on the type of drive used. The HOTCHKISS
drive has an open drive shaft that operates a rear axle
assembly mounted on springs (fig. 5-2). The
HOTCHKISS drive requires that the springs be rigid
enough to withstand the twisting action (torque) of the
rear axle and the driving and braking forces that the
springs transmit to the frame. This type of drive is
common to the equipment you will encounter in the
shaft, and the rear of the drive shaft is attached to the
axle drive pinion through a flexible coupler.
A universal joint, also called a U-joint, is a flexible
coupling between two shafts that permits one shaft to
drive another at an angle to it. The universal joint is
flexible in a sense that it will permit power to be
transmitted while the angle of the other shaft is
continually varied.
Another type of drive is a torque tube. Torque
tubes differ from the Hotchkiss design in that a solid
drive shaft is enclosed in a hollow torque tube and
rotates within a support bearing to prevent whipping.
One universal joint is used at the front of the drive
A simple universal joint is composed of three
fundamental units consisting of a journal (cross) and
two yokes (fig. 5-3). The two yokes are set at right
angles to each other and their open ends are connected
by the journal. This construction permits each yoke to
pivot on the axis of the journal and also permits the
transmission of rotary motion from one yoke to the
other. As a result, the universal joint can transmit
power from the engine through the shaft to the rear
axle, even though the engine is mounted in the frame at
a higher level than the rear axle, which is constantly
moving up and down in relation to the engine.
A peculiarity of the conventional universal joint is
that it causes a driven shaft to rotate at a variable speed
in respect to the driving shaft. There is a cyclic
variation in the form of an acceleration and
deceleration of speed (fig. 5-4). Two universal joints
are placed in a drive shaft to eliminate the speed
fluctuations of the shaft while the shaft is at an angle to
the power source. The universal joints are placed at a
90-degree angle to each other and one counteracts the
action of the other while in motion.
Three common types of automotive drive shaft
universal joints are used on rear-wheel drive vehicles:
cross and roller, ball and trunnion, and double-cardan
(constant velocity) universal joints.
Cross and Roller Universal Joint
The cross and roller design is the most common
type of drive shaft U-joint. It consists of four bearing
caps, four needle roller bearings, a cross or journal,
grease seals, and snap rings (fig. 5-5).
The bearing caps are held stationary in the drive
shaft yokes. Roller bearings fit between the caps and
the cross to reduce friction. The cross is free to rotate
inside the caps and yokes. Snap rings usually fit into
grooves cut in the caps or the yoke bores to secure the
bearing caps and bearings. There are several other
methods of securing the bearing caps in the yokes.
These are bearing covers, U-bolts, and bearing caps.
Figure 5-3.—Simple universal joint.
Figure 5-4.—Speed fluctuations caused by conventional universal joints.
creating a slip joint. Compensating springs at each end
of the drive shaft hold it in a centered position.
Variations in length is permitted by the longitudinal
movement of the balls in the body grooves. Angular
displacement is allowed by outward movement of the
balls on the trunnion pins. This type of universal joint
is recognized easily by the flexible dust boot that
covers it.
Double-Cardan Universal Joint
The double-cardan universal joint uses two cross
and roller joints in tandem to form a single joint (fig.
5-7). The joints are linked through a centering yoke
that works in conjunction with a specially designed
spring-loaded centering ball. The components are
contained within the centering coupling yoke.
As the shafts rotate, the action of the centering ball
and yoke acts to maintain an equally divided drive
angle between the connected shafts, resulting in a
constant drive velocity.
Figure 5-5.—Cross and roller universal joint—disassembled
Ball and Trunnion Universal Joint
The speed fluctuations caused by the conventional
universal joints do not cause much difficulty in the
rear-wheel drive shaft where they have to drive
through small angles only. In front-wheel drives, the
wheels are cramped up to 30 degrees in steering. For
this reason velocity fluctuations present a serious
problem. Conventional universal joints would cause
The ball and trunnion universal joint is a T-shaped
shaft that is enclosed in the body of the joint (fig. 5-6).
The trunnion ends are each equipped with a ball,
mounted in needle bearings. and move freely in
grooves in the outer body of the joint, in effect,
Figure 5-6.—Ball and trunnion universal joint.
Figure 5-7.—Double-cardan universal joint.
hard steering, slippage, and tire wear each time the
vehicle turns a corner. Constant velocity joints
eliminate the pulsations because they are designed to
be used exclusively to connect the front axle shaft to
the driving wheels.
of driving contact between the two halves of the
coupling. A Rzeppa CV joint consists of a star-shaped
inner race, several ball bearings, bearing cage, outer
race or housing, and a rubber boot (fig. 5-8).
The inner race (driving member) is splined to the
inner axle shaft. The outer race (driven member) is a
spherical housing that is an integral part of the outer
shaft; the balls and ball cage are fitted between the two
races. The close spherical fit between the three main
members supports the inner shaft whenever it is
required to slide in the inner race, relieving the balls of
any duty other than the transmission of power.
Basic operation of a CV joint is as follows:
The outboard CV joint is a fixed joint that
transfers rotating power from the axle shaft to
the hub assembly.
The inboard CV joint is a sliding joint that
functions as a slip joint in a drive shaft for rearwheel drive vehicles.
The movement of the balls is controlled by the ball
cage. The ball cage positions the balls in a plane at right
angles to the two shafts when the shafts are in the same
line. A pilot pin, located in the outer shaft, moves the
pilot and the ball cage by simple leverage in such a
manner that the angular movement of the cage and
balls is one half of the angular movement of the driven
shaft. For example, when the driven shaft is moved 20
The constant velocity joints you will normally
encounter are the Rzeppa, Bendix-Weiss, and tripod
Rzeppa Constant Velocity (CV) Joint
The Rzeppa constant velocity (CV) joint is a ballbearing type in which the balls furnish the only points
Figure 5-8.—Rzeppa constant velocity (CV) joint.
but its construction differs from that of the Rzeppa in
that the balls are a tight fit between two halves of the
coupling and that no cage is used (fig. 5-9). The center
ball rotates on a pin inserted in the outer race and serves
as a locking medium for the four other balls.
degrees, the cage and balls move 10 degrees. As a
result. the balls of the Rzeppa joint are positioned,
from the top view, to bisect the angle formed.
Bendix-Weiss Constant Velocity
(CV) Joint
The driving contact remains on the plane that
bisects the angle between the two shafts; however, it is
the rolling friction between the four balls and the
The Bendix-Weiss constant velocity (CV) joint
also uses balls that furnish points of driving contact,
Figure 5-9.—Bendix-Weiss constant velocity (CV) joint.
universal joint housing that positions the balls. When
both shafts are in line, that is, at an angle of 180
degrees, the balls lie in a plane that is 90 degrees to the
shafts. If the driving shaft remains in the original
position, any movement of the driven shaft will cause
the balls to move one half of the angular distance. For
example, when the driven shaft moves through an
angle of 20 degrees, the angle between the two shafts is
reduced to 160 degrees. The balls will move 10 degrees
in the same direction, and the angle between the
driving shaft and the plane in which the balls lie will be
reduced to 80 degrees. This action fulfills the
requirement that the balls lie in the plane that bisects
the angle of drive.
support bearing bolts to the frame or underbody of the
vehicle. It supports the center of the drive shaft where
the two shafts come together.
A sealed ball bearing allows the drive shaft to spin
freely. The outside of the ball bearing is held by a thick,
rubber, doughnut-shaped mount. The rubber mount
prevents vibration and noise from transferring into the
operator’s compartment.
A bearing similar to the center support bearing is
often used with long drive lines, containing a single
drive shaft. This bearing is called a PILLOW BLOCK
BEARING. It is commonly used in drive lines that
power auxiliary equipment. Its purpose is to provide
support for the drive shaft and maintain alignment.
When used at or near the center of the shaft, it reduces
the whipping tendency of the shaft at high speed or
when under heavy loads. The construction of pillow
blocks varies. The simplest form is used on solid power
takeoff drive shafts, which is no more than a steel
sleeve with a bronze bushing.
Tripod Joint
A tripod or ball and housing CV joint consists of a
spider, usually three balls, needle bearings, outer yoke,
and boot. The inner spider is splined to the axle shaft
with the needle bearings and three balls fitting around
the spider. The yoke then slides over the balls. Slots in
the yoke allow the balls to slide in and out and also
A drive line is subjected to very high loads and
rotating speeds. When a vehicle is cruising down the
road, the drive shaft and universal joints or constant
velocity joints may be spinning at full engine rpm.
They are also sending engine power to either the front
or rear axle assemblies. This makes drive line
maintenance very important.
During operation, the axle shaft turns the spider
and ball assembly. The balls transfer power to the outer
housing. Since the outer housing is connected to the
axle stub shaft or hub, power is sent through the joint to
propel the vehicle.
The drive shafts must be perfectly straight and the
joints must be unworn to function properly. If any
component allows the drive shafts to wobble, severe
vibration, abnormal noises, or even major damage can
When two or more drive shafts are connected in
tandem, their alignment is maintained by a rubber
bushed center support bearing (fig. 5-10). The center
Figure 5-10.—Center support bearing.
yoke or the bushing is worn. Inspect the rear yoke bolts
for tightness. Make sure the rear motor mount is NOT
broken. Look at any condition that can upset the
operation of the drive shaft.
Drive Shaft Noises
When operating a vehicle to verify a complaint.
keep in mind that other components could be at fault. A
worn wheel bearing, squeaking spring, defective tire.
transmission, or differential troubles could be at fault.
You must use your knowledge of each system to detect
which component is causing the trouble.
If after a thorough check of the drive shaft you fail
to determine the problem, notify the shop supervisor.
The drive shaft may require detailed measuring (drive
shaft runout and drive shaft angle) or have its balance
Drive shaft noises are usually caused by worn Ujoints, slip joint wear, or a faulty center support
bearing. Drive shaft noises and possible causes are as
Universal Joint Service
The universal joints on many automotive
vehicles are factory lubricated. However, construction equipment have universal joints that have
lubrication fittings that should be lubricated at
regular intervals.
Grinding and squeaking from the drive shaft is
frequently caused by worn universal joints. The joints
become dry, causing the rollers to wear. The
unlubricated, damaged rollers then produce a grinding
or squeaking sound, as they operate on the scored cap
and cross surfaces.
Service to universal joints that are factory
lubricated is limited to replacement when signs of
excessive wear are present. The universal joints
provided with lubrication fittings are only lubricated
with a hand operated low-pressure grease guns. Use of
a high-pressure grease gun will damage the seals,
resulting in early failure of the universal joint.
A clunking sound, when going from acceleration
to deceleration or deceleration to acceleration, may be
caused by slip yoke problems. The splines may be worn.
The yoke transmission extension housing bushing may
also be worn. This will let the yoke move up and down
with changes in drive line torque. An excessively worn
U-joint or differential problem can also cause a similar
Another area to be concerned with when servicing
the universal joints is the slip yoke (joint). Slip yokes
may be lubricated from the transmission or lubricated
through a lubrication fitting.
A whining sound from the drive shaft is
sometimes caused by a dry, worn center support
bearing. Since this bearing makes complete revolutions.
it will make a different sound than a bad universal joint.
A high pitched. more constant, whine will usually come
from a faulty center support bearing.
Always consult the manufacturer’s service
manual for lubrication intervals and proper
lubricants to be used.
Any other abnormal sound should be traced using
your knowledge of mechanics. a stethoscope, and the
vehicles service manual troubleshooting chart.
A worn universal joint is the most common drive
line problem, causing squeaking, grinding, clunking,
or clicking sounds. The grease inside the joint can dry
out. The roller bearings will wear small indentations in
the cross. When the bearings try to roll over these
dents, a loud metal-on-metal grinding or chirp sound
can result.
Drive Shaft Inspection
To inspect the drive shaft for wear or damage, raise
the vehicle and place it on jack stands. Look for
undercoating or mud on the drive shaft. Check for
missing balance weights, cracked welds, and other
drive shaft problems.
Quite often, a worn U-joint is discovered when the
transmission is placed in REVERSE. When the vehicle
is backed up, the roller bearing is forced over the wear
indentation against normal rotation. When this occurs,
the rollers will catch on the sharp edges in the worn
joint, causing even a louder sound.
To check for working U-joints, wiggle and rotate
each U-joint back and forth. Watch the universal joint
carefully. Try to detect any play between the cross and
the yoke. If the cross moves inside the yoke, the U-joint
is worn and needs to be replaced.
universal joint may require removal and disassembly
to enable you to check the condition of the joint
Also, wiggle the slip yoke up and down. If it moves
in the transmission bushing excessively, either the
physically. Steps for the removal and disassembly of
a U-joint are as follows:
1. Raise the vehicle and place it on jack stands.
2. Scribe the alignment marks on the differential
yoke and universal joint, so drive shaft balance
is ensured upon reassembly.
3. Unbolt the rear joint from the differential. If
used, also unbolt the center support bearing. Pry
the shaft forward and lower the shaft slightly.
Do NOT allow the full weight of the drive
shaft to hang from the slip yoke. Support the
drive shaft to prevent damage to the extension
housing, rear bushing, and front U-joint.
Figure 5-11.—Universal joint removal.
Normally, a universal joint is replaced anytime it is
disassembled. However, if the joint is relatively new,
you can inspect, lubricate, and reassemble it.
4. Wrap the tape around the caps to prevent them
from falling off and spilling the roller bearings.
During the inspection, clean the roller bearings
and other parts in solvent. Then check the cross and
rollers for signs of wear. If the slightest sign of
roughness or wear is found on any part, REPLACE the
5. Slide the drive shaft out of the transmission. If
the transmission lubricant begins to leak, install
a plastic plug into the extension housing.
6. Before disassembling the universal joint,
especially constant velocity joints, scribe mark
each component. The marks will show you how
to reassemble the joint.
the U-joint has be cleaned and inspected and found to
be in a serviceable condition, it must be reassembled.
Steps for reassembling a U-joint are as follows:
7. Clamp the drive shaft yoke in a vise. Do NOT
clamp the weaker center section of the drive
shaft or it will bend. If used, remove the snap
rings, using a screwdriver, snap-ring pliers, or
needle nose pliers.
1. Pack the roller bearings in high-temperature
grease. A good method of keeping the bearing in
place is to fill the bearing cap with grease.
2. Position the cross inside the yoke. Align your
marks. Then fit the bearing caps into each end of
the yoke.
Wear safety glasses to protect your eyes in
case the snap rings fly out of the universal joint
during removal.
3. Center the cross partially into each cap to keep
the roller bearing from falling.
4. Place the assembly in a vise. Tighten the vise so
that the bearing caps are forced into the yoke.
8. Use two sockets—one LARGER than the
bearing cap and one SMALLER than the
bearing cap. Place the SMALLER socket on the
bearing cap of the universal joint (fig. 5-11). The
LARGER socket is to be placed over the outside
diameter of the bearing cap on the opposite side
of the joint (fig. 5-11).
If the bearing cap fails to press into place
with normal pressure, disassemble the joint
and check the roller bearings. It is easy for a
roller bearing to fall and block cap installation.
If you try to force the cap with excess pressure,
the universal and drive shaft could be
9. With both sockets and the universal inside the
vise, slowly tighten the vise to force the bearing
caps out of the yoke. Use the same procedure on
the remaining bearing caps, as required.
will cause boot deterioration and joint failure.
CV joint kits provide the correct type and
amount of grease required.
5. Press the caps fully into position by placing a
small socket on one bearing cap. Tighten the
vise until the cap is pushed in far enough to
install the snap ring. With one snap ring in place,
use the socket to force the other cap into
position. Install its snap ring.
After reassembling the CV joint, fit the boot over
the joint. Make sure the boot ends fit into their grooves.
Install the bootstraps. Do not overtighten the straps, as
they may cut the boot or break.
6. Repeat this procedure on the other universal
joint, if needed.
After assembly, check the action of the U-joint.
Swing it back and forth into various positions. The
joint should move freely, without binding. Doublecheck that all snap rings have been installed properly.
Once the U-joint has be checked and is working
properly, reinstall the drive shaft back into the vehicle
as follows:
Center Support Bearing Service
The center support bearing is normally
prelubricated and sealed at the factory. However, some
support bearings have lubrication fittings and require
lubrication at regular intervals. Even though
lubrication extends the useful life of the bearing, they
eventually wear out. The first indication of support
bearing failure is excessive chassis vibration at low
speed. This is caused by the bearing turning with the
drive shaft in the rubber support.
1. Wipe off the outside slip yoke and place a small
amount of grease on the internal splines. Align
the marks and slide the yoke into the rear of the
When a faulty bearing is suspected, it should be
inspected for wear and damage. If the rubber support
shows any evidence ofhardening, cracking, or tearing,
it should be replaced.
2. Push the slip yoke all the way into the extension
housing and position the rear U-joint at the
3 . Pull back on the drive shaft and center the rear
universal properly. Check your rear alignment
Should you encounter a faulty support bearing,
replacement procedures are usually limited to
separating the drive shafts, unbolting the bearing
support from the frame or cross member, and sliding
the bearing and support assembly from the shaft.
4. Install the U-bolts, bearing caps, or yoke bolts to
secure the rear universal joint.
5. With the rear universal joint secured, lower the
vehicle to the ground.
If only the bearing is available from the parts room,
disassemble the unit by gently prying the bearing out
of the rubber support. Next, remove the dust shield
from the bearing. All parts that are to be reused should
be cleaned. When the bearing is being replaced, some
manufacturers recommend that waterproof grease be
placed on both sides of the bearing, not for a lubricant
but to exclude water and dust from the bearing. Install
the dust shield and press the new bearing into the
6. Test-drive the vehicle for proper operation.
Check for unusual noises, vibration, and other
Constant Velocity Joint Service
Constant velocity joint service requires the
disassemble of the joint. Refer to the service manual
for the vehicle when servicing a CV joint. The manual
will give special detailed directions that are required
depending on the type of joint.
Once the CV joint is disassembled, obtain a CV
joint repair kit (usually includes new joint components,
grease, boot, and bootstraps). When the joint is being
assembled, refer back to the service manual for
detailed directions.
Before securing the bearing support to the frame or
cross member, check the service manual to determine
if shims are required for alignment purposes. When
reassembling support bearings, you should exercise
care to ensure that proper alignment of the drive line is
maintained. This will prevent abnormal wear of the
universal joints.
Always use the recommended type of
grease on a CV joint. The wrong type of grease
What are the four functions of a drive line
The movement of the rear axle assembly also
causes the distance between the rear axle and
transmission to change. (T/F)
When is a center support bearing needed and
Grinding or squeaking from the drive shaft is
frequently caused by
How do you check for worn universal joints?
Q6. If a universal joint fails to press together with
normal force, it is possible that one of the needle
bearings has fallen out of place. (T/F)
Figure 5-12.—Conventional differential.
Learning Objective: Identify differential design
variations. Describe the principles of the limited slip
differential. Explain basic service and repair of a
differential. Explain the adjustment of the ring and
pinion gears.
alignment. A gasket is installed between the
carrier and the housing to prevent leakage.
INTEGRAL TYPE—a carrier that is
constructed as part of the axle housing. A
stamped metal or cast aluminum cover bolts to
the rear of the carrier for inspection of the gears.
Another important unit in the power train is the
differential, which is driven by the final drive. The
differential is located between the axles and permits
one axle to turn at a different speed from that of the
other. The variations in axle speed are necessary when
a vehicle rounds a corner or travels over uneven
ground. At the same time, the differential transmits
engine torque to the drive axles. The drive axles are on
a rotational axis that is 90 degrees different than the
rotational axis of the drive shaft.
Differential Case
The differential case holds the ring gear, the spider
gears, and the inner ends of the axles. It mounts and
rotates in the carrier. Case bearings fit between the
outer ends of the differential case and the carrier.
Pinion Gear
The pinion gear turns the ring gear when the drive
shaft is rotating. The outer end of the pinion gear is
splined to the rear U-joint companion flange or yoke.
The inner end of the pinion gear meshes with the teeth
on the ring gear.
A differential assembly uses drive shaft rotation to
transfer power to the axle shafts. The term differential
can be remembered by thinking of the words different
and axle. The differential must be capable ofproviding
torque to both axles, even when they are turning at
different speeds. The differential assembly is
constructed from the following: the differential
carrier, the differential case, the pinion gear, the ring
gear, and the spider gears (fig. 5-12).
The pinion gear is mounted on tapered roller
bearings that allow the pinion gear to move freely on
the carrier. Either a crushable sleeve or shims are used
to preload the pinion gear bearings. Some differentials
use a pinion pilot bearing that supports the extreme
inner end of the pinion gear. The pinion pilot bearing
assists the tapered roller bearings in supporting the
pinion gear during periods of heavy loads.
Differential Carrier
The differential carrier provides a mounting place
for the pinion gear, the differential case, and other
differential components. There are two types of
differential carriers: the removable type and the
integral (unitized) type.
Ring Gear
The pinion gear drives the ring gear. It is bolted
securely to the differential case and has more teeth than
the pinion gear. The ring gear transfers rotating power
through an angle change or 90 degrees.
REMOVABLE TYPE—a carrier that bolts to
the front of the axle housing. Stud bolts are
installed in the housing to provide proper carrier
The ring and pinion gears are a matched set. They
are lapped (meshed and spun together with an abrasive
compound on the teeth) at the factory. Then one tooth
on each gear is marked to show the correct teeth
engagement. Lapping produces quieter operation and
assures longer gear life.
Spider Gears
The spider gears are a set of small bevel gears that
include two axle gears (differential side gears) and hvo
pinion gears (differential idler gears). The spider gears
mount inside the differential case. A pinion shaft
passes through the two pinion gears and case. The two
side gears are splined to the inner ends of the axles.
A final drive is that part of a power transmission
system between the drive shaft and the differential. Its
function is to change the direction of the power
transmitted by the drive shaft through 90 degrees to the
driving axles. At the same time. it provides a fixed
reduction between the speed of the drive shaft and the
axle driving the wheels.
The reduction or gear ratio of the final drive is
determined by dividing the number of teeth on the ring
gear by the number of teeth on the pinion gear. In
passenger vehicles, this speed reduction varies from
about 3:1 to 5:1. In trucks it varies from about 5:1 to
11:1. To calculate rear axle ratio, count the number of
teeth on each gear. Then divide the number of pinion
teeth into the number of ring gear teeth. For example, if
the pinion gear has 10 teeth and the ring gear has 30 (30
divided by 10), the rear axle ratio would be 3:1.
Manufacturers install a rear axle ratio that provides a
compromise between performance and economy. The
average passenger car ratio is 3.50:1.
differential assembly are mounted in bearings. The
bevel drive pinion is supported by two tapered roller
bearings, mounted in the differential carrier. This
pinion shaft is straddle mounted. meaning that a
bearing is located on each side of the pinion shaft teeth.
Oil seals prevent the loss of lubricant from the housing
where the pinion shaft and axle shafts protrude. As a
mechanic, you will encounter the final drive gears in
the spiral bevel and hypoid design. as shown in figure
Spiral Bevel Gear
Spiral bevel gears have curved gear teeth with the
pinion and ring gear on the same center line. This type
of final drive is used extensively in truck and
occasionally in older automobiles. This design allows
for constant contact between the ring gear and pinion.
It also necessitates the use of heavy grade lubricants.
Hypoid Gear
The hypoid gear final drive is an improvement or
variation of the spiral bevel design and is commonly
used in light and medium trucks and all domestic rearwheel drive automobiles. Hypoid gears have replaced
spiral bevel gears because they lower the hump in the
floor of the vehicle and improve gear-meshing action.
As you can see in figure 5-13, the pinion meshes
with the ring gear below the center line and is at a slight
angle (less than 90 degrees). This angle and the use of
The higher axle ratio, 4.11:1 for instance, would
increase acceleration and pulling power but would
decrease fuel economy. The engine would have to run
at a higher rpm to maintain an equal cruising speed.
The lower axle ratio. 3:1, would reduce
acceleration and pulling power but would increase fuel
mileage. The engine would run at a lower rpm while
maintaining the same speed.
The major components of the final drive include
the pinion gear, connected to the drive shaft, and a
bevel gear or ring gear that is bolted or riveted to the
differential carrier. To maintain accurate and proper
alignment and tooth contact, the ring gear and
Figure 5-13.—Types of final drives.
heavier (larger) teeth permit an increased amount of
power to be transmitted while the size of the ring gear
and housing remain constant.
reduction in most automobiles and light- and some
medium-duty trucks between the drive shaft and the
The tooth design is similar to the spiral bevel but
includes some of the characteristics of the worm gear.
This permits the reduced drive angle. The hypoid gear
teeth have a more pronounced curve and steeper angle,
resulting in larger tooth areas and more teeth to be in
contact at the same time. With more than one gear tooth
in contact, a hypoid design increases gear life and
reduces gear noise. The wiping action of the teeth
causes heavy tooth pressure that requires the use of
heavy grade lubricants.
Double-reduction final drives are used for heavyduty trucks. With this arrangement (fig. 5-14) it is not
necessary to have a large ring gear to get the necessary
gear reduction. The first gear reduction is obtained
through a pinion and ring gear as the single fixed gear
reduction final drive. Referring to figure 5-14, notice
that the secondary pinion is mounted on the primary
ring gear shaft. The second gear reduction is the result
of the secondary pinion which is rigidly attached to the
primary ring gear, driving a large helical gear which is
attached to the differential case. Double-reduction
final drives may be found on military design vehicles,
such as the 5-ton truck. Many commercially designed
vehicles of this size use a single- or double-reduction
Double-Reduction Final Drive
In the final drives shown in figure 5-13, there is a
single fixed gear reduction. This is the only gear
Figure 5-14.—Double-reduction final drive.
final drive with provisions for two speeds to be
The rear wheels of a vehicle do not always turn at
the same speed. When the vehicle is turning or when
tire diameters differ slightly, the rear wheels must
rotate at different speeds.
Two-Speed Final Drive
The two-speed or dual-ratio final drive is used to
supplement the gearing of the other drive train
components and is used in vehicles with a single drive
axle (fig. 5-15). The operator can select the range or
speed of this axle with a button on the shifting lever of
the transmission or by a lever through linkage.
If there were a solid connection between each axle
and the differential case, the tires would tend to slide,
squeal, and wear whenever the operator turned the
steering wheel of the vehicle. A differential is designed
to prevent this problem (fig. 5-16).
The two-speed final drive doubles the number of
gear ratios available for driving the vehicle under
various load and road conditions. For example, a
vehicle with a two-speed unit and a five-speed
transmission, ten different forward speeds are
available. This unit provides a gear ratio high enough
to permit pulling a heavy load up steep grades and a
low ratio to permit the vehicle to run at high speeds
with a light load or no load.
Driving Straight Ahead
When a vehicle is driving straight ahead, the ring
gear, the differential case, the differential pinion gears,
and the differential side gears turn as a unit. The two
differential pinion gears do NOT rotate on the pinion
shaft, because they exert equal force on the side gears.
As a result, the side gears turn at the same speed as the
ring gear, causing both rear wheels to turn at the same
The conventional spiral bevel pinion and ring gear
drives the two-speed unit, but a planetary gear train is
placed between the differential drive ring gear and the
differential case. The internal gear of the planetary
gear train is bolted rigidly to the bevel drive gear. A
ring on which the planetary gears are pivoted is bolted
to the differential case. A member, consisting of the
sun gear and a dog clutch, slides on one of the axle
shafts and is controlled through a button or lever
accessible to the operator.
Turning Corners
When the vehicle begins to round a curve, the
differential pinion gears rotate on the pinion shaft. This
occurs because the pinion gears must walk around the
slower turning differential side gear. Therefore, the
pinion gears carry additional rotary motion to the faster
turning outer wheel on the turn.
Differential speed is considered to be 100 percent.
The rotating action of the pinion gears carries 90
percent of this speed to the slowing mover inner wheel
and sends 110 percent of the speed to the faster rotating
outer wheel. This action allows the vehicle to make the
turn without sliding or squealing the wheels.
When in high range, the sun gear meshes with the
internal teeth on the ring carrying the planetary gears
and disengages the dog clutch from the left bearing
adjusting ring, which is rigidly held in the differential
carrier. In this position, the planetary gear train is
locked together. There is no relative motion between
the differential case and the gears in the planetary drive
train. The differential case is driven directly by the
differential ring gear, the same as in the conventional
single fixed gear final drive.
The conventional differential delivers the same
amount of torque to each rear wheel when both wheels
have equal traction. When one wheel has less traction
than the other, for example, when one wheel slips on
ice, the other wheel cannot deliver torque. All turning
effort goes to the slipping wheel. To provide good even
traction even though one wheel is slipping, a limited
slip differential is used in many vehicles. It is very
similar to the standard unit but has some means of
preventing wheel spin and loss of traction. The
standard differential delivers maximum torque to the
wheel with minimum traction. The limited slip
differential delivers maximum torque to the wheel
with maximum traction. Other names for a limited slip
When shifted into low range, the sun gear is slid
out of mesh with the ring carrying the planetary gears.
The dog clutch makes a rigid connection with the left
bearing adjusting ring. Because the sun gear is integral
with the dog clutch, it is also locked to the bearing
adjusting rings and remains stationary. The internal
gear rotates the planetary gears around the stationary
sun gear, and the differential case is driven by the ring
on which the planetary gears are pivoted. This action
produces the gear reduction, or low speed, of the axle.
Figure 5-15.—Two speed final drive.
Figure 5-16.—Differential operation.
Spring force and thrust action of the spider gears
applies the clutch pack. Under high torque conditions,
the rotation of the differential pinion gears PUSHES
OUT on the axle side gears. The axle side gears then
push on the clutch discs. This action helps lock the disc
and keeps both wheels turning.
differential are posi-traction, sure-grip, equal-lock,
and no-spin.
Clutch Pack Limited Slip Differential
The clutch pack limited slip differential (fig. 5-17)
uses a set of friction discs and steel plates to lock the
axles together whenever one drive wheel experiences
uncontrolled slippage. The friction discs are
sandwiched between the steel plates inside the
differential case. The friction disc is splined and turns
with the differential side gears. The steel plates turn
with the differential case.
However, when driving normally, the vehicle can
turn a comer without both wheels rotating at the same
speed. As the vehicle turns a comer, the inner drive
wheel must slow down. The unequal speed between
the side gears causes the side gear pinions to walk
around the side gears. This walking will cause the
outer axle shaft to rotate faster than the differential
case, allowing the pinion shaft on the side to slide
down a V-shaped ramp. This action releases the outer
clutches causing the clutch pack to slip when the
vehicle is turning.
Springs (bellville springs, coil springs, or leaf
springs) force the friction disc and steel plates
together. As a result, both rear axles try to turn with the
differential case.
Figure 5-17.—Clutch pack limited slip differential.
Cone Clutch Limited Slip Differential
end result is the majority of the engine torque is sent to
the inner drive wheel.
A cone clutch limited slip differential uses the
friction produced by cone-shaped axle gears to provide
improved traction (fig. 5-18). These cones fit behind
and are splined to the axle shafts. With the axles
splined to the cones. the axles tend to rotate with the
differential case. Coil springs are situated between the
side gears to wedge the clutches into the differential
Under rapid acceleration or when one wheel loses
traction. the differential pinion gears, as they drive the
cones, push outward on the cone gears. This action
increases friction between the cones and case, driving
the wheels with even greater torque.
When a vehicle goes around a comer, the inner
drive wheel must slow down. The unequal speed
between the side gears will cause the side gear pinions
to walk around the side gears. This walking action
causes the outer axle shaft to rotate faster than the
differential case. Because the cones have spiral
grooves cut into their clutch surfaces, the inner cone
will draw itself into the case and lock tight and the
outer cone clutch will back itself out of the case. This
action allows the outer drive axle to free wheel. The
Differentials in a properly operated vehicle seldom
cause any maintenance problems. By maintaining the
proper lubrication level and occasionally changing a
seal or gasket, the assembly will normally last as long
as the vehicle.
The first hint of existing trouble is generally an
unusual noise in the axle housing. To diagnose the
trouble properly, you must determine the source of the
noise and under what operating conditions the noise is
most pronounced. Defective universal joints, rough
wheel bearings, or tire noises may be improperly
diagnosed by an inexperienced mechanic as
differential trouble.
Some clue may be gained as to the cause of trouble
by noting whether the noise is a growl, hum, or knock;
whether it is heard when the vehicle is operating on a
straight road, or on turns only; and whether the noise is
most noticeable when the engine is driving the vehicle
or when it is coasting with the vehicle driving the
Figure 5-18.—Cone clutch limited slip differential.
A humming noise in the differential generally
means the ring gear or pinion needs an adjustment. An
improperly adjusted ring gear or pinion prevents
normal tooth contact between the gears and therefore
produces rapid tooth wear. If the trouble is not
corrected immediately, the humming noise will
gradually take on a growling sound, and the ring and
pinion will probably have to be replaced.
differentials require the removal of the inspection
cover to drain the lubricant. With all the fluid drained,
replace the drain plug or inspection cover and refill
with the proper lubricant.
Always install the correct type of
differential lubricant. Limited slip differentials
often require a special type of lubricant for the
friction clutches.
It is very easy to mistake tire noise for differential
noise. Tire noise will vary according to the type of
pavement the vehicle is being operated on, while
differential noise will not. To confirm a doubt as to
whether the noise is caused by tire or differential, drive
the vehicle over various pavement surfaces. If the
noise is present in the differential only when the
vehicle is rounding a comer, the trouble is likely to be
in the differential case.
Differential Removal, Disassembly,
and Reassembly
Procedures for removal, disassembly, and
reassembly vary depending on the type of differential,
make, and model. Always refer to the manufacturer’s
service manual. However, there are several procedures
that relate to almost any type of differential.
If the backlash (clearance) between the ring and
pinion is too great, a CLUNKING sound is produced
by the gears. For example, when an automatic
transmission is shifted into drive, the abrupt rotation of
the drive shaft can bring the gears together with a loud
To remove a separate carrier differential, perform
the following:
Remove the drive shaft.
The ring and pinion gears can become worn,
scored, out of adjustment, or damaged. The problems
can result from prolonged service, fatigue, and from
lack of lubricant. You need to inspect the differential to
determine whether adjustment or part replacement is
Place a drain pan under the differential. Remove
the drain plug and drain the lubricant.
Unbolt the nuts around the outside of the carrier.
Force the differential carrier away from the
A differential identification (ID) number is
provided to show the exact type of differential for
ordering parts and looking up specifications. The
number may be on a tag under one of the carrier or
inspection cover bolts; it also may be stamped on the
housing or carrier. Use the ID number to find the axle
type, axle ratio, make of the unit, and other information
located in the service manual.
A differential can be surprisingly heavy.
Grasp it securely during removal. If the
differential is dropped, painful injuries can
To remove an integral differential, perform the
Remove the drive shaft.
Differential Lubricant Service
Place a drain pan under the differential. Remove
the inspection cover and drain the lubricant.
Many vehicle manufacturers recommend that the
differential fluid be checked and replaced at specific
intervals. To check the fluid level in a differential,
remove the filler plug, which is located either in the
front or rear of the assembly. The lubricant should be
even with the fill hole when hot and slightly below the
hole when cold.
With the cover off, inspect and MARK the
individual components as they are removed.
The procedure for repairing a differential will vary
with the particular unit. Always refer to the service
manual. When using a service to repair a differential,
remember the following:
When the manufacturer recommends that the
differential fluid be replaced, remove the drain plug
located on the bottom of the differential housing. Some
Check for markings before disassembly. The
carrier caps, adjustment nuts, shims, ring and
This will match the proper teeth that have been
lapped together at the factory.
pinion, spider gears, and pinion yoke or flange
should be installed exactly as they were
removed. If needed. punch mark, label, or scribe
these components so they can be reassembled
Torque all fasteners to specifications. Refer to
the service manual for torque values.
Use new gaskets and/or approved sealer.
Clean all parts carefully and inspect them closely
for damage.
Align all markings during reassembly. If you
install the carrier caps backwards, for example,
the caps can crush and damage the bearing and
races. The differential could fail soon after it is
returned to service.
Rotate the pinion and case bearing by hand while
checking for roughness. Inspect each bearing
and race. Replace the bearing and race as a set if
Use the service manual for detailed directions.
Differential designs and repair procedures vary.
Special tools and methods are frequently
If the pinion gear has a collapsible spacer (device
for preloading the pinion bearings), always
replace. it.
To avoid seal damage, use a seal driver. Coat the
outside of the seal with a nonhardening sealer.
Lubricate the inside of the seal using the proper
grade of differential fluid. Make sure the seal lip
faces the inside of the differential.
Differential Measurements and Adjustments
Several measurements and adjustments are made
when assembling a differential. When “setting up”
(measuring and adjusting) a differential. correct
bearing preloads and gear clearances are extremely
critical. The most important differential measurements
and adjustments (fig. 5-19) include the following:
When tightening the pinion yoke nut, clamp the
yoke in a vise or use a special holding bar.
Replace the ring and pinion gears as a set. Mesh
and align the gear timing marks (painted lines or
other markings) on the ring and pinion gears.
1. Pinion gear depth
Figure 5-19.—Pinion and ring gear adjustments.
RING GEAR RUNOUT.—The ring gear runout
is the amount of wobble or side-to-side movement
produced when the ring gear is rotated. Ring gear
runout must not be beyond the manufacturer’s
2. Pinion bearing preload
3. Case bearing preload
4. Ring gear runout
5. Ring and pinion backlash
To measure ring gear runout, mount a dial
indicator against the back of the ring gear (fig. 5-20).
The indicator stem should be perpendicular to the ring
gear surface. Then turn the ring gear and note the
indicator reading. If the ring gear is within
specifications, locate a position on the ring gear that
indicates ONE HALF of the maximum runout on the
gauge. Mark the gear at that point. Then rotate the ring
gear until the teeth on the opposite side of the gear from
the mark are in mesh with the pinion gear.
6. Ring and pinion contact pattern
PINION GEAR DEPTH.—The pinion gear
depth refers to the distance the pinion gear extends into
the carrier. Pinion depth affects where the pinion gear
teeth meshes with the ring gear teeth. Pinion gear depth
is commonly adjusted by varying shim thickness on
the pinion gear and bearing assembly.
bearing preload is frequently adjusted by torquing the
pinion nut to compress a collapsible spacer. The more
the pinion nut is torqued, the more the spacer will
compress to increase the preload or tightness of the
If ring gear runout is excessive, check the ring gear
mounting and differential case runout. If not a
mounting problem, replace either the ring gear and
pinion or the case as needed.
With a collapsible spacer, only tighten the pinion
nut in small increments. Then measure the pinion
preload by turning the pinion nut with an inch-pound
torque wrench.
and pinion backlash refers to the amount of space
between the meshing teeth of the gears. Backlash is
needed to allow for heat expansion
When a solid spacer and pinion nut are used, shims
control pinion bearing preload. The pinion nut is
torqued to a specific value found in the service manual.
As the gears operate, they produce friction and
heat. This makes the gears expand, reducing the
clearance between the meshing teeth of the gears.
Without backlash, the ring and pinion teeth can jam
into each other and fail in a very short period of time.
However, too much ring and pinion backlash can cause
gear noise (whirring, roaring, or clunking).
To set pinion bearing preload, use a holding tool to
keep the pinion gear stationary. Then a breaker bar or
torque wrench can be used to tighten the pinion nut.
bearing preload is the amount of force pushing the
differential case bearings together. As with pinion
bearing preload, it is critical.
If preload is too low (bearings too loose),
differential case movement and ring and pinion gear
noise can result. If preload is too high (bearings too
tight), bearing overheating and failure can result.
When adjusting nuts are used, the nuts are
typically tightened until all of the play is out of the
bearings. Then each nut is tightened a specific portion
of a turn to preload the bearings. This is done when
adjusting backlash.
When shims are used, a feeler gauge is used to
check side clearance between the case bearing and the
carrier. This action will let you calculate the correct
shim thickness to preload the case bearings. Refer to
the service manual for special equipment and
Figure 5-20.—Measuring ring gear runout.
Note the names of the areas on the ring gear. These
include the following:
To measure ring and pinion backlash, position a
dial indicator stem on one of the ring gear teeth. Then,
while holding the pinion gear STATIONARY, wiggle
the ring gear back and forth. Indicator needle
movement will equal gear backlash. Compare your
measurements to the manufacturer’s specifications and
adjust as needed.
TOE (narrow part of the gear tooth)
HEEL (wide part of the gear tooth)
DRIVE SIDE (convex side of the gear tooth)
COAST SIDE (concave side of the gear tooth)
Backlash adjustment can be made by adjusting
nuts or by moving shims from one side to the other. To
increase backlash, move the ring gear away from the
pinion gear. To decrease backlash, move the ring gear
towards the pinion gear.
When used gears are adjusted properly, the contact
pattern will vary from that of new gears. The important
thing to keep in mind with used gears is that the pattern
should be closer to the toe than the heel of the tooth, as
shown in figure 5-21. Notice that the ideal tooth pattern
on new teeth is uniform on both sides, whereas the used
gear indicates considerably more contact on the
coasting side.
PATTERN.—The ring and pinion tooth contact
pattern is used to double-check ring and pinion
Once you have obtained the proper adjustment on
the ring and pinion, bolt the carrier housing in place.
Make sure you use a new gasket. Tighten the bolts
according to the manufacturer’s specifications to
prevent them from working loose. Reinstall the axle
shafts and new gaskets. Reconnect the drive shaft and
fill the axle housing with the proper lubricant.
To check the accuracy of your adjustments, coat
the ring gear teeth with a thin coat of red lead, white
grease, hydrated ferric oxide (yellow oxide or iron), or
Prussian blue. Turn the ring gear one way and then the
other to rub the teeth together, producing a contact
pattern on the teeth. Carefully note the contact pattern
that shows up on the teeth where the substance used has
been wiped off.
A good contact pattern is one located in the center
of the gear teeth (fig. 5-21). Figure 5-21 shows several
ring and pinion gear contact patterns. Study each and
note the suggested correction for the faulty contact.
must be capable of
Q1. The
providing torque to both axles when turning
Figure 5-21.—Tooth contact patterns.
The shaft in a live axle assembly may or may not
actually support part of the weight of a vehicle, but it
does drive the wheels connected to it. A live axle is
involved with steering when it is a front drive axle.
Some live rear axles are also designed to steer. The rear
axle of conventional passenger vehicles is a live axle,
while in a four-wheel drive vehicle both front and rear
axles are live. In some six-wheel vehicles, all three
axles are live axles.
Q2. An integral carrier is constructed as part of the
axle housing. (T/F)
Rear axle ratio is determined by comparing the
number of teeth on the
to the
number of teeth on the
Excess ring and pinion backlash can cause a
"clunking" s o u n d w h e n a n a u t o m a t i c
transmission is placed in drive. True/False
often require a
lubricant that is compatible with friction
The axle housing may be of the one-piece or split
(banjo) type construction. The former, known as the
banjo type because of its appearance, is far more
common (fig. 5-22). Notice that openings, both front
and rear, are provided in the center housing. The front
opening is closed by the differential carrier, while the
rear is closed by a spherical cover plate.
Q6. Ring and pinion preload is a common
differential adjustment. (T/F)
Learning Objective: Identify the parts of the rear drive
axle and front drive axle. List the function of the rear
axle. Compare the different types of axles. Describe the
procedures for replacing axle bearings and seals.
Since the assembly must carry the weight of the
vehicle, the axle housing in heavy trucks and tractors is
a heavy cast unit. In light-duty trucks it may be a
combination of cast and steel tube; in general, the
center or differential and final drive case is a cast and
machined unit, whereas the axle housings themselves
may be welded or extruded steel tubing.
Axles are classified as either LIVE or DEAD. The
live axle is used to transmit power. The dead axle only
serves as a support for part of the vehicle while
providing a mounting for the wheel assembly. Many
commercial trucks and truck-tractors have dead axles
on the front, whereas practically all passenger vehicles
use independent front-wheel suspensions and have no
front axles.
Items, such as brake backing plates, mounting
flanges, spring mounting plates, and accessory units,
may be riveted, welded, or cast into the axle housing.
Inspection covers are often provided through which
Figure 5-22.—Axle assembly.
the internal parts can be inspected, removed, and
installed. Lubricant filler plugs are usually
incorporated in the housing inspection cover.
To prevent pressure buildup when the axle
becomes warm, a breather vent or valve is provided
atop the housing. Without this valve, the resulting
pressure could force the axle lubricant past the rear
wheel oil seals and damage the brake linings. The
valve is constructed so air may pass in or out of the axle
housing; however, dirt and moisture are kept out.
The rear drive axle connects the differential side
gears to the drive wheels. The axle may or may not
support the weight of the vehicle. Rear axles are
normally induction hardened for increased strength.
There are several types of rear axle designs:
semifloating, three-quarter floating, and full floating.
However the semi- and full-floating types are the most
common. Most automobiles use the semifloating type,
whereas four-wheel drive vehicles and trucks use full
floating axles.
Semifloating Axle
Figure 5-23.—Semifloating axle installation.
The semifloating axle is used in passenger vehicles
and light trucks. In vehicles equipped with this type of
axle, the shaft, as well as the housing, supports the
weight of the vehicle. The inner end of the axle is
carried by the side gears in the differential housing.
This relieves the axle shafts of the weight of the
differential and the stresses caused by its operation that
are taken by the axle housing. The inner ends of the
axle transmit only turning effort, or torque, and are not
acted upon by any other force.
Full-Floating Axle
The full-floating axle (fig. 5-24) is used in many
heavy-duty trucks. The drive wheel is carried on the
outer end of the axle housing by a pair of tapered roller
bearings. The bearings are located outside the axle
housing. In this way, the axle housings take the full
weight of the vehicle and absorb all stresses or end
thrust caused by turning, skidding, and pulling. Only
the axle shaft transmits torque from the differential.
The outer end is carried by a bearing located
between the shaft and the housing. A tapered roller of
ball-type bearing transfers the load from the shaft to
the housing. The axle shafts take the stresses caused by
turning, skidding, or wobbling of the wheels.
The axle shafts (fig. 5-23) are flanged or tapered on
the ends. When the tapered axle is used, the brake drum
and hub are pressed onto the shafts, using keys to
prevent the assemblies from turning on the shafts. In
some cases, the outer ends of the shafts may have
serrations or splines to correspond with those on the
drum and hub assembly. Should the axle break with
this type of axle assembly, the wheel can separate from
the vehicle.
Figure 5-24.—Full-floating axle shaft.
The axle shaft is connected to the drive wheel
through a bolted flange. This allows the axle shaft to be
removed for servicing without removing the wheel.
engine oil pan and maintain sufficient road clearance
without excessive height at the front end of the vehicle.
Since the front wheels must turn on the spindle arm
pivots, they must be driven by the axle shaft through
universal joints, which are located on the outer ends of
the axles. The universal joints allow the front wheels
and hubs to swivel while still transferring driving
power to the hubs and wheels.
A front drive axle (fig. 5-25) is very similar to a
rear drive axle; however, provisions must be made for
steering the front wheels. Power is transmitted from
the transfer case to the front axle by a drive shaft. The
differential housing may be set off center in the axle
housing to permit the drive shaft to pass beside the
The cross and roller joint shown in figure 5-25 is
similar to conventional U-joints used on the rear drive
shaft, and, in some cases, they are interchangeable.
Figure 5-25.—Front drive axle.
This type of U-joint is limited to use in light-duty,
vehicles. Other types of universal joints are used in the
axles of heavy-duty vehicles. The types you will
encounter in military designed vehicles are the Rzeppa
and Bendix-Weiss constant velocity joints (fig. 5-26).
The front drive axle of a four-wheel drive axle
requires locking hubs. Locking hubs transfer power
from the driving axles to the driving wheels on a fourwheel drive vehicle. There are three basic types of
locking hubs, which are as follows:
operator to turn a latch on the hub to lock the hub
for four-wheel drive action.
the front wheels to the axles when the operator
shifts into four-wheel drive.
FULL TIME HUB—front hubs are always
locked and drive the front wheels.
Figure 5-26.—Constant velocity universal joints.
Manual and automatic locking hubs are the most
common. Used with part-time, four-wheel drive. they
enable the drive line to be in two-wheel drive for use on
dry pavement. The front wheels can turn without
turning the front axles. This allows for increased fuel
economy and reduces drive line wear.
assembly. The inner CV joint is called a PLUNGING
(sliding) ball and housing or tripod-type joint that acts
like a slip joint in a drive shaft for a rear-wheel drive
The plunging action of the inner CV joint allows
for a change in distance between the transaxle and the
wheel hub. As the front wheels move up and down over
bumps in the road, the length of the drive axle (inner
joint) must change.
Front-wheel drive axles, also called axle shafts or
front drive shafts, transfer power from the transaxle
differential to the hubs and wheel of a vehicle. Frontwheel drive axles turn much slower than a drive shaft
for a rear-wheel drive vehicle. They turn about one
third slower. They are connected directly to the drive
wheels and do NOT have to act through the reduction
of the axle ring gear and pinion gears.
Rear axle service is needed when an axle bearing is
noisy, when an axle is broken, bent, or damaged, or
when an axle seal is leaking. The rear axles must be
removed to allow removal and repair of the differential
Front-wheel drive axles typically consists of the
INNER STUB SHAFT—the short shaft splined
to the side gears in the differential and connected
to the inner universal joint.
Axle Bearing Service
Worn or damaged bearings in the carrier or on the
axles produce a CONSTANT whirring or humming
sound. These bearings, when bad, make about the same
sound whether accelerating, decelerating, or coasting.
When diagnosing and repairing bearing failures, do the
OUTER STUB SHAFT—the short shaft
connected to the outer universal joint and the
front-wheel hub.
shaft that fits between the two universal joints.
Universal joints that connect the drive axle are
called CV joints. The outer CV joint is a FIXED
(nonsliding) ball and cage or Rzeppa-type joint that
transfers rotating power from the axle shaft to the hub
Check the general condition of all parts during
disassembly,, not just the most badly worn or
damaged parts.
Compare the failure to any added information in
the service manual and your knowledge of the
components operation.
Wear eye and face protection when
grinding or chiseling the collar from the axle.
Small metal particles may fly into your eyes
causing eye damage.
Determine the cause of the part failure. This
helps in assuring that the problems do NOT
Perform all repairs following the manufacturer’s
recommendations and specifications.
NEVER press on the outer race; bearing
damage or explosion will result.
When an axle bearing is faulty, it must be removed
from the axle or housing carefully and a new one
installed. Depending on the type of axle configuration
determines how the bearing is to be removed and
replaced. Always refer to the manufacturer's service
manual for instructions for the removal and
installation of the bearing.
Wear face and eye protection when
pressing a bearing on or off the axle shaft. The
tremendous pressure used can cause the
bearing to shatter and fly into your face with
deadly force.
The procedures we will discuss are for a
semifloating axle with the bearing and collar pressed
on. With the axle removed from the vehicle, proceed as
Do NOT attempt to press the bearing and
collar on at the same time. Bearing and collar
damage can result.
Axle Seal Service
Procedures for axle removal may be found
in the service manual for the applicable
Rear axle lubricant leaks can occur at numerous
spots, such as the pinion gear seal, carrier or inspection
cover gaskets, and at the two axle seals. The leak will
show up as a darkened, oily, dirty area below the pinion
gear, carrier, or on the inside of the wheel and brake
1. Carefully cut off the collar with a grinder and a
sharp chisel.
2. With the collar off, place the axle in a
hydraulic press. The driving tool should be
positioned so that it contacts the inner bearing
race. Use the press to push the axle through the
Always make sure that a possible axle seal leak is
not a brake fluid leak. Touch and smell the wet area to
determine the type of leak.
Anytime the axle is removed for service, it is wise
to install a new axle seal. This action ensures that the
seal between the axle and axle seal is tight. The axle
seal is normally force-fitted in the end of the axle
3. To install the new bearing, slide the bearing onto
the axle. Make sure that the bearing is facing the
right direction. Some bearings have a chamfered
edge on the inner bearing race, which must face
the axle flange.
To remove a housing mounted seal, use a slide
hammer puller equipped with a hooknose. Place the
hook on the metal part of the seal. With an outward jerk
on the puller slide, pop out the seal. If a slide hammer
puller is not available, a large screwdriver will also
4. Applying force on the inner bearing race, press
the bearing into place by pressing the axle back
through the bearing. Then press the collar or
retaining ring onto the axle.
Do NOT use a cutting torch to remove the
collar and bearing. The heat will weaken and
damage the axle.
Be careful not to scratch the bearing bore
in the axle housing.
Make sure that you have the correct new seal. Its
outside and inside diameters must be the same as the
old seal. A seal part number is stamped on the outside
Learning Objective: Explain the operation of a
transfer case. Explain basic service operations on a
transfer case.
of the seal. This number and the seal manufacturer’s
name will assist you when ordering a new seal.
Before installing the new seal, coat the outer
diameter with a non-hardening sealer. Coat the inside
of the seal with lubricant that is the same grade that is in
the axle assembly. With the seal facing in the right
direction (sealing lip towards inside of the housing),
drive the seal squarely into place, using a seal-driving
tool. Be careful not to bend the metal seal housing or a
leak can result. Make sure the seal is fully seated.
What component prevents pressure from
building up inside the axle housing?
What type of axle only transmits torque from the
differential and carries no vehicle weight?
What two types of CV joints are used on
front-wheel drive vehicles?
Worn and damaged axle bearings produce what
type of sound(s)?
What tool is used to remove a housing mounted
Transfer cases are used in off-road vehicles to
divide engine torque between the front and rear driving
axles. The transfer case also allows the front driving
axle to be disengaged, which is necessary to prevent
undue drive line component wear during highway use.
Another purpose of the transfer case is to move the
drive shaft for the front driving axle off to the side so
that it can clear the engine. This arrangement is
necessary to allow adequate ground clearance and to
allow the body of the vehicle to remain at a practical
height. Figure 5-27 shows a typical drive line
arrangement with a transfer case.
A conventional transfer case is constructed similar
to a transmission, in that it uses shift forks, splines,
gears, shims, bearings, and other components found in
manual and automatic transmissions. The transfer case
has an outer case made of either cast iron or aluminum
that is filled with a lubricant that cuts friction on all
moving parts. Seals hold the lubricant in the case and
prevent leakage from around the shafts and yokes.
Shims are used to set up the proper clearances between
the internal components and the case.
Figure 5-27.—Typical drive line arrangement with a transfer case.
Conventional transfer cases in heavier vehicles
have two-speed positions and a de-clutching device for
disconnecting the front-driving wheels. A cross
section of a conventional two-speed transfer case is
shown in figure 5-28. This type of transfer case is used
for a six-wheel drive vehicle. Some light-duty vehicles
use a chain to transmit torque to the front-driving axle
(fig. 5-29).
The conventional transfer case provides a high and
low final drive gear range in the same manner as an
auxiliary transmission. In most cases, the shifting is
accomplished through a sliding dog clutch, and
shifting must be done while the vehicle is not moving.
Typical operation of a conventional two-speed transfer
case is as follows:
High Range (fig. 5-30)—When driving the
front and rear axles in the high range (1:1 gear
ratio), the external teeth of the sliding gear
Figure 5-29.—Typical conventional transfer case using chain
Figure 5-28.—Cross-section of a typical conventional transfer case.
Figure 5-30.—Transfer case power flow.
engaged. Disengagement of the drive to the front
axle is accomplished by shifting the sliding gear
on the front axle main shaft out of mesh with the
constant mesh gear, permitting the latter to roll
free on the shaft or sliding the clutches out of
(splined to the transmission main shaft) are in
mesh with the internal teeth on the constant mesh
gear, mounted on the transmission main shaft.
Likewise, the external teeth of the front axle
sliding gear are in mesh with the internal teeth of
the constant mesh gear or the sliding clutches are
Low Range (fig. 5-29)—When using the low
range in the transfer case, the sliding gear on the
transmission main shaft is disengaged from the
constant mesh gear and engaged with the idler
gear on the idler shaft. This design reduces the
speed by having the sliding gear mesh with the
larger idler gear. The shifting linkage on some
vehicles is arranged so shifting into low range is
possible only when the drive to the front axle is
engaged. This design prevents the operator from
applying maximum torque to the rear drive only,
which can cause damage.
The positive traction transfer case is very similar to
the conventional transfer case—the basic difference
being that a sprag unit has been substituted for the
hand-operated sliding clutch on the front output shaft.
A sprag unit is a steel block shaped to act as a
wedge in the complete assembly. In the sprag unit there
are 42 sprags assembled into an outer race and held into
place by two energizing springs (fig. 5-31). The
springs fit into notches in the ends of the sprags and
hold them in position. The outer race is the driven gear
on the front output shaft. The inner race is on the front
output shaft itself.
On these units, the transfer case is designed to
drive the front axle slightly slower than the rear axle.
During normal operation, when both front and rear
wheels of the vehicle are turning at the same speed, the
outer race of the sprag unit (in the driven gear) turns
slower than the inner race (on the output shaft). This
design prevents the sprags from wedging between the
races. No lockup occurs and the front wheels turn
freely; they are not driven (fig. 5-32). However, if the
rear wheels should lose traction and begin to slip, they
tend to turn faster than the front wheels; the outer race
tends to turn faster than the inner race. When this
happens, the sprags wedge or jam between the two
races and the races turn as a unit to provide power to the
front wheels (fig. 5-32).
Figure 5-31 .—Transfer case sprag unit.
lubricant should be almost even with the fill hole. If
required, add the recommended type and amount.
The fluid level in a transfer case should be checked
at recommended intervals. To check the lubricant
level, remove the transfer case fill plug, which is
normally located on the side or rear of the case. The
The first indication of trouble within a transfer
case, as with other components of the power train, is
usually noisy operation. If an operator reports trouble,
make a visual inspection before removing the unit
Figure 5-32.—Positive traction transfer case operation.
from the vehicle. Check for such things as oil level, oil
leakage, and water in the oil.
Make sure the shift lever linkages are not bent or
improperly, lubricated. This will make it hard to shift
or, in some cases, impossible to shift. Make sure other
possible troubles, such as clutch slippage, damaged
drive shaft, and damaged axles, have been eliminated.
Worn or broken gears, worn bearings, and
excessive end play in the shafts can cause noisy
operation. When transfer case service is required,
follow the procedures outlined in the service manual. It
will give directions for repairing the particular make
and model.
Q1. What is the gear ratio when a conventional
transfer case is in high range?
What component in a positive traction transfer
case provides power to the front wheels when the
rear wheel begins to slip?
Learning Objective: Explain the operation of a power
takeoff unit.
A power takeoff (PTO) is an attachment for
connecting the engine to power-driven auxiliary
equipment. It is attached to the transmission, auxiliary
transmission. or transfer case. A power takeoff
installed at the left side of a transmission is shown in
figure 5-33. It is used to drive a winch at the front of a
truck through a universal joint and drive shaft.
The simplest type of power takeoff is the
single-speed, single-gear shown in figure 5-34. This
unit may be bolted to an opening provided in the side of
a transmission, as shown in figure 5-35.
Shims or spacers are often used to ensure proper
contact is maintained between the teeth of the two
meshing units. The sliding gear of the PTO can then
mesh with, and be driven by, the countershaft gear of
the transmission or the auxiliary transmission when
engaged by the operator. The operator, by the use of a
control lever, can move the gear in and out of mesh
with the transmission gear. A spring-loaded ball
(poppet) holds the shifter shaft in position.
On some vehicles you will find PTOs with gear
arrangements that give you two speeds forward and
one in reverse. Several forward speeds and a reverse
gear are usually provided in a PTO unit used to operate
a winch or hoist. Operation of this type of PTO is
similar to that of the single-speed unit.
Faulty operation of a PTO is caused by damaged or
broken linkage. To prevent this, exercise care when
shifting. Trying to engage the unit with the
transmission gears turning can damage the teeth, and
rapid clutch engagement can break the housing. Rapid
shifting may bend or damage the linkage. Forcing the
control lever can bend or break the linkage.
Figure 5-33.—Power takeoff and winch installation.
Figure 5-34.—Single-speed, single-gear power takeoff.
Adjustment of the linkage to compensate for wear
and lubrication is normally all the maintenance
required for the PTO unit. The gears and bearings are
lubricated from the transmission sump.
If the PTO is to be removed for repairs. disconnect
the drive shaft and shift linkage and drain the
transmission. Once the transmission is completely
drained, remove the bolts that secure the unit to the
transmission. DO NOT misplace or lose any shims or
spacers that are between the two housings. Once the unit
is removed from the vehicle, the inspection and repair
procedures are the same as for a transmission. When
reinstalling or replacing the PTO, carefully follow the
manufacturer’s procedures on the installation shims or
spacers to prevent damage or unit failure.
Q1. What is the simplest type of power takeoff
Figure 5-35.—Single-speed, single-gear power takeoff
To send turning power from the transmission to the rear axle assembly, flex
and allow up and down movement of the rear axle assembly, provide a sliding
action to adjust for changes in drive line length, andprovide smooth power
Q2. True
To maintain alignment of two or more drive shafts when connected in tandem
Worn universal joint
Wiggle and rotate the universal joint back and forth
Q6. True
Q1. Differential
Pinion gear, ring gear
Q5. Limited slip differential
Breather vent
Q2. Full-floating axle
Q3. Rzeppa and Bendix- Weiss
Constant whirring or humming sound
Slide-hammer puller
Sprag unit
Q1. Single-speed single-gear
modern construction equipment are the mechanical
and the hydrostatic drive trains.
Learning Objective: Identify the operational
characteristics and components of drive trains, track
assemblies, and track frames that are common to
construction equipment power trains. Describe the
operation of a winch. Identify the characteristics and
maintenance of wire rope.
The mechanical drive train found in construction
equipment is similar to that of the automatic
transmission in that a transmission is used in
conjunction with a torque converter and shifting is
accomplished hydraulically when the operator moves
the range selector lever.
The construction equipment used by the Navy are
equipped with power trains that are similar in many
ways to the automotive vehicle power trains described
in chapters 4 and 5. However, factors, such as size,
weight, design, and use, of the construction equipment
require power trains that vary greatly in configuration.
Power Shift Transmission
The power shift transmission (fig. 6-1) uses a
torque converter and is designed to provide high-speed
shifting through hydraulically actuated clutches. The
transmission has two forward and two reverse speeds
in both high and low ranges. The hi-lo shifting lever
mounted on the transmission front cover controls
shifting from one range to another.
Learning Objective: Identify the operational
characteristics and components of construction
equipment drive trams.
There are numerous types of equipment used in
construction, from crawler tractors to excavators.
However, the way power is distributed varies from
piece to piece. The most common drive trains used in
The principles of a torque converter are
presented in chapter 4 of this TRAMAN.
Figure 6-1.—Power shift transmission.
The power shift transmission is coupled to the
torque converter by a universal joint. Gears are
mounted in the power shift transmission on four shafts,
which are as follows:
The SPLINE SHAFT (fig. 6-4) rotates on two
straight roller bearings. The rear bearing is
mounted in the transmission case; the front
bearing is mounted in the transmission cover.
The first and second driven gears are held in
position on the spindle by snap rings and are
constantly meshed with the first and second
speed drive gears on the clutch shafts. The hi-lo
driving gear slides freely on the shaft and drives
the bevel pinion shaft when brought into mesh
with either the high or low range driven gear by
means of the hi-lo shifting lever.
The REVERSE CLUTCH SHAFT (fig. 6-2) has
a straight roller bearing at each end, with the
reverse driven gear keyed to the front of the
shaft. The shaft consists of first and second speed
drive gears riding on bushings and is welded to
the dual hydraulic clutch pack assemblies.
rotates on straight roller bearings at the rear and
ball bearings at the front, with the reverse drive
gear keyed to the front of the shaft. As with the
reverse clutch shaft. the forward clutch shaft
consists of first and second speed drive gears
riding on bushings and is welded to the dual
hydraulic clutch pack assemblies.
The BEVEL PINION SHAFT (fig. 6-5) consists
of the high and low range gears, which are keyed
to the shaft. The shaft is supported at the rear by a
straight roller bearing, and, at the front, by a
double-row taper roller bearing. The pinion gear
is splined to the rear of the pinion shaft and is
held in place by a nut. A shim pack is provided
between the front bearing cage and the
transmission case front cover for adjusting
pinion depth.
Figure 6-2.—Reverse clutch shaft.
Figure 6-4.—Spline shaft.
Figure 6-5.—Bevel pinion shaft.
Figure 6-3.—Forward clutch shaft.
drive gear bushing, the drum assemblies, and the
clutch hubs for distribution through the clutch plates.
In neutral, neither clutch is engaged, the drive gear and
drum assemblies are free. and no torque is transmitted
through the clutch, as shown in figure 6-6.
CLUTCH OPERATION.—The forward and reverse
hydraulic clutches actually have two clutches on a
common shaft with a common apply force piston
between them. The clutches allow the simple transfer
of oil from the disengaging clutch into a cavity created
by the engaging clutch. This allows a low volume of
main pressure to actuate the clutch for high-speed
Upon application of the clutch, main oil pressure
(approximately 200 to 300 psi) is directed through the
clutch shaft for the specific side of the clutch desired.
The oil enters the force piston cavity causing the clutch
to engage (fig. 6-7). When engaged, the clutch holds
the gear stationary in relation to the shaft. Power then
flows from the shaft, via the clutch, to the gear.
The heart of the clutch is contained in two
pistons—the accelerator piston and the force piston.
Pump oil volume is not needed to fill the applying
clutch cavity, and only relatively low volume is needed
to pressurize the clutch. In neutral, all accelerator and
force piston cavities are filled with oil at lube pressure
(10 to 25 psi). A selector valve, located on the top of the
transmission case, directs the oil to the accelerator
piston cavity and, in turn, to the force piston cavity.
Once the pistons are filled with oil, they remain full
under lube pressure. Other small cross-drilled
passages furnish a constant supply of lube oil to the
When the transmission is returned to neutral, an
immediate pressure drop occurs within the
disengaging accelerator piston cavity and the
compressed piston centering springs return the
common apply force piston to its centered position or
older models, the gearshift lever is connected through
Figure 6-6.—Flow of oil through the clutch in NEUTRAL position.
Figure 6-7.—Flow of oil through the clutch in ENGAGED position.
proper relation with the sun and ring gear. The
planetary gears are free to "walk" around the sun gear
or inside the ring gear.
linkage to the range selector valve assembly on top of
the transmission case. Movement of the gearshift lever
positions the selector valve to allow main oil pressure
to engage the desired clutch assembly.
To cause a reduction or increase in torque, six
different methods of connecting this gearset to the
power train are possible (fig. 6-9). Direct drive is
achieved by locking any two members together. and
neutral is obtained by allowing all the gears to turn
In modern power shift transmissions, the gearshift
lever is connected to a range selector valve by
hydraulic means. A spool valve (pilot control valve),
actuated by the gearshift lever, directs main oil
pressure to the range selector valve and causes it to
direct main oil pressure to the desired clutch assembly.
The hi-lo-shifting lever (on the transmission front
cover) is held in position by a poppet lock in the hi-lo
shifting housing. To shift from one range to another,
the engine must be running and the gearshift lever must
be in NEUTRAL position. This allows main oil
pressure from the pump to pass through a drilled hole
in the pilot valve and through an oil line to the shifter
housing. Here it releases the poppet lock to enable
Planetary Gearsets
Some power shift transmissions use planetary
gearsets to perform the same functions as the
transmission just described. A planetary gearset (fig.
6-8) consist of three members—sun gear, ring gear,
and a planetary carrier that holds the planetary gears in
Figure 6-8.—Planetary gearset.
Figure 6-9.—Planetary gear arrangements that will provide an increase or decrease in speed.
in the stationary ring gear and move the carrier in the
same direction of rotation as the sun gear. The carrier is
connected to the hub on which the sprocket is mounted,
causing it to rotate with the carrier. This arrangement
produces the maximum torque and speed reduction
obtainable from a planetary gearset.
In figure 6-9 notice the direction of rotation as
power is applied to the various members and others are
stationary. In actual application, planetary gearsets are
used as single or multiple units, depending on the
number of speed (gear) ranges desired.
On tracked equipment, power for turning the drive
sprockets may flow through a planetary gear
arrangement that provides maximum reduction (fig.
6-9). The sun gear forces the planetary gears to revolve
Planetary Steering
Some tracked equipment may be steered by a
system that combines planetary steering and pivot
brakes. The planetary steering system (fig. 6-10)
differs from the one previously described in that the
planetary pinion gears are two gears of different sizes,
machined into one piece. Two sun gears are also
included. One sun gear is splined to the sprocket pinion
shaft, and the other is machined on the steering brake
hub. The sun gear, machined to the steering brake hub,
performs the same function as the ring gear in a
conventional planetary system. Bushings are used to
isolate the sprocket drive shafts and the steering brake
hubs from the bevel gear carrier and the planetary
carrier. Lubrication is provided from the oil sump
located below the assembly.
When the tracked equipment travels straight
ahead, its steering brakes are held in the applied
position by heavy coil springs. Braking prevents the
steering brake hub and sun gear from rotating and
forces the large planetary pinion gears to "walk"
around the sun gear. Then power is transmitted to the
sun gear on the sprocket drive shaft from the smaller
planetary pinion gears.
When a gradual turn is being made, the operator
moves one of the steering levers back far enough to
release the steering brake on one end of the planetary
system. When the brake is released, the planetary
pinion gears stop "walking" around the sun gear on
Figure 6-10.—Planetary steering systems.
The hydrostatic drive functions as both a clutch
and transmission. The final gear train then can be
simplified with the hydrostatic unit supplying infinite
speed and torque ranges as well as reverses speeds.
the steering brake hub. This hub then rotates with the
planetary carrier, and no power is transmitted to the
sprocket drive shaft.
Occasionally, an adjustment of the steering brake
is required to prevent slippage when it is engaged.
Consult the manufacturer's service manual for
adjustment procedures.
To understand hydrostatic drive, you must
understand two principles of hydraulics:
Liquids have no shape of their own.
Liquids are not compressible.
Pivot Brakes
The basic hydrostatic principle is as follows (fig.
The pivot brakes on tracked equipment are of the
multiple disc type. Pulling the steering brake levers
fully to the rear operates them. The middle discs
(splined to the sprocket drive shaft) have laminated
linings. The intermediate discs (held in position by
studs) are smooth steel discs. An actuating disc
assembly is two steel plates with steel balls between
them. The assembly is located in the center of the discs
and is connected to the operating linkage.
Two cylinders connected by a line both filled
with oil. Each cylinder contains a piston.
When a force is applied to one of the pistons, the
piston moves against the oil. Since the oil will
not compress, it acts as a solid connection and
moves the other piston.
In a hydrostatic drive, several pistons are used to
transmit power—one group in the PUMP sending
power to another group. in the MOTOR. The pistons are
in a cylinder block and revolve around a shaft. The
pistons also move in and out of the block parallel to the
Ramps are machined on the steel plate of the
actuating disc assembly, so when the brakes are
applied, the steel balls move up the ramps and force the
plates apart. Movement of the plates causes the discs to
be squeezed together and to stop rotation of the
sprocket drive shaft. When these brakes are fully
applied, the tracks will stop. The steering levers are
linked to the brakes independently to actuate them for
sharp turns.
Adjustment of the pivot brakes is required to
provide adequate braking with the steering levers. An
adjustment is required when the steering levers can be
pulled against the seat with the engine running.
Consult the manufacturer's service manual for proper
adjustment procedures.
The hydrostatic drive is an automatic fluid drive
that uses fluid under pressure to transmit engine power
to the drive wheels or tracks.
Figure 6-11.—Pump and motor form a closed hydraulic loop.
Mechanical power from the engine is converted to
hydraulic power by a pump-motor team. This power is
then converted back to mechanical power for the drive
wheels or tracks.
The pump-motor team is the heart of the
hydrostatic drive system. Basically, the pump and
motor are joined in a closed hydraulic loop; the return
line from the motor is joined directly to the intake of
the pump, rather than to the reservoir (fig. 6-11). A
charge pump maintains system pressure, using supply
oil from the reservoir.
Figure 6-12.—Basic hydrostatic principle.
torque at the output with a steady input speed. If
input speed varied, horsepower and speed will
vary but torque will remain constant. Because
both the pump and motor are fixed displacement,
this system is like a gear drive; it transmits power
without altering the speed or horsepower
between the engine and the load.
To provide a pumping action for the pistons, a
plate, called a SWASH PLATE, is located in both the
pump and motor (fig. 6-13). The pistons ride against
the swash plates. The angle of the swash plates can
be varied, so the volume and pressure of oil pumped
by the pistons can be changed or direction of the oil
reversed. A pump or motor with a movable swash
plate is called a variable-displacement unit. A pump
or motor with a fixed swash plate is called a fixed
displacement unit. There are four pump-motor
combinations, which are as follows (fig. 6-14):
Variable displacement pump driving a fixed
displacement motor (fig. 6-14, view B). Since
the pump is variable, output speed is variable and
torque output is constant for any given pressure.
This setup provides variable speed and constant
Fixed displacement pump driving a fixed
displacement motor (fig. 6-14, view A). This
setup will give you constant horsepower and
Fixed displacement pump driving a variable
displacement motor (fig. 6-14, view C). In this
setup changing the motor displacement varies
output speed. When motor displacement
decreases, output speed increases, but output
torque drops. When the setup is balanced, it
gives a constant horsepower output.
Variable displacement pump driving a variable
displacement motor (fig. 6-14, view D). This
setup gives an output of both constant torque and
constant horsepower. It is the most flexible of all
the setups, but it is also the most difficult to
Figure 6-13.—Connected cylinders with swash plates.
Figure 6-14.—Pump and motor combinations for hydrostatic drives.
Flexible location—no drive lines
The direction of output shaft rotation can be
reversed in variable setups by shifting either the pump
or the swash plate of the motor over center.
Low maintenance and service
Reduces shock loads
Remember three factors control the operation of a
hydrostatic drive. These factors are as follows:
Compact size
Eliminates clutches and large gear trains
RATE of oil flow—gives the speed
DIRECTION of oil flow—gives the direction
Hydrostatic Drive Operation
PRESSURE of the oil—gives the power
For you to understand how a hydrostatic drive
operates, we will explain the operation of a typical
system. The system we will use has an axial piston
pump and motor which is the ‘most common
hydrostatic drive system. The pump has a variable
displacement, while the motor has a fixed
displacement. Now look at the complete system in
operation—forward, neutral, and reverse.
The pump is driven by the engine of the machine
and is linked to the speed set by the operator. It pumps a
constant stream of high-pressure oil to the motor.
Since the motor is linked to the drive wheels or tracks
of the machine, it gives the machine its travel speed.
The advantages ofhydrostatic drive are as follows:
Infinite speeds and torque
FORWARD (fig. 6-15).—When the operator
moves the speed control lever forward, the spool in the
displacement control valve, also known as the FNR
valve (Forward, Neutral, and Reverse), moves from its
NEUTRAL position. This action allows pressure oil to
flow into the upper servo cylinder forcing the swash
Easy one-lever control
Smooth shifting
Shifts "on the go"
High torque available for starting up
Figure 6-15.—Forward operation.
The high-pressure relief valve, located in the
motor manifold, monitors the pressure of the forward
flow of oil and protects the system from too high
pressures. If pressure exceeds the rated psi, a relief
valve opens and oil bypasses the cylinder block in the
motor. This will either slow or stop the machine. The
bypassed oil returns to the pump. This action continues
until the load is reduced below the rated psi. Then the
relief valve closes and oil again flows to the cylinder
block, moving the machine forward.
plate to tilt. Oil, expelled by the opposing servo
cylinder. returns through the displacement control
valve (FNR valve) to the pump case.
As the swash plate reaches the tilt set by the speed
control lever, the displacement control valve (FNR
valve) spool returns to a NEUTRAL position, trapping
the oil to both servo cylinders and holds the swash plate
in its titled position. The swash plate will remain titled
until the operator moves the speed control lever.
With the pump drive shaft and cylinder block
rotating clockwise and the swash plate is titled to the
rear, it is now time to start pumping. As the cylinder
rotates past the pump inlet port, the inlet check valve
opens: oil is then forced by the charge pump into the
piston bores that align with the inlet port under low
charge pressure. As rotation continues, oil is forced out
of the outlet port at high pressure by the pump pistons
when they align with the outlet port. This flow of oil
drives the motor.
NEUTRAL (fig. 6-16).—With the speed control
lever in neutral, free oil flows from the reservoir
through the oil filter to the charge pump. The charge
pump pumps the oil past the high charge pressure
control valve and into the main pump housing. The oil
circulates through the housing and returns through the
oil cooler and back to the reservoir.
Trapped oil is held in the cylinder block of the
pump, in the motor, and in the connecting lines
between the pump and motor by two check valves in
the pump end cap.
The distance the pistons reciprocate in and out of
the cylinder block depends on the angle of the swash
plate of the pump. This determines the volume of oil
displaced per revolution of the pump. The greater the
angle, the greater the volume and the more oil flows
from the pump. As the angle of the swash plate is
varied so will the volume of oil displaced from the
When the control lever is in neutral, the swash
plate in the pump is also in neutral and the pistons
within the pump are not pumping. Therefore no oil is
being moved to provide either forward or reverse
The cylinder block in the pump rotates in a
clockwise direction and is driven by the engine of the
equipment. Rotation is viewed from the drive shaft end
of the pump. Because the oil is not being pumped to the
motor, the cylinder block in the motor is stationary and
the output shaft does not move.
As pressure oil enters the inlet port of the motor,
the pistons that align with the inlet port pushes against
the swash plate. Since the fixed swash plate is always
tilted, the pistons slide down the inclined surface and
the resulting forces rotate the cylinder block. This, in
turn. rotates the output shaft driving the machine
As the cylinder block continues to rotate
clockwise, oil is forced out the outlet port at low
pressure and returns to the pump where it is
recirculated through the pump and back to the motor.
This is called a “closed system” because the oil
keeps circulating between the pump and the motor.
The only extra oil comes from the charge pump that
maintains a given flow of oil through the system
whenever the machine is running.
With the drive system in neutral, the high
charge pressure control valve, (located at the
charge pump) controls pump pressure. When
the system is activated for reverse or forward,
the low charge pressure control valve located
in the motor manifold controls the charge
pressure at a lower psi.
REVERSE (fig. 6-17).—As the speed control
valve is moved to reverse, the spool in the
displacement control valve (FNR valve) moves out of
neutral allowing pressure oil to flow into the lower
servo cylinder, tilting the swash plate forward.
A shuttle valve, located in the motor manifold and
controlled by high oil pressure, prevents high oil
pressure from entering the low-pressure side of the
system. This action keeps the charge circuit open to the
low-pressure valve while the system is running.
When the swash plate reaches its desired tilt,
which is set by the control lever, the displacement
control spool returns to neutral. This action traps the
Figure 6-16.—Neutral operation.
Figure 6-17.—Reverse operation.
oil to both servo cylinders and keeps the swash plate
tilted. The swash plate will remain in position until the
speed control lever is moved again by the operator.
Clean the workbench or table before
disassembling any hydrostatic system component for
servicing. Be sure that all tools are clean and free of
dirt and grease.
With the swash plate tilted forward and the pump
drive shaft and cylinder block rotating clockwise, the
ports reverse and the inlet port becomes the outlet and
the outlet port becomes the inlet. As the pump cylinder
block rotates past the pump inlet port, a check valve
opens and oil is forced by the charge pump into the
piston bores that align with the inlet port of the pump.
As rotation continues, the oil is pressurized and forced
out of the outlet port of the pump by each of the pistons,
as they align with the outlet port. This action forces oil
to flow to the motor, and as high-pressure oil from the
pump enters the inlet port of the motor, the pistons are
pushed against the swash plate. The pistons slide down
the inclined surface of the swash plate, rotating the
cylinder block. This action rotates the drive shaft
counterclockwise, driving the piece of equipment in
reverse. As the motor cylinder block continues to
rotate, oil is forced out the outlet port at low pressure
and returns to the pump.
NEVER perform internal service work on
the shop floor or ground or where there is a
danger of dust or dirt being blown into the
Before disassemble of any system component for
internal service, certain items must be available. These
items include the following:
Clean plastic plugs of various sizes to seal the
openings when removing hydraulic hoses and
Clean plastic bags to place over the ends of the
lines and hoses. Secure the bags to the line and
hoses with rubber bands.
A container of solvent to clean internal parts.
Ensure that all parts are clean before replacing
them. Compressed air may be used to dry the
parts after cleaning.
The PUMP DRIVE SHAFT and cylinder
block always rotate clockwise, but the
MOTOR DRIVE SHAFT and cylinder block
rotate in clockwise and counterclockwise
directions, depending on the direction of the
oil entering the pump.
A container of hydraulic fluid to lubricate the
internal parts as they are reassembled.
A container of petroleum jelly to lubricate
surfaces where noted by the manufacturer
during reassembly.
Maintenance of Hydrostatic Drives
Anytime the components are serviced and
reassembled, always install new O rings, seals, and
gaskets. This provides tight seals for mating parts and
eliminates leakage.
As with any hydraulic system, the hydrostatic
drive system is fairly easy to’ maintain. The fluid
provides a lubricant and protects against overload.
Like any other mechanism, it must be operated
properly; too much speed, too much heat, too much
pressure, or too much contamination will cause
For instructions on the disassembly and
reassembly of hydrostatic components, refer
to the manufacturer’s service manual.
Before removing any part of the system, ensure
that the area is clean. Use steam-cleaning equipment if
available; however, do NOT let any water into the
system. Ensure that all hose and line connections are
tight. If steam cleaning is not possible, diesel fuel or a
suitable solvent may be used. Be certain to remove all
loose dirt and foreign matter that may contaminate the
system. Impurities, such as dirt, lint, and chaff, cause
more damage than any one thing. Always seal
openings when doing work to prevent foreign matter
from entering the system.
Never operate the hydraulic system empty.
Always check the fluid supply after servicing the
system. If fluid is to be added to the system. use ONLY
the fluid recommended in the service manual.
Q1. A power shift transmission has what total
number offorward and reverse speeds?
What shaft in a power shift transmission has the
reverse drive gear keyed to the front of the shaft?
What components are the heart of a hydrostatic
drive system?
What component in a hydrostatic drive system
maintains system pressure by using oil from the
Q5. A hydrostatic drive pump with a movable swash
plate is known as what type of pump?
Learning Objective: Identify the operational
components of the track and track frame. Describe the
maintenance procedures used on tracks and track frame
The undercarriage of crawler-mounted equipment
contains two major components—TRACK
ASSEMBLY and TRACK FRAME. This undercarriage (fig. 6-18) is provided on equipment that must
have positive traction to operate efficiently.
Figure 6-19.—Track chain cutaway.
sprocket teeth contact the track pin bushings and
propel the tractor along the track assembly.
The pins and bushings wear much faster than other
parts of the track because of their constant pivoting, as
the track rotates around the track frame. This pivoting
results in internal wear of both the pin and the bushing.
As the pins and bushings wear, the track lengthens.
When it does, the track is adjusted to remove excessive
The track assembly consists of a continuous chain
surrounding the track frame and drive sprocket. The
links of the chain provide a flat surface for the track
rollers to pass over, as they support the equipment.
Track shoes are bolted to the outside links of the chain
and distribute the weight of the equipment over a large
surface area.
Bushings that show lots of wear on the outside are
good indicators of inner wear that is also nearing the
maximum allowed by the manufacturer, if the track is
to be rebuilt. To determine whether the track should be
removed for rebuilding or replacement, measure the
outside of the bushings and track "pitch" (length of the
Track Chain
Figure 6-19 shows a cutaway view of a section of
track chain, showing the internal arrangement of the
pins and bushings. As the tractor operates, the drive
Figure 6-18.—Side view of crawler tractor chassis.
track). Use an outside caliper and ruler, as shown in
figure 6-20. Measure the outside of the bushing where
it shows the most wear and compare it to the
manufacturer’s specifications.
Measure track pitch with a ruler or tape measure
after tightening the track to remove any slack, as
shown in figure 6-21.
Should the bushing wear or track length be
excessive, remove the track for rebuilding unless
facilities and time do not permit. Rebuilding a track
will nearly double the useful life of the pin and
Track Shoes
The most common track shoe is the grouser shoe
shown in figure 6-22. This shoe is standard on all
crawler-mounted dozers. The extreme service track
shoe (fig. 6-23) is equipped on crawler-mounted
dozers that operate primarily in rocky locations, such
as rock quarries and coral beaches. Notice the grouser,
or raised portion of the shoe, is heavier than the
standard grouser shoe.
Another shoe common to track-mounted front-end
loaders is the multipurpose shoe. This shoe has three
grousers that extend a short distance above the shoe
and are equally spaced across its face. The multipurpose shoe allows more maneuverability with less
wear on the track and track frame components.
The grouser absorbs most of the wear and
its condition indicates when the track needs
replacement or overhaul.
Figure 6-22.—Standard grouser shoe.
Figure 6-20.—Bushing wear measurement.
Figure 6-23.—Extreme service track shoe.
Figure 6-21.—Track pitch measurement.
Track rollers (fig. 6-25) are double- and singleflanged rollers that supports the weight of the
tractor, ensures that the track chain is aligned
with the track frame at it passes under the rollers,
and prevents side to side track movement and
derailment. In a normal arrangement, a doubleflanged roller is directly in front of the drive
sprocket, followed by a single-flanged roller.
The rollers alternate forward to the front idler.
The track frame, as the name implies, serves as a
framework and support for the track assembly, rollers,
front idler, recoil spring, and adjusting mechanism.
Track frame alignment may be fixed or shim
adjusted depending on the manufacturer. When shims
are used, there are a couple of ways alignment may be
maintained. One way is using shims where the frame
attaches to the rear pivot and also near the center of the
track frame where it is mounted against the main frame
guide brackets. Another way is to use a diagonal brace
and shims at the rear pivot to align the track frame.
The front idler, as shown in figure 6-25, serves as a
guiding support for the track chain. The idler is springloaded and mounted on slides or guides that allow it to
move back and forth inside the track frame, as the
tractor passes over uneven terrain. The spring loading
Track Frame Rollers
Two types of track frame rollers are used on
tracked equipment—those located on the lower
portion of the track frame which supports the weight of
the tractor, and those above the track frame which
supports the track assembly, as it passes over the track
Carrier rollers (fig. 6-24) are single-flanged
rollers mounted on brackets, which extend
above the track frame and supports the track
assembly. Two of these rollers are on each side
of the tractor. The flange extends upward
between the links of the track chain. keeping the
chain in alignment between the drive sprocket
and the front idler.
Figure 6-25.—Track rollers in position in the track frame..
Figure 6-24.—Track carrier rollers.
tractors have manual adjustments, whereas newer
tractors are adjusted hydraulically with a grease gun.
Grease is pumped into the yoke cylinder and extends it
until enough tension is placed on the recoil spring to
remove the slack from the track. Tension is released by
loosening the vent screw located next to the adjustment
effect causes the idler to maintain the desired tension
regardless of operating conditions.
Recoil Spring
The recoil spring is a large coil spring placed in the
track frame in a way that enables the spring to absorb
shock from the front idler. The spring is compressed
before installation and held in place by stops or
spacers. The track adjusting mechanism, by pressing
against the spring stop, maintains the desired tension
on the track assembly by holding the idler and yoke in a
FORWARD position. The operation of the recoil
springs depends on the amount oftension on the track.
DO NOT lubricate the adjustment fitting
when performing maintenance on the tractor.
Adjusting Mechanism
Track Guiding Guards
The adjusting mechanism must be extended
enough to remove slack between the front idler and
spring. This adjustment may be made by either manual
(fig. 6-26) or hydraulic (fig. 6-27) means. Many older
Accumulation of rock and dirt packed in the track
causes the tracks to tighten, resulting in additional
wear and stress on track components. The use of track
guiding guards minimizes these sources of possible
depreciation. Another function of the track guiding
guards is maintaining proper track alignment; this is
considered secondary, but actually is the most
important function.
Guiding guards should be repaired when damaged,
since a damaged guard is worthless as far as protection
for track components or assisting in maintaining track
alignment. When installing new tracks on a piece of
equipment, check the condition of the guards. These
guards should be in a condition to guide the track
squarely into alignment with the rollers properly. The
three guards are as follows:
track from the idler and hold it in line for the first
roller. The front roller then can fully be utilized
for its intended purpose—carrying its share of
the load without having to climb the side of an
improperly aligned track.
Figure 6-26.—Manual track adjustment.
The REAR GUIDING GUARDS hold the track
in correct alignment with the driving sprocket,
permitting a smooth even power flow from the
sprocket to the track. With proper alignment,
gouging of the track link and sprocket teeth is
roller guards are available as attachments. These
center guards keep the track in line between the
rollers when operating in rocky, steep, or uneven
terrain. The center guards reduce the wear on
roller flanges and track links.
Figure 6-27.—Hydraulic track adjuster.
slack from the track. With all slack removed, release
the pressure until the front idler moves back 1/2 inch.
This will provide the required slack in the track until
the tractor can be readjusted to the manufacturer’s
Some maintenance of track and track frames are
performed at the jobsite by the field maintenance crew.
This maintenance consists of track adjustment,
lubrication based on hours as required by the
manufacturer, and inspection of the track and track
frame components.
Always check the manufacturer's
maintenance manual for the proper procedures
when adjusting tracks.
Track Adjustment
If the tracks are adjusted too tightly, there will be
too much friction between the pins and bushings when
the track links swivel. as they travel around the
sprocket and front idler. This friction causes the pins,
bushings, links, sprocket, and idler to wear rapidly.
Friction in a tight track also robs the tractor of needed
The track pins and bushing are hardened and
require no lubrication. Many rollers and idlers are
equipped with lifetime seals that are factory
lubricated and sealed. However, track rollers, carrier
rollers, and idlers equipped with grease fittings must
be lubricated on a scheduled basis that is set by the
Tracks that are too loose fail to stay aligned and
tend to come off when the tractor is turned. As a result,
the idler flanges, roller flanges, and the sides of the
sprocket teeth wear down. A loose track will whip at
high tractor ground speed, damaging the carrier rollers
and their supports. If loose enough, the drive sprockets
will jump teeth (slide over track bushings) when the
tractor moves in reverse. Should this happen, the
sprocket and bushings will wear rapidly.
ONLY use a hand-operated grease gun on
these fittings and pump only until resistance is
felt. Further pumping will damage the seals.
One method for determining proper track tension
is placing a straightedge over the front carrier roller
and idler with all the slack removed from the rest of the
track. Using a ruler. measure from the top of the track
shoe to the bottom edge of the straightedge (fig. 6-28).
For the correct measurement, refer to the
manufacturer’s manual.
If it becomes necessary to adjust the track in the
field, the following method can be used. Remove all
When performing routine maintenance, inspect
the complete track and undercarriage for signs of
abnormal wear, leaking rollers or idlers, and
misaligned, loose, or missing parts. Should you find
any loose track shoes, you should check the torque on
all the shoe bolts. Any bolts not meeting specifications
should be retightened to the prescribed torque.
If the track appears to be out of alignment, report
this to your supervisor who shall determine what
action is required. Leaking roller and idler seals should
be replaced as soon as possible to prevent any further
damage to the equipment.
Shop Repairs
Repairs made to tracks and track frames in the
maintenance shop are usually limited to replacing
roller or idler seals and bearings or repairing a
hydraulic track adjuster. On occasion, you may find a
roller or track that is badly worn and requires
Figure 6-28.—Checking track adjustment.
NEVER replace components of the track
or track frame without consulting the wear
limitation charts in the manufacturer’s service
After removing the tracks, always see that
the tractor is securely blocked while repairs
are being performed.
Anytime a track is removed, thoroughly inspect
the track frame components for excessive wear and
misalignment. R e m o v a l , d i s a s s e m b l y , a n d
replacement vary by model and manufacturer. Consult
the manufacturer’s service manual for exact
TRACK REMOVAL (fig. 6-29).—Steps for the
removal of the track are as follows:
manually backing off the track adjuster or loosening the
vent screw on the hydraulic track adjuster.
tracks, back the tractor off the plank and onto the new
tracks so the drive sprocket properly meshes with the
track rail. Continue backing until the tractor is just
ahead of the rear end of the track. Then place a bar in
the track (fig. 6-30), and help the track climb over the
sprocket, carrier rollers, and idler as the tractor is
driven forward. When the track comes together, install
the master pin and any locking device. Once the track
is together, adjust the track tension using the
manufacturer’s recommended procedures.
2. REMOVE THE MASTER PIN. The master pin
can be identified by a locking device or hole drilled in its
end that distinguishes it from the other pins in the chain.
Move the tractor backward slowly or, on some models,
forward to bring the master pin just below the level of
the drawbar. Place a block under the grouser on a shoe
that allows the master pin to be centered on the front
idler. With the master pin centered on the front idler,
remove any locking device. If the master pin had a
locking device, the pin can be removed by using a
sledgehammer and a soft metal driftpin. Should the pin
be drilled, a portable press must be used to remove the
pin. Do not lose the bushings, which may drop out with
the pin.
tractor forward or backward away from the loose ends
of the track. Make sure no one is in the way of the tractor
or the loose end of the track when it falls off the sprocket
or front idler.
Place a plank at the rear of the track. The plank should
be about the same thickness as the track, yet narrow
enough to fit between the track frame and guards, and
long enough so that the entire tractor can rest on the
Figure 6-30.—Pulling track over sprocket.
Figure 6-29.—Removing tracks.
What components of a track chain wear faster
than the other components?
What measuring device is used to measure track
What is the most common type of track shoe?
What component of the track frame serves as a
guiding support for the track chain?
What component of the track frame holds the
track in correct alignment with the driving
Slings and Rigging Hardware in the Naval Construction Force and the NAVFAC P-307, Management of
Weight Handling Equipment.
Most winches that you will encounter are used on
tactical vehicles and construction equipment. On
tactical equipment, the winch is mounted behind the
front bumper and is secured to the front cross member
of the frame or between the two side frame rails. In
some cases, it may be mounted behind the cab of the
vehicle. The typical front-mounted winch is a jawclutch worm-gear type (fig. 6-31).
Using a winch and some type of rigging, a vehicle
can pull itself or another vehicle through such
obstacles as muddy or rough terrain. This is the
primary reason for providing winches on military
The jaw-clutch winch consists of a worm gear that
is keyed to a shaft. A bushed drum is mounted on the
worm-gear shaft, which is controlled by a handoperated sliding clutch. The worm shaft is driven by
power from the power takeoff through a solid drive
shaft and universal joints. The universal joint yoke,
connected to the worm shaft of the winch, has a
provision for a shear pin that is made of mild steel. This
pin has a predetermined breaking strength that allows
it to shear when the winch is overloaded.
In the Naval Construction Force (NCF), an indepth management program for maintenance and use
of all rigging gear is required to ensure all operations
are performed safely and professionally. These
guidelines are outlined in the COMSECOND/
COMTHIRDNCBINST 11200.11, Use of Wire Rope
A hand-operated sliding clutch is keyed to the
worm-gear shaft outside of the winch drum and must
be engaged with the jaws on the side of the winch drum
when the winch is to be operated. Disengagement of
the sliding clutch permits the drum to turn on the
worm-gear shaft.
Learning Objective: Describe the operation of a
winch. Identify the characteristics and maintenance of
wire rope.
Figure 6-31.—Jaw-clutch worm-gear winch.
The two brakes that provide control of the winch
drum are as follows:
NEVER install a shear pin that in not of the
proper shearing strength. Damage to the winch
will occur when overloaded.
The WORM BRAKE SHAFT prevents the
winch drum from rotating under load when the
power takeoff is disengaged.
the drum from overrunning the cable when the
cable is being unreeled.
The winch that you will most likely encounter
on construction equipment is the one attached to
the rear of a crawler tractor, also known as a dozer.
It is mounted on the rear of the dozer (fig. 6-32) and
is directly geared to the rear power takeoff. This
arrangement permits development of a line of pull
that is 50 to 100 percent greater than straight dozer
pull. The winch is used for uprooting trees and
stumps, hoisting and skidding stress, freeing mired
equipment, and support amphibious construction
Some winches may be equipped with an automatic
level-winding device to spool the cable on the drum in
tight, even coils, and layers. This prevents crushing of
the cable due to loose, crossed coils and layers, and it
allows off leads of the cable while maintaining level
A broken shear pin usually causes faulty operation
of winches. Internal damage of the winch can be
caused by the use of a shear pin that has too high a
breaking strength. Internal winch failure, resulting
from overload, is commonly found to be sheared keys
or a broken worm shaft. Often, when the cable is
wound unevenly under tension, the winch housing will
be cracked or broken. This will require replacement of
the assembly.
When performing maintenance on a winch, ensure
that the gear case has the recommended amount and
type of lubricant. Should disassemble of the winch be
required for repairs, follow the procedures given in the
manufacturer's manual.
Figure 6-32.—Winch attachment on a dozer.
Many of the movable components on cranes and
attachments are moved by wire rope. Wire rope is a
complex machine, composed of a number of precise
moving parts. The moving parts of wire rope are
designed and manufactured to bear a definite
relationship to one another to have the necessary
flexibility during operation.
When the wire is cut or broken, the almost
instantaneous unlaying of the wire or strands
of the non-preformed wire rope can cause
serious injury. This situation is apt to occur
especially to someone who is careless or not
familiar with this characteristic of the rope.
Wire rope may be manufactured by either of two
methods. If the strands, or wires, are shaped to conform
to the curvature of the finished rope before laying up,
the rope is termed PREFORMED WIRE ROPE. If they
are not shaped before fabrication, the wire rope is
common type of manufactured wire rope is preformed.
When cut, the wire rope tends not to unlay and is more
flexible than non-preformed wire rope. With nonpreformed wire rope, twisting produces a stress in the
wires; therefore, when it is cut or broken, the stress
causes the strands to unlay.
Composition of Wire Rope
Wire rope is composed of three parts—wires,
strands, and core (fig. 6-33). A predetermined number
of wires of the same or different size are fabricated in a
uniform arrangement of definite lay to form a strand.
The required number of strands are then laid together
symmetrically around the core to form the wire rope.
WIRE.—The basic component of the wire rope is
the wire. The wire may be made of steel, iron, or other
metal in various sizes. The number of wires to a strand
varies, depending on the purpose for which the wire
rope is intended. The number of strands per rope and
the number of wire per strand designate wire rope.
Thus a 1/2-inch 6 x 19 rope has six strands with
nineteen wires per strand. It has the same outside
diameter as a 1/2-inch 6 x 37 rope that has six strands
with thirty-seven wires (of a smaller size) per strand.
STRAND.—The design arrangement of a strand is
called the construction. The wires in the strand may be
all the same size or a mixture of sizes. The most
common strand constructions are Ordinary, Seale,
Warrington, and Filler (fig. 6-34) as follows:
ORDINARY construction wires are all the same
Figure 6-33.—Composition of wire rope.
Figure 6-34.—Common strand construction.
SEALE is where larger diameter wires are used
on the outside of the strand to resist abrasion and
smaller wires inside to provide flexibility.
(psi). These characteristics make it desirable for
cable tool drilling and other purposes where
abrasion is encountered.
WARRINGTON is where alternate wires are
large and small to combine great flexibility with
resistance to abrasion.
Plow steel wire rope is usually tough and strong.
This steel has a tensile strength of 220,000 to
240,000 psi. Plow steel wire rope is suitable for
hauling, hoisting, and logging.
FILLER is where very small wires fill in the
valleys between the outer and inner rows of
wires to provide good abrasion and fatigue
Improved plow steel wire rope is one of the best
grades of rope available and is the most common
rope used in the NCF. This type of rope is
stronger, tougher, and more resistant to wear
than the others. Each square inch of improved
plow steel can stand a strain of 240,000 to
260,000 psi. This makes it especially useful for
heavy-duty service, such as on cranes with
excavating and weight-handling equipment.
CORE.—The wire rope core supports the
strands laid around it. The three types of wire rope
cores are fiber, wire strand, and independent wire
rope (fig. 6-35).
A fiber core may be a hard fiber, such as manila
hemp, plastic, paper, or sisal. The fiber core
offers the advantage of increased flexibility. It
also serves as a cushion to reduce the effects of
sudden strain and acts as an oil reservoir to
lubricate the wire and strands (to reduce
friction). Wire rope with a fiber core is used
when flexibility of the rope is important.
Lays of Wire Rope
The term lay refers to the direction of the twist of
the wires in a strand and to the direction that the strands
are laid in the rope. In some instances, both the wires in
the strand and the strands in the rope are laid in the
same direction; and, in other instances, the wires are
laid in one direction and the strands are laid in the
opposite direction, depending on the intended use of
the rope. Most manufacturers specify the types and
lays of wire rope to be used on their piece of
equipment. Be sure and consult the operator's manual
for proper application.
A wire strand core resists more heat than a fiber
core and also adds about 15 percent to the
strength of the rope; however, the wire strand
core make the wire less flexible than a fiber core.
An independent wire rope core is a separate wire
rope over which the main strands of the rope are
laid. This core strengthens the rope, provides
support against crushing, and supplies
maximum resistance to heat.
The five different lays used in wire rope are as
follows (fig. 6-36):
RIGHT REGULAR LAY has the wires in the
strands laid to the left, while the strands are laid
to the right to form the wire rope.
Grades of Wire Rope
The three primary grades of wire rope are as
LEFT REGULAR LAY has the wires in the
strands laid to the right, while the strands are laid
to the left to form the wire rope. In this lay, each
step of fabrication is exactly opposite from the
right regular lay.
Mild plow steel wire rope is tough and pliable. It
can stand repeated strain and stress and has a
tensile strength (resistance to lengthwise stress)
from 200,000 to 220,000 pounds per square inch
RIGHT LANG LAY has the wires in the strands
and the strands in the rope laid to the right.
LEFT LANG LAY has the wire in the strands
and the strands in the rope laid to the left.
REVERSE LAY has the wires in one strand laid
to the right, the wire in the nearby strand are laid
to the left, the wire in the next strand are to the
right, and so forth, alternating direction from one
strand to the other. Then all strands are laid to the
Figure 6-35.—Core construction.
may be subjected to, is not possible. Because of this,
selecting a rope is often a matter of compromise—
sacrificing one quality to have some other more
urgently needed characteristic.
TENSILE STRENGTH.—Tensile strength is the
strength necessary to withstand a certain maximum
load applied to the rope. It includes a reserve of
strength measured in a so-called factor of safety.
CRUSHING STRENGTH.—Crushing strength
is the strength necessary to resist the compressive and
squeezing forces that distort the cross section of a wire
rope, as it runs over sheaves, rollers, and hoist drums
when under a heavy load. Regular lay rope distorts less
in these situations than lang lay.
FATIGUE RESISTANCE.—Fatigue resistance
is the ability to withstand the constant bending and
flexing of wire rope that runs continuously on sheaves
and hoist drums. Fatigue resistance is important when
wire rope must run at high speeds. Such constant and
rapid bending of the rope can break individual wires in
the strands. Lang lay ropes are best for service
requiring high fatigue resistance. Ropes with similar
wires around the outside of their strands also have a
greater resistance, since these strands are more
Figure 6-36.—Lays of wire rope.
Characteristics of Wire Rope
The main types of wire rope used consist of 6, 7,
12, 19, 24, or 37 wires per strand. Usually, the wire
rope has six strands laid around the core.
Several factors must be considered whenever a
wire rope is selected for use in a particular kind of
operation. The manufacture of wire rope which can
withstand equally well all kinds of wear and stress, it
A B R A S I O N R E S I S T A N C E .—Abrasion
resistance is the ability to withstand the gradual
wearing away of the outer metal, as the rope runs
across sheaves and hoist drums. The rate of abrasion
depends mainly on the load carried by the rope and its
running speed. Generally, abrasion resistance in a rope
depends on the type of metal of which the rope is made
and the size of the individual outer wires. Wire rope
made of harder steels, such as improved plow steel, has
a considerable resistance to abrasion. Ropes that have
larger wires forming the outside of their strands are
more resistant to wear than rope having smaller wires
which wear away more quickly.
Figure 6-37.—A. 6 x 19 wire rope; B. 6 x 37 wire rope.
C O R R O S I O N R E S I S T A N C E .—Corrosion
resistance is the ability to withstand the dissolution of
the wire metal that results from chemical attack by
moisture in the atmosphere or elsewhere in the
working environment. Ropes that are put to static
work, such as guy wires, may be protected from
corrosive elements by paints or other special dressings.
Wire rope may be galvanized for corrosion protection.
Most wire rope used in crane operations must rely on
their lubricating dressing to double as a corrosion
The two most common types of wire rope, 6 x 19
and 6 x 37, are shown in figure 6-37. The 6 x 19 type
(having six strands with 19 wires in each strand) are
the stiffest and strongest construction of the types of
wire rope suitable for general hoisting operations.
The 6 x 37 wire rope (six strands with 37 wires in each
strand) are very flexible, making it suitable for cranes
and similar equipment.
Measuring Wire Rope
Jumping of sheaves
Exposing to acid or corrosive liquid or gases
Wire rope is designated by its diameter in inches,
as shown in figure 6-38. The correct methods of
measuring wire rope is to measure from the top of one
strand to the top of the strand directly opposite it. The
wrong way is to measure across two strands side by
Using an improperly attached fitting
Allowing grit to penetrate between the strands
promoting internal wear
Subjecting to severe or continuing overload
Using an excessive fleet angle
To ensure an accurate measurement of the
diameter of a wire rope, always measure the rope at
three places at least 5 feet apart. Use the average of the
three measurements as the diameter of the rope.
Handling and Care of Wire Rope
To render safe, dependable service over a
maximum period of time, you should take good care
and upkeep that is necessary to keep wire rope in good
condition. Various ways of caring for and handling
wire rope are described below.
Wire Rope Safe Working Load
The term safe working load (SWL) of wire rope
means the load that can be applied and still obtain the
most efficient service and also prolong the life of the
rope. For the safe working load of wire rope, refer to
the manufacturer’s certification of published breaking
strength or the actual breaking strength of a piece of
wire rope taken from the reel and tested.
reel has been opened, it may be coiled or faked down,
like line. The proper direction of coiling is
counterclockwise for left lay and clockwise for right
lay wire rope. Because of the general toughness and
resilience of wire, it tends now and then to resist being
coiled down. When this occurs, it is useless to fight the
wire by forcing down the turn because it will only
spring up again. But if it is thrown in a back turn, as
shown in figure 6-39, it will lie down properly. A wire
rope, when faked down, will run right off, like line; but
when wound in a coil, it must always be unwound.
Wire Rope Failure
Some of the common causes of wire rope failure
are the following:
Using incorrect size, construction, or grade
Dragging over obstacles
Wire rope tends to kink during uncoiling or
unreeling, especially if it has been in service long. A
kink can cause a weak spot in the rope that wears out
quicker than the rest of the rope.
Lubricating improperly
Operating over sheaves and drums of inadequate
Overriding or cross winding on drums
Operating over sheaves and drums with
improperly fitted grooves or broken flanges
Figure 6-38.—Correct and incorrect methods of measuring
wire rope.
Figure 6-39.—Throwing a back turn.
A good method for unreeling wire rope is to run a
pipe or rod through the center and mount the reel on
drum jacks or other supports so the reel is off the
ground, as shown in figure 6-40. In this way, the reel
will turn as the rope is unwound, and the rotation of the
reel helps keep the rope straight. During unreeling, pull
the rope straightforward, and avoid hurrying the
operation. As a safeguard against kinking, NEVER
unreel wire rope from a reel that is stationary.
Figure 6-42.—Wire rope loop.
To uncoil a small coil of wire rope, simply stand
the coil on edge and roll it along the ground like a
wheel, or hoop, as also shown in figure 6-40. NEVER
lay the coil flat on the floor or ground and uncoil it by
pulling on the end, because such practice can kink or
twist the rope.
KINKS.—One of the most common forms of
damage resulting from improper handled wire rope is
the development of a kink. A kink starts with the
formation of a loop, as shown in figures 6-41 and 6-42.
A loop that has not been pulled tight enough to set
the wires or strands or the rope into a kink can be
removed by turning the rope at either end in the proper
direction to restore the lay (fig. 6-43). If this is not done
and the loop is pulled tight enough to cause a kink (fig.
6-44), the kink will result in irreparable damage to the
rope (fig. 6-45).
Figure 6-43.—The correct way to take out a loop in a wire
Figure 6-44.—Wire rope kink.
Figure 6-40.—Unreeling wire rope (left); uncoiling wire rope
Figure 6-45.—Kink damage.
Kinking can be prevented by proper uncoiling and
unreeling methods and by the correct handling of the
rope throughout its installation.
DRUM WINDING.—Spooling wire rope on a
crane hoist drum causes a slight rotating tendency of
the rope due to the spiral lay of the strands. Two types
Figure 6-41.—Improper handling.
overwind rope, the rotating tendency of right lay rope
is toward the left; whereas the rotating tendency of a
left lay rope is to the right.
of hoist drums used for spooling wire rope are as
1. Grooved drum. When grooved drums are used,
the grooves generally give sufficient control to wind the
wire rope properly, whether it is right or left lay rope.
Refer to figure 6-46. With overwind reeving and a
right lay rope on a smooth-faced drum, the wire rope
bitter end attachment to the drum flange should be at
the left flange. With underwind reeving and a right lay
rope, the wire rope bitter end should be at the right
2. Smooth-faced drum. Smooth-faced drums are
used where the only other influence on the wire rope is
winding on the first layer is the fleet angle. The slight
rotational tendency of the rope can be used as an
advantage in keeping the winding tight and uniform.
When wire rope is run off one reel onto another or
onto a winch or drum, it should be run from TOP TO
TOP or from BOTTOM TO BOTTOM, as shown in
figure 6-47.
Using the wrong type of wire rope lay
causes the rotational tendency of the rope to be
a disadvantage, because it results in loose and
nonuniform winding of the rope on the hoist
Figure 6-46 shows drum-winding diagrams for
selection of the proper lay of rope. Standing behind the
hoist drum and looking towards an oncoming
Figure 6-47.—Transferring wire rope from reel to drum.
Figure 6-46.—Different lays of wire rope winding on hoisting drums.
A rule of thumb for determining the size, number,
and distance between seizing is as follows:
FLEET ANGLE.—The fleet angle is formed by
running wire rope between a sheave and a hoist drum
whose axles are parallel to each other (fig. 6-48). Too
large a fleet angle can cause the wire rope to climb the
flange of the sheave and can also cause the wire rope to
climb over itself on the hoist drum.
The number of seizing to be applied equals
approximately three times the diameter of the
Example: 3 x 3/4-inch-diameter rope = 2 1/4
inches. Round up to the next higher whole number and
use three seizing.
SIZES OF SHEAVES.—The diameter of a
sheave should never be less than 20 times the diameter
of the wire rope. An exception is 6 x 37 wire for which
a smaller sheave can be used, because it is more
The width of each seizing should be 1 to 1 1/2
times as long as the diameter of the rope.
Example: 1 x 3/4-inch-diameter rope = 3/4 inch.
Use a 1-inch width of seizing.
drums, sheaves, and blocks used with wire rope should
be placed to avoid reverse or S-shaped bends. Reverse
bends cause the individual wires or strands to shift too
much and increase wear and fatigue. For ‘a reverse
bend, the drums and blocks affecting the reversal
should be of a larger diameter than ordinarily used and
should be spaced as far apart as possible.
The seizing should be spaced a distance equal to
twice the diameter of the wire rope.
Example: 2 x 3/4-inch-diameter rope = 1 1/2
inches. Space the seizing 2 inches apart.
A common method used to make a temporary wire
rope seizing is as follows (fig. 6-49):
SEIZING AND CUTTING.—The makes of wire
rope are careful to lay each wire in the strand and each
strand in the rope under uniform tension. If the ends of
the rope are not secured properly, the original balance
of tension will be disturbed. Maximum service is not
obtainable because some strands can carry a greater
portion of the load than others can. Before cutting steel
wire rope, place seizing on each side of the point where
the rope is to be cut.
Wind the seizing wire uniformly, using tension on
the wire. After making the required number of turns, as
shown in step 1, twist the ends of the wires
counterclockwise by hand, so the twisted portion of the
wires is near the middle of the seizing, as shown in step 2.
Figure 6-48.—Fleet angle relationship.
Figure 6-49.—Seizing wire rope.
Grasp the ends with end-cutting nippers and twist up
slack, as shown in step 3. Do not try to tighten the
seizing by twisting. Draw up on the seizing, as shown
in step 4. Again twist up the slack, using the nippers as
shown in step 5. Repeat steps 4 and 5 as needed. Cut the
ends and pound them down on the rope, as shown in
step 6. If the seizing is to be permanent, use a serving
bar, or iron, to increase tension on the seizing wire
when putting on the turns.
For wire rope to work right, its wires and strands must
be free to move. Friction from corrosion or lack of
lubrication shortens the service life of wire rope.
Deterioration from corrosion is more dangerous
than that from wear because corrosion ruins the inside
wires—a process hard to detect by inspection.
Deterioration caused by wear can be detected by
examining the outside wires of the rope, because these
wires become flattened and reduced in diameter, as the
wire rope wears.
Wire rope can be cut successfully by a number of
methods. An effective and simple method is to use a
hydraulic type of wire rope cutter, as shown in figure
6-50. Remember that all wire should be seized before
it is cut. For best results in using this method, place the
rope in the cutter so the blade comes between the two
central seizing. With the release valve closed, jack the
blade against the rope at the location of the cut and
continue to operate the cutter until the wire rope is cut.
Replace wire rope that has one third of the
original diameter of the outside individual
Both internal and external lubrication protects a
wire rope against wear and corrosion. Internal
lubrication can be properly applied only when the wire
rope is being manufactured, and manufacturers
customarily coat every wire with a rust-inhibiting
lubricant, as it is laid into the strand. The core is also
lubricated in manufacturing.
When a hydraulic type of wire cutter is NOT
available, other methods can be used. such as a
hammer-type wire rope cutter (fig. 6-51), a cutting
torch, and, if need be, a hacksaw and cold chisel.
Wire Rope Maintenance
Lubrication that is applied in the field is designed
not only to maintain surface lubrication but also to
prevent loss of internal lubrication provided by the
manufacturer. The Navy issues an asphaltic petroleum
oil that must be heated before using. This lubricant is
known as Lubricating Oil for Chain, Wire Rope, and
Exposed Gear and comes in two types:
Wire rope bending around hoist drums and
sheaves will wear like any other metal article, so
lubrication is just as important to an operating wire
rope as it is to any other piece of working machinery.
Type I, Regular: Does not prevent rust and is
used where rust prevention is not needed; for
example, elevator wires used inside are not
exposed to the weather but need lubrication.
Type II, Protective: A lubricant and an
anticorrosive—it comes in three grades: grade
A, for cold weather (60°F and below); grade B,
for warm weather (between 60°F and 80°F); and
grade C, for hot weather (80°F and above).
Figure 6-50.—Hydraulic type of wire cutter.
The oil, issued in 25-pound and 35-pound buckets
and in 100-pound drums, can be applied with a stiff
brush, or the wire rope can be drawn through a trough
of hot lubricant (fig. 6-52). The frequency of
application depends upon service conditions; as soon
as the last coating has appreciably deteriorated, it
should be renewed. A good lubricant to use when
working in the field, as recommended by
a mixture of new motor oil and diesel fuel at a ratio of
70-percent oil and 30-percent diesel fuel.
Figure 6-51.—Hammer-type wire rope cutter.
Figure 6-53.—Wedge socket.
The wedge socket develops only 70
percent of the breaking strength of the wire
rope due to the crushing action of the wedge.
SPELTERED SOCKET.—Speltering is the best
way to attach a closed or open socket in the field.
"Speltering" means to attach the socket to the wire
rope by pouring hot zinc around it, as shown in figure
6-54. Speltering should be done by qualified
Figure 6-52.—Trough method of lubricating wire rope.
Avoid prolonged skin contact with oils
and lubricants. Consult the Materials Safety
Data Sheets (MSDS) on each item before use
for precautions and hazards. See your
supervisor for copies of MSDSs.
Forged steel speltered sockets are as strong as the
wire rope itself. Speltered sockets are required on all
cranes used to lift personnel, ammunition, acids, and
other dangerous materials.
As a safety precaution, always wipe off any excess
oil when lubricating wire rope especially with hoisting
equipment. Too much lubricant can get into brakes or
clutches and cause them to fail. While in use, the
motion of machinery may sling excess oil around over
cranes cabs and onto catwalks making them unsafe.
Spelter sockets develop 100 percent of the
breaking strength of the wire rope.
WIRE ROPE CLIPS.—Wire rope clips are used
to make eyes in wire rope, as shown in figure 6-55. The
U-shaped part of the clip with the threaded ends is
called the U-bolt; the other part is called the saddle.
The saddle is stamped with the diameter of the wire
rope that the clip will fit. Always place a clip with the
Properly dispose of wiping rags and used
or excess lubricants as hazardous waste. See
your supervisor for details on local disposal
Wire Rope Attachments
Attachments are fitted to the ends of wire rope, so
the rope can be connected to other wire ropes, pad eyes,
or equipment. The common attachments used are the
wedge socket, the speltered socket, wire rope clips, the
thimble, swaged connections, and hooks and shackles.
WEDGE SOCKET.—The attachment used most
often to attach dead ends of wire ropes to pad eyes or
like fittings on cranes and earthmoving equipment is
the wedge socket (fig. 6-53). The socket is applied to
the bitter end of the wire rope.
Figure 6-54.—Speltering a socket.
After the eye made with clips has been strained, the
nuts on the clips must be re-tightened. Checks should
be made now and then for tightness or the clips will
cause damage to the rope.
an efficient and permanent attachment for wire rope, as
shown in figure 6-57. A swaged connection is made by
compressing a steel sleeve over the rope by using a
hydraulic press. When the connection is made
properly, it provides 100 percent capacity of the wire
Figure 6-55.—Wire rope clips.
Careful inspection of the wires leading into these
connections is important because of the pressure put
upon the wires in this section. If one broken wire is
found at the swaged connection or a crack in the swage,
replace the fitting.
U-bolt on the bitter (dead) end, not on the standing part
of the wire rope. If clips are attached incorrectly, the
standing part (live end) of the wire rope will be
distorted or have mashed spots. A rule of thumb when
attaching a wire rope is to NEVER saddle a dead horse.
shackles are handy for hauling or lifting loads without
tying them directly to the object with line, wire rope, or
chain. They can be attached to wire rope, fiber line,
blocks, or chains. Shackles should be used for loads
too heavy for hooks to handle.
Two simple formulas for figuring the number of
wire rope clips needed are as follows:
3 x wire rope diameter + 1 = Number of clips
6 x wire rope diameter = Spacing between clips
When hooks fail due to overloading, they usually
straighten out and lose or drop their load. When a hook
has been bent by overloading, it should NEVER be
straightened and put back into service. It should be cut
in half with a cutting torch and discarded.
Another type of wire rope clip is the twin-base
clip, often referred to as the universal or two clamp
(fig. 6-56). Both parts of this clip are shaped to fit the
wire rope, so the clip cannot be attached incorrectly.
The twin-base clip allows for a clear 360-degree swing
with the wrench when the nuts are being tightened.
Hooks should be inspected at the beginning of
each workday and before lifting a full-rated load. If
you are not sure a hook is strong enough to lift the load,
by all means use a shackle.
THIMBLE.—When an eye is made in a wire rope,
a metal fitting, called a thimble, is placed in the eye, as
shown in figure 6-55. The thimble protects the eye
against wear. Wire rope eyes with thimbles and wire
rope clips can hold approximately 80 percent of the
wire rope strength.
Hooks that close and lock should be used where
there is a danger of catching on an obstruction,
particularly in hoisting buckets, cages, or skips, and
especially in shaft work. Hooks and rings used with a
chain should have about the same strength as the chain.
Figure 6-57.—Swaged connections.
Figure 6-56.—Twin-base wire rope clip.
The manufacturer's recommendations should be
followed in determining the safe working loads of the
various sizes and types of specific and identifiable
hooks. All hooks for which no applicable
manufacturer’s recommendations are available should
be tested to twice the intended safe working load
before they are initially put into service.
Mousing is a technique often used to close the open
section of a hook to keep slings, straps, and similar
attachments from slipping off the hook, as shown in
figure 6-58.
Figure 6-59.—Anchor shackles.
Hooks may be moused with rope yarn, seizing
wire, or a shackle. When using rope yam or wire, make
8 to 10 wraps around both sides of the hook. To finish
off, make several turns with the yarn or wire around the
sides of the mousing, and then tie the ends securely.
Two types of shackles used in rigging are the
anchor (fig. 6-59) and the chain (fig. 6-60). Both are
available with screw pins or round pins.
Shackles should be used in the same configuration
as they were manufactured. All pins must be straight
and cotter pins must be used or all screw pins must be
seated. When the original pin is lost or does not fit
properly, do not use the shackle. Never replace the
shackle pin with a bolt.
Figure 6-60.—Chain shackles.
Shackles are moused whenever there is a chance of
the shackle pin working loose and coming out due to
vibration. To mouse a shackle, simply take several
turns with seizing wire through the eye of the pin and
around the bow of the shackle. Refer to figure 6-58 for
proper mousing.
A shackle should never be pulled from the side.
This causes the shackle to bend reducing its capacity
tremendously. Always attach a screw pin shackle with
the screw pin on the dead end of the rope. If placed on
the running end, the movement of the rope may loosen
the pin.
Figure 6-58.—Mousing.
What are the two types of brakes used on a jawclutch type winch?
What device is used on a winch to prevent
crushing of the cable due to loose crossed coils
and layers?
Wire rope is composed of what total number of
What is the most common type of wire rope used
by the NCF?
What is the recommended ratio of new oil to
diesel for the lubrication of wire rope?
Two forward and two reverse speeds
Forward clutch shaft
Pump-motor team
Charge pump
Variable displacement
Pins and bushings
Ruler and tape measure
Front idler
Rear guiding guards
Worm shaft brake and shifter bracket brake
Q2. Automatic level winding device
Improved plow steel wire rope
70 percent new oil to 30 percent diesel
mechanism by a liquid. To understand how pressure is
transmitted by a hydraulic braking system, it is
necessary to understand the fundamentals of
hydraulics (refer to chapter 3 of this TRAMAN). There
are two common types of hydraulic brake systems used
on modern vehicles—drum and disc brakes.
Learning Objective: Explain the hydraulic and
mechanical principles of a brake system. Describe and
define the major components of hydraulic, air, and
air-over-hydraulic brake systems. Explain the operation
of hydraulic, air, and air-over-hydraulic brake systems.
Summarize the operation of antilock braking systems.
The brake system is the most important system on
a vehicle from a safety standpoint. You, as the
mechanic, are trusted to do every service and repair
operation correctly. When working on a brake system,
always keep in mind that a brake system failure could
result in a fatal vehicle accident. It is up to you to make
sure the vehicle brake system is in perfect operating
condition before the vehicle leaves the shop.
It is known that to increase the speed of a vehicle
requires an increase in the power output of the engine.
It is also true, although not so apparent, that an increase
in speed requires an increase in the braking action to
bring a vehicle to a stop (fig. 7-2). A moving vehicle,
just as any other moving body, has what is known as
kinetic energy. Kinetic energy is the energy an object
possesses due to its relative motion. This kinetic
energy, which increases with speed, must be overcome
by braking action. If the speed of the vehicle is
doubled, its kinetic energy is increased fourfold;
therefore, four times as much energy must be
overcome by the braking action.
Braking action is the use of a controlled force to
accomplish three basic tasks—to slow down, stop, or
hold the wheels of a vehicle stationary. Braking action
is accomplished by rubbing two surfaces together that
cause friction and heat (fig. 7-1). Friction is the
resistance to relative motion between two surfaces in
contact. The brakes convert kinetic (moving) energy
into heat to stop the vehicle. Heat energy is an
unwanted product of friction and must be dissipated to
the surrounding environment as efficiently as possible.
Brakes must not only be capable of stopping a
vehicle but must stop in as short a distance as possible.
Because brakes are expected to decelerate a vehicle at
a faster rate than the engine can accelerate, they must
be able to control a greater power than that developed
Learning Objective: Describe the operation, terms,
and component functions of a hydraulic brake system.
Describe the procedures for servicing a hydraulic brake
In hydraulic braking systems, the pressure applied
at the brake pedal is transmitted to the brake
Figure 7-2.—Braking requirements.
Figure 7-1.—Development of friction and heat.
by the engine. This is the reason that well-designed,
powerful brakes have to be used to control the modern
high-speed vehicle.
It is possible to accelerate an average vehicle with
an 80 horsepower engine from a standing start to 80
mph in about 36 seconds. By applying the full force of
the brakes, such a vehicle can be decelerated from 80
mph to a full stop in about 4.5 seconds. The time
required to decelerate to a stop is one eighth of the time
required to accelerate from a standing start. Therefore,
the brakes harness eight times the power developed by
the engine. Thus about 640 (8 x 80) horsepower has to
be spent by the friction surfaces of the brakes of an
average vehicle to bring it to a stop from 80 mph in 4.5
Vehicle Stopping Distance
Operator reaction time is the time frame between
the instant the operator decides that the brakes should
be applied and the moment the brake system is
activated. During the time that the operator is thinking
about applying the brakes and moving his or her foot to
do so, the vehicle will travel a certain distance
depending on the speed of the vehicle. After the brakes
are applied, the vehicle will travel an additional
distance before it is brought to a stop.
Total stopping distance of a vehicle is the total of
the distance covered during the operator’s reaction
time and the distance during which the brakes are
applied before the vehicle stops. Figure 7-3 shows the
total stopping distance required at various vehicle
speeds, assuming the average reaction time of 3/4
second and that good brakes are applied under most
favorable road conditions.
Figure 7-3.—Total vehicle stopping distance of an average
Factors that tend to increase brake temperatures
include the following:
Braking Temperature
Load on the vehicle
Brakes are devices that convert the energy of a
moving vehicle into heat whenever the brakes are
applied. This heat must be absorbed and dissipated by
the brake parts. Unless the heat is carried away as fast
as it is produced, brake part temperatures will rise.
Operator abuse
Speed of the vehicle
Maladjustment of brakes
Incorrect installation of brake parts
Since the heat generated by brake applications
usually is greater that the rate of heat dissipation, high
brake temperatures result. Ordinarily, the time interval
between brake applications avoids a heat buildup. If,
however, repeated panic stops are made, temperatures
become high enough to damage the brake linings,
brake drums. brake fluid, and, in some extreme cases,
even tires have been set on fire.
Unbalanced braking
If road speeds are increased and/or more weight is
placed in the vehicle, brake temperatures increase. In
fact, under extreme conditions of unbalanced brakes
on a heavy truck making an emergency stop from high
speed, enough heat is generated to melt a cube of iron
weighing 11.2 pounds.
and water. The master cylinder has four basic functions
that are as follows:
Braking Ratio
Braking ratio refers to the comparison of
front-wheel to rear-wheel braking effort. When a
vehicle stops, its weight tends to transfer to the front
wheels. The front tires are pressed against the road
with greater force. The rear tires lose some of their grip
on the road. As a result, the front wheels do more of the
braking than the rear.
It develops pressure, causing the wheel cylinder
pistons to move towards the drum or rotor.
After all of the shoes or pads produce sufficient
friction, the master cylinder assists in equalizing
the pressure required for braking.
It keeps the system full of fluid as the brake
linings wear.
For this reason, many vehicles have disc brakes on
the front and drum brakes on the rear. Disc brakes are
capable of producing more stopping effort than drum
brakes. If drum brakes are used on both the front and
rear wheels, the front shoe linings and drums typically
have a larger surface area.
It can maintain a slight pressure to keep
contaminants (air and water) from entering the
In its simplest form, a master cylinder consists of a
housing, a reservoir, a piston, a rubber cup, a return
spring, a rubber boot, and a residual pressure check
valve (fig. 7-4). There are two ports (inlet port and
compensating port) drilled between the cylinder and
reservoir. The description of the components of a
master cylinder is as follows:
Typically, front-wheel brakes handle 60 to 70
percent of the braking power. Rear wheels handle 30 to
40 percent of the braking. Front-wheel drive vehicles,
having even more weight on the front wheels, have
even a higher braking ratio at the front wheels.
The master cylinder housing is an aluminum or
iron casting having either an integral or detachable
reservoir. A cylinder is machined in the housing of the
master cylinder. The spring, the cups, and the metal
piston move within this cylinder.
The hydraulic system applies the brakes at all four
wheels with equalized pressure. It is pedal operated.
The system consists of the master cylinder, the wheel
cylinder, the brake lines and hoses, and the brake fluid.
The piston is a long spoonlike member with a
rubber secondary cup seal at the outer end and a rubber
primary cup at the inner end, which are used to
pressurize the brake system. The primary cup is held
against the end of the piston by the return spring. A steel
stop disc, held in the outer end of the cylinder by a
retainer spring, acts as a piston stop.
Master Cylinder
The master cylinder is the primary unit in the brake
system that converts the force of the operator's foot
into fluid pressure to operate the wheel cylinders. It is
normally mounted to the firewall, which allows for
easy inspection and service, and is less prone to dirt
Figure 7-4.—Cutaway view of a single master cylinder.
A rubber boot prevents dust, dirt, and moisture
from entering the back of the master cylinder. The boot
fits over the master cylinder housing and the brake pedal
compensating port. The action of both ports keeps the
system full of fluid.
The residual pressure check valve maintains
residual fluid pressure of approximately 10 psi. This
pressure prevents fluid from seeping past the cups in the
wheel cylinders and also prevents air from entering the
hydraulic passages when the brakes are released.
The reservoir carries a sufficient reserve of fluid
to allow for expansion and contraction of brake fluid
and brake lining wear. The reservoir is filled at the top
and is well sealed by a removable filler cap containing a
vent. Integral reservoirs are made of the same material
as the cylinder. whereas detachable reservoirs are made
of plastic.
Older vehicles used single piston, single reservoir
master cylinders that were dangerous. If a fluid leak
developed (cracked brake hose, seal damage, or line
rupture). a sudden loss of braking ability occurred.
Modern vehicles use dual master cylinders. These
master cylinders provide an additional safety feature in
that should one portion of the brake system fail. the
other system will allow the vehicle to maintain some
braking ability.
The intake port or vent allows fluid to enter the
rear of the cylinder, as the piston moves forward. Fluid
flows out of the reservoir, through the intake port, and
into the area behind the piston and cup.
The compensating port releases extra pressure
when the piston returns to the released position. Fluid
can flow back into the reservoir through the
The dual master cylinder (fig. 7-5). also called a
tandem master cylinder, has two separate hydraulic
Figure 7-5.—Dual master cylinder.
available. The secondary piston slides completely
forward in the cylinder, as shown in figure 7-5. Then
the primary piston provides hydraulic pressure to the
other two brake assemblies. It is very unlikely that both
systems will fail at the same time.
pistons and two fluid reservoirs. In the dual master
cylinder, the rear piston assembly is termed the
primary piston and the front piston is termed the
secondary piston.
In some dual master cylinders, the individual
systems are designed where one master cylinder piston
operates the front brake assemblies and the other
operates the rear brake assemblies. This is knownI as a
longitudinally split system (fig. 7-6). A system that has
each master cylinder piston operating the brake
assembly on opposite corners of the vehicle is known a
diagonally split system (fig. 7-6). In either system, if
there is a leak, the other master cylinder system can
still provide braking action on two wheels.
When performing maintenance on a dual master
cylinder, you may notice that the front reservoir is
larger than the rear. This is a longitudinally split
system. The larger reservoir is for disc brakes. The
larger reservoir is necessary because as the disc pads
wear, they move outward creating a larger cavity in the
caliper cylinder and fluid moves from the master
cylinder to fill the additional area. To allow this action
to occur, the front reservoir of a longitudinally split
system has no residual check valve. However, with a
diagonally split system both reservoirs are the same
size and the residual check valve for the rear brakes are
located in the tees that split the system front to rear.
When the systems are intact (no leaks), the pistons
produce and supply pressure to all four of the wheel
cylinders. However, if there is a pressure loss in the
primary circuit of the brake system (rear section of the
master cylinder), the primary piston slides forward and
pushes on the secondary piston. As shown in figure
7-5, this action forces the secondary piston forward
mechanically, building pressure in two of the wheel
cylinder assemblies. Should the secondary circuit fail,
braking for the other two wheels would still be
Wheel Cylinder
A wheel cylinder (fig. 7-7) changes hydraulic
pressure into mechanical force that pushes the brake
shoes against the drums. Other than the standard wheel
cylinder, there are two other types that you may come
in contact with—the stepped wheel cylinder and the
single-piston wheel cylinder.
The stepped wheel cylinder (fig. 7-7) is used to
compensate for a faster rate of wear on the front shoe
than on the rear shoe because of the self-energizing
action of the brakes. This condition requires a stepped
wheel cylinder with two bore sizes.
The single-piston wheel cylinder (fig. 7-7) is
used when it is desired that both brake shoes be
independently self-energizing, especially on the front
wheels. With this design it is necessary to have two
wheel cylinders, one for each shoe. Each cylinder has a
single piston and is mounted on the opposite side of the
brake backing plate from the other cylinder. Such an
arrangement is shown in figure 7-8.
For further information on wheel
cylinders, refer to "Drum Brake Assemblies"
in this chapter.
Brake Lines and Hoses
Brake lines and hoses transmit fluid under pressure
from the master cylinder to the wheel cylinders. The
brake lines are made of double-wall steel tubing with
double-lap flares on their ends. Rubber brake hoses are
Figure 7-6.—Dual master cylinder braking systems.
Figure 7-7.—Wheel cylinder configurations.
used where a flexing action is required. For example, a
brake hose is used between the frame and the
front-wheel cylinders or disc brake calipers. This
design allows the wheels to move up and down, as well
as side to side without damaging the brake line. Figure
7-9 shows the details of how brake lines and brake
hoses fit together.
A junction block is used where a single brake line
must feed two wheel cylindersorcalipers. It is a simply
a hollow fittingwith one inlet and two or more outlets.
Mounting brackets and clips are used to secure
brake lines and hoses to the unibody or frame of the
vehicle. The mounting brackets help hold the
assemblies secure and reduce the vibration which
causes metal fatigue, thereby preventing line
Figure 7-8.—Double-anchor, double-wheel cylinder
Maintain correct viscosity (free flowing at all
High boiling point (remains liquid at the highest
system operating temperature)
Standard brake fluid (DOT 3) is composed chiefly
of equal parts of alcohol and castor oil. This
combination of fluids works well under normal
conditions but it easily boils and becomes a vapor
under heavy-duty applications. Standard fluid also
tends to separate when exposed to low temperatures.
The increasing requirements of brake fluid led to the
development of silicone brake fluid.
After many years of research and development, a
brake fluid that was acceptable under extreme
operating conditions was developed. This fluid
achieved low water pickup and good corrosion
protection. The fluid also provides good lubrication
qualities and rubber compatibility. Silicone brake fluid
has been used in most military vehicles since the end of
Figure 7-9.—Brake lines and hoses.
Steel lines seldom need replacing except in areas
where they rust from exposure to salt air or constant
high humidity. Flexible hoses should be inspected at
regular maintenance periods for any signs of cracking
or abrasion. Should the outer protective covering be
cracked or badly abraded, it should be replaced.
There are many types of brake system designs in
use on modern vehicles. Regardless of the design, all
systems require the use of rotating and nonrotating
units. Each of these units houses one of the braking
surfaces, which, when forced together, produce the
friction for braking action. The rotating unit on many
motor vehicle wheel brakes consists of a drum that is
secured to and driven by the wheel. The nonrotating
unit consists of the brake shoes and linkage required to
applying the shoes to the drum.
Brake Fluid
Brake fluid is a specially blended hydraulic fluid
that transfers pressure to the wheel cylinders or
calipers. Brake fluid is one of the most important
components of a brake system because it ties all of the
other components into a functioning unit.
Drum Brake Assemblies
Vehicle manufacturers recommend brake fluid
that meets or exceeds SAE (Society of Automotive
Engineers) and DOT (Department of Transportation)
Drum brakes have a large drum that surrounds the
brake shoes and hydraulic wheel cylinder. Drum brake
assemblies consist of a backing plate, wheel cylinder,
brake shoes and linings, retracting springs, hold-down
springs, brake drum, and adjusting mechanism.
Brake fluid must have the following
BACKING PLATE.—The backing plate holds
the brake shoes, springs (retracting and hold-down),
wheel cylinder, and other associated parts inside the
brake drum. It also assists in keeping road dirt and
water out of the brakes. The backing plate bolts to the
axle housing or spindle.
Low freezing point (not freeze during cold
Water tolerance (absorb moisture that collects in
the system)
WHEEL CYLINDER.—The wheel cylinder
assembly uses master cylinder pressure to force the
brake shoes out against the brake drum. It is normally
bolted to the top of the backing plate. The wheel
Lubricate (reduce wear of pistons and cups)
Noncorrosive (not attack metal or rubber brake
system components)
cylinder consists of a cylinder or housing, expander
spring, rubber cups, pistons, dust boots, and bleeder
screw (fig. 7-10).
Brake shoes are made of malleable iron, cast steel,
drop forged steel, pressed steel, or cast aluminum.
Pressed steel is the most common because it is cheaper
to produce in large quantities. Steel shoes expand at
about the same rate as the drum when heat is generated
by braking application, thereby maintaining the
correct clearance between the brake drum and brake
shoe under most conditions.
The wheel cylinder housing encloses all the
other parts of the assembly. It has a precision cylinder in
it for the pistons, cups, and spring.
The expander spring assists in holding the rubber
cups against the pistons when the assembly is NOT
pressurized. Sometimes the end of the springs has metal
expanders (cup expanders) that help to press the outer
edges of the cups against the wall of the wheel cylinder.
Automotive brake shoes consist of a primary and
secondary shoe. The primary brake shoe is the front
shoe and normally has a slightly shorter lining than the
secondary shoe. The secondary shoe is the rear shoe
and has the largest lining surface area.
The wheel cylinder cups are special rubber seals
that keeps fluid from leaking past the pistons. They fit in
the cylinder and against the pistons.
Variation in brake design and operating conditions
makes it necessary to have different types of brake
linings. Brake linings come in woven and molded form
(fig. 7-11).
The wheel cylinder pistons transfer force out of
the wheel cylinder. These metal or plastic plungers act
on pushrods that are connected to or directly on the
brake shoes.
The molded form is currently used on modern
vehicles. Molded brake lining is made of dense,
compact, asbestos fibers, sometimes impregnated with
fine copper wire, and cut into sizes to match the brake
shoe. Depending on how much metal fiber is used in
their construction determines how they are classified,
either as nonmetallic, semimetallic, and metallic
The dust boots keep road dirt and water from
entering the cylinder. They snap into grooves that are
cast on the outside of the housing.
The bleeder screw provides a means of removing
air from the brake system. It threads into a hole in the
back of the wheel cylinder. When the screw is loosened,
hydraulic pressure is used to force air and fluid out of the
Nonmetallic linings contain very few metal
fibers. This type of lining is used on many vehicles
because of its quiet operation and good heat transfer
qualities. Because of the lack of metal particles, the
nonmetallic linings wear well with brake drums and do
not tend to wear the drum excessively.
BRAKE SHOES.—Brake shoes are used to
support, strengthen, and move the brake lining.
Because the brake lining material is soft and brittle, it is
necessary to add a supportive foundation to the lining
so it will not collapse and break during use. The brake
shoes also serve to attach the brake lining to a
stationary unit. usually the backing plate. so braking
action can be accomplished.
Semimetallic linings have some metal particles
in their composition. They also have good wearing
properties and are quiet during application.
Metallic linings have a high degree of metal fiber
in their construction and are generally characterized by
small pads bonded or welded to the brake shoe. The
pads may have a small space between them to aid in
cooling. The metallic linings operate at high
temperatures and may require the use of special
high-temperature brake parts. Metallic brake linings are
generally used for heavy-duty brake application where
large loads must be stopped or brakes are applied often.
Brake lining is riveted or bonded to the face of the
brake shoe. Semitubular brass rivets are used to attach
the lining to the shoe. Brass rivets are chosen over
other types because brass does not score the brake
drums excessively if the lining should be neglected and
worn past the point of replacement.
Figure 7-10.—Cross section of a wheel cylinder.
Figure 7-11.—Brake shoes and brake lining.
The lining may also be bonded directly to the brake
shoe. In this process, a special bonding agent (glue) is
used to adhere the lining to the brake shoe. After
application, the shoe is baked at a predetermined
temperature to ensure proper setting of the bonding
capable of withstanding the high temperatures
encountered inside the brake drum.
BRAKE DRUMS.—The brake drum is attached
to the wheel and provides the rotating surface for the
brake linings to rub against to achieve braking action.
The brake drum is grooved to mate with a lip on the
backing plate that provides the rotating seal to keep
water and dirt from entering the brake assembly.
BRAKE SPRINGS.—The brake springs within
the brake drum assembly are the retracting springs and
the hold-down springs. The retracting springs pull the
brake shoes away from the brake drum when the brake
pedal is released. The springs apply pressure to the
brake shoes which push the wheel cylinder pistons
inward. The retracting springs fit in holes in the brake
shoes and around the anchor pin at the top of the
backing plate.
Brake drums may be made of pressed steel, cast
iron, a combination of the two metals, or aluminum.
Cast-iron drums dissipate the heat generated by
friction faster than steel drums and have a higher
coefficient of friction with any particular brake lining.
However, cast-iron drums of sufficient strength are
heavier than steel drums. To provide lightweight and
sufficient strength, use CENTRIFUSE brake drums
(fig. 7-12). These drums are made of steel with a
cast-iron liner for the braking surface. A solid cast-iron
drum of the same total thickness as the centrifuse drum
would be too weak, while one of sufficient strength
would be too heavy for the average vehicle.
Hold-down springs hold the brake shoes against
the backing plate when the brakes are in a released
position. A hold-down pin fits through the back of the
backing plate, the spring placed over the pin, and a
metal cup locks onto the pins to secure the hold-down
springs to the shoes. Other springs are used on the
adjusting mechanism. Brake springs are high quality,
Figure 7-12.—Brake drum construction.
if exceeded, it should be discarded and replaced with a
new one.
Aluminum brake drums are constructed similar to
the centrifuse drums. They consist of an aluminum
casting with a cast-iron liner for a braking surface. This
design allows heat to be transferred to the surrounding
atmosphere more readily and also reduces weight.
adjusters maintain correct drum-to-lining clearance, as
the brake linings wear. Automatic brake shoe adjusters
normally function when the brakes are applied with the
vehicle moving in reverse. If there is too much lining
clearance, the brake shoes move outward and rotate
with the drum enough to operate the adjusting lever.
This lengthens the adjusting mechanism, and the
linings are moved closer to the brake drum, thereby
maintaining the correct lining-to-drum clearance.
Cooling fins or ribs are added to most brake drums.
The fins or ribs increase the surface area of the outside
portion of the brake drum, allowing the heat to be
transferred to the atmosphere more readily, which
keeps the drum cooler and helps minimize brake fade.
For good braking action, the brake drum should be
perfectly round and have a uniform surface. Brake
drums become out-of-round from pressure exerted by
brake shoes and from heat developed by application of
the brakes. The brake drum surface becomes scored
when it is worn by braking action. When the braking
surface is scored or the brake drum is out-of-round, it
may be necessary to machine the brake drum until it is
smooth and true again. Care must be taken not to
exceed the maximum allowable diameter according to
the manufacturer's specification. Each drum is
stamped with the maximum diameter information and.
Many vehicles use a star wheel (screw) type brake
shoe adjusting mechanism. This type consists of a star
wheel (adjusting screw assembly), adjuster lever,
adjuster spring, and an adjusting mechanism. The
adjustment system may grouped as follows (fig. 7-13):
Cable type—The cable type self-adjusting
system (fig. 7-13) uses a braided steel cable and the
expanding action of both brake shoes to accomplish the
self-adjusting action in forward and reverse directions.
A one-piece cable is attached to the adjusting lever and
passes through a cable guide on the primary shoe. The
Figure 7-13.—Self-adjusting mechanisms.
the adjusting lever will engage the next tooth on the star
wheel. The brake shoes retract and the cable slackens, as
the brakes are released. The return spring then helps
force the adjusting lever downward, rotating the star
wheel, which expands the brake shoes. In the reverse
direction, the toe of the primary shoe is forced against
the anchor, and the secondary shoe moves around to
tighten the adjusting cable. The adjusting process is
then completed.
cable then is passed up and over the anchor and attached
to the secondary shoe. Operation is as follows:
1. Brakes are applied and the shoes expand and
contact the drum.
2. The primary shoe self-energizes, and, through
servo action, applies the secondary shoe.
3. The heel of the secondary shoe is lodged against
the anchor pin.
Link type—The link type self-adjusting system
(fig. 7-13) uses solid linkage rods to connect the
adjusting lever to the stationary anchor point. The two
linkage rods, connected together by a bell crank that
pivots on the secondary brake shoe, operate the adjuster.
One rod attaches to the anchor point and the bell crank,
4. The movement of the primary shoe tightens the
cable by shifting the cable guide outward and in the
direction of rotation.
5. The cable then moves the adjusting lever
upward. If enough shoe-to-drum clearance is available,
both shoes are linked together, the rotating force of the
primary shoe applies the secondary, (rear) shoe.
while the other rod connects the bell crank and the
adjusting lever. In this configuration. the self-adjuster
works only in reverse direction. As the vehicle is
backing up and the brakes are applied, the adjusting
process is as follows:
In the forward position, the anchor point for both
brake shoes is at the heel of the secondary, shoe. As the
vehicle changes direction from forward to reverse, the
toe of the primary shoe becomes the anchor point, and
the direction of self-energization and servo action
changes (fig. 7-14). The most popular brake drum
configurations (fig. 7-15) are as follows:
1. The secondary, shoe moves away from the
anchor because of the self-energizing action.
2. The pivot point of the bell crank is moved in
the direction of rotation.
Single anchor, self-energizing servo action (fig.
7-15)—In this configuration both brake shoes are
self-energizing in both forward and reverse directions.
The brake shoes are self-centering and provide servo
action during brake application. This system is provided
with one anchor pin. which is rigidly mounted to the
backing plate and is nonadjustable. Both forward and
reverse torque is transmitted to the backing plate
through the anchor pin. One wheel cylinder with dual
pistons is used in this system.
3. The lever moves up on the star wheel
through the connection of the linkage. If enough
clearance is available between the brake shoes and
the drum, the lever will engage another tooth on the
star wheel. As the brakes are released. the shoes
retract and the return spring helps force the adjusting
lever down, rotating the star wheel and expanding the
adjusting screw to remove excess shoe-to-drum
Single anchor, self-centering (fig. 7-15)—In this
configuration only the primary brake shoe is
self-energizing in the forward direction; therefore. it
provides the majority of the brake force. This system is
self-centering in that the lower brake shoe anchor does
not fix the position of the brake shoes in relation to the
drum. The shoes are allowed to move up and down as
needed. Some systems provide eccentric cams for front
and rear brake shoe adjustments. One wheel cylinder is
provided in this system.
Lever type—The lever type self-adjusting
system (fig. 7-13) is similar to the link type, in that it
operates in reverse direction only. While the link type
system uses linkage rods to perform the adjusting
process, the lever type uses a stamped metal lever to
engage the star wheel and actuating link to connect to
the anchor pin. The adjusting process is the same as the
link type system.
Brake Shoe Energization
Double anchor, single cylinder (fig. 7-15)—In
this arrangement, each brake shoe is anchored at the
bottom by rotating eccentric-shaped anchor pins. Only
the primary shoe is self-energizing. and the system does
not develop servo action. Spring clips are used in the
middle of the shoe to hold the shoes against the backing
plate. Brake shoes are adjusted manually by rotating the
anchor pins. One wheel cylinder is provided in this
The primary function of the brake drum assembly
is to force the brake shoes against the rotating drum to
provide the braking action. When the brake shoes are
forced against the rotating drum. they are pulled away
from their pivot point by friction. This movement,
called self-energizing action (fig. 7-14), draws the
shoes tighter against the drum.
As the brake actuating mechanism forces the
brake shoes outward, the top of the brake shoe tends
to stick or wedge to the rotating brake drum and
rotates with it. This effect on brake shoes greatly
reduces the amount of effort required to stop or slow
down the vehicle.
Double anchor. double cylinder (fig. 7-15)—In
this system the brake shoes are provided with an anchor
at each heel. The anchors are eccentric-shaped to allow
for adjustment and centering. Each shoe has a single
piston wheel cylinder mounted at the toe of the brake
shoe. Which allows both shoes to be self-energizing in
the forward direction only. Eccentrics mounted in the
middle of the shoe also allow for brake adjustment.
With most drum brake designs, shoe energization
is supplemented by servo action. When two brake
shoes are linked together, as shown in figure 7-14, the
application of the brakes will produce a
self-energizing effect and also a servo effect. Servo
action is a result of the primary (front) shoe attempting
to rotate with the brake drum. Because of the fact that
Disadvantages of Drum Brakes
The drum brake assembly, although well suited for
wheeled vehicles, has some disadvantages. One
Figure 7-14.—Self-energizing and servo action.
problem that occurs during heavy braking is brake
fade. During panic stops or repeated harsh stops, the
brake linings and drum develop large amounts of heat
that reduces the amount of friction between the brake
shoe and drum. This reduction in friction greatly
decreases the stopping ability of the vehicle, and, in
most cases, additional pressure directed on the brake
pedal would not increase the stopping performance of
the vehicle.
cooling air flowing past the drums and backing plates
is limited. This condition causes the radius of the drum
to increase more than the radius of the brake shoe. As a
result, a change in pressure distribution between the
linings and the drum occurs, which reduces the braking
ability of a vehicle by up to 20 percent.
The enclosed design also does not allow for water
to be expelled rapidly should the brake cavity become
wet due to adverse weather conditions. The water
reduces the frictional properties of the brake system
and must be removed to restore braking ability. This is
a very dangerous situation and drastically reduces the
stopping ability of the vehicle until the system is dry.
The enclosed design of the brake drum assembly
does not allow for cooling air to enter the assembly and
therefore heat developed during braking must be
dissipated through the brake drum and backing plate.
As the brakes heat up due to repeated application,
Figure 7-15.—Brake drum configurations.
consequent marked reduction in the distance required
to stop the vehicle.
The use of many clips and springs makes overhaul
of the brake drum assembly very time-consuming.
Because of the enclosed drum. asbestos dust is
collected in the brake cavity and certain parts of the
brake drum.
Braking with disc brakes is accomplished by
forcing friction pads against both sides of a rotating
metal disc, or rotor. The rotor turns with the wheel of
the vehicle and is straddled by the caliper assembly.
When the brake pedal is depressed, hydraulic fluid
forcesthe pistonsand friction linings (pads) against the
machined surfaces of the rotor. The pinching action of
the pads quickly creates friction and heat to slow down
or stop the vehicle.
Asbestos can cause cancer. Grinding
brake lining and cleaning of the brake
assembly can cause small particles of asbestos
to become airborne. Always wear personal
protection equipment. Dispose of waste
material and cleaning rags as hazardous waste.
For more information. see OPNAVINST
4110.2, Hazardous Material Control and
Disc brakes do not have servo or self-energizing
action. Therefore, the applying force on the brake
pedal must be very great in order to obtain a brake force
comparable to that obtained with the conventional
drum brake. Consequently, disc brakes are provided
with a power or booster unit and a conventional master
With the demands for increased safety in the
operation of automotive vehicles, many are now
equipped with disc brakes. The major advantage of the
disc brake is a great reduction in brake fade and the
In many installations, disc brakes are used only on
the front wheels and drum brakes are continued on the
rear. However, you may on occasion find disc brakes
used on all four wheels.
the caliper housing. When loosened, system pressure is
used to force fluid and air out of the bleeder screw.
Disc Brake Assembly
Disc brakes are basically like the brakes on a
ten-speed bicycle. The friction elements are shaped
like pads and are squeezed inwards to clamp a rotating
disc or wheel. A disc brake assembly consists of a
caliper, brake pads, rotor, and related hardware (bolts,
clips, and springs), as shown in figure 7-16.
DISC BRAKE PADS.—Disc brake pads consist
of steel shoes to which the lining is riveted or bonded.
Brake pad linings are made of either asbestos (asbestos
fiber filled) or semimetallic (metal particle filled)
friction material. Many new vehicles, especially those
with front-wheel drive, use semimetallic linings.
Semimetallic linings withstand higher operating
temperatures without losing their frictional properties.
nonrotating unit in the system and it may be mounted to
the spindle or splash shield to provide support. The
brake caliper assembly includes the caliper housing,
the piston(s), the piston seal(s), the dust boot(s), the
brake pads or shoes, and the bleeder screw.
Antirattle clips are frequently used to keep the
brake pads from vibrating and rattling. The clip snaps
onto the brake pad to produce a force fit in the caliper.
In some cases, an antirattle spring is used instead of a
The caliper is fitted with one or more pistons that
are hydraulically actuated by the fluid pressure
developed in the system. When the brake pedal is
applied, brake fluid flows into the caliper cylinder. The
piston is then forced outward by fluid pressure to apply
the brake pads to the rotor.
A pad wear indicator (a metal tab) informs the
operator of worn brake pad linings. The wear indicator
produces an audible high-pitch squeak or squeal, as it
scrapes against the brake disc. This harsh noise is a
result of the linings wearing to a point, allowing the
indicator to rub against the brake disc, as the wheel
The piston seal in the caliper cylinder prevents
pressure leakage between the piston and cylinder. The
piston seal also helps pull the piston back into the
cylinder when the brakes are released. The elastic
action of the seal acts as a spring to retract the piston
and maintain a clearance of approximately 0.005 inch
when the brakes are released.
BRAKE DISC.—Also called brake rotor, the
brake disc uses friction from the brake pads to slow or
stop the vehicle. Made of cast iron, the rotor may be an
integral part of the wheel hub. However, on many
front-wheel drive vehicles, the disc and hub are
separate units.
The piston boot keeps road dirt and water off the
caliper piston and wall of the cylinder. The boot and
seal fit into grooves cut in the caliper cylinder and
The brake disc may be a ventilated rib or solid
type. The ventilated rib disc is hollow that allows
cooling air to circulate inside the disc.
A bleeder screw allows air to be removed from the
hydraulic system. It is threaded into the top or side of
Disc Brake Types
Disc brakes can be classified as floating, sliding,
and fixed caliper types. Floating and sliding are the
most common types. The fixed caliper may be found
on older vehicles.
FLOATING CALIPER.—The floating caliper
type disc brake (fig. 7-17) is designed to move laterally
on its mount. This movement allows the caliper to
maintain a centered position with respect to the rotor.
This design also permits the braking force to be applied
equally to both sides of the rotor. The floating caliper
usually is a one-piece solid construction and uses a
single piston to develop the braking force.
Operation of a floating caliper is as follows:
Fluid under pressure enters the piston cavity and
forces the piston outward. As this happens the
brake pad contacts the rotor.
Figure 7-16.—Disc brake assembly.
Figure 7-17.—Floating caliper.
Additional pressure then forces the caliper
assembly to move in the opposite direction of the
piston, thereby forcing the brake pad on the
opposite side to contact the rotor.
surfaces of the caliper adapter when the brakes are
FIXED CALIPER.—The fixed caliper disc brake
(fig. 7-19) is rigidly mounted to the spindle or splash
shield. In this design, the caliper usually is made in two
pieces and has two or more pistons in use.
As pressure is built up behind the piston, it forces
the brake pads to tighten against the rotor. This
action develops additional braking force.
The pistons accomplish the centering action of the
fixed caliper, as they move in their bores. If the lining
should wear unevenly on one side of the caliper, the
piston would take up the excess clearance simply by
moving further out of the bore.
caliper type disc brake (fig. 7-18) is mounted in a slot
in the caliper adapter. It is a variation of the floating
caliper, using a single piston and operating on the same
principle, whereby the piston applies pressure to one
brake pad and the movable caliper applies pressure to
the other.
As the brakes are applied, fluid pressure enters the
caliper on one side and is routed to the other through an
internal passage or by an external tube connected to the
opposite half of the caliper. As pressure is increased,
the pistons force the brake pads against the rotor
evenly, therefore maintaining an equal amount of
pressure on both sides of the rotor.
This design has two major sections—the sliding
caliper and the caliper adapter (anchor plate). Each has
two angular machined surfaces: this is where the
sliding contacts come into play. The machined
surfaces of the caliper housing slide on the mated
There are several types of switches and control
valves used in hydraulic brake systems. Switches are
normally safety devices. and there are two types
used—the stoplight switch and the braking warning
light switch. Control valves regulate pressure within
the braking system, and there are three types—the
metering valve, the proportioning valve. and the
combination valve.
Figure 7-18.—Sliding caliper.
Figure 7-19.—Fixed multipiston caliper.
preventing the disc brakes from applying until
approximately 75 to 135 psi has built up in the system.
Stoplight Switch
The stoplight switch is a spring-loaded electrical
switch that operates the rear brake lights of the vehicle.
Most modern vehicles use a mechanical switch on the
brake pedal mechanism. The switch is normally open,
and when the brake pedal is depressed, the switch
closes and turns on the brake lights.
Proportioning Valve
The proportioning valve also equalizes braking
action with front disc brakes and rear drum brakes. It is
located in the brake line to the rear brakes. The
function of the proportioning valve is to limit pressure
to the rear brakes when high pressure is required to
apply the front disc. This prevents rear wheel lockup
and skidding during heavy brake applications.
On some older vehicles you may find
hydraulically operated stoplight switches. In this
system, brake pressure acts on a switch diaphragm,
which closes the switch to turn on the brake lights.
Combination Valve
The combination valve (fig. 7-20) combines
several valve functions into a single assembly. It
functions as a—
Brake light circuits are covered in chapter
2 of this TRAMAN.
Metering valve—holds off front disc braking
until the rear drum brakes make contact with the
Brake Warning Light Switch
Proportioning valve—improves front to rear
brake balance at high deceleration by reducing
rear brake pressure to delay rear wheel skid.
The brake Learning light switch, also called the
pressure differential valve, warns the operator of a
pressure loss on one side of a dual brake system. If a
leak develops in either the primary or secondary brake
system. unequal pressure acts on each side of the
warning light piston, moving the piston to one side
thereby grounding the switch.
Brake light warning switch (pressure differential
valve)—lights a dash-warning lamp if either
front or rear brake systems fail.
Metering Valve
The antilock brake system (ABS) is used because
it provides CONTROL. Skidding causes a high
percentage ofvehicle accidents on the highway and the
ABS (fig. 7-21), also known as a skid control brake
system, uses wheel speed sensors, hydraulic valves,
and the on-board computer to prevent or limit tire
The metering valve is designed to equalize braking
action at each wheel during light brake applications. A
metering valve is used on vehicles with front disc
brakes and rear drum brakes and is located in the line to
the disc brakes. The metering valve functions by
lockup. The basic parts of an antilock brake system are
as follows:
ABS COMPUTER—a microcomputer that
functions as the "brain" of the ABS system. The
computer receives wheel-end performance data from
each wheel speed sensor. When the wheels try to lock,
the computer delivers commands to operate the
hydraulic actuator to control brake pressure. The
computer also monitors brake pedal position, detects
and prevents potential wheel lockup conditions while
maintaining optimum braking performance, stores and
displays diagnostic codes, and alerts the operator of a
system malfunction by turning on the system lamp.
HYDRAULIC ACTUATOR—an electrichydraulic valve that modulates the amount of braking
pressure (psi) going to a specific wheel circuit.
TRIGGER WHEELS—a toothed ring that is
mounted on each wheel spindle or hub.
sensor that uses trigger wheel rotation to produce a
weak alternating current.
The operation of an antilock brake system is as
Figure 7-20.—Combination valve.
A wheel speed sensor is mounted at each wheel
to measure trigger wheel rotation in rpms. The sensor
sends alternating or pulsing current signals to the ABS
If one or more wheels decelerate at a rate above
an acceptable perimeter, the sensor signals reduce
frequency and the ABS computer activates the
hydraulic actuators. The actuator then cycles ON and
OFF as much as 15 times per second to reduce braking
pressure to the brake assembly for that wheel. This
action prevents the vehicle from skidding.
The ABS computer will continue to modulate
brake pressure until the operator releases the brake
pedal, the wheel speed sensor no longer detects a lockup
condition, or the vehicle stops.
Tips on using antilock braking systems are as
Always "brake and steer" when using antilock
brakes. Most operators were taught to pump the brakes
and turn hard to the right or left to compensate for
skidding. With antilock brakes, all a operator needs to
do is "brake and steer." With four-wheel antilock
brakes, push the brake pedal hard while steering
normally and keep your foot firmly on the brake pedal
until the vehicle comes to a complete stop. Operators
Figure 7-21.—Basic antilock brake system.
with rear-wheel antilock brakes should step firmly with
care. and if they feel the wheel locking, they should
release some pressure.
stopping or holding a vehicle stationary. The booster is
located between the brake pedal linkage and the master
Expect noise and vibration in the brake pedal
when antitock brakes are in use. The mechanical noise
or pulsation of antilock brakes when in use might catch
an operator by surprise; however, these sensations tell
you that the system is working.
Most power brake systems use the difference
between intake manifold vacuum and atmospheric
pressure to develop the additional force required to
apply the brakes. When the operator depresses the
brake pedal, the power booster increases the amount of
pressure applied to the piston within the master
cylinder without the operator having to greatly
increase brake pedal pressure.
Remember that you can steer while braking with
a four-wheel antilock brake system. Steering is not
always instinctive in an emergency. But steer out of
danger while braking with antilock brakes. And
remember that while you have steering capability, your
vehicle may not turn as quickly white braking on a
slippery road, as it would on dry pavement.
When a vehicle is powered by a diesel engine, the
absence of intake manifold vacuum requires the use of
an auxiliary vacuum pump. This pump may be driven
by the engine or by an electric motor.
Vacuum Boosters
The rear-wheel antitock brakes typically found on
light-duty trucks provide vehicle stability but do not give
you the steering capability of four-wheel antilock brakes.
On many modern vehicles, vacuum boosters are
used with the hydraulic brake system to provide easier
brake application. In a hydraulic brake system there
are limitations as to the size of the master cylinder and
wheel cylinders that can be practically employed.
Furthermore, the physical strength of the operator
limits the amount of force that can be applied, unless
the brakes are self-energizing. These factors restrict
the brake shoe to brake drum pressure obtainable.
Vacuum boosters increase braking force.
Anti lock brakes can often stop more quickly than
conventional brakes but they can’t overcome the law of
physics. Antilock brakes function well on wet-paved
surfaces and icy or packed snow-covered roads.
Stopping times will be longer on gravel or fresh snow,
although operators won’t experience the dangerous
lockup of wheels usually associated with conventional
A vacuum booster consists of a round enclosed
housing and a diaphragm. The power brake vacuum
booster uses engine vacuum (or vacuum pump action on a
diesel engine) to apply the hydraulic brake system.
Vacuum boosters are classified into two types (fig.7-22)—
atmospheric suspended and vacuum suspended. The
descriptions of the two types are as follows:
Drive safely because antilock brakes are only as
good as the operators using them. Antilock brakes
cannot compensate for driving too fast, too aggressively
or failing to maintain a safe distance between vehicles.
They cannot guarantee recovery from a spin or skid
before braking. Also avoid extreme steering maneuvers
while antilock brakes are engaged.
An atmospheric suspended brake booster (fig.
7-22) has normal air pressure on both sides of the
diaphragm when the brake pedal is released. As the
brakes are applied, a vacuum is formed in one side of the
booster. Atmospheric pressure then pushes on and
moves the diaphragm.
Your antilock braking system instrument panel
tight will go on for a few seconds after starting the
ignition. The tight goes on so the system can conduct the
normal system test. If the tight does not go on during
ignition or if the tight goes on during normal driving,
this means that a problem has been detected and the
antilock braking system has been shut off. Conventional
braking will continue. Consult the manufacturer’s
service manual if this problem occurs.
An vacuum suspended brake booster (fig. 7-22)
has vacuum on both sides of the diaphragm when the
brake pedal is released. Pushing down on the brake
pedal releases vacuum on one side of the booster. The
difference in air pressure pushes the diaphragm for
braking action.
Since exact antitock brake systems vary, consult
the vehicle manufacturer’s service and repair manuals
for more details of system operation.
Air has a weight of approximately 15 pounds per
square inch at sea level. The weight of the air or
atmospheric pressure is what is used to operate the
vacuum booster.
Power brakes systems are designed to reduce the
effort required to depress the brake pedal when
Figure 7-22.—Vacuum power booster and operation.
were suddenly opened, outside air would rush into the
container to equalize the pressure. It is upon this
principle that the power cylinder of a vacuum booster
system operates.
It is impossible to create a perfect vacuum, but by
pumping air from a container, it is possible to obtain a
difference in pressure between the outside and inside
of the container. or a partial vacuum. If the container
while heavy pressure upon the brake pedal will cause
severe brake application. If the vacuum section of the
power booster should fail, brake application can still
be obtained by direct mechanical pressure on the
master cylinder piston. However, the operator must
apply a greater force to the brake pedal to achieve even
minimal braking force.
The power brake operates during three phases of
braking application—brakes released, brakes applied,
and brakes holding. The operations of a typical
vacuum-suspended power booster are as follows:
RELEASED POSITION (fig. 7-22)—With the
brakes fully released and the engine operating, the rod
and plunger return spring moves the valve operating rod
and valve plunger to the right. As this happens, the right
end of the valve plunger is pressed against the face of the
poppet valve, closing off the atmospheric port and
opening the vacuum port. With the vacuum port opened,
vacuum is directed to both sides of the diaphragm, and
the return spring holds the diaphragm away from the
master cylinder.
The vacuum-hydraulic power booster, used in
most passenger vehicles and light trucks, is of the
integral type, so-called because the power booster and
the master cylinder are combined in a single assembly.
The most common integral types all use a single or
tandem diaphragm (fig. 7-23) and are of the vacuum
suspended type. The power unit uses a master cylinder
constructed in the same manner as the conventional
dual master cylinder.
APPLIED POSITION (fig. 7-22)—As the brake
pedal is depressed, the valve operating rod moves to the
left, which causes the valve plunger to move left also.
The valve return spring is then compressed as the
plunger moves and the poppet valve comes in contact
with the vacuum port seat. As this happens, the vacuum
port closes off. Continued application of the brake pedal
causes the valve rod to force the valve plunger from the
poppet, thereby opening the atmospheric port.
Atmospheric pressure then rushes into the control
vacuum chamber and applies pressure to the hydraulic
If brake trouble is encountered, check the brake
system in the same manner as for conventional brakes.
When a vehicle has vacuum type power brakes, you
should inspect the brake booster and vacuum hose.
Make sure the vacuum hose from the engine is in good
condition. It should not be hardened, cracked, or
swollen. Also check the hose fitting in the booster. If
the system is not performing properly, you should
check the power booster for correct operation as
Stop the engine and apply the brakes several
times to deplete the vacuum reserve in the
HOLDING POSITION (fig. 7-22)—As the
operator stops depressing the brake pedal, the plunger
will also stop moving. The reaction of the brake fluid
transmitted through the reaction disc now will shift the
valve plunger slightly to the right, shutting off the
atmospheric port. As this position is held, both sides of
the diaphragm contain unchanging amounts of pressure,
which exerts a steady amount of pressure on the
cylinder piston.
Partly depress the brake pedal, and while
holding it in this position, start the engine.
If the booster is operating properly, the brake
pedal will move downward slightly. If no action
is felt, the booster is not functioning.
If the power unit is not giving enough assistance,
check the engine vacuum. If engine vacuum is
abnormally low (below 14 inches at idle), tune up the
engine to raise the vacuum reading and again try the
brakes. A steady hiss, when the brake pedal is
depressed, indicates a vacuum leak, preventing proper
operation of the booster.
On many installations a vacuum reservoir is
inserted between the power booster and the intake
manifold. The purpose of the reservoir is to make
vacuum available for a short time to the booster unit
should the vehicle have to stop quickly with a stalled
engine. A check valve in the reservoir maintains a
uniform vacuum within the system should engine
vacuum drop off. This check valve prevents vacuum
from bleeding back to the intake manifold when
manifold vacuum is less than the vacuum in the
Vacuum failure, which results in a hard pedal, may
be due to a faulty check valve, a collapsed vacuum hose
to the intake manifold, or an internal leak in the power
A tight pedal linkage (insufficient pushrod
clearance) will also result in a hard pedal. If this
connection is free and the brakes still fail to release
properly, the power booster must be replaced.
All modern power brakes retain some pedal
resistance, permitting the operator to maintain a
certain amount of pedal feel. For example, a light
pressure upon the pedal will give a light braking force,
Figure 7-23.—Tandem-type booster.
as braking occurs. A lever assembly has control over
the valve position and the boost piston provides the
necessary force that operates the master cylinder. See
figure 7-25 for a parts breakdown of a booster
In addition to hydraulic system problems, the
brakes may fail to release as a result of a blocked
passage in the power piston, a sticking air valve, or a
broken air valve spring.
Any malfunction occurring in the power booster
will require removing the booster from the vehicle for
repair or replacement. Some power boosters may be
rebuilt or repaired; others are sealed and cannot be
disassembled. Should you have any questions
concerning repairs on the power brake system you are
working on, consult the manufacturer’s service manual
for proper procedures to follow when testing or
repairing a unit.
The hydroboost system has an accumulator built
into the system. The accumulator, which is either
spring-loaded or pressurized gas, is filled with fluid
and pressurized whenever the brakes are applied.
Should the power steering system fail because of lack
of fluid or a broken belt, the accumulator will retain
enough fluid and pressure for at least two brake
Hydraulic Boosters
The hydraulic-power booster, also called a
hydroboost (fig. 7-24), is attached directly to the
master cylinder and uses power steering pump
pressure to assist the operator in applying the brake
pedal. The hydraulic booster contains a spool valve
that has an open center that controls the pump pressure
Parking/emergency brakes are essential to the safe
operation of any piece of automotive or construction
equipment. Parking brakes interconnected with
service brakes are usually found on automotive
vehicles (fig. 7-26). A foot pedal actuates this type of
parking/emergency brake or a dash-mounted handle.
Figure 7-24.—Hydraulic power booster system.
Figure 7-25.—Hydraulic power booster assembly.
Figure 7-26.—Automotive type parking/emergency brakes, axle mounted.
Several types of parking/emergency brakes are
manufactured for construction equipment, such as the
external contracting, the drum, and the disc types (fig.
7-28). These are drive line brakes common to heavy
construction equipment. They are usually mounted on
the output shaft of the transmission or transfer case
directly in the drive line.
They are connected through a linkage to an equalizer
lever (fig. 7-27) rod assembly, and cables connected
to the parking/emergency brake mechanism within the
drums/discs (fig. 7-26) at the rear wheels.
Theoretically, this type of system is preferred for
heavy equipment because the braking force is
multiplied through the drive line by the final drive
ratio. Also, braking action is equalized perfectly
through the differential. There are some drawbacks to
this system, however—severe strain is placed on the
transmission system, and also the vehicle may move
when being lifted since the differential is not locked
Figure 7-27.—Equalizer linkage.
Figure 7-28.—Examples of drive line parking/emergency brakes, transmission mounted.
The parking/emergency brake must hold the
vehicle on any grade. This requirement covers both
passenger and commercial motor vehicles equipped
with either the enclosed type brake at each rear wheel
or a single brake mounted on the drive line. The
Federal Motor Carrier Safety Regulations
Pocketbook, par. 393-52. lists emergency brake
BRAKE PEDAL HEIGHT, which is the
distance from the pedal to the floor with the pedal at rest.
If the height is incorrect, there may be worn pedal
bushings, weak return springs, or a maladjusted master
cylinder pushrod.
which is measured from the floor to the brake pedal with
the brake applied. The average brake pedal reserve
distance is 2 inches for manual brakes and 1 inch for
power brakes. If the reserve distance is incorrect, check
the master cylinder pushrod adjustment. Also, there
may be air in the system or the automatic brake adjusters
may not be working.
Most vehicle manufacturers recommend periodic
inspection of the brake system. This involves checking
the fluid level in the master cylinder, brake pedal
action, condition of the lines and hoses, and the brake
assemblies. These checks are to be performed during
the preventive maintenance (PM) cycle.
Brake System Leaks
If the fluid level in the master cylinder is low, you
should check the system for leaks. Check all brake
lines, hoses, and wheel cylinders. Brake fluid leakage
will show up as a darkened, damp area around one of
the components.
Checking Master Cylinder Fluid Level
An important part of the brake system inspection is
checking the level of the brake fluid. To check the
fluid, remove the master cylinder cover, either by
unbolting the cover or prying off the spring clip. The
brake fluid level should be 1/4 inch from the top of the
Checking Brake Assemblies
When inspecting the brake system, remove one of
the front and rear wheels. This will let you inspect the
condition of the brake linings and other components.
check when inspecting disc brakes are the pads, the
disc, and the caliper. You should check the thickness of
the brake pad linings. Pads should be replaced when
the thinnest (most worn) part of the lining is
approximately 1/8 inch thick.
Use only the manufacturer’s recommended type of brake fluid. Keep grease, oil,
or other contaminates out of the brake fluid.
Contamination of the brake fluid can cause
deterioration of the master cylinder cups,
resulting in a sudden loss of braking ability.
Check the caliper for fluid leakage at the piston
seal and missing or damaged clips/springs. The disc
should be checked for damage, such as heat cracks,
heat checks (overheating causes small hardened and
cracked areas), and scoring. Wheel bearings should be
checked and adjusted if necessary. To check for rattles,
strike the caliper with a soft-faced rubber mallet. To
repair any of these problems, consult the
manufacturer’s service manual.
Brake Pedal Action
A quick and accurate way to check many of the
components of the brake system is by performing a
brake pedal check. Applying the brake pedal and
comparing its movement to the manufacturer’s
specifications does this. The three brake pedal
application distances are as follows:
check when inspecting drum brakes are the brake
shoes, the brake drums, the wheel cylinders, and other
related parts. Once the wheel is removed, you must
remove the brake drum that will expose all parts
requiring inspection.
amount of pedal movement before the beginning of
brake application. It is the difference between the “at
rest” and initially applied position. Free play is required
to prevent brake drag and overheating. If pedal free play
is NOT correct, check the adjustment of the master
cylinder pushrod. If this adjustment is correct, check for
a worn pedal bushing or a bad return spring, which can
also increase pedal free play.
The brake shoe linings must NOT be worn thinner
than 1/16 inch. They also should NOT be glazed or
coated with grease, brake fluid, or differential fluid.
Any of these conditions require lining replacement.
Check the brake drum for cracks, heat cracks. heat
checks, hard spots, scoring, or worn beyond
specifications. Damaged drums may be machined
(turned) as long as they still meet the manufacturer’s
specifications. Badly damaged or worn drums must be
If the cylinder is not pitted, scored, or corroded
badly, it may be honed using a cylinder hone. When the
cylinder is honed, the hone is ran ONLY once in and
out. After honing, measure the piston-to-cylinder
clearance, using a telescoping gauge and an outside
micrometer or a narrow (1/8" to 1/4" wide) 0.006"
feeler gauge. When a feeler gauge is used, if the gauge
can be inserted between the cylinder wall and the
piston, the master cylinder must be replaced. The
cylinder must NOT be tapered or worn beyond the
manufacturer’s specifications. Replace the master
cylinder if the cylinder is not in perfect condition after
To check the wheel cylinder for leakage, pull back
the cylinder boots. If the boot is full of fluid, the wheel
cylinder should be rebuilt or replaced. Also, check the
return springs and the automatic adjusting mechanism.
When major brake service is being performed, the
master cylinder is to be inspected for proper operation.
A faulty master cylinder usually leaks externally out
the rear piston or leaks internally. You are able to
detect external brake fluid leaks by checking the
master cylinder boot for fluid or dampness on the
firewall. When the leak is internal. the brake pedal will
slowly move to the floor. Inoperative valves in the
master cylinder are also a reason for service.
Blow-dry all parts with low-pressure compressed
air. Blow out the ports and check for obstructions.
Lubricate all parts with the recommended brake fluid
and assemble the master cylinder, using the
manufacturer’s service manual.
After the master cylinder is reassembled, it is good
practice to bench bleed a new or rebuilt master cylinder
before installation on the vehicle. A master cylinder is
bled to remove air from the inside of the cylinder.
Bench bleeding procedures are as follows:
To remove the master cylinder, disconnect the
brakes lines from the master cylinder using tubing
wrenches. With the brake lines disconnected, unbolt
the master cylinder from the brake booster or firewall.
In some cases. the pushrod must be disconnected from
the brake pedal.
Mount the master cylinder in a vise
Install short sections of brake line and bend them
back into each reservoir
Fill the reservoir with approved brake fluid
Many shops, however, simply, replace a bad master
cylinder with a factory rebuild or a new one. A
replacement master cylinder is normally cheaper than
the labor cost and parts for an in-shop rebuild.
Pump the piston in and out by hand until air
bubbles no longer form in the fluid
Remove the brake lines and install the reservoir
Once the master cylinder has been bench bled. it is
ready to be reinstalled on the vehicle. Bolt the master
cylinder to the booster or firewall. Check the
adjustment of the pushrod if there is a means of
adjustment provided. Without cross threading the
fittings, screw the brake lines into the master cylinder,
and lightly snug the fittings. Then bleed (remove air
from) the system. Tighten the brake line fittings. Refill
the reservoir to the proper level and check brake pedal
fall. Last but not least, test the vehicle.
NCF units require replacement of faulty
master cylinders. Rebuilding of master
cylinders is NOT authorized.
To rebuild a master cylinder, drain the fluid from
the reservoir. Disassemble the master cylinder
following the instructions in the manufacturer’s
service manual. After disassembly, clean the parts in
brake fluid or a recommended cleaner.
You should understand the most important
methods for servicing a drum brake. However. specific
procedures vary and you should always consult the
manufacturer’s service manual. Brake service is
required anytime you find faulty brake components. A
leaking wheel cylinder, worn linings, scored drum, or
Do NOT clean the hydraulic parts of the brake
system with conventional parts cleaners. They can
destroy the rubber cups in the brake system. Only use
brake fluid or a manufacturer’s suggested cleaner
(denatured alcohol. for example).
After honing, clean the cylinder thoroughly using
clean rags and recommended brake fluid. Make sure
the cylinder is clean and in perfect condition before
reassembly. The slightest bit of grit or roughness can
cause cup leakage.
other troubles require immediate repairs. A complete
drum brake service involves the following:
Removing, cleaning, and inspecting parts from
the backing plate
Replacing brake shoes
When reassembling the wheel cylinder, make sure
the new wheel cylinder cups are the same size as the
originals. Cup size is normally printed on the face of the cup.
Lubricate all parts with clean brake fluid and reassemble.
Resurfacing brake drums
Replacing or rebuilding wheel cylinders
Lubricating and reassembling brake parts
Readjusting, bleeding, and testing the brakes
Never allow any grease or oil to contact
the rubber parts or other internal components.
Grease or oil will cause the rubber parts to
swell. which will lead to brake failure.
Servicing Wheel Cylinders
Normally, faulty wheel cylinders aredetected when
fluid leaks appear or the pistons stick in the cylinders,
preventing brake application. Many shops service the
wheel cylinders anytime the brake linings are replaced.
Replacing Brake Shoe Linings
To replace the brake shoes, first remove the wheel
and brake drum. With the drum removed, note how the
springs and retainers are installed before attempting to
remove the shoes from the backing plate. This will
assist you during reassembly.
NCF units require replacement of faulty
wheel cylinders. Rebuilding of wheel
cylinders is NOT authorized.
If hydraulic brakes are being repaired, install a
wheel cylinder clamp (fig. 7-29) to prevent the pistons
from coming out of the wheel cylinder. Next, remove
the retracting springs with brake spring pliers or a
removal and installation tool (fig. 7-30). The brake
To rebuild a wheel cylinder, remove the boots, the
pistons, the cups, and the springs. Most wheel
cylinders can be disassembled and rebuilt on the
vehicle. However, many manufacturers recommend
that the wheel cylinder be removed from the backing
plate and serviced on the bench. This makes it easier
too properly clean, inspect, and reassemble. A rebuild
normally involves honing the cylinder and replacing
the cups and boots.
It is important that the cylinder be in good
condition. Inspect the cylinder bore for signs of pitting,
scoring, or scratching. Any sign of pitting, scoring, or
scratching requires cylinder replacement.
A brake cylinder hone is used when honing is
required. With the cylinder hone attached to an electric
drill, lubricate the hone with brake fluid and insert into
the cylinder. Turn the drill on and move the hone back
and forth one time ONLY. The cylinder bore must not
be honed more than 0.003 inch larger than the original
diameter. Replace the cylinder if the scoring cannot be
cleaned out or if the clearance between the bore and
pistons is excessive.
Figure 7-29.—Wheel cylinder clamp in use.
When honing a wheel cylinder, do not let
the hone pull out of the cylinder. The spinning
hone can fly apart causing bodily harm. Wear
eye protection.
Figure 7-30.—Removal of the brake return springs.
If the lining is riveted and is to be replaced, you
should mark the front and rear shoe. This action will
aid in reassembly. Wipe off the backing plate
thoroughly with a rag. If the backing plate is coated
with brake fluid or axle lubricant, wash it with an
approved cleaner. Once the backing plate is clean,
apply a light coat of high-temperature lubricant to the
raised pads on the backing plate. This will keep the
shoes from squeaking after they are reassembled.
Avoid using too much lubricant or the linings can
become contaminated and ruined.
shoe retainers must be removed next. Figure 7-31
shows one type being removed with a pair of ordinary
combination pliers. Heavy-duty brake shoes are
mounted on separate anchor pins. Some of these
installations require the removal of the anchor pins,
while others require the removal of clips on the end of
these pins before the brake shoes can be removed.
On light-duty applications, you can now grasp the
shoes (fig. 7-32) and lift them off the backing plate.
After they are removed, allow the shoes to move
together (fig. 7-33). This allows easy removal of the
spring and adjusting screw assembly. Disassemble the
adjusting screw and lubricate with a high-temperature
New linings are secured to the shoes by riveting or
bonding. Bonded brake linings are supplied with the
linings already attached to the shoes. At some
activities, the old shoes must be exchanged when
issued new shoes from the parts room. Linings that
require rivets to attach the linings to the shoes are
provided in kits. These kits provide enough linings and
rivets for one or more wheels. The linings are
predrilled and countersunk for the rivets and arced to
match the brake shoes.
Some shops have specialized equipment to remove
and replace the riveted linings. However, if the
equipment is not available. the old linings can be
removed with a drill and oversized bit, punch, and
hammer. Take care not to enlarge the rivet holes in the
shoes. If the rivet holes are enlarged, the shoe should be
Figure 7-31.—Removal of a brake shoe retainer.
Most NCF shops have a device for installing rivets.
This device comes with adapters for use with various
size rivets. When installing rivets. you always start in
the center of the lining and work alternately to each
end. Make sure the rivets are tight enough to hold the
lining securely without splitting the lining at the rivet
For installation of the new shoes, refer to the
manufacturer’s service manual. Your service manual
will have illustrations for the particular brake design
being serviced. Use them to ensure all parts are
positioned correctly, on the backing plate. When
reassembling the brake assemblies, ask yourself the
following questions:
Figure 7-32.—Removing shoes from the backing plate.
Are the wheel cylinders in perfect condition and
assembled properly?
Did I lubricate the backing plate and star wheel?
Is the primary (smaller) lining facing the front of
the vehicle and the secondary (larger) lining
facing the rear?
Figure 7-33.—Removing adjusting screw assembly.
Are the brake shoes centered on the backing
plate and contacting the anchor pin correctly?
Are all springs installed properly?
Does the automatic adjusting mechanism work?
Are the linings perfectly clean (sand if needed)?
Do I need to bleed the brakes?
Servicing Brake Drums
With the drum removed, inspect the shoes to
determine the condition of the drum. For instance, if
the linings are worn thin on one side, the drums are
likely to be tapered or bell-shaped. Linings with ridges
in their contact surfaces point out the need for
resurfacing (turning) the drum to remove the matching
Figure 7-35.—Using a drum micrometer to measure a brake
diameter quickly and accurately. Replace the drum if it
is worn beyond specifications.
For maximum braking efficiency after the drums
have been resurfaced, the arc of the shoes must match
the drums. This means that the linings must be ground
to match the curvature of the drum when it is
resurfaced. There should be a small clearance between
the ends of the lining and the drum. The shoes should
rock slightly when moved in the drum. If the center of
the linings is not touching the drum, the linings should
be arced (ground). Shops equipped with a commercial
brake lathe have a special attachment to perform this
task. If no attachment is available, the shoes can be
installed but the brakes will not become fully effective
until the linings wear enough to match the braking
surface of the drum. Frequent adjustments will be
needed until they wear sufficiently.
Resurfacing is needed when the drum is scored,
out-of-round, or worn unevenly. Some shops resurface
a drum anytime the brake linings are replaced, others
only when needed. Drums are resurfaced using a lathe
in the machine shop of an NMCB and at some shore
installations. Commercial brake drum lathes can be
found in some shops. Make sure you know how to
operate the lathe before attempting to resurface a
drum. Using the wrong procedures will damage the
drum and possible deadline the vehicle.
Before resurfacing the drum, check the
specifications that are cast into the drum (fig. 7-34) or
are provided in the maintenance manual. These
specifications tell you the maximum amount of surface
material that can be removed from the drum and still
provide adequate braking. Typically, a brake drum
should not be more than .060 inch oversize. For
esample. a drum that is 9 inches in diameter, when
new, must not be over 9.060 after resurfacing. To
measure brake drum diameter, use a special brake
drum micrometer (fig. 7-35). It will measure drum
All disc brake services begin with sight, sound,
and stopping test. The feel of the brake pedal adds a
check on the condition of the hydraulic system.
Stopping the vehicle will indicate whether the
brakes pull in one direction, stop straight, or require
excessive effort to stop. Listening while stopping
permits a fair diagnosis of braking noises, such as
rattles, groans, squeals, or chatters. Visually
inspecting the parts provides valuable information on
the condition of the braking system.
A complete disc brake service typically involves
four major operations, which are as follows:
Replacing worn brake pads
Rebuilding the caliper assembly
Resurfacing the brake discs
Figure 7-34.—Example of specification cast into a brake
Bleeding the system
Depending on the condition of the parts, the
mechanic may need to do one or more of the
operations. In any case. you must make sure the brake
assembly is in sound operating condition.
8. After new pads are installed, road test the
vehicle to make sure that the brakes are
operating properly and also seat the new pads.
Several (3 to 3) heavy braking applications will
Disc Brake Pad Replacement
Disc brakes have flat linings bonded to a metal
plate or shoe. The pad is not rigidly mounted inside the
caliper assembly; thus, it is said to float. These pads are
held in position by retainers or internal depressions
(pockets machined into the caliper).
It is acceptable to service just the rear or
front disc brakes. However. NEVER service
only the left or right brake assemblies; always
replace both sets to assure equal braking
A visual inspection on the condition of the pads
can be made after the wheel and tire is removed. The
inner shoe and lining can be viewed through a hole in
the top of the caliper, whereas the outer shoe and
linings can be viewed from the end of the caliper.
Since disc brake systems vary, consult the vehicle
manufacturer’s service and repair manuals for specific
details on the type of disc brakes you are working on.
Servicing Caliper Assemblies
A good rule in determining the need for pad
replacement is to compare lining thickness to the
thickness of the metal shoe. If the lining is not as thick
as the metal shoe, it should be replaced. The basic steps
for disc brake service are as follows:
When a caliper is frozen, leaking, or has extremely
high mileage, it is to be serviced. Servicing disc brake
caliper assemblies involve the replacement of the
piston, seals, and dust-boots. To perform this type of
service. it is necessary to remove the caliper assembly
from the vehicle. Basic steps for servicing the caliper
assemblies are as follows:
1. Siphon two thirds of the brake fluid from the
master cylinder. This action prevents fluid
overflow when the caliper piston is pushed
1. Remove the piston from the caliper by using air
pressure to push the piston from the cylinder.
Keep your fingers out of the way when using
compressed air to remove the pistons from the
caliper. Serious hand injuries can result.
7. Remove the caliper guide pins that holds the
caliper to the adapter. In typical applications,
positioners and bushings will come off with the
2. With the piston removed, pry out the old dust
boot and seal from the caliper. Keep all parts
organized on the workbench. Do not mix up
right and left side or front and rear parts.
3. Lift the caliper off the adapter and away from
the rotor. Do NOT let the caliper hang by the
brake hose. Hook or tie the caliper to a
suspension member. This will allow the rotor to
be tested and inspected.
3. Check the caliper cylinder wall for scoring.
pitting, and wear. Light surface imperfections
can usually be cleaned with a cylinder hone or
emery cloth. When honing, use brake fluid to
lubricate the hone. If excessive honing is
required, replace the caliper.
4. Remove old pads from the caliper and adapter.
Note the position of antirattle clips because they
may be reused if they are in good condition.
5. Using a C-clamp or large screwdriver. force the
piston back into the caliper. This action will
open the caliper wide enough for new, thicker
4. Check the piston for wear and damage. If any
problems are found, replace the piston. The
piston and cylinder are critical and must be in
perfect condition.
6. Install the antirattle clips on the new pads. Fit
the pads back into the caliper.
5. Clean all parts with an approved cleaner. Wipe
the parts with a dry, clean rag. Then coat the
parts with brake fluid.
7. Slide the caliper assembly over the rotor.
Assemble the caliper mounting hardware in
reverse order of disassembly. Make sure all
bolts are torqued to the manufacturer’s
6. Assemble the caliper in reverse order of
disassembly. Using new seals and boots, fit the
new seal in the cylinder bore groove. Work the
seal into its groove with your fingers. Install the
new boot in its groove. Coat the piston with
more brake fluid. Spread the boot with your
fingers and slide the piston into the cylinder.
The caliper can now be reinstalled on the
Using a magnetic base, attach the dial indicator to the
hub. Position the dial indicator so it touches the face of
the disc. Rotate the disc by hand and read the indicator.
Compare the indicator reading to factory
specifications. Typically, disc runout should not
exceed .004 inch. If runout is beyond specifications,
resurface the disc to its true friction surface.
Carefully follow the procedures given in the
manufacturer’s service and repair manuals for specific
details when removing, repairing, and reinstalling disc
brake caliper assemblies.
disc is in good condition, most manufacturers do NOT
recommend disc resurfacing. Disc resurfacing is done
when absolutely necessary.
Brake Disc (Rotor) Service
When using a brake lathe to resurface a brake disc,
you use the appropriate spacers and cones to position
the disc on the arbor of the machine. Wrap a spring or
rubber damper around the disc to prevent vibration.
Follow the directions provided with the brake lathe.
It is important to check the condition of the brake
disc when servicing the brake system. Vehicle
manufacturers provide specifications for minimum
disc thickness and maximum disc runout. The disc
must also be checked for scoring, cracking, and heat
checking. Disc resurfacing is required to correct
runout, thickness variation, or scoring.
Do not attempt to operate a brake lathe
without first obtaining proper training.
Damage to the machine or injury to the
operator can occur as a result of incorrect
operating procedures.
M E A S U R I N G D I S C T H I C K N E S S .—To
measure disc thickness, use an outside micrometer.
Disc thickness is measured across the two friction
surfaces in several locations. Variation in disc
thickness indicates wear. Compare your
measurements to the manufacturer’s specifications.
Only take off enough metal to true the disc. Then
without touching the machined surfaces with your
fingers, remove the disc. This prevents body oil from
penetrating the machined surfaces. Check the disc for
thickness and reinstall on the vehicle.
Minimum disc thickness will sometimes be
printed on the side of the disc (fig. 7-36). If not, refer to
the manufacturer’s service manual or a brake
specification chart. If disc thickness is under
specifications. replace the disc, because a thin disc
cannot dissipate heat properly and may warp or fail
during service.
Brake system bleeding is the use of fluid pressure
to force air from the system. The brake system must be
free of air to function properly. Air in the system will
compress, causing a springy or spongy brake pedal.
Air may enter the system any time a hydraulic
component (wheel cylinder, master cylinder, hose, or
brake line) is disconnected or removed. There are two
methods of bleeding brakes—manual bleeding and
pressure bleeding.
BRAKE DISC RUNOUT.—The amount of
side-to-side movement, measured near the outer
friction surface of the disc, is known as brake disc
runout. Runout is measured using a dial indicator.
Manual Bleeding
Manual bleeding uses master cylinder pressure to
force fluid and trapped air out of the system. To bleed
the system, proceed as follows:
Fill the master cylinder reservoir with brake
fluid to 1/4 inch from the top, and keep it full
during bleeding operations.
Figure 7-36.—Example of minimum thickness specification
cast into a brake disc.
Attach a short length of a rubber hose to the
wheel cylinder bleeder screw and allow the other
end of the hose to be submerged in a jar halfway
filled with brake fluid (fig. 7-37).
Have an assistant push on the brake pedal to
apply pressure on the brake system. It may be
necessary to pump the brake six to seven times to
build up pressure in the system.
Open the bleeder screw while watching for air
bubbles in the fluid located in the jar.
Close the bleeder screw and tell your assistant to
release the brake pedal. Repeat this procedure
until no air bubbles come out of the hose.
Figure 7-38.—Pressure bleeding a brake system.
Bleed one wheel cylinder at a time. Do the one
farthest away from the master cylinder first and work
your way to the closest. This ensures that all the air
possible can be removed at the first bleeding operation.
Pour enough brake fluid in the bleeder ball to
reach the prescribed level. Charge the ball with
10 to 15 psi of air pressure.
Pressure Bleeding
Fill the master cylinder with brake fluid. Install
the adapter and hose on the master cylinder.
Open the valve on the hose.
Pressure bleeding of a brake system is preferred to
the method just described but requires equipment of
the type shown in figure 7-38. Pressure bleeding a
brake system is done using air pressure trapped inside a
metal air tank (bleeder ball). Pressure bleeding is quick
and easy because of the following:
A special pressure-bleeding adapter is
required on master cylinders using a
PLASTIC RESERVOIR. Use an adapter that
seals over the ports in the bottom of the master
cylinder. This will avoid possible reservoir
It does not require an assistant.
It maintains a constant pressure in the system.
It keeps the master cylinder full during bleeding
To pressure bleed the system, proceed as follows:
Attach a bleeder hose to the farthest wheel
cylinder bleed screw. Submerge the free end of
the hose in a glass container halfway filled with
brake fluid.
Loosen the bleed screw. When fluid coming
from the submerged end of the hose is free of air
bubbles, close off the bleed screw and remove
the bleeder hose. Repeat bleeding operation on
the other wheel cylinders in proper order.
When the bleeding operation is completed, close
the valve at the bleeder ball hose and disconnect the
bleeder from the master cylinder. Check the brake fluid
level in the reservoir, ensuring it is within 1/4 inch
from the top and install the master cylinder cover.
Q1. The time frame between the instant the operator
decides to apply the brakes and the moment the
brake system is activated is known by what term?
Figure 7-37.—Manual bleeding brake lines: (1) Bleeder
screw: (2) Bleeder hose.
Q2. What term is used to refer to the comparison of
front-wheel to rear-wheel braking effort?
Learning Objective: Describe the operation, terms,
and component functions of an air brake system.
Describe the procedures for servicing an air brake
Q3. Typically, what percentage of the braking does
the rear brake handle?
Q4. What component of a hydraulic brake system
coverts the force of an operator’s foot into
hydraulic pressure?
Unlike liquids, gases are compressed easily. If a
gas, such as air, is contained and a force applied to it, it
is compressed and has less volume. Placing a weight
on a piston that fits in the container can exert such a
force. The air that originally filled the entire container
is pressed into only a portion of the container due to the
force of the weight upon it. The pressure of the
compressed air, resulting from the force exerted upon
it by the weight, will be distributed equally in all
directions just as it is in a liquid.
Q5. In a vehicle using a dual master cylinder, what
type of system operates the brake assemblies on
opposite corners?
Q6. What component in a hydraulic brake system is
used where a single brake line feeds two wheel
Q7. What type of self-adjusting system uses braided
steel cable?
An air brake system performs the following basic
Q8. Disc brakes use servo actions. (T/F)
An air pump or compressor driven by the engine
is used to compress air and force it into a
reservoir where it is forced under pressure and
made available for operating the brakes.
Q9. What are the three types of brake shoes?
Q10. What component of a disc brake system is a
nonrotating unit?
Air under pressure in the reservoir is released to
the brake lines by an air valve operated by the
brake pedal.
Q11. Why is a metering valve used?
Q12. Describe a combination valve.
Q13. What component of an ABS system uses a wheel
speed sensor signal to operate the hydraulic
This released air goes to brake chambers
(located at each wheel) that contains a flexible
diaphragm. Against this diaphragm is a plate that
is connected directly to the mechanism on the
wheel brakes by linkage.
Q14. What component of an ABS system is mounted on
each spindle or hub?
The force of the compressed air admitted to the
brake chamber causes the diaphragm to move
the plate and operate the brake shoes through the
Q15. A hydroboostpower brake system uses pressure
from the power steering pump. (T/F)
Q16. What are the three brake pedal application
Considerable force is available for braking
because the operating pressure may be as high as 110
psi. All brakes on a vehicle, and on a trailer when one is
used, are operated together by means of special
regulating valves. A diagram of a typical air brake
system is shown in figure 7-39.
Q17. At what thickness should disc brake pads be
Q18. What action should be taken before installing a
new master cylinder on a vehicle?
Q19. What device is used to measure brake drum
Q20. The amount of side-to-side movement of a brake
disc is known by what term?
The COMPRESSOR is driven from the engine
crankshaft or one of the auxiliary shafts. The three
common methods of driving the compressor from the
engine are gear, belt, and chain. The compressor may
be lubricated from the engine crankcase or
self-lubricating. Cooling may be either by air or liquid
Q21. How much metal is to be removed when
resurfacing a brake disc?
Q22. When pressure bleeding a brake system, what is
the charging pressure of the bleeder ball?
Figure 7-39.—Typical air brake system.
from the engine. Compressors, having a displacement
of approximately 7 cubic feet per minute (cfm), have
two cylinders, while those with a displacement of 12
cfm have three cylinders.
The purpose of the compressor GOVERNOR is to
maintain the air pressure in the reservoir between the
maximum pressure desired (100 to 110 psi) and the
minimum pressure required automatically for safe
operation (80 to 85 psi) by controlling the compressor
unloading mechanism.
The reciprocal air compressor (fig. 7-40) operates
continuously while the engine is running, but the
governor controls the actual compression. The
operation of the compressor is as follows:
In the type O-1 governor (fig. 7-41) air pressure
from the reservoir enters the governor through the
strainer and is always present below the tower valve
and in the spring tube. As the air pressure increases, the
tube tends to straighten out and decrease pressure on
the valve.
The partial vacuum created on the piston
downstroke draws air through the air strainer and
intake ports into the cylinder.
As the piston starts its upstroke. the intake ports
are closed off, and the air trapped in the cylinder
is compressed.
When the reservoir air pressure reaches the cutout
setting of the governor (100 to 110 psi), the spring load
of the tube on the tower valve has been reduced enough
to permit air pressure to raise the tower valve off its
seat. This movement of the lower valve raises the
upper valve to its seat, which closes the exhaust port.
Air then flows up through the small hole in the lower
The pressure developed lifts the discharge valve,
and the compressed air is discharged to the
reservoirs. As the piston starts its downstroke.
pressure is relieved, closing the discharge valve.
Figure 7-40.—Typical two-cylinder reciprocal air compressor.
Figure 7-41.—Type O-1 governor.
This action allows the valve mechanism to move up,
permitting the exhaust stem to close the exhaust valve
and to open the inlet valve. Reservoir pressure then
passes through the governor to operate the compressor
unloading mechanism. stopping further compression
of the air compressor.
valve and out the upper connection to the unloader
assembly located in the compressor cylinder head.
When the unloader valves open, the compression of air
is stopped.
When reservoir pressure is reduced to the cut-in
setting of the compressor governor (80 to 85 psi), the
governor tube again exerts sufficient spring pressure
on the valve mechanism to depress and close the lower
valve and open the upper valve, thereby shutting off
and exhausting the air from the compressor unloading
mechanism and compression is resumed.
When the reservoir pressure is reduced to the
cut-in setting (80 to 85 psi). the spring loading within
the governor overcomes the air pressure under the
diaphragm. The valve mechanism is actuated, closing
the inlet valve and opening the exhaust valve, thereby
shutting off and exhausting the air from the
compressor unloading mechanism and compression is
The pressure range and setting should be checked
periodically using an air gauge known to be accurate.
Pressure range may be changed in the type O-1
governor by adding shims beneath the upper valve
guide to decrease the range, or removing shims to
increase the range. Pressure settings may be changed,
if necessary, by turning the adjusting screw to the left
to increase the setting or to the right to decrease the
Pressure range and setting should be checked
periodically, using an accurate air gauge. The pressure
range (pressure differential) between loading and
unloading of the type D governor is a function of the
design of the unit and should not be changed. The
designed range for this governor is approximately 20
percent of the cutout pressure setting. The pressure
settings of the type D governor may be adjusted by
turning the adjusting nut clockwise to increase or
counterclockwise to decrease the settings.
The strainer should be removed periodically and
cleaned. Check the governor periodically for excessive
leakage in both the cut-in and cutout positions. If the
governor fails to operate properly, it should be repaired
or replaced.
Both strainers should be removed periodically and
cleaned or replaced. The governor should periodically
be checked for leakage at the exhaust port in both the
cut-in and cutout positions. If the governor fails to
operate properly, it should be repaired or replaced.
In the type D governor (fig. 7-42) when the
reservoir pressure reaches the cut-out setting (100 to
110 psi), the governor diaphragm is subjected to
sufficient air pressure to overcome the spring loading.
Figure 7-42.—Type D governor.
The UNLOADER assembly (fig. 7-43) is mounted
in the compressor head and controlled by the governor.
The unloader valve may be either a poppet-type or a
spring-loaded control valve. Air pressure from the
governor opens the unloader valves to unload or stop
compression in the compressor.
cavity between the cylinders and compression is
stopped. A drop in air pressure below the minimum
setting of the governor causes it to release the air
pressure from beneath the unloading diaphragm,
allowing the unloading valves to return to their seats
resuming compression.
When the reservoir air pressure reaches the
maximum setting of the governor, air under pressure is
allowed by the governor to pass into a cavity below an
unloading diaphragm. This air pressure lifts one end of
the unloading lever, which pivots on its pin and forces
the unloading valves off their seats. With the
unloading valves off their seats, the unloading cavity
forms a passage between the cylinders above the
pistons. Air then passes back and forth through the
The two steel air tanks, commonly known as
reservoirs, are used to cool, store, remove moisture
from the air, and give a smooth flow of air to the brake
At the bottom of each tank is a drain valve (fig.
7-44). This valve is used to allow the operator a means
to drain the air from the tanks daily, thereby preventing
Figure 7-43.—Unloader assembly.
Figure 7-44.—Air reservoir with an air drain valve.
Replace the diaphragm if it is worn or leaking.
Replace the boot if it is worn or cracked. With the
brakes applied, cover the edges of the diaphragm and
bolt with soapy water to detect leakage. If leaks are
present, tighten the bolts uniformly until the leaks stop.
Bolts should not be tightened so that the diaphragm
shows signs of bulging or distortion.
any moisture buildup in the system. Moisture in the
system prevents the brakes from actuating smoothly.
A safety, valve is located on top of the first
reservoir and consists of an adjustable spring-loaded
bail-check valve in a body. It is used to protect the
system against excessive pressures. normally set at
approximately 150 psi.
The slack adjusters (fig. 7-46) function as
adjustable levers and provide a means of adjusting the
brakes to compensate for wear of linings. Air pressure,
admitted to the brake chamber when the brake pedal is
depressed, moves the slack adjuster toward the
position indicated by the dotted lines.
The brake chamber (fig. 7-45) converts the energy
of the compressed air into mechanical force to operate
the brakes. When the brake pedal is actuated, air under
pressure enters the brake chamber behind the
diaphragm and forces the pushrod out against the
return spring force. Because the yoke on the end of the
pushrod is connected to the slack adjuster, this
movement rotates the slack adjuster. brake camshaft,
and cam to apply the brakes.
The entire slack adjuster rotates as a lever with the
brake camshaft, as the brakes are applied or released.
Turning the adjusting screw makes the brake
adjustments necessary to maintain proper slack
adjuster arm travel (shoe and drum clearance). This
action rotates the worm gear, camshaft, and cam.
expanding the brake shoes so that the slack caused by
brake lining wear is eliminated and the slack adjuster
arm travel is returned to the correct setting. The
movement of the cam forces the brake shoes against
the brake drum. Friction of the brake lining against the
drum stops the turning movement of the wheel. When
the brakes are released, the brake shoe return spring
pulls the shoes back to a DISENGAGED position.
When the pedal is released, air is forced from the
brake chamber by the brake shoe return spring acting
on the linkage. After the shoes reach the fully released
position, the return springs acting on the diaphragm
causes it to return to its original position in the
When performing maintenance of the brake
system, check the brake chamber alignment to avoid
binding action. Check the pushrod travel periodically,
and when necessary’. adjust the brakes so that pushrod
travel is as short as possible without the brakes
dragging. The pushrod length should be adjusted so
that the angle between the center line of the slack
adjuster and the brake chamber pushrod is 90 degrees
when the pushrod is extended to the center of its
working stroke.
There are numerous brake valves used in an air
brake system. These valves either apply or release air
Figure 7-45.—Brake chamber.
Figure 7-46.—Slack adjuster.
moved downward and contacts the exhaust valve and
closes it. Continued movement opens the inlet valve
and air pressure from the reservoir flows through the
valve and into the delivery lines to apply the brakes. As
the air pressure increases below the diaphragm, it
overcomes the force above the diaphragm and the
diaphragm raises slightly. This action allows the inlet
valve to close but also keeps the exhaust valve closed,
thereby obtaining a balanced position. Further
depression of the treadle valve increases the forces
above the diaphragm and correspondingly increases
the delivered air pressure until a new balanced position
is reached.
from the brakes and work together to ensure control
and safe braking application. These valves are as
Treadle valve (brake valve)
Trailer control valve (brake valve)
Quick-release valve
Combined-limiting and quick-release valve
Tractor protection valve
Relay emergency valve
Check valves
In the following paragraphs we will discuss each
valve in more detail.
Maintenance of the treadle valve consists of
periodic lubrication of the hinge and roller. Should the
valve malfunction, it can be disassembled and cleaned.
After cleaning, the internal parts should be lubricated
with Vaseline before reassembly. This prevents
moisture in the air system from causing corrosion and
freezing of the valve. If cleaning does not remedy the
malfunction, the valve must be replaced.
Treadle Valve
The treadle valve (fig. 7-47) controls the air
pressure delivered to the brake chambers. When the
treadle valve is depressed, force is transmitted to the
pressure regulating spring and diaphragm that is
Figure 7-47.—Treadle valve.
Trailer Control Valve
The independent trailer control valve (fig. 7-48)
provides the operator with control of the trailing load at
all times. This valve functions in the same manner as
the treadle valve except that the handle is turned, rather
than depressed, to operate the valve.
Quick-Release Valve
The quick-release valve (fig. 7-49) exhausts brake
chamber air pressure and speeds up brake release by
reducing the distance the air would have to travel back
to the brake valve exhaust port.
When the brakes are engaged, air from the brake
valve enters into the quick-release valve, forcing the
diaphragm down and closing off the exhaust port. This
action allows air pressure to rush through the
quick-release valve outlet ports to the wheel brake
chambers. When the brakes are released, the air
pressure above the quick-release diaphragm is
exhausted at the brake valve. As air pressure above the
diaphragm is released, the air pressure below the
diaphragm raises off the exhaust port. This action
allows the air in the brake chambers to exhaust at the
quick-release valve.
When air is leaking from the system, a leakage test
can determine if there is air leaking at the quick-release
valve. The leakage test is performed with the brakes
applied and coating the exhaust port with soapsuds. If
air bubbles form, this is a sign of a defective valve,
which can be corrected by either cleaning and
replacing worn parts or by replacing the unit. Dirt,
worn diaphragm, or a worn seat causes leakage.
Combined-Limiting and Quick-Release Valve
The combined-limiting and quick-release valve
(fig. 7-50) is used in combination with a two-way
check valve in the air brake system of trucks and
tractors. The combined-limiting and quick-release
valve is interchangeable in mounting with the
quick-release valve and serves the same purpose with
the additional function of providing an automatic
reduction of front-wheel brake pressure, at the option
of the operator, on slippery roads.
Tractor Protection Valve
The primary purpose of the tractor protection
valve (fig. 7-51) is to protect the tractor air brake
system under trailer breakaway conditions and under
conditions where severe leakage develops in the
tractor or trailer.
Figure 7-48.—Trailer control valve.
Figure 7-50.—Combined-limiting and quick-release valve.
Figure 7-49.—Quick-release valve.
disconnected over long periods of time. The operator
should move the control to the EMERGENCY position
when disconnecting a trailer or when operating a
tractor without a trailer if cut-off valves are not
installed in the trailer connections on the tractor. The
tractor protection valve should NOT be used as a
parking brake, because it was not designed for that
Relay Emergency Valve
The relay emergency valve (fig. 7-53) acts as a
relay station to speed up the application and release of
trailer brakes. It automatically applies the trailer
brakes when the emergency line of the trailer is broken,
disconnected, or otherwise vented to the atmosphere if
the trailer air brake system is charged. It is used on
trailers that require an emergency brake application
upon breakaway from the truck or tractor.
Figure 7-51.—Tractor protection valve and switch.
When a tractor is connected to a trailer and the
service and emergency lines are opened, the relay
emergency valve permits charging the trailer air brake
reservoir to approximately the same air pressure as that
in the tractor reservoirs. During normal operation of a
tractor-trailer unit, the relay emergency valve
functions as a relay valve and synchronizes trailer
service brake air pressure and tractor service brake air
pressure, as the treadle valve on the tractor is operated.
The trailer brakes can also be applied independently of
the tractor brakes by use of the hand control on the
tractor protection valve on the tractor and the relay
emergency valve on the trailer.
The tractor protection system functions as a set of
remotely controlled cutout valves (fig. 7-52). The
trailer service and emergency lines pass through the
valve. When the control valve is in the NORMAL
position, service and emergency braking functions of
both the tractor and trailer are normal. When the valve
lever is in the EMERGENCY position, the trailer air
brakes lines are closed off.
Should acondition resulting in severe air loss from
the tractor or trailer air brake system be detected or if
for any other reason it is desirable to cause an
emergency application of the trailer brakes, the
operator can move the control valve lever to the
EMERGENCY position. At this time both the trailer
service and emergency brake line will be closed off at
the tractor protection valve. Such operation offers a
convenient daily check of the relay emergency valve
on the trailer where tractors and trailers are not
If a trailer is disconnected from a tractor for
loading or unloading or if the trailer is separated from
the tractor under emergency breakaway conditions or
if the emergency line of the trailer is vented to the
atmosphere by other means, the relay emergency valve
applies the trailer brakes. This is automatically
achieved by using the existing trailer reservoir air
pressure. If the trailer is to remain parked under these
conditions, the wheels should be blocked to prevent the
possibility of a runaway.
If you are required to release the emergency brake
application on a trailer under these conditions, the
trailer reservoir drain valve can be opened or the trailer
air brake system can be recharged through the trailer
emergency line.
You can check the relay emergency valve by
moving the tractor protection valve control lever to the
EMERGENCY position, if tractor protection
equipment is installed. If no tractor protection is
Figure 7-52.—Tractor protection valve piping.
Figure 7-53.—Relay emergency valve.
installed, by closing the emergency line cutout valve
and uncoupling the emergency brake line, the valve
can be checked. Either way the trailer brakes should
apply automatically. Trailer brakes should release, in
the first case, when the tractor protection valve control
lever is moved to the NORMAL position, and, in the
second case, when the emergency line is coupled and
the cutout valve is opened.
rupture while in operation. These are placed at the
entrance of the main air tanks and prevent the loss of air
should the inlet line from the compressor fail. The
ball-type check valve (fig. 7-54) is typical of the type
used on trailer braking systems. Check valves may be
either disc or ball and double or single units.
Regardless of their design, their function is the same.
The relay emergency valve is checked for leakage
by application of soapsuds with the brakes released.
Check the emergency air line coupling with soapsuds
to determine leakage with the valve in emergency
application position. Leakage may be caused by dirt or
worn parts which may be corrected by cleaning and/or
replacing the unit.
Check Valves
Check valves are located in the lines of air brake
systems to prevent the loss of air should the line
Figure 7-54.—Ball-type single check valve.
Air hoses and fittings (fig. 7-55) provide a means
of making a flexible air connection between points on a
vehicle which change their position in relation to each
other or between two vehicles. All air brake assemblies
used to connect the air brake systems from one vehicle
to another are equipped with detachable fittings and
spring guards.
When installing a hose assembly where both ends
are permanently connected, use the air hose connector
assembly at each end as the union to permit tightening
the hose connectors in place. Loosen the nut on one of
the connector assemblies and then turn the hose in the
loose connector to avoid kinking the hose.
Figure 7-56.—Dummy couplings.
To prevent dirt and moisture from entering unused
air lines, use dummy couplings (fig. 7-56). The two
types of dummy couplings are as follows:
Bracket-type couplings are mounted to the
vehicle for storage of unused hose.
Chain-type couplings are attached to the vehicle
by a chain and placed in couplings mounted on
the vehicle.
The switches and indicators in an air brake system
are designed as safety devices. The two most common
safety devices found in an air brake system are the
low-pressure warning indicator and the stoplight
Figure 7-57.—Low-pressure warning indicator.
Low-Pressure Warning Indicator
device. Normal operating pressure is 60 psi, plus or
minus 6 pounds.
The low-pressure warning indicator (fig. 7-57) is
an electro-pneumatic switch connected with a warning
buzzer and, in some designs, a warning light or both. It
remains in the OPEN position when air pressure is
above approximately 60 psi. When pressure drops
below 60 psi, the spring forces the diaphragm down
and closes the contacts, which operate the warning
Stoplight Switches
Stoplight switches (fig. 7-58) in an air brake
system are electro-pneumatic devices, which operate
in conjunction with the treadle valve to close the
Figure 7-55.—Air hose and fittings.
While some places are authorized some amount of
leakage, others are not. For example, castings and the
tube in the governor should have no leakage. Points
with authorized leakage will have a specified
maximum in pounds per a specified time.
Soapsuds can also be used to check the internal
condition of a component. By covering exhaust ports
or casting openings, you can check the condition of the
diaphragms and valves. For example, to check the
condition of the treadle valve, release the brakes and
cover the exhaust ports with soapsuds. Engage the
brakes: any leakage indicates the valve is not sealing
properly. If the diaphragm in the brake chamber is
faulty, leakage will appear around the pushrod with the
brakes applied.
Figure 7-58.—Stoplight switch.
stoplight circuit when the brakes are applied. When air
pressure from the treadle valve enters the cavity on the
one side of the diaphragm, the diaphragm changes
position. This action overcomes the force of the spring
and moves the contact plunger until the contacts close.
This closes the stoplight electrical circuit causing the
brake lights to come on. The switch is designed to close
as soon as 5 psi is delivered to it. This means that the
stoplight circuit closes immediately on brake
As with the drum brake system the linings used
with air brakes gradually wear from use and require
periodic adjustment or replacement. Always consult
the manufacturer’s specifications before making any
adjustments to the air brake system. This is to ensure
that the correct adjustment is made and that any
variations in procedure are followed.
Servicing is the most important part of air brake
maintenance. If the air brake system is kept clean.
tight, and moisture-free, brake failures will be few and
far between. Particular care must be taken to keep the
air compressor intake filters clean and foreign material
out of the lines.
Q1. What are the three common methods for driving
the air compressor from the engine?
The basic test made to an air brake system is the
operational test. This test may be performed on the
road or in the shop. During an operational test, the
brakes are applied and released while observing for
equal application, sluggish engagement or release,
binding linkage, and exhaust of units.
Q2. What is the purpose of the governor in an air
brake system?
Q3. What component controls the compressor
unloading mechanism?
Q4. On a type O-1 air compressor the pressure range
may be adjusted by adding or removing shims
from what location?
To check the leakage of the overall system, fully
charge the system. shut off the ignition, and observe
the pressure drop on the gauge mounted on the vehicle
dash. The maximum leakage will be expressed in
pounds per a specific time.
Q5. What valve controls the air pressure delivered to
the brake chambers?
Q6. What is the function of the relay emergency
Q7. What component is used to prevent dirt and
moisture entering unused air lines?
Before making any leakage or pressure
test. consult the manufacturer’s specifications
for correct pressure and maximum leakage.
To determine if leakage of various components is
within permissible or authorized limits, use the
soapsuds test. To make this test, use a thick mixture of
soapsuds: do not use lye soap. This misture is applied
to places in the system where leakage may occur.
Learning Objective: Describe the operation, terms,
and component functions of an air-over-hydraulic brake
The air-over-hydraulic brake system is shown in
figure 7-59. This system combines the use of
compressed air and hydraulic pressure for brake
application. Air pressure is supplied by a compressor
and stored in reservoirs as with the air brake system.
The master cylinder, wheel cylinders, and brake
construction are very similar to that used in a hydraulic
brake system. The essential difference between the
straight hydraulic brake system and the air-overhydraulic system lies in the AIR-HYDRAULICPOWER CYLINDER.
Figure 7-60.—Air-hydraulic power cylinder assembly
The air-hydraulic-power cylinder (fig. 7-60) is a
self-contained power brake unit. The three essential
components of the air-hydraulic-power cylinder are as
Movement of the piston in the compressed air cylinder
is controlled by the amount of air, under pressure, that is
allowed to enter through the control valve. The
compressed air cylinder body is attached to the end plate
on which the slave cylinder and control valve is
of a large diameter air piston operating within a cylinder
body. This piston actuates a pushrod, which is attached
to the hydraulic piston within the slave cylinder.
Figure 7-59.—Air-over-hydraulic brake system.
mounted. A return spring forces the power piston to the
released position when the brake pedal is released.
the relay piston in the control valve. As hydraulic
pressure builds, the relay piston moves the control
valve diaphragm forward, closing the atmospheric
poppet and slightly opening the air pressure poppet.
Air under pressure then passes through the air control
line forcing the power piston in the air cylinder
forward until the air pressure on the diaphragm, in
combination with spring pressure, allows the air
poppet to close. The degree of brake application is
determined by the amount of compressed air trapped in
the power cylinder when brake pedal movement is
stopped. Unless more pressure is applied or the brake
pedal is released, the brakes will remain in the partially
applied position.
The SLAVE CYLINDER consists of a
cylindrical housing in which a small diameter hydraulic
piston operates. The outlet cap houses a residual check
valve and a ball-check valve is located in the hydraulic
The CONTROL VALVE consists of two
poppets operating within a housing and actuated by a
hydraulic relay piston and a reactionary-type
diaphragm. An air control line connects the control
valve to the compressed air cylinder.
View B of figure 7-61 shows the effect of applying
high brake pedal pressure. Under this condition, the air
pressure poppet is held open, allowing a full volume of
compressed air to enter the air cylinder and cause full
brake application.
The air-over-hydraulic cylinder consists of an air
cylinder and hydraulic cylinder in tandem, each fitted
with a piston with a common piston rod between. The
air piston is of greater diameter than the hydraulic
piston. This difference in areas of the two pistons gives
a resultant hydraulic pressure much greater than the air
pressure admitted to the air cylinder. Automatic
valves. actuated by fluid pressure from the master
cylinder, control the air admitted to the air cylinder.
Thus fluid pressure in the brake lines is always in direct
ratio to foot pressure on the brake pedal.
As in a conventional hydraulic brake system the
residual check valve maintains a small amount of
pressure in the hydraulic system when the brakes are
released. This prevents the cups in the wheel cylinders
from collapsing and leaking.
Q1. What are the three essential components of an
air-hydraulic-power cylinder?
Figure 7-61 shows the air-hydraulic power
cylinder in the released position. Views A and B show
the position of the valves and slave cylinder during
light and heavy brake pedal application.
Q2. In what component of the air-hydraulic-power
cylinder is the residual check valve located?
When the brakes are applied, as shown in view A
of figure 7-61. pressure is transmitted by the brake
fluid to the hydraulic piston in the slave cylinder and
Q3. What action actuates the automatic valves that
control the air pressure admitted to the air
A. Double check valve assembly
B. Air control line
C. Relay piston
D. Diaphragm assembly
E. Exhaust port
F. Atmospheric inlet
G Atmospheric poppet
H. Air pressure poppet
J. Poppet return spring
K Residual line check valve assembly
L. Brake pedal
M. Master cylinder
N. Diaphragm return spring
P. Hydraulic piston
Q. Piston return spring
R. Pushrod
S. Power piston
T. Trailer connection
Figure 7-61.—Air-hydraulic power cylinder (Air-Pak) during operation.
Q1. Operator reaction time
Q2. Braking ratio
Q3. 30 to 40 percent
Q4. Master cylinder
Q5. Diagonally split
Q6. Junction block
Q7. Cable type
Q8. False
Q9. Nonmetallic, semimetallic, and metallic
Q10. Caliper
Q11. Equalizes braking action at each wheel during light brake applications
Q12. A valve combing several valve junctions into a single assembly
Q13. ABS computer
Q14. Trigger wheels
Q15. True
Q16. Brake pedal free play, brake pedal height, and brake pedal reserve distance
Q17. 1/8 inch
Q18. Bench bleed the master cylinder
Q19. Brake drum micrometer
Q20. Brake disc runout
Q21. Only enough to true the disc
Q22. 10 to 15 psi
Q1. Gear, belt. and chain
Q2. To maintain the air pressure in the reservoirs between maximum and
minimum pressure automatically
Q3. Governor
Q4. Beneath the upper valve guide
Q5. Treadle valve
Q6. Acts as a relay station to speed up the release and application of trailer
Q7 Dummy couplings
Q1. Compressed air cylinder. slave cylinder, and control valve
Q2. Slave cylinder
Q3. Fluid pressure from the master cylindersed off
passenger compartment. It is made of relatively light
sheet metal or composite plastics. The components
which make up the chassis are held together in proper
relation to each other by the frame.
Learning Objective: Identify the types of automotive
suspension and steering systems, their components,
their functions, and maintenance requirements. State
the characteristics and basic construction of a tire.
Describe the procedures for maintaining tires, wheels,
and wheel bearings. State the purpose of each wheel
alignment setting. Describe the different types of
equipment used during wheel alignment service.
Describe the procedures for repairing and refinishing
automotive bodies.
Learning Objective: Describe the function,
construction, and types of frames used on wheeled
The separate frame and body type of vehicle
construction (fig. 8-1) is the most common technique
used when producing most full-sized and cargo
vehicles. In this type of construction, the frame and the
vehicle body are made separately, and each is a
complete unit by itself. The frame is designed to
support the weight of the body and absorb all of the
loads imposed by the terrain, suspension system,
engine, drive train, and steering system, and the body
merely contains and, in some cases, protects the cargo.
The body generally is bolted to the frame at a few points
to allow for flexure of the frame and to distribute the loads
to the intended load-carrying members. The components
of this type of frame are as follows (fig. 8-2):
The automotive chassis provides the strength
necessary to support the vehicular components and the
payload placed upon it. The suspension system
contains the springs, the shock absorbers, and other
components that allow the vehicle to pass over uneven
terrain without an excessive amount of shock reaching
the passengers or cargo. The steering mechanism is an
integral portion of the chassis, as it provides the
operator with a means of controlling the direction of
travel. The tires grip the road surface to provide good
traction that enables the vehicle to accelerate, brake,
and make turns without skidding. Working in
conjunction with the suspension, the tires absorb most
of the shocks caused byroad irregularities. The body of
the vehicle encloses the mechanical components and
The SIDE MEMBERS or rails are the heaviest
part of the frame. The side members are shaped to
Figure 8-1.—Separate frame and body.
Figure 8-2.—Components of a typical frame design.
accommodate the body and support the weight. They
are narrow toward the front of the vehicle to permit a
shorter turning radius for the wheels and then widen
under the main part of the body where the body is
secured to the frame. Trucks and trailers commonly
have frames with straight side members to
accommodate several designs of bodies and to give the
vehicle added strength to withstand heavier loads.
bending rigidity; the balance is supplied by the body
structure. The most important advantages of the
separate body and frame construction are as follows:
The CROSS MEMBERS are fixed to the side
members to prevent weaving and twisting of the frame.
The number, size, and arrangement of the cross
members depend on the type of vehicle for which the
frame was designed. Usually, a front cross member
supports the radiator and the front of the engine. The
rear cross members furnish support for the fuel tanks
and rear trunk on passenger cars and the tow bar
connections for trucks. Additional cross members are
added to the frame to support the rear of the engine or
power train components.
Strong, rugged designs are achieved easily;
however, vehicle weight is increased.
Ease of mounting and dismounting the body
Versatility; various body types can be adapted to
a standard truck chassis.
Isolation of noise generated by drive train
components from the passenger compartment
through the use of rubber mounts between the
frame and the body.
Simplistic design that yields a relatively
inexpensive and easy manufacturing process.
Frame members serve as supports to which
springs, independent suspensions, radiators, or
transmissions may be attached. Additional brackets,
outriggers, and engine supports are added for the
mounting of running boards, longitudinal springs,
bumpers, engines, towing blocks, shock absorbers, gas
tanks, and spare tires.
The GUSSET PLATES are angular pieces of
metal used for additional reinforcement on heavy-duty
truck frames.
With this type of frame construction, the body
structure only needs to be strong and rigid enough to
contain the weight of the cargo and resist any dynamic
loads associated with cargo handling and cargo
movement during vehicle operation and to absorb
shocks and vibrations transferred from the frame. In
some cases. particularly under severe operating
conditions, the body structure may be subjected to
some torsional loads that are not absorbed completely
by the frame. This basically applies to heavy truck and
not passenger vehicles. In a typical passenger vehicle.
the frame supplies approximately 37 percent of the
torsional rigidity and approximately 34 percent of the
The integrated frame and body type of
construction (fig. 8-3) also referred to as unitized
construction, combines the frame and body into a
single, one-piece structure. This is done by welding the
components together, by forming or casting the entire
structure as one piece, or by a combination of these
techniques. Simply by welding a body to a
conventional frame, however, does not constitute an
Figure 8-3.—Integrated frame and body.
Protection from mud and water required for
drive line components on amphibious vehicles
integral frame and body construction. In a truly
integrated structure, the entire frame-body unit is
treated as a load-carrying member that reacts to all
loads experienced by the vehicle-road loads as well as
cargo loads.
Reduction in the amount of vibration present in
the vehicle structure
Integrated-type bodies for wheeled vehicles are
fabricated by welding preformed metal panels
together. The panels are preformed in various
load-bearing shapes that are located and oriented so as
to result in a uniformly stressed structure. Some
portions of the integrated structure resemble framelike
components, while other resembles bodylike panels.
This is not surprising, because the structure must
perform the functions of both of these elements.
The truck frame (fig. 8-4) allows for different
types of truck beds or enclosures to be attached to the
frame. For larger trucks, the frames are simple, rugged,
and of channel iron construction. The side rails are
parallel to each other at standardized widths to permit
the mounting of stock transmissions, transfer cases,
rear axles, and other similar components. Trucks that
are to be used as prime movers have an additional
reinforcement of the side rails and rear cross members
to compensate for the added towing stresses.
An integrated frame and body type construction
allows an increase in the amount of noise transmitted
into the passenger compartment of the vehicle.
However, this disadvantage is negated by the
following advantages:
Frames require little, if any, maintenance.
However, if the frame is bent enough to cause
misalignment of the vehicle or cause faulty steering,
the vehicle should be removed from service. Drilling
the frame and fishplating can temporarily repair small
Substantial weight reduction, which is possible
when using a well-designed unitized body
Lower cargo floor and vehicle height
Figure 8-4.—Truck frame (Ladder).
cracks in the frame side rails. Care should be exercised
when performing this task, as the frame can be
weakened. The frame of the vehicle should not be
welded by gas or arc welding unless specified by the
manufacturer. The heat removes temper from the
metal, and, if cooled too quickly, causes the metal to
crystallize. Minor bends can be removed by the use of
hydraulic jacks, bars, and clamps.
Provide a smooth, comfortable ride by allowing
the wheels and tires to move up and down with
minimum movement of the vehicle.
Work with the steering system to help keep the
wheels in correct alignment.
Keep the tires in firm contact with the road, even
after striking bumps or holes in the road.
Allow rapid cornering without extreme body roll
(vehicle leans to one side).
What component of the frame prevents the side
members from weaving and twisting the frame?
The integrated frame and body type of
construction is also known by what term?
Allow the front wheels to turn from side to side
for steering.
Prevent excessive body squat (body tilts down in
rear) when accelerating or with heavy loads.
Prevent excessive body dive (body tilts down in
the front) when braking.
One advantage of an integrated frame and body
is that the amount of noise transmitted into the
passenger compartment is decreased. (T/F)
The suspension systems are grouped into two
categories, which are as follows:
Axle) (fig. 8-5)—The nonindependent suspension has
both left and right wheels attached to the same solid
axle. When one tire hits a bump in the road, its upward
movement causes a slight tilt in the other wheel. With a
solid axle setup, the steering knuckle and wheel spindle
assemblies are connected to the axle beam by
bronze-bushed kingpins, or spindle bolts, which
provide pivot points for each wheel.
Learning Objective: Identify automotive suspension
components, their functions, and maintenance
The suspension system works with the tires. frame
or unitized body, wheels, wheel bearings, brake
system. and steering system. All of the components of
these systems work together to provide a safe and
comfortable means of transportation. The suspension
system functions are as follows:
independent suspension allows one wheel to move up
and down with a minimum effect on the other wheels.
Since each wheel is attached to its own suspension unit,
movement of one wheel does NOT cause direct
movement of the wheel on the opposite side of the
Support the weight of the frame, body, engine,
transmission, drive train, passengers, and cargo.
Figure 8-5.—Nonindependent suspension system.
Figure 8-6.—Independent suspension.
vehicle. With the independent front suspension the use
of ball joints provides pivot points for each wheel. In
operation, the swiveling action of the ball joints allows
the wheel and spindle assemblies to be turned left and
right and to move up and down with changes in road
surfaces. This type of suspension is most widely used on
modern vehicles.
This prevents the control arm from swinging toward
the rear or front of the vehicle. The front of the strut rod
has rubber bushings that soften the action of the strut
rod. These bushings allow a controlled amount of
lower control arm movement while allowing full
suspension travel.
Ball Joints
The ball joints (fig. 8-7) are connections that allow
limited rotation in every direction and support the
weight of the vehicle. They are used at the outer ends of
the control arms where the arms attach to the steering
knuckle. In operation, the swiveling action of the ball
joints allows the wheel and steering knuckle to be
turned left or right and to move up and down with
changes in road surface.
The basic components of a suspension system are
as follows:
CONTROL ARM (a movable lever that fastens
the steering knuckle to the vehicle frame or
CONTROL ARM BUSHING (a sleeve, which
allows the control arm to move up and down on
the frame)
Since the ball joint must be filled with grease, a
grease fitting and grease seal are normally placed on
the joint. The end of the stud on the ball joint is
threaded for a large nut. When the nut is tightened, it
force fits the tapered stud in the steering knuckle or
bearing support.
STRUT ROD (prevents the control arm from
swinging to the front or rear of the vehicle)
BALL JOINTS (a swivel joint that allows the
control arm and steering knuckle to move up and
down, as well as side to side)
Shock Absorbers and Struts
suspension from continuing to bounce after
spring compression and extension)
Shock absorbers are necessary because springs do
not "settle down" fast enough. After a spring has been
compressed and released, it continues to shorten and
lengthen for a time. Such spring action on a vehicle
would produce a very bumpy and uncomfortable ride.
It would also be dangerous because a bouncing wheel
makes the vehicle difficult to control; therefore, a
dampening device is needed to control the spring
STABILIZER BAR (limits body roll of the
vehicle during cornering)
SPRING (supports the weight of the vehicle;
permits the control arm and wheel to move up
and down)
Control Arms and Bushings
The control arm, as shown in figure 8-6, holds the
steering knuckle, bearing support, or axle housing in
position, as the wheel moves up and down. The outer
end of the control arm has a ball joint and the inner end
has bushings. Vehicles, having control arms on the rear
suspension, may have bushings on both ends.
The control arm bushings act as bearings, which
allows the control arm to move up and down on a shaft
bolted to the frame or suspension unit. These bushings
may be either pressed or screwed into the openings of
the control arm.
Strut Rods
The strut rod. as shown in figure 8-6, fastens to the
outer end of the lower control arm and to the frame.
Figure 8-7.—Upper and lower ball joint.
oscillations. This device is the shock absorber. The
most common type of shock absorber (fig. 8-8) used on
modern vehicles is the double-acting, direct-action
type, because it allows the use of more flexible springs.
excessive. When the valves are open, a slightly faster
spring movement occurs; however, restraint is still
imposed on the spring.
An outer metal cover protects the shock absorber
from damage by stones that may be kicked up by the
wheels. One end of the shock absorber connects to a
suspension component, usually a control arm. The
other end fastens to the frame. In this way, the shock
absorber piston rod is pulled in and out and resists
these movements.
The direct-action shock absorber consists of an
inner cylinder filled with special hydraulic oil divided
into an upper and lower chamber by a double-acting
piston. In operation, the shock absorbers lengthen and
shorten, as the wheels meet irregularities in the road.
As they do this, the piston inside the shock absorber
moves within the cylinder filled with oil; therefore, the
fluid is put under high pressure and forced to flow
through small openings. The fluid can only pass
through the openings slowly. This action slows piston
motion and restrains spring action.
The strut assembly, also called a MacPherson
strut, is similar to a conventional shock absorber.
However, it is longer and has provisions (brackets and
connections) for mounting and holding the steering
knuckle (front of vehicle) or bearing support (rear of
vehicle) and spring. The strut assembly consists of a
shock absorber, coil spring (in most cases), and an
upper damper unit. The strut assembly replaces the
upper control arm. Only the lower control arm and strut
are required to support the front-wheel assembly. The
During compression and rebound, the piston is
moving. The fluid in the shock absorber is being forced
through small openings which restrains spring
movement. There are small valves in the shock
absorber that open when internal pressure becomes
Figure 8-8.—Double-acting, direct-action type shock absorber.
RUBBER BUMPERS—jounce and rebound
bumpers which prevent metal-to-metal contact
during extreme suspension compression and
basic components of a typical strut assembly, are as
follows (fig. 8-9):
STRUT SHOCK ABSORBER—pistonoperated oil-filled cylinder that prevents coil
spring oscillations.
RUBBER ISOLATORS—parts of the strut
damper which prevents noise from being
transmitted into the body structure of the
DUST SHIELD—metal shroud or rubber boot
that keeps road dirt off the shock absorber.
LOWER SPRING SEAT—lower mount formed
around the body of the shock absorber for the
coil spring.
secures the upper end of the strut assembly to the
frame or unitized body.
COIL SPRING—supports the weight of the
vehicle and allows for suspension action.
In a MacPherson strut type suspension, only one
control arm and a strut is used to support each wheel
assembly. A conventional lower control arm attaches
to the frame and to the lower ball joint. The ball joint
holds the control arm to the steering knuckle or bearing
support. The top of the steering knuckle or bearing
support is bolted to the strut. The top of the strut is
UPPER STRUT SEAT—holds the upper end of
the coil spring and contacts the strut bearing.
STRUT BEARING—a ball bearing that allows
the shock absorber and coil spring assembly to
rotate for steering action.
Figure 8-9.—Exploded and cutaway views of a strut assembly.
absorb some of the irregularities in the road. The
springs in the seats of the vehicle also help absorb
shock. However, the passengers feel little shock from
road bumps and holes.
bolted to the frame or reinforced body structure. This
type of suspension is the most common type used on
late model passenger vehicles. The advantages are a
reduced number of parts in the suspension system,
lower unsprung weight, and a smoother ride.
The ideal spring for an automotive suspension
should absorb road shock rapidly and then return to its
normal position slowly; however, this action is
difficult to attain. An extremely flexible, or soft, spring
allows too much movement. A stiff, or hard, spring
gives too rough a ride. To attain the action to produce
satisfactory riding qualities, use a fairly soft spring
with a shock absorber.
On some vehicles you may find a MODIFIED
STRUT SUSPENSION that has the coil springs
mounted on the top of the control arm, not around the
Stabilizer Bar
The stabilizer bar, as shown in figure 8-6, also
called the sway bar, is used to keep the body of the
vehicle from leaning excessively in sharp turns. Made
of spring steel, the stabilizer bar fastens to both lower
control arms and to the frame. Rubber bushings fit
between the stabilizer bar, the control arms, and the
Spring Terminology
There are three basic types of automotive
springs—coil, leaf, and torsion bar. Before discussing
these types of springs, you must understand three basic
terms—spring rate, sprung weight, and unsprung
When the vehicle rounds a corner, centrifugal
force tends to keep the vehicle moving in a straight
line. Therefore, the vehicle “leans out” on the turn.
This lean out is also called a body roll. With lean out, or
body roll, additional weight is thrown on the outer
spring. This puts additional compression on the outer
spring, and the control arm pivots upward. As the
control arm pivots upward, it carries its end of the
stabilizer bar up with it. At the inner wheel on the turn,
there is less weight on the spring. Weight has shifted to
the outer spring because of centrifugal force.
Therefore, the inner spring tends to expand. The
expansion of the inner spring tends to pivot the lower
control arm downward. As this happens, the lower
control arm carries its end of the stabilizer bar
SPRING RATE refers to the stiffness or tension
of a spring. The rate of a spring is the weight required to
deflect it 1 inch. The rate of most automotive springs is
almost constant through their operating range, or
deflection, in the vehicle. Hooke’s law, as applied to coil
springs states: that a spring will compress in direct
proportion to the weight applied. Therefore, if 600
pounds will compress a spring 3 inches, then 1,200
pounds will compress the spring twice as far, or 6
SPRUNG WEIGHT refers to the weight of the
parts that are supported by the springs and suspension
system. Sprung weight should be kept HIGH in
proportion to unsprung weight.
The outer end of the stabilizer bar is carried
upward by the outer control arm. The inner end is
carried downward. This combined action twists the
stabilizer bar. This action twists the stabilizer bar and
its resistance to this twisting action limits body lean in
UNSPRUNG WEIGHT refers to the weight of
the components that are NOT supported by the springs.
The tires, wheels, wheel bearings, steering knuckles, or
axle housing is considered unsprung weight. Unsprung
weight should be kept LOW to improve ride
smoothness. Movement of high unsprung weight
(heavy wheel and suspension components) will tend to
transfer movement into the passenger compartment.
The vehicle body or frame supports the weight of
the engine, the power train, and the passengers. The
body and frame is supported by the springs on each
wheel. The weight of the frame, body, and attached
components applies an initial compression to the
springs. The springs compress further as the wheels of
the vehicle hit bumps or expand such as when the
wheels drop into a hole in the road. The springs cannot
do the complete job of absorbing road shocks. The tires
The coil spring is made of round spring steel
wound into a coil (fig. 8-10). Because of their
simplicity, they are less costly to manufacture and also
have the widest application. This spring is more
flexible than the leaf spring, allowing a smoother
reaction when passing over irregularities in the road.
Coil springs are frictionless and require the use of a
shock absorber to dampen vibrations. Their cylindrical
shape requires less space to operate in. Pads are
sometimes used between the spring and the chassis to
eliminate transferring vibrations to the body. Because
of its design, the coil spring cannot be used for torque
reaction or absorbing side thrust. Therefore, control
arms and stabilizers are required to maintain the proper
geometry between the body and suspension system.
This is the most common type of spring found on
modern suspension systems.
that is thick in the center and tapers down at each end.
Single leaf springs are used in lighter suspension
systems that do not carry great loads. A multileaf
spring is made up of a single leaf with additional
leaves. The additional leaves make the spring stiffer,
allowing it to carry greater loads.
The most common type is the multileaf spring (fig.
8-12) that consists of a single leaf with a number of
additional leaves attached to it using spring clips.
Spring clips, also known as rebound clips, surround the
leaves at intervals along the spring to keep the leaves
from separating on the rebound after the spring has
been depressed. The clips allow the springs to slide,
but prevent them from separating and causing the
entire rebound stress to act on the master leaf. The
multileaf spring uses an insulator (frictional material)
between the leaves to reduce wear and eliminate any
squeaks that might develop. To keep the leaves equally
spaced lengthwise, use a center bolt for the multileaf
spring. The center bolt rigidly holds the leaves together
in the middle of the spring, preventing the leaves from
moving off center. Each end of the largest leaf is rolled
into an eye, which serves as a means of attaching the
spring to the vehicle. Leaf springs are attached to the
vehicle using a spring hanger that is rigidly mounted to
the frame in the front and the spring shackle in the rear,
which allows the spring to expand and contract without
binding as it moves through its arc. Bushings and pins
provide the bearing or support points for the vehicle.
Spring bushings may be made of bronze or rubber and
are pressed into the spring eye. The pins that pass
Coil spring mountings are quite simple in
construction. The hanger and spring seat are shaped to
fit the coil ends and hold the spring in place. Cups that
fit snugly on each coil end are often used for mounting.
The upper cup can be formed within the frame, in the
control arms, or part of a support bracket rigidly fixed
to the cross member or frame rail. The lower cup is
fastened to a control arm hinged to a cross member or
frame rail. Rubber bumpers are included on the lower
spring support to prevent metal-to-metal contact
between the frame and control arm, as the limits of
compression are reached.
Leaf Spring
The leaf spring acts as a flexible beam on
self-propelled vehicles and transmits the driving and
breaking forces to the frame from the axle assembly.
Leaf springs are semi-elliptical in shape and are made
of high quality alloy steel. There are two types of leaf
springs—single leaf and multileaf (fig. 8-11). The
single leaf spring, or monoleaf, is a single layer spring
Figure 8-10.—Coil springs.
Figure 8-11.—Leaf springs.
Figure 8-12.—Multileaf spring.
through the bushings may be plain or threaded.
Threaded bushings and pins offer a greater bearing
surface and are equipped with lubrication fittings.
and light trucks. Trucks that carry a wide variety of
loads use an auxiliary or overload spring. This
auxiliary spring (fig. 8-13) may be mounted on top of
the rear springs and clamped together with long
U-bolts, or it may be located under the axle separate
Leaf springs are used on the front and rear of
heavy-duty trucks and the rear of passenger vehicles
heavier load than a single axle without losing its ability
to move over unimproved terrain.
When one wheel of a bogie suspension is moved
up or down because of an irregularity in the road, the
spring pivots on the trunnion shaft and both ends of the
spring deflect to absorb the road shock. This causes the
load to be placed on the center of the spring resulting in
equal distribution of the load to both axles. The torque
rods ensure proper spacing and alignment of the axles
and transmit the driving and braking forces to the
Figure 8-13.—Auxiliary spring.
Torsion Bar
from the main spring. In either case, the ends of the
spring has it own support brackets. When the truck is
under a load, the auxiliary spring assumes part of the
load when its ends contact the bearing plates or special
brackets attached to the frame side rails.
A large portion of six-wheel drive vehicles utilize
a bogie suspension (fig. 8-14) which uses leaf springs.
This suspension is a unit consisting of two axles joined
by torque rods. A trunnion axle acts as a pivot for the
drive axles and is supported by bearings that are part of
the spring seat. The ends of each spring rest in the
guide brackets bolted to the axle housings. Mounting
the springs on central pivots enable them to distribute
half of the rear load onto each axle. As a result, this
type of suspension allows the vehicle to carry a much
The torsion bar consists of a steel rod made of
spring steel and treated with heat or pressure to make it
elastic, so it will retain its original shape after being
twisted. Torsion bars, like coil springs, are frictionless
and require the use of shock absorbers. The torsion bar
is serrated on each end and attached to the torsion bar
anchor at one end and the suspension system at the
other end (fig. 8-15). Torsion bars are marked to
indicate proper installation by an arrow stamped into
the metal. It is essential that they be installed properly
because they are designed to take the stress in one
direction only. The up-and-down movement of the
suspension system twists the steel bar. The torque
resistance will return the suspension to its normal
position in the same manner as a spring arrangement.
Figure 8-14.—Bogie suspension.
Figure 8-15.—Torsion bar.
removed from the vehicle. With the control arm placed
in a vise, either press or screw out the old bushings and
install new ones.
A suspension system takes a tremendous
"pounding" during normal vehicle operation. Bumps
and potholes in the road surface cause constant
movement, fatigue. and wear of the shock absorbers, or
struts. ball joints, bushings, springs, and other
components. Suspension system problems usually
show up as abnormal noises (pops, squeaks, and
clunks), tire wear, steering wheel pull, or front end
shimmy (side-to-side vibration). Suspension system
wear can upset the operation of the steering system and
change wheel alignment angles. Proper service and
maintenance of these components greatly increase
roadability, reliability, and vehicle life.
With new bushings installed, replace the control
arm in reverse order. Torque all bolts to the
manufacturer’s specifications. Install the ball joints
cotter pin. Check the manufacturer’s service manual
for information concerning preloading control arm
Always refer to the manufacturer’s service
manual for exact directions and specifications.
This will assure a safe, quality ride.
Suspension Bushing Service
Rubber bushings are commonly used in the inner
ends of front control arms and rear control arms. These
bushings are prone to wear and should be inspected
Ball Joint Service
Worn ball joints cause the steering knuckle and
wheel assembly to be loose on the control arm. A worn
ball joint may make a clunking or popping sound when
turning or driving over a bump. Ball joint wear is
usually the result of improper lubrication or prolonged
use. The load-carrying ball joints support the weight of
the vehicle while swiveling into various angles. If the
joints are improperly lubricated (dry), the swiveling
action will cause them to wear out quickly.
Worn control arm bushings can let the control
arms move sideways. This action causes tire wear and
steering problems. To check for control arm bushing
wear, try to move the control arm against normal
movement. For example, pry the control arm back and
forth while watching the bushings. If the control arm
moves in relation to its shaft, the bushings are worn and
must be replaced.
Grease fittings are provided for ball joint
lubrication. If the ball joint has a lube plug, it must be
removed and replaced with a grease fitting. Using a
hand-powered grease gun, inject only enough grease to
fill the boot of the ball joint. Do not overfill the boot,
because too much grease will rupture the boot. A
ruptured boot will allow dirt to enter the joint, which
causes them to wear out quicker.
Generally, to replace the bushings in a front
suspension requires the removal of the control arm.
This usually requires the separation of the ball joints
and compression of the coil spring. The stabilizer bar
and strut rod are also unbolted from the control arm.
The bolts passing through the bushings are then
removed which allows for the control arm to be
Ball joints can be checked for wear while the wheel
is supported, as shown in figures 8-16 and 8-17. Axial
play or tolerance, also called vertical movement, is
checked by moving the wheel straight up and down.
The actual amount of play in a ball joint is measured
with a dial indicator. Figure 8-18 shows the dial
indicator clamped to the lower control arm. The dial
indicator tip rests against the leg of the steering
knuckle. With a pry bar. try to raise and lower the
steering knuckle. If you use too much force, the ball
joint may give you a false reading. You want to
measure the movement of the wheel and ball joint, as
the joint is moved up to the LOAD position. Note the
movement as indicated on the dial indicator.
Rocking the wheel in and out at the top and bottom
checks radial play or tolerance. This action also is
known as horizontal movement. Grasp the tire at the
top and bottom, and try to wobble it. However, now we
are assuming that the wheel bearings have been
checked and either adjusted or properly tightened.
Therefore, we are now checking the horizontal
movement of the ball joints. Some manufacturers do
not accept horizontal movement as an indicator of ball
joint wear.
The actual specifications for allowable wear limits
of the ball joints are listed in the manufacturer’s service
manual. Refer to the specifications for the vehicle you
are checking. Any ball joint should be replaced if there
is excessive play.
Ball joint replacement can usually be done without
removing the control arm. Generally, place the vehicle
on jack stands. Remove the shock absorber and install
a spring compressor on the coil spring. Unbolt the
steering knuckle and separate the steering knuckle and
Figure 8-17.—Support points for checking ball joints in front
suspension system using torsion bars.
Figure 8-16.—Support points for checking ball joints in
various front suspension systems using coil springs.
rebounds. A BAD shock absorber will let the body
bounce over three times.
Visually inspect the shock absorbers for any signs
of leakage (oily wetness) and damage. Also, check the
bushing on each end of the shock for being smashed or
split. Make sure that the shock absorber fasteners are
tight. When shock absorber replacement is required,
ALWAYS replace them as a pair, even if but one is
defective. This action ensures the riding equilibrium of
the vehicle.
For instructions on removal and
installation of shock absorbers, refer to the
manufacturer’s service manual.
Figure 8-18.—A dial indicator mounted to measure the
amount of play in a ball joint.
With many suspension systems, you must
place jack stands or lift devices under the
control arms or axle when replacing the shock
absorbers. This will keep the control arms or
axle from flying downward when the shock is
ball joint. The ball joint may be pressed, riveted,
bolted, or screwed into the control arm. If the ball joint
is riveted to the control arm, replace the rivets with
Strut Service
For exact ball joint removal and
installation procedures, consult the manufacturer’s service manual.
The most common trouble with a strut type
suspension is worn shock absorbers. Just like
conventional shock absorbers, the pistons and
cylinders inside the struts can begin to leak. This
reduces the dampening action and the vehicle rides
poorly. As with the conventional shock absorber when
a strut shock absorber leaks, it must be replaced, and
ALWAYS as a pair.
Shock Absorber Service
Worn shock absorbers will cause the vehicle to
ride poorly on rough roads. When the tire strikes a
bump, a bad shock will not dampen spring oscillations.
The suspension system will continue to rebound and
bounce. This move is then transferred to the frame, the
body, and the passenger compartment.
Basically, strut removal involves unbolting the
steering knuckle (front suspension) or bearing support
(rear suspension), any brake lines, and the upper strut
assembly-to-body fasteners. Remove the strut
assembly (coil spring and shock) as a single unit.
Loose or damaged shocks produce a loud clanking
or banging sound. The rapid up-and-down movement
of the suspension can hammer the loose shock
absorber against the body, the shock tower, or the
control arm.
Do NOT remove the nut on the end of the
shock rod or the unit can fly apart.
To check shock absorber condition, locate any
problems with a bounce test and a visual inspection. To
perform a shock absorber bounce test, simply push up
and down on each corner of the vehicle body. Then
release the body and count the number of times the
vehicle moves up and down. Generally a GOOD shock
absorber should stop movement in two to three
A strut spring compressor is required to remove
the coil spring from the strut. After the coil spring is
compressed, remove the upper damper assembly. With
the upper damper assembly removed, release the
tension on the coil spring and lift the spring off the
strut. Inspect all parts closely for damage.
The vehicle should also be at CURB WEIGHT
when checking spring condition and curb height. Curb
weight is generally the total weight of the vehicle with
a full tank of fuel and no passengers or cargo. Also,
make sure nothing is in the passenger compartment
that could possibly increase curb weight. Curb weight
is given in pounds or kilograms.
When compressing any suspension
system spring, be extremely careful to
position the spring compressor properly.. If
the spring were to pop out of the compressor,
serious injuries or death could result.
With the coil spring and upper damper unit
removed, you can now remove the shock cartridge. A
new shock cartridge can be installed in the strut outer
housing to restore the strut to perfect condition. Some
manufacturers recommend that the strut shock
absorber be rebuilt once the strut shock absorber is
repaired or replaced. The strut can be reassembled and
installed in reverse order of disassembly,.
What component of the suspension system
prevents the control arm from swinging to the
front or rear of the vehicle?
In the suspension system, what is the function of
the stabilizer bar?
Q3. At what location on the control am is the ball
joint attached?
For exact procedures for the removal,
repair, and installation of a strut assembly,
refer to the manufacturer’s service manual.
What is the most common type of shock absorber
used on modern vehicles?
On a vehicle that uses struts on the front, the
struts replace what suspension component?
What term is used to describe the stiffness or
tension of a spring?
The radial play of a ball joint can be checked
by moving the wheel straight up and down.
What tool is required to remove the coil spring
form the strut?
Spring Service
Springs require very little periodic service. Leaf
spring service usually involves bushing replacement.
Torsion bars require adjustment and coil springs
require no periodic service.
Spring service requirements can be found in the
service manual of the vehicle you are working on.
Spring fatigue (weakening) can occur after
prolonged service. The fatigue lowers the height of the
vehicle, allowing the body to settle toward the axles.
This settling or sagging changes the position of the
control arms, resulting in misalignment of the wheels.
This condition also affects the ride and appearance of
the vehicle.
Learning Objective: Identify the major components
of a steering system. Explain the operating principles
of steering systems. Describe the differences between
the linkage and rack and pinion type steering.
Describe the operation of power steering. Describe
service and repair procedures for manual and rack and
pinion type steering mechanisms. Explain the service
procedures for servicing power steering belts, hoses,
and fluid.
To check spring condition or torsion bar
adjustment, measure CURB HEIGHT (distance from a
point on the vehicle to the ground). Place the vehicle on
a level surface. Then measure from a service manual
specified point on the frame, body. or suspension down
to the shop floor. Compare the measurement to the
specifications in the service manual. If the curb height
is too low (measurement too small). replace the
fatigued springs or adjust the torsion bar.
The steering system allows the operator to guide
the vehicle along the road and turn left or right as
desired. The system includes the steering wheel, which
the operator controls, the steering mechanism, which
changes the rotary motion of the steering wheel into
straight-line motion, and the steering linkage. Most
systems were manual until a few years ago. Then
power steering became popular. It is now installed in
most vehicles manufactured today. The steering
For instructions on the removal and
installation of springs. refer to the manufacturer’s service manual.
system must perform several important functions,
which are as follows:
pitman arm normally uses a ball-and-socket joint to
connect to the center link.
Provide precise control of front-wheel direction.
Center Link
Maintain the correct amount of effort needed to
turn the front wheels.
The parallelogram steering linkage (fig. 8-19) uses
a center link, otherwise known as an intermediate rod,
track rod, or relay rod, which is simply a steel bar that
connects the steering arms (pitman arm, tie-rod ends,
and idler arm) together. The turning action of the
steering mechanism is transmitted to the center link
through the pitman arm.
Transmit road feel (slight steering wheel pull
caused by road surface) to the operator’s hands.
Absorb most of the shock going to the steering
wheel, as the tires hit bumps and holes in the
Allow for suspension action.
Idler Arm
The center link is hinged on the opposite end of the
pitman arm by means of an idler arm (fig. 8-19). The
idler arm supports the free end of the center link and
allows it to move left and right with ease. The idler arm
bolts to the frame or subframe.
Steering linkage is a series or arms, rods, and ball
sockets that connect the steering mechanism to the
steering knuckles. The steering linkage used with most
manual and power steering mechanisms typically
includes a pitman arm, center link, idler arm, and two
tie-rod assemblies. This configuration of linkage is
known as parallelogram steering linkage (fig. 8-19)
and is used on many passenger vehicles.
Ball Sockets
Ball sockets (fig. 8-19) are like small ball joints;
they provide for motion in all directions between two
connected components. Ball sockets are needed so the
steering linkage is NOT damaged or bent when the
wheels turn or move up and down over rough roads.
Ball sockets are filled with grease to reduce friction
and wear. Some have a grease fitting that allows
chassis grease to be inserted with a grease gun. Others
are sealed by the manufacturer and cannot be serviced.
Pitman Arm
The pitman arm transfers steering mechanism
motion to the steering linkage (fig. 8-19). The pitman
arm is splined to the steering mechanisms output shaft
(pitman arm shaft). A large nut and lock washer secure
the pitman arm to the output shaft. The outer end of the
Figure 8-19.—Parallelogram steering linkage.
When the effective lengths of the pitman arm and
the steering arm are equal, the linkage has a ratio of 1:1.
If the pitman arm is shorter or longer than the steering
arm, the ratio is less than or more than 1:1. For
example, the pitman arm is about twice as tong as the
steering arm. This means that for every degree the
pitman arm swings, the wheels will pivot about 2
degrees. Therefore, the steering linkage ratio is about
Tie-Rod Assemblies
Two tie-rod assemblies (fig. 8-19) are used to
fasten the center link to the steering knuckles. Ball
sockets are used on both ends of the tie-rod assembly.
An adjustment sleeve connects the inner and outer tie
rods. These sleeves are tubular in design and threaded
over the inner and outer tie rods. The adjusting sleeves
provide a location for toe adjustment. Clamps and
clamp bolts are used to secure the sleeve. Some
manufacturers require the clamps be placed in a certain
position in relation to the tie rod top or front surface to
prevent interference with other components.
Most of the steering ratio is developed in the
steering mechanism. The ratio is due to the angle or
pitch of the teeth on the worm gear to the angle or pitch
on the sector gear. Steering ratio is also determined
somewhat by the effective length and shape of the teeth
on the sector gear.
One purpose of the steering mechanism is to
provide mechanical advantage. In a machine or
mechanical device, it is the ratio of the output force to
the input force applied to it. This means that a
relativety small applied force can produce a much
greater force at the other end of the device.
In a rack-and-pinion steering system, the steering
ratio is determined largely by the diameter of the
pinion gear. The smatter the pinion, the higher the
steering ratio. However, there is a limit to how small
the pinion can be made.
In the steering system, the operator applies a
relatively small force to the steering wheel. This action
results in a much larger steering force at the front
wheels. For example, in one steering system, applying
10 pounds to the steering wheel can produce up to 270
pounds at the wheels. This increase in steering force is
produced by the steering ratio.
Manual steering is considered to be entirely
adequate for smatter vehicles. It is tight. fast, and
accurate in maintaining steering control. However,
larger and heavier engines. greater front overhang on
larger vehicles, and a trend toward wide tread tires
have increased the steering effort required. Steering
mechanisms with higher gear ratios were tried, but
dependable power steering systems were found to be
the answer. There are several different types of manual
steering systems, which are as follows:
The steering ratio is a number of degrees that the
steering wheel must be turned to pivot the front wheels
1 degree. The higher the steering ratio (30:1 for
example). the easier it is to steer the vehicle, all other
things being equal. However, the higher steering ratio,
the more the steering wheel has to be turned to achieve
steering. With a 30:1 steering ratio, the steering wheel
must turn 30 degrees to pivot the front wheels 1 degree.
Worm and sector
Worm and rotter
Cam and lever
Actual steering ratio varies greatly, depending on
the type of vehicle and type of operation. High steering
ratios are often catted stow steering because the
steering wheel has to be turned many degrees to
produce a small steering effect. Low steering ratios,
called fast or quick steering require much less steering
wheel movement to produce the desired steering
Worm and nut
Rack and pinion
Worm and Sector
In the worm and sector steering gear (fig. 8-20),
the pitman arm shaft carries the sector gear that meshes
with the worm gear on the steering gear shaft. Only a
sector of gear is used because it turns through an arc of
approximately 70 degrees. The steering wheel turns
the worm on the lower end of the steering gear shaft,
which rotates the sector and the pitman arm through the
use of the shaft. The worm is assembled between
tapered rotter bearings that take up the thrust and toad.
Steering ratio is determined by two factors—
steering-linkage ratio and the gear ratio in the steering
mechanism. The relative length of the pitman arm and
the steering arm determines the steering linkage ratio.
The steering arm is bolted to the steering spindle at one
end and connected to the steering linkage at the other.
"Variable steering ratio" means that the ratio is
larger at one position than another. Therefore the
wheels are turned faster at certain positions than at
others. At the center or straight-ahead position, the
steering gear ratio is high, giving more steering
control. However, as the wheels are turned, the ratio
decreases so that the steering action is much more
rapid. This design is very helpful for parking and
maneuvering the vehicle.
Cam and Lever
The cam and lever steering gear. in which the
worm is known as a cam and the sector as the lever, is
shown in figure 8-22. The lever carries two studs that
are mounted in bearings and engage the cam. As the
steering wheel is turned, the studs move up and down
on the cam. This action causes the lever and pitman
arm shaft to rotate. The lever moves more rapidly as it
nears either end of the cam. This action is caused by the
increased angle of the lever in relation to the cam. Like
the worm and roller, this design allows for variable
steering ratio.
Figure 8-20.—Worm and sector steering gear.
An adjusting nut or plug is provided for adjusting the
end play of the worm gear.
Worm and Roller
The worm and rotter steering gear (fig. 8-21) is
quite similar to the worm and sector, except a roller is
supported by ball or rotter bearings within the sector
mounted on the pitman arm shaft. These bearings assist
in reducing sliding friction between the worm and
sector. As the steering wheel turns the worm, the roller
turns with it, forcing the sector and pitman arm shaft to
Worm and Nut
The worm and nut steering gear is made in several
different combinations. A nut is meshed with and
screws up and down on the worm gear. The nut may
operate the pitman arm directly through a lever or
through a sector on the pitman arm shaft.
The hourglass shape of the worm, which tapers
from both ends to the center, affords better contact
between the worm and roller in all positions. This
design provides a variable steering ratio to permit
faster and more efficient steering.
Figure 8-22.—Cam and lever steering gear
Figure 8-21.—Worm and roller steering gear.
The recirculating ball is the most common type of
worm and nut steering gear (fig. 8-23). In this steering
gear, the nut, which is in the form of a sleeve block, is
mounted on a continuous row of balls on the worm gear
to reduce friction. Grooves are cut into the ball nut to
match the shape of the worm gear. The ball nut is fitted
with tubular ball guides to return the balls diagonally
across the nut to recirculate them, as the nut moves up
and down on the worm gear. With this design, the nut is
moved on the worm gear by rolling instead of sliding
contact. Turning the worm gear moves the nut and
forces the sector and pitman arm shaft to turn.
Rack and Pinion
The rack-and-pinion steering gear has become
increasingly popular on smaller passenger vehicles. It
is simpler, more direct acting, and may be straight
mechanical or power-assisted.
The manual rack-and-pinion steering gear
basically consists of a steering gear shaft, pinion gear,
rack. thrust spring, bearings, seals, and gear housing.
In the rack-and-pinion steering system the end of the
steering gear shaft contains a pinion gear, which
meshes with a long rack (fig. 8-24). The rack is
connected to the steering arms by tie rods, which are
adjustable for maintaining proper toe angle. The thrust
spring preloads the rack-and-pinion gear teeth to
prevent excessive gear backlash. Thrust spring tension
may be adjusted by using shims or an adjusting screw.
As the steering wheel is rotated, the pinion gear on
the end of the steering shaft rotates. The pinion gear
moves the rack from one side to the other. This action
pushes or pulls on the tie rods, forcing the steering
knuckles or wheel spindles to pivot on their ball joints.
This turns the wheels to one side or the other so the
vehicle can be steered.
Figure 8-23.—Worm and nut steering gear (recirculating ball
Figure 8-24.—Rack-and-pinion steering gear.
The components that are common to all power
steering systems are as follows:
in the system. There are four basic types of power
steering pumps—vane, roller, slipper, and gear types. A
belt running from the engine crankshaft pulley normally
powers the pump. During pump operation, the drive belt
turns the pump shaft and pumping elements. Oil is
pulled into one side of the pump by vacuum. The oil is
then trapped and squeezed into a smaller area inside the
pump. This action pressurizes the oil at the output, as it
flows to the rest of the system. A pressure relief/flow
valve is built into the pump to control maximum oil
pressure. This action prevents system damage by
limiting pressure developed throughout the different
engine speeds.
power steering pump is engine-driven and supplies
hydraulic fluid under pressure to the other components
CONTROL VALVE (fig. 8-26)—The control
valve (rotary or spool type), which is actuated by
steering wheel movements, is designed to direct the
Power steering systems normally use an
engine-driven pump and hydraulic system to assist
steering action. Pressure from the oil pump is used to
operate a piston and cylinder assembly. When the
control valve routes oil pressure into one end of the
piston, the piston slides in its cylinders. Piston
movement can then be used to help move the steering
system components and front wheels of the vehicles.
Figure 8-25.—Typical power steering pump.
Figure 8-26.—Control valve.
of a power steering pump, hydraulic lines, and a
special integral power-assist gearbox.
hydraulic fluid under pressure to the proper location in
the steering system. The control valve may be mounted
either in the steering mechanism or on the steering
linkage. depending on which system configuration is
The integral piston power steering gearbox (fig.
8-28) contains a conventional worm and sector gear
arrangement, a hydraulic piston, and a control valve.
The control valve may be either a spool valve or a
rotary valve depending upon manufacturer.
hoses are high-pressure. hydraulic rubber hoses that
connect the power steering pump and the integral
gearbox or power cylinder. One line serves as a supply
line, the other acts as a return line to the reservoir of the
power steering pump.
The operation of an integral power steering system
is as follows:
With the steering wheel held straight ahead or in
NEUTRAL position, the control valve balances
hydraulic pressure on both sides of the power piston. Oil
returns to the pump reservoir from the control valve.
There are three major types of power steering
systems used on modern passenger vehicles (fig. 8-27)—
integral piston (linkage type), external cylinder
(linkage type), and rack and pinion. The rack and
pinion can further be divided into integral and external
power piston. The integral rack and pinion steering
system is the most common.
For a right turn, the control valve routes oil to the
left side of the power piston. The piston is pushed to the
right in the cylinder to aid pitman shaft rotation.
For a left turn, the control valve routes oil to the
right side of the power piston. The piston is pushed to
the left in the cylinder to aid pitman shaft rotation.
Integral Piston (Linkage Type)
The integral piston (linkage type) power steering
system has the hydraulic piston mounted inside the
steering gearbox. This is the most common type of
power steering system. Basically, this system consists
In both left and right turns piston movement forces
oil on the nonpressurized side of the piston back
through the control valve and to the pump.
Figure 8-27.—The three major power steering systems. (A) Integral piston (linkage type), (B) External cylinder (linkage type),
and (C) Rack and pinion type.
formed by attaching a hydraulic piston to the
center of the rack. A rubber seal fits around the
piston to prevent fluid from leaking from one
side of the power cylinder to the other.
External Cylinder (Linkage Type)
The external cylinder power steering system has
the power cylinder mounted to the frame and the center
link. In this system the control valve may be located in
the gearbox or on the steering linkage. Operation of
this system is similar to the one previously described.
HYDRAULIC LINES (steel tubing that
connects the control valve and power cylinder).
CONTROL VALVE (a hydraulic valve which
regulates hydraulic pressure entering each end
of the power piston)—There are two types of
control valves—rotary and spool. Using a
torsion bar connected to the pinion gear
operates the rotary valve, whereas the spool
valve is operated by the thrust action of the
pinion shaft.
Power Rack and Pinion
Power rack-and-pinion steering uses hydraulic
pump pressure to assist the operator in moving the rack
and front wheels. A basic power rack-and-pinion
assembly consists of the following:
POWER CYLINDER (hydraulic cylinder
formed around the rack)—The power cylinder is
precisely machined to accept the power piston.
Provisions are made for the hydraulic lines. The
power cylinder bolts to the vehicle frame, just
like the rack of a manual unit.
Other components of the power rack and pinion
are similar to those that are found on manual
rack-and-pinion steering system.
Power rack-and-pinion operation is fairly simple.
When the steering wheel is turned, the weight of the
vehicle causes the front tire to resist turning. This
resistance twists a torsion bar (rotary valve) or thrusts
POWER PISTON (a double-acting hydraulic
piston formed on the rack)—The power piston is
Figure 8-28.—Power steering gearbox.
the pinion shaft (spool valve) slightly. This action
moves the control valve and aligns the specific oil
passages. Pump pressure is then allowed to flow
through the control valve, the hydraulic line, and into
the power cylinder. Hydraulic pressure then acts on the
power piston and the piston action assists in pushing
the rack and front wheels for turning.
With the outer end removed from the center link,
unbolt and remove the idler arm from the frame.
Install the new idler arm in reverse order of
removal. Make sure that all fasteners are torqued to
manufacturer’s specifications. Install a new cotter pin
and bend it properly.
TIE-ROD END SERVICE.—A worn tie-rod end
will also cause steering play. When movement is
detected between the ball stud and the socket,
replacement is necessary.
Maintenance of the steering system consists of
regular inspection, lubrication, and adjusting
components to compensate for wear. When inspecting
the steering system, you will need someone to assist you
by turning the steering wheel back and forth through the
free play while you check the steering linkage and
connections. You will also be able to determine if the
steering mechanism is securely fastened to the frame. A
slight amount of free play may seem insignificant, but if
allowed to remain, the free play will quickly increase,
resulting in poor steering control.
The replacement of a worn tie-rod end is as
Separate the tie rod from the steering knuckle or
center link. As with the idler arm, a ball joint fork or
puller can be used.
With the tie rod removed from the steering
knuckle or center link, measure tie-rod length. This will
allow you to set the new tie rod at about the same length
as the old one.
After prolonged use, steering components can fail.
It is important that the steering system be kept in good
working condition for obvious safety reasons. It is
your job to find and correct any system malfunctions
quickly and properly
The alignment of the front wheel is altered
when the length of the tie rod is changed.
Steering Linkage Service
Loosen and unscrew the tie-rod adjustment
sleeve from the tie-rod end. Turn the new tie-rod end
into the adjustment sleeve until it is the exact length of
the old tie rod.
Any area containing a ball-and-socket joint is
subjected to extreme movements and dirt. The
combination of these two will cause the balland-socket joint to wear. When your inspection finds
worn steering linkage components, they must be
replaced with new components. Two areas of concern
are the idler arm and the tie-rod ends.
Install the tie-rod ball stud into the center link or
steering knuckle. T i g h t e n t h e f a s t e n e r s t o
manufacturer's specifications. Install new cotter pins
and bend correctly. Tighten the adjustment sleeve and
check steering action.
IDLER ARM SERVICE.—A worn idler arm
causes play in the steering wheel. The front wheels,
mostly the right wheel, can turn without causing
movement of the steering wheel. This is a very
common wear point in the steering linkage and should
be checked carefully.
Manual Steering System Service
Steering system service normally involves the
adjusting or replacement of worn parts. Service is
required when the worm shaft rotates back and forth
without normal pitman arm shaft movement. This
would indicate that there is play inside the gearbox. If
excess clearance is NOT corrected after the
adjustments, the steering gearbox must be replaced or
To check an idler arm for wear, grab the outer end
of the arm (end opposite the frame) and force it up and
down by hand. Note the amount of movement at the
end of the arm and compare it to the manufacturer’s
specifications. Typically, an idler arm should NOT
move up and down more than 1/4 inch.
Since there are numerous steering gearbox
configurations, we will discuss the most common type,
recirculating ball and nut. There are two basic
adjustments—worm bearing preload and over center
The replacement of a worn idler arm is as follows:
Separate the outer end of the arm from the center
link. A ball joint fork or puller can be used to force the
idler arms joint from the center link.
the worm shaft is held snugly inside the gearbox
housing. If the worm shaft bearings are too loose, the
worm shaft can move sideways and up and down during
Most gearboxes are designed to have more
geartooth backlash (clearance) when turned to
the right or left. A slight preload is produced in
the center position to avoid steering wheel
play during straight-ahead driving.
amount of play between the pitman arm shaft gear
(sector) and the teeth on the ball nut. It is the most
critical adjustment affecting steering wheel play.
With the steering wheel centered, loosen the over
center adjusting screw locknut. Turn the over center
adjusting screw in until it bottoms lightly. This will
remove the backlash.
Using the instructions in the service manual,
measure the amount of force required to turn the
steering wheel. Loosen or tighten the adjustment screw
to meet the manufacturer’s specifications. Tighten the
locknut and recheck the gearbox action.
Set the worm bearing preload first and
then the over center clearance.
The basic procedures for adjusting worm-bearing
preload are as follows:
When adjustment fails to correct the problems, the
steering gearbox needs to be overhauled or replaced.
Overhauling a gearbox is done by disassembling,
cleaning, inspecting, replacing worn components, and
seals. After reassembling the gearbox. fill the housing
with the correct type of lubricant. Most manual
steering systems use SAE 90 gear oil. Make sure that
you do NOT overfill the gearbox. Refer to the
manufacturer's service manual for the particular
gearbox you are working on since procedures,
specifications, and type of lubricants vary.
Disconnect the pitman arm from the pitman arm
shaft. Loosen the pitman arm shaft overcenter adjusting
locknut and screw out the adjusting screw a couple of
turns. Then turn the steering wheel from side to side
Using a torque wrench or spring scale. measure
the amount of force required to turn the steering wheel
to the CENTER position. Note the reading on the torque
wrench or the spring scale and compare it to the
manufacturers specifications.
R A C K - A N D - P I N I O N S E R V I C E .—Rackand-pinion steering systems have few parts that fail.
When problems do develop, they are frequently in the
tie-rod ends. When NOT properly lubricated, the rack
and pinion will also wear, causing problems.
If readings are out of specifications. loosen the
worm-bearing locknut. Then tighten the worm bearing
adjustment nut to increase the preload. Loosen it to
decrease preload and turning effort. With the preload set
to specifications. tighten the locknut. Make sure the
steering wheel turns freely from stop to stop.
Depending upon the manufacturer, some
rack-and-pinion steering systems need periodic
lubrication. Others only need lubrication when the unit
is being reassembled after being repaired.
Most rack-and-pinion systems have a rack guide
adjustment screw. This screw is adjusted when there is
excessive play in the steering. Basic procedure for
adjusting rack-and-pinion steering system is as
If the steering wheel binds or feels rough,
then the gearbox has damaged components
and should be rebuilt or replaced.
Loosen the locknut on the adjusting screw. Then
turn the rack guide screw until it bottoms slightly. Back
off the rack guide screw the recommended amount
(approximately 45 degrees or until the prescribed
turning effort is achieved).
The basic procedures for adjusting the over center
clearance are as follows:
Find the CENTER position of the steering wheel.
This is done by turning the steering wheel from full right
to full left while counting the number of turns. Divide
the number of turns by two to find the middle. This
allows you to turn the steering wheel from full stop to
the center.
Tighten the locknut. Check for tight or loose
steering and measure steering effort. Compare with the
manufacturer's specifications. If not with
specifications, an overhaul of the system will be
For instructions on the removal/installation and
overhaul of the rack-and-pinion system, refer to the
manufacturer’s service manual for the equipment you
are repairing.
Do NOT overfill the system. Overfilling
will cause fluid to spray out the top of the
reservoir and onto the engine and other
AND BELT.—Always inspect the condition of the
hoses and the belt very carefully.
Power Steering System Service
Many of the components of a power steering
system are the same as those used on a manual steering
system. However, a pump, hoses, a power piston, and a
control valve are added. These components can also
fail. requiring repair or replacement. Power steering
system service typically consists of the following:
The hoses are exposed to tremendous pressures; if a
hose ruptures, a sudden and dangerous loss of power
assist occurs. Make sure that the hose is NOT rubbing on
moving or hot components. This can cause hose failure.
Checking power steering fluid level
Power steering pump pressure can exceed
1,000 psi. This is enough pressure to cause
serious eye injury. Wear eye protection when
working on a power steering system.
Checking belts and hoses
Checking the system for leaks
If it is necessary to replace a power steering hose,
use a flare nut or tubing wrench. This action will
prevent you from stripping the nut. When starting a
new hose fitting, use your hand. This action will
prevent cross threading. Always tighten the hose fitting
Pressure testing the system
Bleeding the system
To check the level of the power steering fluid, you
should NOT let the engine run. With the parking brake
set, place the transmission in either PARK or
NEUTRAL. Basic procedures for checking the level of
the power steering fluid are as follows:
A loose power steering belt can slip, causing belt
squeal and erratic or high steering effort. A worn or
cracked belt may break during operation, which would
cause a loss of power assist.
Unscrew and remove the cap to the power
steering reservoir. The cap will normally have a dipstick
When it is necessary to tighten a power steering
belt, do NOT pry on the side of the power steering
pump. The thin housing on the pump can easily be
dented and ruined. ONLY pry on the reinforced
flanged or a recommended point.
Wipe off the dipstick and reinstall the cap.
Remove the cap and inspect the level of the fluid on the
dipstick. Most dipsticks will have HOT and COLD
markings. Make sure you read the correct marking on
the dipstick.
The basic procedures for installing a power
steering belt are as follows:
Loosen the bolts that hold the power steering
pump to its brackets.
The fluid level will rise on the dipstick as
the steering system warms.
Push inward on the pump to release tension on
the belt. With the tension removed, slide the belt
from the pulley.
If required, only add enough fluid to reach the
correct mark on the dipstick. Automatic transmission
fluid is commonly used in a power steering system.
Some power steering systems, however, do NOT use
automatic transmission fluid and require a special
power steering fluid. Always refer to the
manufacturer’s service for the correct type of fluid for
your system.
Obtain a new belt and install it in reverse order.
Remember when adjusting belt tension to
specifications, only pry on the reinforced flange or a
recommended pry point.
problem with power steering systems is fluid leakage.
With pressure over 1,000 psi, leaks can develop easily
around fittings. in hoses. at the gearbox seals, or at the
rack-and-pinion assembly.
To bleed out any air, start the engine and turn the
steering wheel fully from side to side. Keep checking
the fluid and add as needed. This will force the air into
the reservoir and out of the system.
To check for leaks. wipe the fluid-soaked area(s)
with a clean rag. Then have another person start and
idle the engine. While watching for leaks, have the
steering wheel turned to the right and left. This action
will pressurize all components of the system that might
be leaking. After locating the leaking component.
remove and repair or replace it.
The most common problems of a steering system
are as follows:
power steering pressure test checks the operation of the
power steering pump, the pressure relief valve, the
control valve. the hoses. and the power piston. Basic
procedures for performing a power steering pressure
test are as follows:
Steering wheel play
Hard steering
Abnormal noises when turning the steering
These problems normally point to component
wear, lack of lubrication. or an incorrect adjustment.
You must inspect and test the steering system to locate
the source of the trouble.
Using a steering system pressure tester, connect
the pressure gauge and shutoff valve to the power
steering pump outlet and hose. Torque the hose fitting
Steering Wheel Play
With the system full of fluid, start and idle the
engine (with the shutoff valve open) while turning the
steering wheel back and forth. This will bring the fluid
up to temperature.
The most common of all problems in a steering
system is excessive steering wheel play. Steering
wheel play is normally caused by worn ball sockets,
worn idler arm, or too much clearance in the steering
gearbox. Typically, you shou Id not be able to turn the
steering wheel more than 1 1/2 inches without causing
the front wheels to move. If the steering wheel rotates
excessively, a serious steering problem exists.
Close the shutoff valve to check system pressure.
Note and compare the pressure reading with
manufacturer’s specifications.
An effective way to check for play in the steering
linkage or rack-and-pinion mechanism is by the
dry-park test. With the full weight of the vehicle on the
front wheels, have someone move the steering wheel
from side to side while you examine the steering
system for looseness. Start your inspection at the
steering column shaft and work your way to the tie-rod
ends. Ensure that the movement of one component
causes an equal amount of movement of the adjoining
Do NOT close the shutoff valve for more than 5
seconds. If the shutoff value is closed longer, damage
will occur to the power steering pump from
To check the action of the power piston. control
valve. and hoses, measure the system pressure while
turning the steering wheel right and left (stop to stop)
with the shutoff valve open. Note and compare the
readings to the manufacturer’s specifications. If the
system is not within specifications, use the
manufacturer’s service manual to determine the source
of the problem.
Watch for ball studs that wiggle in their sockets.
With a rack-and-pinion steering system, squeeze the
rubber boots and feel the inner tie rod to detect wear. If
the tie rod moves sideways in relation to the rack, the
socket is worn and should be replaced.
SYSTEM.—Any time you replace or repair a
hydraulic component (pump. hoses, and power
piston), you should bleed the system. Bleeding the
system assures that all of the air is out of the hoses, the
pump, and the gearbox. Air can cause the power
steering system to make a BUZZING sound. The
sound will occur as the steering wheel is turned right or
Another way of inspecting the steering system
involves moving the steering components and front
wheel BY HAND. With the steering wheel locked,
raise the vehicle and place it on jack stands. Then force
the front wheels right and left while checking for
component looseness.
Belt squeal is a loud screeching sound produced by
belt slippage. A slipping power steering belt will
usually show up when turning. Turning the steering
wheel to the full right or left will increase system
pressure and belt squeal. Belt squeal may be eliminated
by either adjusting or replacing the belt.
Hard Steering
If hard steering occurs, it is probably due to
excessively tight adjustments in the steering gearbox
or linkages. Hard steering can also be caused by low or
uneven tire pressure, abnormal friction in the steering
gearbox, in the linkage, or at the ball joints, or
improper wheel or frame alignment.
The failure of power steering in a vehicle causes
the steering system to revert to straight mechanical
operation, requiring much greater steering force to be
applied by the operator. When this happens, the power
steering gearbox and pump should be checked as
outlined in the manufacturer's service manual.
To check the steering system for excessive
friction, raise the front of the vehicle and turn the
steering wheel and check the steering system
components to locate the source of excessive friction.
Disconnect the pitman arm. If this action eliminates
the frictional drag, then the friction is in either the
linkage or at the steering knuckles. If the friction is
NOT eliminated when the pitman arm is disconnected,
then the steering gearbox is probably faulty.
What type of steering linkage design is used on
most vehicles?
The idler arm supports the pitman arm on the
passenger side of the vehicle. (T/F)
What steering linkage component is used to
fasten the center link to the steering knuckles?
In a manual steering system, what two factors
determine steering ratio?
What is the most common type of worm and nut
steering gear?
In a power steering system, what device supplies
hydraulic fluid under pressure to the other
components in the system?
If hard steering is not due to excessive friction in
the steering system, the most probable causes are
incorrect front end alignment, a misaligned frame, or
sagging springs. Excessive tire caster causes hard
steering. Wheel alignment will be described later in
this chapter.
What are the three major types of power steering
On a manual rack-and-pinion system, what
adjustment is required when there is excessive
play in the steering?
What is the most common steering problem?
Steering System Noises
What is the most probable cause(s) of hard
Steering systems, when problems exist, can
produce abnormal noises (rattles, squeaks, and
squeals). Noises can be signs of worn components,
unlubricated bearingsor ball joints, loose components,
slipping belts, low power steering fluid, or other
Learning Objective: Identify and describe the parts of
a tire and the methods of tire construction. Explain tire
and wheel sizes. Describe tire ratings and the different
types of wheels. Identify the parts of driving and
nondriving hubs and wheel-bearing assemblies.
Diagnose common tire, wheel, and wheel-bearing
problems. Describe tire inflation and rotation
procedures. Explain static and dynamic wheel balance.
Summarize the different methods for balancing tires
and wheels. Explain wheel-bearing service.
Rattles in the steering linkage may develop if
linkage components become loose. Squeaks during
turns can develop due to lack of lubrication in thejoints
or bearings of the steering linkage. This condition can
also produce hard steering.
Some of the connections between the steering
linkage components are connected by ball sockets that
can be lubricated. Some ball sockets are permanently
lubricated on original assembly. If permanently
lubricated ball sockets develop squeaks or excessive
friction. they must be replaced.
This section introduces the various tire designs
used on modern vehicles. It explains how tire and
wheels are constructed to give safe and dependable
service. T h i s s e c t i o n a l s o c o v e r s h u b a n d
bias-ply tire allows the body of the tire to flex easily.
This design improves the cushioning action, which
provides a smooth ride on rough roads.
wheel-bearing construction for both rear-wheel and
front-wheel drives.
A bias-ply tire (fig. 8-29) has the plies running at
an angle from bead to bead. The cord angle is also
reversed from ply to ply, forming a crisscross pattern.
The tread is bonded directly to the top ply.
Most modern passenger vehicles and light trucks
use tubeless tires that do NOT have a separate inner
tube. The tire and wheel form an airtight unit. Many
commercial and construction vehicles use inner tubes
which are a soft. thin. leakproof rubber liner that fit
inside the tire and wheel assemblies. However. in the
last few years tubeless tires have been introduced to
commercial and construction vehicles. reducing the
need for tube type tires. Tires perform the following
two basic functions:
A major disadvantage of a bias-ply tire is that the
weakness of the plies and tread reduce traction at high
speeds and increase rolling resistance.
Belted Bias Tire
A belted bias tire provides a smooth ride, good
traction, and offers some reduction in rolling
resistance over a bias-ply tire. The belted bias tire is a
bias-ply tire with stabilizer belts added to increase
tread stiffness. The belts and plies run at different
angles. The belts do NOT run around to the sidewalls
but lie only under the tread area. Two stabilizer belts
and two or more plies are used to increase tire
They must act as a soft CUSHION between the
road and the metal wheel.
They must provide adequate TRACTION
(friction) with the road surface.
Tires must transmit driving. braking. and
cornering forces to the road in all types of weather. At
the same time, they should resist puncture and wear.
Although there are several tire designs. the six major
parts of a tire are as follows:
Radial Ply Tire
TIRE BEADS (two steel rings encased in rubber
that holds the tire sidewalls against the wheel
The radial ply tire (fig. 8-30) has very flexible
sidewall, but a stiff tread. This design provides for a
very stable footprint (shape and amount of tread
touching the road surface) which improves safety,
cornering, braking, and wear. The radial ply tire has
plies running straight across from bead to bead with
stabilizer belts directly beneath the tread. The belts can
be made of steel, flexten, fiber glass, or other materials.
BODY PLIES (rubberized fabric and cords
wrapped around beads. forming the carcass or
body of the tire).
TREAD (outer surface of the tire that contacts
the road surface).
SIDEWALL (outer surface of the tire extending
bead to tread; it contains tire information).
BELTS (used to stiffen the tread and strengthen
the plies; they lie between the tread and the inner
LINER (a thin layer of rubber bonded to the
inside of the plies: it provides a leakproof
membrane for tubeless tires).
There are many construction and design variations
in tires. A different number of plies may be used and
ran at different angles. Also, many different materials
may be used. The three types of tires, found on late
model vehicles, are bias-ply, belted bias. and radial.
Bias-Ply Tire
A bias-ply tire is one of the oldest designs, and it
does NOT use belts. The position of the cords in a
Figures 8-29.—Bias-ply tire construction.
designations (fig. 8-31)—alphanumeric (conventional
measuring system) and P-metric (metric measuring
The alphanumeric tire size rating system, as shown
in figure 8-31, uses letters and numbers to denote tire
size in inches and load-carrying capacity in pounds.
The letter G indicates the load and size relationship.
The higher the letter the larger the size and
load-carrying capability. The letter R designates the
radial design of the tire. The first number "78" is the
aspect ratio, also known as height-to-width ratio. The
last number "15" is the rim diameter in inches.
The P-metric tire size identification system, as
shown in figure 8-31, uses metric values and
international standards. The letter P indicates a
passenger vehicle (T means temporary and C means
commercial). The first number "155" indicates the
section width in millimeters measured from sidewall to
sidewall. The second number "80" is the aspect ratio,
also known as height-to-width ratio. The letter R
indicates radial (B means bias belted, D means bias-ply
Figure 8-30.—Radial tire construction.
A major disadvantage of the radial ply tire is that it
produces a harder ride at low speeds. The stiff tread
does NOT give or flex as much on rough road surfaces.
There is important information on the sidewall of a
tire. Typically, you’ll find UTQG (Uniform Tire
Quality Grading) ratings for treadwear, traction, and
temperature. Also, you will also find the tire size, load
index and speed rating, and inflation pressure. It is
important that you understand these tire markings.
Truck tires are sometimes marked with the
designation LT for "light truck" before the size.
Tire Size
The ASPECT RATIO or height-to-width ratio in
the tire size is the most difficult value to understand.
Aspect ratio is the comparison of the height of a tire
Tire size on the sidewall of a tire is given in a
letter-number sequence. There are two common size
Figure 8-31.—Tire size designation numbering systems.
the sidewall of the tire, the load rate is used as a quick
reference. Speed ratings (fig. 8-33) signify the safe top
speed of a tire under PERFECT conditions.
(bead to tread) to the width of a tire (sidewall to
sidewall). It is height divided by width. A 80-series
tire, for example, has a section height that is 80 percent
of the section width.
Maximum Inflation Pressure
As the aspect ratio becomes smaller, the tire
becomes more squat (wider and shorter). A 60-series
tire would be "short" and "fat." whereas an 80-series
tire would be "narrower" and "taller."
The maximum inflation pressure. printed on the
sidewall of a tire, is the highest air pressure that should
be induced into the tire. The tire pressure is a “cold”
pressure and should be checked in the morning before
operating the vehicle.
Load Index and Speed Rating
In most parts of the world, fall and early winter
months are the most critical times to check inflation
pressures because the days are getting colder. And
since air is a gas, it contracts when cooled. For every
10°F change in ambient temperature, the inflation
pressure of a tire will change by 1 psi. It will go down
with lower temperatures and up with higher
temperatures. The typical difference between summer
and winter temperatures is about 50°F that results in a
loss of 5 psi and will sacrifice handling, traction,
durability, and safety.
The term load index, or loud range. is used to
identify a given size tire with its load and inflation
limits when used in a specific type of service. The load
index of a tire and proper inflation pressure determines
how much of a load the tire can carry safely.
A letter identifies the load index for most light
trucks. These letters being B. C. or D. A tire with a B
load rate is restricted to a load specified at 32 psi.
Where a greater load-carrying ability is required, load
rate C or D tires are used.
Passenger vehicle tires come with a service
description added to the end of the tire size. These
service descriptions contain a number, which is the
load index, and a letter, which indicates the speed
rating. The load index (fig. 8-32) represents the
maximum load each tire is designed to support.
Because the masimum tire load capacity is branded on
Tire Grades
The Department of Transportation requires each
manufacturer to grade its tires under the Uniform
Tire Quality Grade (UTQG) labeling system and
(lbs *)
Figure 8-32.—Load index chart for a passenger vehicle.
OVER 150
OVER 240
Figure 8-33.—Speed rating chart for a passenger vehicle.
vehicle. Though it is strong enough to hold only a few
pounds of air when not confined, the tube bears
extremely high pressures when enclosed in a tire and
wheel assembly. Because the tube is made of
comparatively soft rubber to fulfill its function, it is easily
chafed, pinched, punctured, or otherwise damaged.
Tubes generally are made of a synthetic rubber that has
air-retention properties superior to natural rubber. There
are two types of synthetic rubber tubes—butyl and GR-S.
A butyl type tube is identified by a blue stripe, and GR-S
has a red stripe. Other than the standard tube, there are
three special typesoftubes—radial tire, puncture sealing,
and safety.
establishes ratings for treadwear, traction. and
temperature resistance (fig. 8-34). These tests are
conducted independently by each manufacturer
following government guidelines to assign values that
represent a comparison between the tested tire and a
control tire. While traction and temperature resistance
ratings are specific performance levels, the treadwear
ratings are assigned by the manufacturers following
field-testing and are most accurate when comparing
tires of the same brand. Tire grades are as follows:
TREADWEAR—Treadwear receives a comparative rating based on wear rate of the tire in field-testing
following a government-specified course. Treadwear is
given as a number: 100, 120, or 130, for instance. The
higher the number, the more resistant the tire is to wear.
For example, a tire grade of 150 wears 1.5 times longer
than a tire graded 100. Actual performance of the tire will
vary significantly depending on conditions, driving habits,
care, road characteristics, and climate.
RADIAL-TIRE TUBE—The construction of an
inner tube for use in a radial tire differs from the tube used
in a bias tire. A radial tire flexes in such a manner that it
concentrates the flex action in one area and at the edge of
the belts in the shoulder of the tire. This concentration of
stress will damage a standard tube causing it to fail. To
overcome this problem, the radial tube is made of a
special rubber compound that is designed to overcome
this concentrated stress; Therefore, standard tubes must
NEVER be used in radial tires.
TRACTION—Straight-a-head wet braking
traction has been represented by a grade of A, B, or C
with A being the highest. In 1997 a new top rating of
"AA" was introduced to indicate even greater wet
braking traction. Traction grades do NOT indicate wet
cornering ability.
tube has a coating of plastic material in the inner
surface. When the tube is punctured, this plastic
material is forced into the puncture by the internal air
pressure. The plastic material then hardens, sealing the
TEMPERATURE—Temperature resistance is
grades A, B. or C. This represents the resistance of the
tire to heat generated by running at high speed. Grade C
is the minimum level of performance for all passenger
vehicle tires as set under Federal Motor Vehicle Safety
Standards. This grade is established for a tire that is
properly inflated and not overloaded.
SAFETY TUBE—The safety tube is really two
tubes in one, one smaller than the other, and joined at the
rim edge. When the tube is filled with air, the air flows
first into the inside tube. From there the air passes
through an, equalizing passage into space between the
two tubes. Therefore, both tubes are filled with air. If a
puncture occurs, air is lost from between the tubes.
However, the inside tube, which has not been damaged,
retains its air pressure. It is sufficiently strong enough to
support the weight of the vehicle until the vehicle can be
slowed and stopped. Usually, the inside tube is
reinforced with nylon fabric. The nylon fabric takes the
suddenly imposed weight of the vehicle, without giving
way, when a blowout occurs.
Uniform Tire Quality Grade ratings are
NOT required on winter, light truck, and
commercial tires.
Tubes (inner tubes) are circular rubber containers
that fit inside the tire and hold the air that supports the
Wheels must have enough strength to carry the
weight of the vehicle and withstand a wide range of
speed and road conditions. Automobiles and light
trucks are equipped with a single piece wheel. Larger
vehicles have a lock ring (side ring) that allows for the
Figure 8-34.—Uniform Tire Quality Grade System ratings on
the sidewall of a tire.
easy removal of the tire from the wheel and. when in
place. it provides a seat for one side of the inflated tire.
Safety Wheel
A safety wheel (fig. 8-37) is similar to the drop
center wheel. The major difference is that the safety
wheel has a slight hump at the edge of the bead ledge
that holds the bead in place when the tire goes flat.
A standard wheel consists of the RIM (outer lip
that contacts the bead) and the SPIDER (center section
that bolts to the vehicle hub). Normally the spider is
welded to the rim. Common wheel designs are as
Split Wheel
A split wheel (rim) (fig. 8-38) has a removable
bead seat on one side of the rim. The seat is split to
allow for its removal so tires can be easily changed.
Some bead seats also require the use of a lock ring to
retain the seat. These wheels are used on large
commerical and military vehicles.
Drop center
Semidrop center
Drop Center Wheel
The drop center wheel (fig. 8-35) is made in one
piece and is commonly used on passenger vehicles
because it allows for easier installation and removal of
the tire. Bead seats are tapered to match a
corresponding taper on the beads of the tire.
Lug nuts hold the wheel and tire assembly on the
vehicle. They fasten onto special studs. The inner face
of the lug nut is tapered to help center the wheel on the
hub. Lug studs are special studs that accept the lug
nuts. The studs are pressed through the back of the hub
or axle flange. A few vehicles use lug bolts instead of
nuts. The bolts screw into threaded holes in the hub or
axle flange.
Semidrop Center Wheel
The semidrop center wheel (fig. 8-36) has a
shallow well, tapered-head seat to fit the taper of the
beads of the tire. It also has a demountable flange or
side ring. which fits into a gutter on the outside of the
rim. holding the tire in place.
Normally, the lug nuts and studs have right-hand
threads (turn clockwise to tighten). When left-hand
threads are used, the nut or stud will be marker with an
"L." Metric threads will be identified with the letter M
or the word Metric.
Figure 8-35.—Drop center wheel.
Figure 8-37.—Safety wheel.
Figure 8-36.—Semidrop center wheel.
Figure 8-38.—Split wheel.
SPINDLE—a stationary shaft extending
outward from the steering knuckle or suspension
system to which the following components are
Wheel bearings allow the wheel and tire assembly
to turn freely around the spindle, in the steering
knuckle, or in the bearing support. Wheel bearings are
lubricated with heavy, high-temperature grease. This
allows the bearing to operate with very little friction
and wear.
WHEEL BEARINGS—normally tapered roller
bearings mounted on the spindle and in the
wheel hub.
HUB—outer housing that holds the brake disc,
or drum, wheel, grease, and wheel bearing.
The two basic wheel-bearing configurations are
tapered roller or ball bearing types. The basic parts of a
wheel bearing are as follows:
OUTER RACE (cup or cone pressed into the
hub, steering knuckle, or bearing support)
GREASE WHEEL—a seal that prevents loss of
lubricant from the inner end of the spindle and
BALLS or ROLLERS (antifriction elements
that fit between the inner and outer races)
SAFETY WASHER—a flat washer that keeps
the outer wheel bearing from rubbing on and
possibly turning the adjusting nut.
INNER RACE (cup or cone that rests on the
spindle or drive axle shaft)
on the end of the spindle for adjusting the wheel
There are two types of wheel bearing and hub
assemblies—nondriving and driving. For example, the
front wheels on a rear-wheel drive vehicle are
NUT LOCK—a thin, slotted nut that fits over the
main spindle nut.
DUST CAP—a metal cap that fits over the outer
end of the hub to keep grease in and dirt out of the
Nondriving Wheel Assembly
The components of a nondriving wheel bearing and
hub assembly (fig. 8-39) includes the following:
Since a nondriving wheel bearing and hub
assembly does NOT transfer driving power, the
Figure 8-39.—Disassembled view of a nondriving wheel bearing and hub assembly.
spindle is stationary. The spindle simply extends
outward and provides a mounting surface for the wheel
bearings. hub. and wheel. With the vehicle moving, the
wheel and hub spin on the wheel bearings and spindle.
The hub simply freewheels.
inside the stationary support. With the hub splined to
the axle shaft, power is transferred to the wheels.
Leaks from a tubeless tire are located by filling the
tire with air and then placing the tire in a drum full of
water. Bubbles will show the location of any leaks. If a
drum of water is not available, coat the tire with soapy
water. Soap bubbles will show the location of the leak.
Driving Wheel Assembly
The components of a driving wheel bearing and
hub assembly (fig. 8-40) includes the following:
OUTER DRIVE AXLE—a stub axle shaft that
extends through the wheel bearings and is
splined to the hub.
It has been common practice to attempt the repair
of some punctures without dismounting the tire
through the use of a rubber plug. However. this
practice is NO LONGER RECOMMENDED, because
of serious safety concerns. Using a plug to attempt tire
repair without dismounting is effective only 80 percent
of the time. The remaining 20 percent of such repairs
will result in TIRE FAILURE, which may take the
form of a dangerous sudden deflation (blowout).
WHEEL BEARINGS—either ball or roller type
bearings that allow the drive axle to turn in the
steering knuckle or bearing support.
SUPPORT—a suspension or steering component that holds the wheel bearings, axle stub.
and hub.
The safe and correct procedure for tire repair is to
ALWAYS remove the tire from the wheel and make
the repairs from the inside of the tire. After the tire has
been dismounted.. it should be thoroughly
INSPECTED. During this inspection, check the inside
surface carefully, to locate the puncture and determine
the nature and extent of the damage.
DRIVE HUB—a mounting place for the wheel
which transfers driving power from the stub axle
to the wheel.
AXLE WASHER—a special washer that fits
between the hub and locknut.
The Rubber Manufacturer's of America list two
requirements for correctly repairing a puncture—the
repair MUST fill the injury to the tire and the repair
MUST soundly patch the inner liner. Various products
are available for repairing the puncture to the tire.
including plugs and liquid sealants.
HUB or AXLE LOCKNUT—a special nut that
screws onto the end of the drive axle stub shaft to
secure the hub and other parts of the assembly.
GREASE SEAL—prevents lubricant loss
between the inside of the axle and the steering
knuckle and bearing support.
The basic procedures for repairing a tubeless tire
are as follows:
The driving wheel bearing and hub assembly has
bearings mounted in a stationary steering knuckle or
bearing support. The drive axle fits through the center
of the bearings. The hub is splined to the axle shaft.
Instead of a stationary spindle. the axle shaft spins
Select a patch of sufficient size to extend well
beyond the damaged area, so it will adhere
properly and withstand the heat and mechanical
stress of the tire.
Figure 8-40.—Disassembled view of a driving wheel bearing and hub assembly.
Scuff (roughen) the area that the patch will
cover, so it will adhere tightly.
Preventive maintenance of tires and wheels
involves periodic inspections, checking inflation
pressure, wheel balancing, and rotation. Wheel
bearings are periodically lubricated and checked for
wear. These preventive maintenance steps will help
assure vehicle safety and a longer component life.
Apply the proper cement (adhesive), following
the directions in the tire repair kit.
Remove the covering from the adhesive side of
the patch and carefully place it on the inner liner.
Using a tool, called a sticher, roll it across the
patch to bond the patch tightly to the inner liner.
Rotating Tires
A few basic safety rules for repairing a tubeless
tire are as follows:
Tire rotation can be beneficial in several ways.
When done at the recommended times, it can preserve
balanced handling and traction of the tires and even out
tire wear. It can even provide performance advantages.
Manufacturers recommend that tires be rotated every
3,000 to 5,000 miles, even if they do not show signs of
wear. Tire rotation when done at the recommended
times helps even out tire wear by allowing each tire to
serve in as many of the wheel positions of the vehicle
as possible.
Do NOT attempt to repair a puncture by
plugging the tire from the outside. ALWAYS
dismount the tire and patch the inner liner.
Do NOT attempt to repair sidewalls or tires with
punctures larger than a 1/2 inch.
Reduce the air pressure to at least 15-psi, when
removing an object from the tire.
Broken strands in a steel belted tire can indicate
more serious damage than initially suspected.
Replace the tire.
Remember that tire rotation can NOT
correct problems due to worn mechanical parts
or incorrect inflation pressures.
Follow the procedures given in the tire repair kit.
While every vehicle is equipped with four tires,
usually tires on the front need to accomplish very
different tasks than the rear tires. And the tasks
encountered on a front-wheel drive vehicle are
considerably different than those of a rear-wheel
drive vehicle. Each wheel position can cause different
wear rates and different types of tire wear. It is to your
advantage when al! four tires wear together because
as wear reduces tread depth of a tire, it allows tires to
respond to the operator's input more quickly,
maintains the handling, and it helps increase the
cornering traction of a tire. Figure 8-41 shows
common tire rotation diagrams. A description of each
is as follows.
If a tube tire has been punctured but has no other
damage, it can be repaired with a patch. Remove the
tube from the tire to find the leak. Inflate the tube and
then submerge it in water. Bubbles will appear where
there is a leak. Mark the spot. Then deflate and dry the
There are two methods to patch a tube leak. They
are the cold-patch method and the hot-patch method.
With the cold-patch method (also known as chemical
vulcanizing), first make sure the area is clean, dry, and
free of grease and oil. Scuff the area around the leak.
Then cover the area with vulcanizing cement. Let the
cement dry until tacky. Press the patch into place. Roll
it from the center out with a "stitching tool" or the edge
of the patch kit can.
On front-wheel drive vehicles, rotate the tires in
a forward cross pattern (A) or the alternative X
pattern (B).
With the hot-patch method, prepare the tube in the
same way as for the cold patch. Put the hot patch into
place and clamp it. Then, with a match, light the fuel on
the back of the patch. As the fuel burns, the heat
vulcanizes the patch to the tube. After the patch has
cooled, inflate the tube and recheck for leaks by
submerging the tube in water. Another kind of hot
patch uses a vulcanizing hot plate. The hot plate
supplies the heat required to bond the patch to the tube.
On rear-wheel drive vehicles, rotate the tires in a
rearward cross pattern (C) or the alternative X
pattern (B).
If the vehicle has directional tires, rotate these
tires from front to back only and vise versa(D).
If the vehicle has nondirectional tires that are a
different size from front to rear, rotate these tires
from side to side only (E).
Figure 8-41.—Tire rotation diagrams.
When your tires wear out together, you can get a
new set of tires without being forced to change tires in
pairs. By replacing tires as sets, you will maintain the
original handling balance.
Figure 8-42.—Dynamic imbalance.
Wheel Balancing
Improper wheel balance is the most common cause
of tire vibration. Often a tire will appear to be round
and true when rotated slowly. However, when one side
is heavier than the other. centrifugal force tries to
throw the heavy area outward during operation. To
obtain maximum tire wear and a comfortable ride, you
should balance the wheels. The two types of tire
imbalance are as follows:
DYNAMIC IMBALANCE (fig. 8-42) lies on
either or both sides of the center line of the tire, which
causes the tire to vibrate up and down (wheel hop) and
from side to side (wheel shimmy). To be in dynamic
balance, the top-to-bottom weight and the side-to-side
weight must all be equal.
STATIC IMBALANCE (fig. 8-43), also called
wheel tramp or hop, lies in the plane of wheel rotation,
which causes the tire to vibrate up and down. For a
wheel and tire assembly to be in static balance, the
weight must be evenly distributed around the axis of
Figure 8-43.—Static imbalance.
tire assembly, the weights must be added exactly
where needed (fig. 8-44).
A wheel-balancing machine is used to determine
which part of a wheel assembly is heavy. The three
types of balancing machines are as follows:
To static balance a wheel and tire assembly, add
wheel weights opposite the heavy area of the wheel. If
a large amount of weight is needed, add half to the
outside and the other half to the inside of the wheel.
This will keep the dynamic balance of the tire.
However. when dynamically balancing a wheel and
BUBBLE BALANCER (fig. 8-45) is the most
common type of balancer used by the NCF. This type of
balancer will ONLY statically balance a wheel
wheel weights are to be added. After the weights are
added to the assembly, spin the assembly to again check
for vibration.
balancer) (fig. 8-46) is also used to balance a tire
statically and dynamically. An electric motor is used to
spin the wheel assembly and either a electronic pick-up
unit or hand-operated device is used to determine the
location for the wheel weights. An on-the-vehicle type
balancer is desirable because it can balance not only the
wheel assembly, but the wheel cover, brake disc or
drum, and lug nuts. Everything is rotated as a unit.
Wheel-Bearing Service
Wheel bearings are normally filled with grease. If
this grease dries out, the bearing will fail. Some wheel
bearings can be disassembled and packed (filled) with
grease, while others are sealed units that require
replacement when worn. When performing tire-related
service, check the wheel bearings for play and wear.
Figure 8-44.—How weights should be placed when balancing
For procedures on checking, removing,
and replacing wheel bearings, refer to the
manufacturer’s service manual.
Tire problems usually show up as vibrations,
abnormal wear patterns, abnormal noises, steering
wheel pull, and other similar symptoms. In some cases,
you may need to operate the vehicle to verify the
problem. Make sure that symptoms are NOT being
caused by steering, suspension, or front-wheel
alignment problems.
Figure 8-45.—Bubble balancer.
assembly. The wheel assembly must be removed from
the vehicle and placed on the balancer. An indicating
bubble on the machine is used to locate the heavy area of
the assembly. Wheel weights are added to the assembly
until the bubble CENTERS on the crosshairs of the
balancer) can statically and dynamically balance a
wheel assembly. The wheel assembly is removed from
the vehicle and mounted on the balancer. The assembly
is then spun at a high rate of speed. The machine detects
any vibration of the assembly and indicates where the
Figure 8-46.—On-the-vehicle balancer.
When inspecting tires, you should look closely at
the outer sidewall, tread area, and inner sidewall for
bulges, splits, cracks, chunking, cupping, and other
abnormal wear or damage. If problems are found
before repairing or replacing the tire, determine what
caused the failure.
Tire Impact Damage
Tire impact damage or road damage includes tears,
punctures, cuts, and other physical injuries. Depending
upon the severity of the damage, the tire must either be
repaired or replaced.
Tire Wear Patterns
Tire wear patterns can be studied to determine the
cause of abnormal tread wear. By inspecting the tread
wear, you can determine what parts should be serviced,
repaired, or replaced. Common tread wear patterns are
as follows (fig. 8-47):
FEATHERING (A) is caused by erratic
scrubbing against the surface of the road when the tire is
in need of toe-in or toe-out alignment correction.
OVERINFLATION (B) causes fast center line
wear in bias and bias belted tires. In this case, the center
of the tread has more contact with the road and wears
faster than the outer area of the tread.
UNDERINFLATION (C) causes the outer tread
areas (shoulders) of the tire to have more contact with
the road; therefore, they wear faster than the center area
of the tread.
ONE-SIDE WEAR (D) is caused by excessive
camber, which means that the tire is leaning too much to
the inside or outside. This places all the work on one
side of the tire, resulting in excessive wear.
CUPPING (E) is caused by several problems,
such as imbalanced wheels. faulty shock absorbers,
faulty ball joints. or a combination of these troubles.
Figure 8-47.—Tread wear patterns.
Tire Inflation Problems
body of the tire to stretch outward, pushing the center
of the tread against the road surface. This action lifts
the outer edges of the tread OFF the road. An
overinflated tire produces a rough or hard ride. It is also
more prone to impact damage.
The correct tire inflation pressure is important to
the service life of the tire. Proper inflation is required to
ensure that the tread of the tire fully contacts the road
surface. This condition allows for even wear across the
tread, therefore. resulting in increased tire life and
improved handling and safety.
Tire underinflation is a very common and
destructive problem. This condition wears the outer
edges of the tread (shoulders) because low pressure
allows the sidewalls of the tire to flex which builds up
Tire overinflation causes the center area of the
tread to wear quickly. The high pressure causes the
heat during operation. The center of the tread flexes
upward and does NOT touch the surface of the road.
Underinflation will cause rapid tread wear, loss of fuel
economy, and possibly ply separation (plies tear away
from each other).
Uneven tire inflation pressure can cause steering
wheel pull. For example, when a vehicle that ha’s the
left front tire underinflated and the right front tire
properly inflated, the vehicle has a tendency to pull to
the left. The low air pressure in the left tire has more
rolling resistance. This action tends to pull the steering
wheel away from the normally inflated tire.
Learning Objective: State the purpose and describe
each wheel alignment setting. Describe the different
types of equipment used during wheel alignment
The term alignment means to position in a straight
line. Relating to vehicles, alignment means to position
the tires so they roll freely and evenly over the road
surface. The main purpose of wheel alignment is to
make the tires roll without scuffing, slipping, or
dragging under all operating conditions. Correct wheel
alignment is essential to vehicle safety, handling,
extending tire life, and achieving maximum fuel
Tire Vibration Problems
When one of the front tires is vibrating, it can be
felt in the steering wheel. When one of the rear tires is
vibrating, the vibration can be felt in the center and rear
of the vehicle. Tire vibration can be attributed to
several problems, such as out-of-balance condition,
ply separation, tire runout, a bent wheel, or tie cupping.
The different types of wheel alignments are front
end alignment, thrust angle alignment, and four-wheel
Tire and Wheel-Bearing Noise
1. In a front end alignment, the front only is
checked. This is fine in some cases, but are the front tires
properly positioned in front of the rear tires?
Tire noise usually shows up as a whine due to
abnormal tread wear or a thumping sound caused by
ply separation. Tire replacement is required to correct
these problems.
2. With the thrust angle alignment, the wheels are
squared to each other. This action will eliminate “dog
tracking” that you may have seen on a vehicle that
appears to be going down the road with the rear end a
foot over from the front.
Wheel-bearing noise is produced by dry, worn
wheel bearings. The bearing will make a steady
humming type sound. This is due to the rollers or balls
being damaged from lack of lubrication and are no
longer smooth. To check for a worn wheel bearing,
raise and secure the vehicle, and rotate the tire by hand.
Feel and listen carefully for bearing roughness. Also,
wiggle the tire back and forth to check for bearing
looseness. It may be necessary to disassemble the
wheel bearing to verify the problem.
3. The best way to align a vehicle is a four-wheel
alignment. This alignment will not only do what the
thrust angle alignment does but also includes adjusting
the settings on the rearofthe vehicle as well as the front.
Not all vehicles are fully adjustable, so before any
alignment always consult the manufacture's service
manual. Regular wheel alignments will save you as
much in tire wear as they cost. It should be considered
routine, preventive maintenance.
What are the two basic functions of a tire?
List the six major parts of a tire.
What is the major disadvantage of a radial tire?
What information is commonly given on the tire
What is the most commonly used wheel used on
passenger vehicles?
For a tire to be in dynamic balance, the weight
must be evenly distributed around the axis of
rotation. (T/F)
Steering geometry is the term manufacturers use to
describe steering and wheel alignment. The six
fundamental angles or specifications that are required
for a proper wheel alignment are as follows:
Q6. What are the two basic wheel-bearing
Steering Axis Inclination
spindle support. It is NOT a tire wear angle. The basic
purposes for caster are as follows:
Toe-Out On Turns
To aid directional control of the vehicle
To cause the wheels to return to the straightahead position
To offset road crown pull (steering wheel pull
caused by the slope of the road surface)
Caster (fig. 8-48) is the steering angle that uses the
weight and momentum of the vehicles chassis to lead
the front wheels in a straight path. Caster is the
backward or forward tilt of the steering axis that tends
to stabilize steering in a straight direction by placing
the weight of the vehicle either ahead or behind the
area of tire-to-road contact.
Caster is measured in DEGREES starting at the
true vertical (plumb line). Manufacturers give
specifications for caster as a specific number of
degrees positive or negative. Typically, specifications
list more positive caster for vehicles with power
steering and more negative caster for vehicles with
manual steering (to ease steering effort). Depending
upon the vehicle manufacturer and type of suspension,
Caster controls where the tire touches the road in
relation to an imaginary center line drawn through the
Figure 8-48.—Caster angle.
To load the larger inner wheel bearing
caster may be adjusted by using wedges or shims,
eccentric cams, or adjustable struts.
Positive and negative camber (fig. 8-49) is
measured from the true vertical (plumb line). If the
wheel is aligned with the plumb line, camber is zero.
Negative caster (fig. 8-48) tilts the top of the
steering knuckle toward the front of the vehicle. With
negative caster, the wheels will be easier to turn.
However, the wheels tend to swivel and follow
imperfections in the road surface.
With positive camber, the tops of the wheels tilt
outward when viewed from the front, With negative
camber, the tops of the wheels tilt inward when viewed
from the front.
Positive caster (fig. 8-48) tilts the top of the
steering knuckle towards the rear of the vehicle.
Positive caster helps keep the wheels of the vehicle
traveling in astraight line. When you turn the wheels, it
lifts the vehicle. Since this takes extra turning effort.
the wheels resist turning and try to return to the
straight-ahead position.
Most vehicle manufacturers suggest a slight
positive camber setting from a 1/4 to a 1/2 degree.
Suspension wear and above normal curb weight
caused by several passengers or heavy loads tend to
increase negative camber. Positive camber counteracts
Camber is the inward and outward tilt of the wheel
and tire assembly when viewed from the front of the
vehicle. It controls whether the tire tread touches the
road surface evenly. Camber is a tire-wearing angle
measured in degrees. The purposes for camber are as
Toe (fig. 8-50) is determined by the difference in
distance between the front and rear of the left and right
side wheels. Toe controls whether the wheels roll in the
direction of travel. Of all the alignment factors, toe is
the most critical. If the wheels do NOT have the correct
toe setting, the tires will scuff or skid sideways. Toe is
measured in fractions of an inch or millimeters.
To aid steering by placing vehicle weight on the
inner end of the spindle
TOE-IN is produced when the front wheels are
closer together in the front than at the rear, when
To prevent tire wear on the outer or inner tread
Figure 8-49.—Camber angle.
Figure 8-50.—A. Toe-in; B. Toe-out.
Steering Axis Inclination
measured at the hub height. Toe-in causes the wheels
to point inward at the front.
Steering axis inclination (SAI) (fig. 8-51) is the
angle away from the vertical, formed by the inward tilt
of the kingpin, ball joints, or MacPherson strut tube.
Steering axis inclination is always an inward tilt
regardless of whether the wheel tilts inward or
outward. Steering axis inclination is NOT a
tire-wearing angle. As with caster it aids directional
stability by helping the steering wheel to return to the
straight-ahead position.
TOE-OUT results when the front of the wheels are
farther apart than the rear. Toe-out causes the front of
the wheels to point away from each other.
The type of drive (rear or front wheel) determines
the toe settings. Rear-wheel drive vehicles are usually
set to have TOE-IN at the front wheels. This design is
due to as a result of the front wheels moving outward
while driving, resulting in toe-out. By adjusting the
wheels for a slight toe-in (1/16 to 1/4 in.), the wheels
and tires will roll straight ahead when driving.
Front-wheel drive vehicles require different
adjustment for toe. This is due to the front wheels
driving the vehicle and are pushed forward by engine
torque. This makes the wheel toe-in or point inward
while driving. To compensate for this. front-wheel
drive vehicles have the front wheels adjusted for a
slight toe-out (1/16 inch). This adjustment will give the
front end a zero toe setting. as the vehicle travels down
the road.
Figure 8-51.—Steering axis inclination angle.
Steering axis inclination is NOT adjustable. It is
designed into the suspension of the vehicle. If the angle
is not correct, then the suspension system should be
checked for damaged or worn parts. Replace the parts
to correct the problem.
Toe-Out On Turns
Toe-out on turns, also known as turning radius
angle, is the amount the front wheels toe-out when
turning corners. As the vehicle goes around a turn, the
inside tire must travel in a smaller radius circle than the
outside tire. To accomplish this, the steering arms are
designed to angle several degrees inside of the parallel
position. The exact amount depends on the tread and
wheelbase of the vehicle and on the arrangement of the
steering control linkage. Toe-out on turns is NOT an
adjustable angle. If the angle is incorrect, it is an
indication of damaged steering components.
Figure 8-53.—Tracking.
Figure 8-52 shows toe-out on turns. Note how each
front wheel turns a different number of degrees. This
prevents tire scrubbing and squeal by keeping the tires
rolling in the right direction on corners.
will increase tire wear, lower fuel economy, and upset
Improper tracking has many causes, such as
shifted or broken leaf springs, bent or broken rear axle
mounts, bent frame, bent steering linkage, or a
misadjusted front end alignment.
Tracking (fig. 8-53) is the ability of the vehicle to
maintain a right angle between the center line of the
vehicle and both front and rear axles or spindles. (The
rear of the vehicle should follow the front wheels.)
With improper tracking, the vehicle rear tires do NOT
follow the tracks of the front tires. This causes the
vehicle body or frame to actually shift partially
sideways when moving down the road. Poor tracking
The most basic types of equipment for wheel
alignment are the turning radius gauge, the
caster-camber gauge, and the tram gauge. These are
Figure 8-52.—Toe-out on turns.
Then read the number ofdegrees showing on the
other gauge. Check toe-out on turns on both right
and left sides. Note the readings.
the least complicated of all alignment equipment and
illustrate the fundamentals for wheel alignment easily.
In larger shore facilities these basic types of
equipment are normally replaced with a large
alignment rack. The alignment rack consists of ramps,
turning radius gauges. and specialized equipment for
measuring alignment angles.
If not within manufacturer specifications, check
for bent or damaged components.
Caster-Camber Gauge
The caster-camber gauge is used with the turning
radius gauge to measure caster and camber in degrees.
The caster-camber gauge either fits on the hub
magnetically (fig. 8-55) or may be mounted on the
wheel with an adapter (fig. 8-56). Caster and camber
are adjusted together since one affects the other.
Turning Radius Gauges
Turning radius gauges (fig. 8-54) measure how
many degrees the front wheels are turned right or left.
They are used when measuring caster, camber, and
toe-out on turns.
The portable type turning radius gauges are the
most common in the Naval Construction Force (NCF).
However, they are also mounted on alignment racks as
integral units.
The front wheels of the vehicle are centered on the
turning radius gauges. With the front wheels centered,
the locking pins are pulled out which allows the gauge
and tire to turn together. The pointer on the gauge will
indicate how many degrees the wheels have been
The procedures for checking toe-out on turns using
turning radius gauges are as follows:
Center the front tiresofthe vehicle on the turning
radius gauges and remove the locking pins.
Turn one of the front wheels until the gauge
reads 20 degrees.
Figure 8-55.—Magnetic Caster-Camber Gauge.
Figure 8-56.—Caster-Camber Gauge mounted on a wheel
Figure 8-54.—Turning radius gauge, portable type.
The procedures for using a caster-camber gauge
for measuring caster are as follows:
With the vehicle centered on the turning radius
gauges, turn one of the front wheels inward until
the turning radius gauge reads 20 degrees.
Turn the adjustment knob on the caster-camber
gauge until the bubble is centered on zero. Then
turn the wheel out 20 degrees.
Figure 8-57.—Tram gauge.
The degree marking next to the bubble will equal
the caster of that front wheel. Compare the
reading to the manufacturer’s specifications and
adjust as needed.
With a scribing tool, rotate each tire and scribe a
fine line on the chalk line. This will give you a
very thin reference line for measuring the
distance between the tires.
Repeat this operation on the opposite side of the
Lower the vehicle back on the turning radius
The procedures for using a caster-camber gauge
for measuring camber are as follows:
Position the tram gauge at the back of the tires.
Move the pointers until they line up with the
scribe marks on the tires.
With the vehicle on a perfectly level surface, turn
the front wheels straight ahead until the turning
radius gauges read zero.
Without bumping the tram gauge pointers,
reposition the gauge to the front of the tires. The
difference between the lines on the front and rear
of the tires shows toe.
Read the number of degrees next to the bubble
on the camber scale of the caster-camber gauge.
This will show camber for that wheel. If not
within manufacturer’s specifications, adjust the
If the lines on the front of the tires are closer
together than on the rear, the wheels are toed-in. If the
lines are the same distance apart at the front and rear,
toe is zero. Use the manufacturer’s service manual for
specifications and adjustment procedures.
Double-check the caster readings, especially
when an excessive amount of camber
adjustment is required.
If shims are used to adjust camber, add or
remove the same amount of shims from the
front and rear of the control arm. This will
keep the caster set correctly,.
Tram Gauge
The tram gauge (fig. 8-57) is a metal rod or shaft
with two pointers, used to compare the distance
between the front and rear of the tires of the vehicle for
toe adjustment. The pointers slide on the gauge so they
can be set to the distance between the tires. The tram
gauge will indicate toe-out or toe-in in inches or
Define the term alignment.
What are the six fundamental angles required for
proper wheel alignment?
What gauge is used to compare the distance
between the front and rear of the tires of the
vehicle for toe adjustment?
Learning Objective: Describe the procedures for
repairing and refinishing automotive bodies. Explain
the Naval Construction Force (NCF) policy on
corrosion control.
The automotive body provides protection for the
engine, power train components, operator, and any
cargo or passengers. At the same time, it adds strength
to the frame and provides adequate vision for the
operator. Last but not least, the body design provides a
pleasant outward appearance.
The procedures for using a tram gauge for
measuring toe are as follows:
Raise the front wheels of the vehicle and rub a
chalk line all the way around the center rib on
each tire.
For military vehicles, appearance is secondary.
The Naval Facility Engineering Command
(NAVFAC) who controls all Navy vehicles states that
transportation equipment will be repainted when
inadequate protection is afforded against rust and
corrosion. It also states that spot painting should be
used instead of complete painting unless necessary for
protection of the entire vehicle.
Part of your job as a Construction Mechanic is to
perform body maintenance of the vehicles assigned to
your command. In order to perform this task, you must
known the procedures used for straightening fenders
and body panels. Preparation and painting of the
vehicle is another important task associated with this
Figure 8-59.—Pushing a body dent out using a portable
hydraulic jack.
Regardless of whether the vehicle is in need of
extensive bodywork or has a dented fender, it is
desirable to have a number of special tools. One of the
most important tools required to repair heavily
damaged areas is a portable hydraulic jack
(porta-power) (fig. 8-58). The porta-power is provided
with a number of adapters or accessories that will
allow you to use it in many types of body repair work.
This tool when applied, as shown in figure 8-59, will
force the damaged area to return to near original shape
and save many hours of labor.
Figure 8-60.—Spoons used in the body repair shop.
Spoons (fig. 8-60) dinging hammers (fig. 8-61)
and dolly blocks (fig. 8-62) are the common working
tools found in the body shop. These tools are used to
remove dents and smooth out and shape damaged
Figure 8-61.—Dinging hammers used to remove dents.
Figure 8-58.—Portable hydraulic jack.
Before attempting any body repairs, scrape off any
undercoating or foreign matter located in the area to be
repaired. Dirt or undercoating will cake on the dolly
block. No amount of hammering will produce a
smooth surface when this occurs. Next make sure the
outer side is clean to protect the hammer.
Without prior body repairing experience, a
mechanic will usually start applying pressure at the
spot where the panel was struck first and is depressed
the most. The CORRECT METHOD is to apply
pressure at the ridge farthest from the point of impact.
To make the procedure clear, refer to the damaged
panel in figure 8-63.
Assume that the original form of the panel is
shown as the dotted line. Point Y is where it was struck,
and X is a ridge that was formed last. With the use of a
spoon and hammer or mallet, place the spoon on the
ridge (X) and strike it with the hammer. Aim your
hammer blows directly at the ridge (X). By following
the ridge with the spoon and hammer, you will find that
the ridge will gradually disappear while the major
portion of the depression at point Y will spring back
and very closely resemble the original contour of the
Figure 8-62.—Dolly blocks used to shape body panels.
Using a dolly block with the same general
curvature as the panel, place it under the panel at point
O and strike the dent as shown. In this way, the dolly
block acts as a hammer and raises the dented portion to
the original contour, as the dolly block is gradually
moved toward point Z. The most common mistake
made by an inexperienced body repairman is trying to
do all the work with one blow of the dolly. All that is
necessary of the hammer or dolly is to press the metal
back into position. A number of light blows with the
hammer or dolly is better than a few heavy ones. Heavy
blows result in the metal stretching excessively during
the straightening process. This requires that the panel
be shrunk later to remove bulges.
Make sure the surfaces of the spoons,
hammers, and dollies are free from scratches
and/or dents. Surface defects on these tools
will cause similar defects in the sheet metal
they are used on. To remove surface defect on
these tools, use a file and fine grit sandpaper
until you have a smooth surface.
With these tools and experience you will be able to
remove the dents and creases while restoring the body
to a like-new condition. The ease and speed with which
you can straighten the sheet metal is dependent on
starting the repair work at the right point and the
correct use of the tools. If this is done, the amount of
“dinging” (light tapping of the metal with a hammer)
required to remove the dent is reduced considerably.
As metal is dinging and formed, a certain amount of
stretching occurs. This causes additional work when
nearing completion of the repair. Always remember,
when straightening a damaged panel, the damage
should be removed in reverse order of how it occurred.
When working with the hammer, apply blows
rapidly with a pulling action so the hammer tends to
slide as it contacts the metal. Above all, don’t try to
rush the job by striking the metal too heavily. Figures
8-64 and 8-65 show the procedures for removing dents
when performing bodywork. Use of a flat-faced
hammer should be confined to the flat or nearly flat
surfaces and the outside of curved surfaces. Hammers
with crowned faces are for use on concave surfaces
Figure 8-63.—The correct and incorrect methods for repairing a damaged body panel.
Figure 8-65.—The spoon can be used as both a lever and dolly
when working in tight places.
Figure 8-64.—Arrow indicates direction metal must move to
return to original contour.
If you decide to replace the damaged panel, make
sure any braces that support the panel are ordered also.
New braces will assist in aligning the new panels with
the rest of the body. Should only a portion of the
damaged panel be replaced, a oxygas cutting and
welding outfit (fig. 8-66) will be required to remove
the damaged portion and weld the new sheet metal into
Generally, a severely damaged panel will be
replaced or repaired by cutting out the damaged area
and replacing it with sheet metal. Should you have to
repair a heavily damaged body panel, there are a few
things you should consider before starting the job.
The first and most important consideration is to
determine the direction of force that caused the
damage. This will enable you to use the hydraulic jack
and its attachments to push the panels back into a near
original position. At the same time, the braces holding
the sheet metal will move back to their original
position and allow access to any bolts and fasteners
that must be removed to disassemble the damaged
body parts. Once you have reached this point, it must
be determined if the damaged panel is to be repaired or
Complete instructions on the use and care
of oxygas cutting and welding outfit are
contained in the current edition of the
Steelworker training manuals. Consult these
manuals for the proper method for adjusting
and using the cutting and welding tips.
Figure 8-66.—Oxygas cutting and welding outfit.
With the new sheet metal welded into place, the
weld should be ground down using a disc sander.
Exercise care while sanding to prevent burning
or cutting holes in the sheet metal.
The procedures for replacing a portion of a
damaged panel are as follows:
Determine the amount of damaged area to be
removed. Using oxygas cutting and welding
equipment removes the damaged area.
When replacing sheet metal, it may be necessary to
shrink the sheet metal in order to achieve a
professional fit and finish. Figure 8-67 shows the
procedure for shrinking sheet metal. Only a small area
at a time is heated and shrunk. This will cause the panel
to return to its original contour when performed
Once the section of the damaged panel has been
removed. straighten the remaining portion to the
original contour.
Place a piece of sheet metal over the area that is
cut away. Mark the new sheet metal so that when
you cut on the lines drawn, the piece will be
slightly larger than the area being replaced.
With the new piece of sheet metal held in place
by clamps, weld the sheet metal into place. Work
out to the sides then down the sides. Make a
continuous weld, doing a length about 6 inches
long at a time. To reduce distortion, stagger the
Before actual painting begins, it is essential that
you prepare the surface for the paint by removing all
traces of wax, grease, oil, and dirt. If the paint on the
vehicle is of poor quality or deteriorated, remove it. In
Figure 8-67.—Metal shrinking process and sequence used for large areas.
this final preparation of the body before applying
paint, you have several methods to choose from. The
method that is selected depends on the condition of the
existing paint, the equipment available, and the quality
of the desired finish product.
paint or by accidents shall be spot painted immediately
to prevent deterioration of the metal.
If the paint on the vehicle is in good condition
(good adherence and without surface defects), go over
the surface with a disc sander. An open-coated disc of
No. 16 to 24 grit is recommended. This will remove
most of the old finish down to the metal. Follow this
with a No. 50 close-coated disc to remove any
When using any paint product,
particularly lead-base paint, all current health
and safety regulations will be strictly
enforced. Contact the activity health/safety
department/office to obtain all applicable
regulations and instructions pertaining to a
safe painting environment.
If the paint is to be removed from only a portion of
the panel, taper the sanded area down into the old paint
to produce a featheredge. Follow-up with ,a 150 grit
paper in a block sander, and complete the featheredge
by water sanding using wet or dry paper of 280 or 320
All Navy equipment shall be treated and painted in
accordance with MIL-STD-1223. Equipment painting
shall meet all specifications and standards referenced
within MIL-STD-1223. Colors and color numbers that
are authorized for use when painting CESE are as
YELLOW 13538
Some manufacturers of abrasive paper
advise different grits with variations of the
above procedure. Follow the instructions of
the manufacturer.
For removing paint from the entire vehicle,
sandblasting is the preferred method. Among the
advantages claimed for sandblasting method are
speed, low cost, and a surface that has good paint
Before painting, a coat of primer should be applied
to prevent peeling and flaking where bare metal is
exposed. The primer serves as a bond between the
paint and the metal of the vehicle. Each coat of primer
that is applied should be allowed to dry and must be
sanded lightly between coats. There may be occasions
to use two coats of primer, but normally one coat is
After removing the old paint, clean the surface
with a cleaning agent. If none is available, a lint-free
cloth saturated with paint thinner can be used to wipe
down the surface. This will help the new paint to
adhere to the metal and remove the dust and other
foreign matter.
Paint and primer must be shaken or stirred
thoroughly, thinned with a thinning agent, and ran
through a strainer or filter when using a spray gun. One
of the "musts" of spray painting is that the paint should
have the correct viscosity. This can be determined by
following the instruction of the paint can. Too many
painters determine the viscosity by the rate at which
the paint runs from the stirring stick. This can lead to
plenty of trouble, since only a slight change in
viscosity can spoil an otherwise good job. This
happens because the amount of thinner not only
determines the thickness of the coat but also influences
the evaporation rate between the time the material
leaves the spray gun and the time it contacts the body
Apply the primer coat as soon as possible after the
paint is removed. This is particularly important when
the surface has been sandblasted, because the surface
is practically in a raw state and quickly starts rusting.
Equipment shall be repainted when inadequate
protection is afforded against rust and corrosion.
Equipment will NOT be repainted merely to change
the color or gloss characteristics if the finish is
serviceable. Spot painting, in lieu of completely
refinishing previously painted sections, should be
done whenever practicable. Bare surfaces of body
sections and sheet metal exposed by deterioration of
spot. Figure 8-68 shows the method for using a spray
High viscosity paint produces paint sag
and orange peel, while low viscosity paint
produces improper flow out and waste of
thinner. To avoid these problems, take care to
measure the proportions of thinner and paint
accurately in a graduated measuring cup.
Another ingredient that is sometimes added to the
paint is "drier." This substance causes the paint to set
and dry much more rapidly than normal. Because a
small amount of drier is all that is required, the
instruction on its use must be followed closely. Mixing
paint and adding drier are two critical parts of painting
vehicles. Use of the wrong type of thinner, paint, or
excessive drier will cause the paint to fade. peel, or
blister within a short period of time after completing
the job.
The temperature at which the spraying is done is
also an important factor in turning out a good job. This
applies not only to the temperature of the shop but also
to the temperature of the vehicle. Shop temperatures
should be maintained at approximately 70°F.
Whenever possible, bring the vehicle into the shop
well in advance of painting so that it becomes the same
temperature as the shop. Spraying paint on a surface
that is too cold or too hot from being in the sun will
upset the flowing time of the material and will cause
orange peel and poor adherence to the surface.
Painting instructions for using chemical agent
resistant coating (CARC) and the camouflage painting
of CESE equipment are found in the NAVFAC P-300.
Epoxy fillers (body fillers) are simple to use in that
the body portions do not have to be straightened as
closely as when making repairs without it. By using the
manufacturer’s instructions, you can apply body filler
over rough places and form it with a body file or
sanding until it conforms to the desired contour.
Another important factor in doing a good job is the
thickness of the paint film on the surface. Obviously, a
thick film takes longer to dry than a thin one. As a
result, the paint will sag, ripple, or orange peel. Ideally,
you should produce a coat that will remain wet long
enough for proper flow out. but no longer. The amount
of material you spray on a surface with one stroke of a
gun will depend on the width of the fan. the distance of
the gun from the sprayed surface, the air pressure, and
the amount of thinner used.
The advantage of using body filler lies in the fact
that a badly damaged vehicle can be returned to a
like-new appearance quickly and with a limited
amount of metal straightening. Additional, the use of
thinner metals in the bodies of modern vehicles makes
it difficult to reform panels into their original shape.
In addition, the speed of the spray stroke will also
affect the thickness of the coat. The best procedure is to
adjust the gun to obtain a wet film, which will remain
wet only long enough for good flow out. Get the final
thickness by spraying an additional coat after the first
one has dried.
Should you have an opportunity to use an epoxy
filler. the recommended thickness of the filler should
be kept to approximately 1/8 inch. If more is required.
it should be applied in coats and allowed to dry before
applying the next coat. Do not exceed an overall
thickness of 1/4 inch.
Nearly all-standard spray guns are designed to
provide optima coverage when held at a distance of 8 to
12 inches from the surface to be painted. When the gun
is held too close, the air pressure tends to ripple the wet
film, especially if the film is too thick. If the distance is
too great, a large percentage of the thinner will be
evaporated in the spraying operation. Orange peel or a
dry film will result. because the spray droplets will not
have opportunity to flow together.
Once a vehicle has been repainted, you will be
required to replace the vehicle identification markings.
The placement of registration numbers and other
equipment markings for identification purposes, as
required by law, are described in the NAVFAC P-300
It is imperative, then. to hold the spray gun at the
specified distance from the work. In addition, do NOT
tilt or hold the spray gun at an angle. Also, never swing
the spray gun in an arc. but move it parallel to the work.
The only time it is permissible to fan the gun is when
you want the paint to thin out over the edges of a small
Civil Engineer Support Equipment (CESE) is
assigned to many locations where atmospheric and
environmental conditions can cause severe corrosion
Figure 8-68.—Proper operation of a spray gun.
and a reduction in equipment life. Corrosion can be
slowed by proper cleaning and the correct application
and maintenance of protective coatings, such as paint,
undercoating, and preservatives. Body corrosion
occurs primarily where poor ventilation caused by
clogged drain holes or accumulations of mud and sand
allow moisture to remain on unprotected metal
the NAVFAC P-434, Construction Equipment
Department Management and Operations Manual.
All automotive CESE will be core-treated. Proper
application and preparation of the areas to be coated or
recoated is necessary. Surfaces shall be reasonably
clean, dry. and free of excessive rust, oil, grease, dust,
road tar, and other foreign matter. Core treatment of a
vehicle will be inspected during each preventive
maintenance (PM) service: one scratch through the
preservative can cause corrosion to start beneath the
The NAVFAC P-300 identifies and describes the
different preservative compounds applicable on
CESE. Additional information can be obtained from
What items are used to remove surface defects on
body spoons, hammers, and body dollies?
What is the preferred method for removing paint
from the entire vehicle?
What instruction provides information for using
chemical agent resistant coating?
Q1. Cross member
Q2. Monocoque
Q3. False
Q1. Strut rod
Q2. Limits body roll of the vehicle during cornering
Q3. Outer end of the control rod
Q4. Double-acting, double-action type
Q5. Upper control arm
Q6. Spring rate
Q7. False
Q8. Strut spring compressor
Q1. Parallelogram
Q2. False
Q3. Tie-rod assemblies
Q4. Steering linkage ratio and gear ratio of the steering mechanism
Q5. Recirculating ball
Q6. Power steering pump
Q7. Integral piston, external cylinder, and rack andpinion
Q8. Rack guide adjustment
Q9. Excessive steering wheel play
Q10. Excessively tight adjustment in the steering gearbox or linkages
Q1. Acts as a soft cushion between the road and the metal wheel and provides
adequate traction with the road surface.
Q2. Tire beads, body plies, tread, sidewall, belts, and liner
Q3. Produces a harder ride at low speeds.
Q4. Tire size, load index, speed rating, inflation pressure, and the UTQG ratings
for treadwear, traction, and temperature
Q5. Drop center
Q6. Tapered roller and ball bearing
Q7. False
To position in a straight line
Q2. Caster, camber, toe, steering axis inclination, toe-out on turns, and tracking
Q3. Tram gauge
Q1. A file and fine grit sandpaper
Q2. Sandblasting
Q3. NAVFAC P-300
that does not have to be shifted manually.
ABS SWITCH—Sensor that monitors hydraulic
system pressure and controls the pump motor in an
ABS application.
with special additives to make it compatible with
friction clutches and bands.
AC —Alternating current.
AUTOMOTIVE CLUTCH—A mechanical device
used to connect and disconnect a manual
transmission from engine power.
ABS—An abbreviation
AC GENERATOR—A device that
alternating current; an alternator.
AXLE —A cross support on a vehicle on which
supporting wheel, or wheels, turn(s).
ACTUATOR —A device that performs an action or
outputs a signal in response to a signal from a
AXLE END PLAY—In-and-out movement of the
axle, adjusted to specification by using shims.
AIR BRAKES—Vehicle brakes actuated by air
AXLE SHAFT RETAINER—Devices that attach to
the outside of an axle housing to prevent the axles
from sliding out.
AIR COMPRESSOR —A pump that forces air, under
pressure, into a storage tank.
ALTERNATOR—An ac generator.
AXLE SHIMS—Used between the axle housing and
retainer to limit end play of the axle.
ALTERNATOR BEARING—Needle- or ball-type
bearings used to provide a low friction surface for
a rotor.
BACKLASH —The backward rotation of a driven
gear that is permitted by clearance between
meshing teeth of two gears.
AMMETER—An electric meter that measures
current, in amperes, in an electric circuit.
BACKING PLATE—A component that holds the
shoes, wheel cylinder, and other parts inside a
brake drum.
BACKUP LIGHT SWITCH—An electrical switch
that completes a circuit to the backup lights
whenever the reverse gear is engaged.
accepts wheels sensor inputs and controls braking
of the vehicle.
BALL JOINT—Swivel joint that provides free
movement for the steering knuckle and control
brakes that will not "lock" and permit the wheels
to skid.
BALL SOCKETS—Component that allows motion
in up-and-down and side-to-side directions.
designed to keep brake pads from vibrating and
BAND—Metal strap with frictional material lining
that can clamp a clutch drum in an automatic
transmission to stop its rotation.
ANTI-SKID SYSTEM—Another name for anti-lock
braking system.
BAND ADJUSTMENT—Checking and altering
tightness of automatic transmission bands as
necessary for proper operation.
ASPECT RATIO—The relationship of tire height to
width or profile.
BATTERY —A device consisting of two or more cells
for converting chemical energy into electrical
ARMATURE —Rotating
windings in a motor.
BRAKE LINES—Metal tubing and rubber hoses
connecting the master cylinder to the wheel brake
BATTERY ACTIVATION—Filling and charging a
dry-charged battery before installation.
BATTERY CABLES—The heavy wires connecting
the battery to the electrical system of the vehicle.
BRAKE PADS—Replaceable friction surfaces
mounted on the caliper of a disc brake system.
BATTERY CAPACITY—The rating of the current
output of a battery.
operating the brake system.
the battery plates and electrolyte.
BRAKE SHOES—Curved, replaceable
surfaces used with drum-type brakes.
BATTERY DRAIN TEST—A method of checking
for unusual current draw with the ignition key off.
BRAKE SYSTEM—Components that are used to
stop a vehicle.
determine if current is discharging across the top
of the battery case.
BRAKE SYSTEM FLUSHING—Removal of all old
fluid by pressure bleeding, then replacing it with
fresh fluid.
BATTERY LOAD TEST—A test for battery
capacity, made under full electrical load.
BRAKE WARNING LIGHT—Dashboard indicator
that warns of low brake system hydraulic pressure.
contact between the cables and terminals.
of the brake pedal, usually caused by out-of-round
brake drum or warped rotor.
BATTERY CHARGER—A device for restoring a
battery to a proper electrical charge.
modern vehicles, 12.3 volts.
BRAKING RATIO—Comparison of front wheel to
rear wheel braking effort.
BRAKE-AWAY TORQUE—The amount of torque
required to make one axle rotate the clutches in a
limited-slip differential.
battery charge with a voltmeter.
BRUSHES—Sliding electrical contacts that ride on
the slip rings of a generator.
BEARING NOISE—A constant whir or humming
sound due to damage or wear of bearings in the
carrier or axle assemblies.
overheating due to slippage of the transmission
BELTED BIAS TIRE—A bias-belted tire with extra
belts added beneath the tread area.
CALIPER —A disc brake assembly that holds the
brake pads and the wheel cylinder.
BELTS—Fabric made of steel or other material that is
placed between body plies and tread.
CAMBER—The inward or outward tilt of a wheel
BENCH BLEED—Method of filling and hand
pumping a master cylinder before installation to
remove trapped air.
CASE BEARING PRELOAD—The amount of force
pushing the differential bearing together.
BIAS PLY TIRE—One with plies running at an angle
from bead to bead.
CASTER—The forward or backward tilt of the
steering knuckle.
BLEEDER SCREW—Fitting on the top of the brake
caliper that allows air to be bled from the system.
CASTER-CAMBER GAUGE—An instrument with
bubbles that indicate the degree of tilt.
BLEEDING—Process of removing any trapped air
from a hydraulic system.
CELL—Electrical energy storage device, consisting
of negative and positive plates immersed in a
conductive fluid (electrolyte).
vacuum or power steering system to decrease
braking effort needed.
CELL VOLTAGE TEST—A check of individual
battery cells for correct charge.
bearing unit that supports the middle of a twopiece drive shaft.
linkage permitting the operator to disengage the
clutch with the foot pedal.
CHARGE INDICATORS—Dash-mounted warning
light, voltmeter, or ammeter used to show charging
system status.
CLUTCH SLIPPAGE—A condition in which engine
rpm increase without increase in the vehicle road
CHARGING—Current flowing into a battery from an
CLUTCH START SWITCH—A safety switch that
prevents the starting motor from operating until
the clutch is disengaged.
CHARGING SYSTEM—One that uses an alternator
to replace the electrical energy drawn from the
battery during starting.
COIL—A transformer used to step-up the battery
voltage (by induction) to the high voltage required
to fire the spark plugs.
measurement of current and voltage output of the
charging system under load.
compress a spring for removal or installation on a
vehicle safely.
CHARGING VOLTAGE—Alternator output that is
higher than battery voltage, between 13 to 15 volts.
COIL WIRE—A conductor carrying high voltage
from the coil to the distributor.
CHASSIS—The frame and other parts of a vehicle,
other than the body.
current a battery can deliver for 30 seconds at 0°F.
resistance in the insulated and ground circuits of
the system.
functions as a metering valve, proportioning
valve, and a brake light warning switch.
CLUTCH—A device that allows the operator to
engage or disengage the engine and transmission.
between the motor winding and brushes.
CLUTCH ADJUSTMENT—A process of setting the
correct amount of free play in the release
on a motor that holds the brushes, brush springs,
and shaft bushing.
arrangement that uses a cable to transmit clutch
pedal movement to the clutch fork.
COMPUTER—Electronic device used to control
many systems of modern vehicles.
CLUTCH CHATTER—A condition in which the
clutch severely vibrates as the vehicle accelerates.
ignition system using sensors, a control unit, and
multiple ignition coils.
CLUTCH DISC—A disc that is splined to the
transmission input shaft and pressed against the
face of the flywheel.
device that provides a smooth dc voltage for
circuits and devices controlled by the computer.
CLUTCH FORK—A lever that forces the throw-out
(release) bearing into the pressure plate of the
CLUTCH LINING—Frictional material riveted to
the face of the clutch disc.
CONDENSER —An electrical component in contact
point of distributors that prevents arcing as points
that open and close.
CLUTCH LINKAGE—A mechanical arrangement
of levers and rods that transmits force from the
clutch pedal to the clutch fork.
two cross-and-roller joints connected by a
centering socket and center yoke.
clutch pedal moves before the throw-out bearing
acts on the pressure plate.
CONTACT PATTERN—The area of a gear tooth
where the matching gear tooth physically contacts
DIFFERENTIAL CASE—Case that holds the ring
gear, spider gear, and inner ends of the axles.
regulator that has been replaced by the electronic
to reduce friction between differential
CONTACT POINTS—A spring-loaded electrical
"make/break" switch contacts.
connects the rear universal of the drive line to the
CONTROL ARM BUSHING—A sleeve that allows
the control arm to swing up and down.
CONTROL ARMS—Movable lever arm that forms
part of the suspension system of the vehicle.
DIMMER SWITCH—Control for high beam and
low beam headlamp functions.
CONVERTER HOUSING—Case containing the
fluid coupling (torque converter) used with an
automatic transmission.
DIODE—Electronic device that allows current flow
in only one direction.
CURB HEIGHT—Distance from a given point on the
vehicle to the ground.
DIODE TEST—A check for open and shorted
conditions in a diode, using an ohmmeter or
special test equipment.
CURB WEIGHT—Weight of the vehicle with a full
gas tank and no passengers or cargo.
DISC BRAKES—Brakes using a caliper that clamps
against a rotor for stopping.
DISC BRAKE SERVICE—Procedure involving
worn pad replacement, caliper rebuilding, rotor
surfacing, and system bleeding.
CUSHIONING SPRINGS—Flat springs under the
friction material on the clutch disc that helps
smooth the clutch engagement.
surface to remove wear marks or correct runout.
CV—Constant velocity.
DISC RUNOUT—Amount of side-to-side movement
of the brake rotor.
DC—Direct current.
DISTILLED WATER—Water that has been purified.
DC GENERATOR—A device that produces direct
DISTRIBUTOR CAP—A plastic, insulating cover
that encloses the distributor rotor and other
DEAD AXLE—A solid, straight rear axle on a frontwheel drive vehicle.
distance between points when fully open.
DEAD BATTERY—One that has become completely
DISTRIBUTOR TESTED—Test device used to
check operation of an ignition system distributor.
with separate hydraulic circuits connecting
diagonal wheels together (RF to LR and LF to RR).
DIAGRAMS —Drawings that are used to show
wiring, vacuum, or hydraulic systems.
DOT NUMBER—The Department of Transportation
code that indicates the tire has passed a required
safety test. Also identifies manufacturer,
construction type, and other data.
uses a single diaphragm spring, rather than several
coil springs, to help release the clutch disc.
partially applied, even though the brake pedal is
DIFFERENTIAL—An assembly of gears used to
provide power to the rear axles and allow them to
rotate at different speeds as necessary.
DRAGGING CLUTCH—Failure of the friction disc
to disengage from the flywheel fully, even though
the clutch pedal is depressed.
mount the differential assembly on the rear axle
DRIVE CHAIN—A chain used with some
longitudinally mounted engines to transfer power
from the engine crankshaft to the transaxle.
DRIVE HOUSING—Case surrounding the pinion
gear on the starter motor.
DWELL—The amount of time distributor points
remain closed between openings.
DRIVE LINE—The parts that transfer power from the
transmission to the drive wheels.
DWELL METER—One that measures point setting
in degrees of distributor rotation.
DRIVE SHAFT—Steel tube that transfers rotating
motion from the transmission to the rear wheel of
the vehicle.
DYNAMIC IMBALANCE—Tire imbalance that
causes both up-and-down and side-to-side
movement while rotating.
DRIVE SHAFT ANGLE—The angle at which the
drive line meets the differential or transmission.
ECM—Electronic control module, another name for
an automotive computer.
D R I V E S H A F T A S S E M B L Y—Components
between the transmission and differential,
including front and rear yokes, universal joints,
and a drive shaft.
ECU—Electronic control unit, another name for an
automotive computer.
D R I V E S H A F T B A L A N C E—Equal
distribution around the axis of the shaft.
ELECTRONIC ADVANCE—A system that uses
sensor input and the computer of the vehicle to
control spark timing.
ELECTROLYTE—Liquid that surrounds the plates
of a battery and allows a free flow of electrons.
DRIVE SHAFT NOISE—Sounds typically caused
by worn U-joints, worn slip joints, or a faulty
center support bearing.
uses an electronic control circuit and distributor
pickup coil.
DRIVE SHAFT RUNOUT—Lack of straightness
due to being bent or because of U-joint wear.
use to identify source of ignition problems.
DRIVE SHAFT VIBRATION—A rapid oscillation
caused by a shaft imbalance or excessive shaft
ELECTRONIC MODULES—Small computers in a
vehicle, used for specific systems (such as antilock brakes).
DRIVING HUB—Mounting for the wheel on the end
of the axle.
E L E C T R O N I C R E G U L A T O R—Solid-state
regulator separate from the alternator.
DRUM—The housing that holds the parts of a clutch
assembly for an automatic transmission.
ELEMENT—One of the cells that can be combined to
form a battery.
DRUM BRAKES—System that forces brake shoes
against the inside of a rotating drum to stop a
applying the rear brakes.
DRUM BRAKE SERVICE—Process that involves
dismounting, disassembling, cleaning, and
replacing parts as necessary. Usually, shoes are
replaced, wheel cylinders are replaced or rebuilt,
and the drum is turned. System is then
reassembled, bled, and tested.
EXTENSION HOUSING—A separate housing
bolted to the transmission housing, containing the
output shaft and rear oil seal.
FACE—Area of a gear tooth above the pitch line.
FAST CHARGER—One that provides a high current
flow for quickly recharging a battery.
DRUM GRINDING—A process done to remove hard
spots on a brake drum.
FIELD FRAME—Housing on a motor that holds the
field coils.
diameter allowed for safe operation of drum
FIXED CALIPER—Brake caliper rigidly mounted to
the steering knuckle.
DRY CHARGED—Battery is filled with electrolyte
just before being installed in a vehicle.
FLOATING CALIPER—Brake caliper mounted on
two rubber bushings, allowing some movement.
DUAL MASTER CYLINDER—Brake system pump
with two pistons and fluid reservoirs for safety.
FORWARD BIAS—Arrangement in which a diode
acts as a conductor.
HALOGEN LAMP—One with a small, high
intensity halogen lamp inside a conventional
sealed housing.
FRAME—The strong steel structure that supports the
body of the vehicle.
FRONT DRIVE AXLES—Shafts that transfer power
from the transaxle differential to the wheels of the
HARD STEERING—Greater than normal
required to turn the steering wheel.
One in which all forward gears are equipped with
synchronizers to allow downshifting while in
HARD TO SHIFT—A manual transmission problem
often caused by damaged or sticking linkage.
HARSH SHIFTS—Transmission changes gears in a
jerky manner.
FUSE—A device that interrupts current if a circuit is
overloaded or a short occurs.
HEADLAMP SYSTEM—Components, such as
battery, switches, fuses, and lamps that make up
the headlamp lighting circuit.
FUSE BLOCK—A boxlike unit that holds the fuses
for the various electric circuits in a vehicle.
HEADLIGHT AIMER—A device used to adjust
headlights to specific positions.
FUSIBLE LINK—A type of circuit protector in
which a special wire melts to open the circuit when
current is excessive.
measured lines on a wall, used to adjust headlight
GEAR BACKLASH—Small amount of clearance
between meshing gear teeth.
HEAT SINK—A device for absorbing heat from one
medium and transferring it to another.
cleaning, adjusting, and replacing parts as
HORN RELAY—A relay connected between the
battery and the horn.
GEARBOX RATIO—The relationship (number of
turns) between the steering wheel and the sector
HOTCHKISS DRIVE—Open drive shaft that
operates a rear axle assembly mounted on springs.
The most common rear wheel drive type.
GEAR CLASH—Noise that is heard when gears fail
to mesh properly in a manual transmission.
HOT PLUG—A spark plug with a long insulator tip,
often used in older engines.
GEAR OIL—A high viscosity oil (80W or 90W) used
for manual transmissions and differentials.
HUB—Mounting place for a vehicle wheel on the end
of the axle or spindle.
GEAR RATIO—The number of rotations a driving
gear must make while the driven gear is
completing one revolution.
H Y D R A U L I C B R A K E B O O S T E R—Braking
system booster actuated by hydraulic pressure
from the power steering pump.
GEAR REDUCTION—The situation in which a
small gear is used to drive a larger gear with an
increase in torque as a result.
HYDROMETER—Tool used to test for specific
gravity (and thus, battery charge).
GRABBING BRAKES—Abrupt, hard application of
brakes when the brake pedal is slightly depressed.
IDLER ARM—A link that supports the tie rod and
transmits steering motion to both wheels through
the tie rod ends.
GREASE SEAL—Component that prevents lubricant
leaking from the axle assembly into the steering
knuckle or bearing support.
IGNITION COIL—Device used to produce the high
voltage needed for ignition spark.
GROUND—The return path for current in an
electrical circuit.
GROWLER—Testing device
armatures for shorts.
ignition timing, based on sensor input.
directs coil voltage to each spark plug at the
appropriate time.
HALL EFFECT—A type of pickup used with many
electronic ignition systems.
IGNITION RESISTOR—A resistance connected
into the primary circuit to reduce battery voltage to
the coil during engine operation.
front drive axle that connects the inner and outer
universal joints.
IGNITION SWITCH—The switch in the ignition
system that opens and closes the ignition-coil
primary circuit.
JOUNCE BUMPER—Rubber blocks that keep
suspension parts from hitting the frame when the
vehicle encounters large bumps or holes.
IGNITION SYSTEM—Components that produce a
spark to ignite the air-fuel mixture in the engine.
JUMPS OUT OF GEAR—A manual transmission
problem in which the transmission will
unexpectedly disengage and move into neutral.
IGNITION TIMING—How early or late the spark
plugs fire in relation to piston position.
JUMP STARTING—Providing current to a vehicle
with a dead battery by connecting cables to the
battery of an operating vehicle.
IMPELLER —Pump component with fanlike blades
that spins inside a housing to move liquid.
KICKDOWN VALVE—Component that causes an
automatic transmission to shift down into a lower
gear during fast acceleration.
INCORRECT CAMBER—Condition that produces
wear on one side of the tire tread.
INCORRECT TOE—Condition that
feathered edge on the tire tread.
KNUCKLE—A steering knuckle; a front suspension
part that acts as a hinge to support a front wheel and
permit it to be turned to steer the vehicle.
permits each wheel to move up and down without
seriously affecting any other wheel.
pressure that a tire can safely handle.
LATERAL RUNOUT—Side-to-side movement of a
wheel or tire.
LEAF SPRING—Flat pieces of spring steel that are
stacked and bound together. Normally used as a
part of the rear suspension of the vehicle.
INLET STUB SHAFT—Section of front drive axle
that is splined to differential gears. It is connected
to the interconnecting shaft through a universal
provides driving force to both rear wheels at all
Sound made when turning a comer, caused by
sticking and releasing of clutches in the
INPUT—The information provided to a computer by a
INPUT SHAFT—Metal shaft that transfers motion
from the engine (via the clutch) to the transmission.
LINER—Thin rubber layer bonded to plies and
forming the inside surface of the tire.
TEST—Check of all parts between the battery
positive and the starting motor for excess
LOAD RATING—The maximum amount of weight a
tire can carry when inflated to the recommended
LOCKED IN GEAR—A manual transmission
problem often caused by damaged or sticking
linkage. Broken gear teeth can also be at fault.
INSULATOR—A material that resists the flow of
which the hydraulic piston is mounted inside the
LOCKING HUB—Components that transfer power
from the driving axles to driving wheels on a fourwheel drive vehicle.
INTEGRAL REGULATOR—A regulator that is
mounted in or on an alternator.
LOCK-UP CONVERTER—A variation of the fluid
coupling with an internal friction clutch
mechanism. It "locks up" in high gear, improving
fuel economy.
silicon, containing complete electronic circuits.
prevents engaging the starter when the vehicle is in
LOW BRAKE PEDAL—Farther than normal brake
pedal travel before braking begins.
LUG NUT—Large steel nuts, used to hold a wheel
into the axle hub.
Altering position of the switch to permit starting of
the engine when gear selector is in the PARK
LUG STUD—Special bolts that are press-fit into the
axle hub and accept lug nuts to mount the wheels of
the vehicle.
NONDRIVING HUB—One that rotates freely on
spindles (axle ends).
MACPHERSON STRUTE—Suspension system that
uses one control arm and one strut for each wheel.
which wheels are attached to each end of a solid
MAGNETIC SENSOR—One that uses part
movement (such as rotation) and induced current
to produce a signal for a computer.
OHM'S LAW—A simple formula for computing
unknown electrical values when two values are
MAIN COMPUTER—The largest and most
powerful microprocessor in a system of the
ONE-WIRE CIRCUIT—One that uses the vehicle
frame as a return wire to the power source.
MAGNETIC FIELD—Field of force
around an electrical conductor.
OPEN CIRCUIT—Electrical circuit with a gap or
break in continuity so that current cannot flow.
M A I N T E N A N C E - F R E E B A T T E R Y—One
without removable filler caps that does not require
periodic filling with water.
bleeding using only the master cylinder.
(driver-operated) transmission.
OPEN LOOP—Control system using preset values in
the computer to operate the engine.
OUTBOARD CV-JOINT—The outer universal joint
on a front-wheel drive vehicle.
OUTER STUB SHAFT—In a front-wheel drive
vehicle, the short shaft connecting outer universal
joint and the front-wheel hub.
MANUAL VALVE—In an automatic transmission, a
valve actuated by the gearshift lever that routes oil
pressure to the components required for the
selected gear.
OUTPUT—The signal sent by a computer as a result
of processing inputs it has received.
OUTPUT SHAFT—Transmission shaft on which the
output gears are mounted.
MASTER CYLINDER—Hydraulic piston type
pump that develops pressure for the braking
OUTPUT SHAFT GEARS—Gears that turn the
output shaft of a manual transmission.
M I L K Y F L U I D—Condition
contamination of transmission fluid by engine
OVERDRIVE RATIO—The situation in which a
large gear is used to drive a smaller gear with an
increase in speed as a result.
dimension allowed for proper and safe operation
of disc brakes.
OVERRUNNING CLUTCH—Device that locks a
pinion gear in one direction and releases it in the
MOVABLE POLE SHOE—Device that uses a yoke
lever to move the pinion gear into contact with the
bearing shells with grease to prevent excessive
discs that can be used to drive planetary gearsets.
PARKING PAWL—A latch that locks the
transmission so that the vehicle will not roll when
the selector lever is in the PARK position.
MUSHY SHIFT—Transmission changes too slowly.
PLUG HEAT RANGE—Numeric indicator of how
hot a spark the plug will develop.
PEDAL FREE PLAY—The amount of brake pedal
movement before braking action begins to take
PLUG REACH—Length of the threaded portion of a
spark plug.
PEDAL HEIGHT—Distance of the brake pedal
above the floor of the vehicle.
PLY SEPARATION—Pulling apart of tire plies as a
result of overheating due to under inflation or other
PICKUP COIL—Component that sends pulses to the
control unit of an electronic ignition system as a
result of trigger wheel action.
POLE PIECE—Magnetic component of a motor that
keeps the armature rotating.
PICKUP COIL AIR GAP—The space between the
pickup coil and the trigger wheel tooth.
usually automatic transmission fluid.
PILOT BEARING—The bushing or bearing that
supports the forward end of the transmission input
pressure gauge to check pump and associated
components for correct pressure.
PINION GEAR—Differential gear turned by the
drive line. It meshes with the ring gear. Also, a
gearbox component that meshes with the rack gear
or a small gear on a starter motor that engages a
larger gear to rotate the engine flywheel.
POWER STEERING PUMP—Unit that provides
the hydraulic pressure needed in a power steering
POWER TRAIN—Gearing system and other
components used. to transfer energy from the
engine to the wheels of the vehicle.
tightness of bearings, adjusted by compressing a
spacer or using shims.
PRESSURE BLEEDING—A method of system
bleeding using additional pressure supplied by an
external air tank.
the pinion gear and drive end frame when the gear
is engaged.
PRESSURE PLATE—Spring-loaded device that
clamps the clutch disc against the flywheel.
PINION GEAR DEPTH—The distance the pinion
gear extends into the carrier to mesh with the ring
PRESSURE PLATE COVER—Lid that bolts on the
pressure plate to hold various components in
PINION PILOT BEARING—A bearing used to
support the pinion gear in the differential.
PRESSURE PLATE FACE—A large ring that
contacts the friction disc as the clutch engages.
PINION SHAFT—Shaft holding the two differential
idler (pinion) gears.
hinged inside the pressure plate that help move the
pressure plate face away from the clutch disc and
PITCH LINE—Imaginary line along the center of a
gear tooth.
PITMAN ARM—Component that transfers gearbox
motion to the steering linkage.
and back shoes in a drum brake system. The
secondary shoe has a larger surface area.
PITMAN SHAFT OVER-CENTER ADJUSTMENT—Adjustment of clearance between the
sector gear and the ball nut teeth in a recirculating
ball gearbox.
PRIMARY CIRCUIT—In an ignition system, all
components are operating on battery (low)
consisting of several
gears rotating
around a central "sun" gear.
PRIMARY WIRE—Small insulated conductor that
carries battery or alternator voltage.
equalize pressure at the wheel cylinders on
vehicles with front disc and rear drum brakes.
PLUG GAP—Distance between the center and side
electrodes on a spark plug.
REGULATOR BYPASS TEST—Test that connects
full battery voltage to the alternator field, leaving
the regulator out of the circuit.
PULLING BRAKES—Situation in which a vehicle
veers to one side when the brakes are applied.
QUICK CHARGE TEST—A method of determining
whether battery plates are sulfated (no longer able
to hold a charge).
steering gear in which a pinion of the end of the
steering shaft meshes with a rack of gear teeth on
the major cross member of the steering linkage.
ADJUSTMENT—Tightening or loosening rack
adjustment screw as needed for optimum steering.
RADIAL RUNOUT—Uneven rotation caused by
differences in diameter.
RADIAL TIRE—One that has cord plies running
straight across, from bead to bead. Additional
stabilizer plies are placed beneath the tread.
READING SPARK PLUGS—Determining cause of
a problem by examining condition of the spark
R E A D I N G T I R E S—Identifying
suspension, and other problems through the wear
patterns on tire treads.
REAR AXLE ASSEMBLY—A combination of
gears and axles converting rotary motion of the
drive shaft to forward or backward motion of a
axles, and other components transferring power
from the drive line to the rear wheels.
REAR DRIVE AXLES—The components that
transmit power from the differential gears to the
time a battery will continue to provide as
acceptable current flow when not being recharged
by the alternator.
remaining between pedal and floor when the
brakes are applied.
RESISTANCE —Opposition to current flow.
RESISTANCE PLUG WIRE—Special type of spark
plug wire that eliminates most radio interference.
Springs that pull the shoes away from the brake
drum surface when the pedal is released.
REVERSE BIAS—Arrangement in which a diode
acts as an insulator.
REVERSE IDLER SHAFT—Shaft in a manual
transmission on which the reverse idler gear is
connection of primary wires.
RING AND PINION NOISE—Whining or howling
sounds that change pitch with speed change,
usually cause by wear or damage to differential
RING GEAR—Large gear in the differential that is
driven by the pinion gear and, in turn, drives the
spider gears.
RING GEAR RUNOUT—The amount of wobble
that occurs as the gear rotates.
RECIRCULATING BALL—Most common type of
gearbox used with linkage steering system.
REDUCTION STARTER—One that uses extra
gears to increase the torque applied to the flywheel
RELAY —Electrically operated switch.
space between the meshing gear teeth.
REAR AXLE RATIO—The relationship between
the numbers of teeth on the pinion gear and ring
gear. Ratio affects acceleration, pulling power,
and fuel economy.
RECTIFIED —Term used to describe ac current that
has been changed to dc.
charging system under low output, low load
amount of resistance that is generated as a tire rolls
on the road surface.
ROTOR—A rotating contact inside the distributor
that routes electrical pulses from the coil to the
spark plugs. Also, the metal disc against which
brake pads are forced to stop a vehicle.
ROTOR CURRENT TEST—Method used to check
alternator windings for an internal short.
SHIFT RAIL—A manual transmission linkage that is
contained within the transmission case.
winding in an alternator rotor.
fault in an alternator rotor.
SHOCK ABSORBER—Device that uses air or
hydraulic pressure to dampen up-and-down
motion of a vehicle.
SHORT CIRCUIT—Excess current flow that occurs
when a conductor touches ground.
RZEPPA CV-JOINT—Ball-and-cage type constant
velocity joint used on front-wheel drive vehicles.
electrical connection to ground.
SAFETY RIM—Wheel designed with small ridges
that holds a tire in place if a blowout or flat occurs.
SIDEWALL—Portion of a tire between the tread and
SECONDARY CIRCUIT—In an ignition circuit, all
components are operating on coil (high) voltage.
SIMPLE CIRCUIT—One consisting of a power
source, a load, and conductors.
SECONDARY WIRE—Wire used in a vehicle
ignition system. It carries high voltage from the
coil to the spark plugs.
SLOW CHARGER—One that feeds a small current
into the battery over a long period of time.
performed to check condition of a spark plug or
coil wire.
SOLENOID ACTUATOR—One with a moving
metal core that is actuated by an induced magnetic
SECTOR SHAFT—Output gear in a recirculating
ball gearbox.
SPARK PLUG—Devices that emit an electrical arc at
the tip to ignite the air-fuel mixture in an engine
SEMICONDUCTOR —Substance that acts as an
insulator or conductor, depending upon
SPARK TEST—Check of the
(brightness and length of arc).
SENSOR—Device that monitors and reports a
condition to the vehicle computer.
SPECIFIC GRAVITY—Weight or density of a
SENSOR ROTOR—A toothed wheel that operates at
the same rpm as the vehicle wheel.
SEPARATOR —An insulating material
between the plates of a battery.
SPIDER GEARS—Idler and axle gears in the
differential that drive the rear axles of a vehicle.
SPINDLE—Stationary shaft used to support rotating
wheel assembly on nondriving wheels.
SERVO—Piston that operates a band in an automatic
SPONGY BRAKES—Braking system that is "soft"
feeling, usually as a result of air trapped in the
hydraulic system.
SERVO ACTION—Situation in which the primary
shoe of a drum brake system helps apply the
secondary shoe.
SPRING RATE—The stiffness or tension; amount of
weight required to compress or bend a spring.
SHAFT RUNOUT—Wear or damage (bending),
causing a shaft not to run true around its axis.
test that establishes the number of amps used by
the starting system.
SHIFT FORK—Device that physically moves the
synchronizer and gear together as a result of shift
lever movement.
SHIFT LEVER—The handle operated by the vehicle
operator to shift from gear to gear manually.
TEST—Check of all parts between the battery
negative and the starting motor.
the transmission linkage positions match the gear
selector positions.
plunger that moves to engage the pinion gear with
the flywheel gear.
S T R U T C A R T R I D G E—Replaceable
absorber unit on a MacPherson strut.
STARTER RELAY—Device that uses a small
current flow from the ignition switch to control a
larger current flow to the starter solenoid.
STARTER SOLENOID—A high current relay that
energizes the starter motor.
STRUT ROD—Rod that fastens to the control arm
and frame to keep the control arm properly
conducted with the headlights turned on to provide
a load on the battery.
SUSPENSION SYSTEM—Components that let the
wheels move up and down without body
STARTING SYSTEM—Electric motor and other
components used to rotate the engine until it starts.
SWAY BAR—A stabilizer that keeps the vehicle body
from leaning excessively in turns.
STATIC IMBALANCE—Lack of balance that
causes a wheel to vibrate up and down as it rolls.
SYNCHRONIZER —Assembly of hub, sleeve, and
other components that locks the selected output
gear to the output shaft to transmit power. It
permits meshing of gears with grinding.
STATOR —The stationary magnetic field in a
generator. Also, component of a torque converter
that improves oil circulation and thus, torque.
STATOR TEST—Ohmmeter check for open and
shorted windings in the stator.
by the inward tilt of the ball joints, kingpin, or
STEERING COLUMN—Assembly consisting of the
steering wheel, steering shaft, ignition key
mechanism, and associated parts.
STEERING GEARBOX—Gear assembly that turns
rotary motion into linear (straight line) left-right
STEERING KNUCKLE—Component that provides
support for the wheel spindle or bearings
surrounding an axle.
TERMINALS—The positive and negative posts or
threaded connectors on a battery.
THROW-OUT BEARING—Bearing that decreases
friction between the clutch fork and pressure plate.
TIE ROD—Connectors between rack ends and
steering knuckles.
TIMING ADVANCE—Making the spark plug fire
sooner in the compression stroke.
TIRE—The casing-and-tread assembly that is
mounted on a vehicle to provide pneumatically
cushioned contact and traction with the road.
TIRE BEAD—Wire ring encased in rubber that helps
hold the tire sidewall against the rim.
TIRE IMPACT DAMAGE—Punctures, cuts, or
tears caused by running over debris in the road.
STEERING LINKAGE—Components connecting
the steering gearbox to the steering knuckles.
TIRE MARKINGS—Information shown on the
sidewall to indicate inflation pressure, loadcarrying ability, size, and other data.
STEERING SHAFT—Component that transfers
turning motion from the steering wheel to the
steering gearbox.
TIRE PLY—Layer of fabric or other material that
forms the carcass or body of the tire.
STEERING SYSTEM—The components that allow
the operator to change direction of a vehicle.
TIRE ROTATION—Moving tires to
wheels periodically to even out wear.
STEERING WHEEL PLAY—Excessive movement
of the steering wheel without causing any frontwheel movement.
TIRE WEAR ANGLE—Usually, a reference to
camber because tilting the wheels puts more load
on one side of the tire tread than on the other side.
STIFF CLUTCH PEDAL—A condition caused by
binding or other restriction in the clutch
mechanism, making the pedal hard to depress.
TIRE WEAR PATTERN—Areas of tread that are
worn off, which can provide information on causes
of wear.
combining shock absorber, coil spring, and upper
damper unit. It replaces the upper control arm.
TOE—Degree to which opposing wheels are on
converging or diverging lines (not parallel). Also,
the narrow part of a gear tooth.
TOE-OUT ON TURNS—Steering feature that turns
the inside wheel more sharply than the outside
radiator, used to cool transmission oil in vehicles
pulling heavy loads.
TORQUE CONVERTER—Fluid coupling that acts
as a clutch on an automatic transmission.
connects the shift lever with the transmission shift
torque achieved by turning the impeller of a torque
converter faster than the turbine.
TORQUE TUBE—A solid steel drive shaft enclosed
in a hollow tube with a single swivel joint at the
TORSION BAR—Spring steel rod that operates by
twisting and untwisting.
TORSION SPRINGS—Small coil springs that help
absorb the shock and vibration that occur when the
clutch engages.
TRACKING—The position or direction of the front
wheels in relation to the rear wheels.
within the radiator, used to regulate transmission
fluid temperature.
TRIGGER WHEEL—Rotating component with one
tooth for each cylinder.
TRIPOD CV-JOINT—Constant velocity joint used
on front-wheel drive vehicles, consisting of a
spider and ball arrangement inside a housing.
TUBELESS—A tire that does not have a separate
inner tube to hold air.
TURBINE—The driven fan in a torque converter.
TRACK ROD—Metal rod used to prevent axle sideto-side movement when cornering.
TURNING—Tem, usually used for machining a
brake drum or rotor, since this process is carried
out on a lathe.
TRAM GAUGE—Instrument used to compare
distances between the front and rear set of tires for
toe adjustment.
measure how many degrees left or right the front
wheels are turned.
TRANSAXLE—A combination of transmission and
differential in one case, used on front-wheel drive
made on U-joint components before disassembly,
allowing the joint components to be reassembled
in the same positions to avoid possible imbalance
and vibration.
T R A N S A X L E D I F F E R E N T I A L—Transaxle
assembly that transfers torque to the driving
wheels and allows them to rotate at different
section of the transaxle, housing the forward and
reverse gears.
turns the gears in a transaxle.
transfers power to the ring and pinion gears of the
TRANSFER CASE—A power takeoff unit that sends
power to both the front and rear axle assemblies on
a multiwheel drive vehicle.
TRANSISTOR—Tiny electronic component that
functions as a switch, but has no moving parts.
T R A N S M I S S I O N C A S E—Metal
surrounding and supporting the transmission.
UNDER INFLATION—Operating tires with a lower
than recommended air pressure.
UNIBODY—A vehicle structure in which the body
and frame are one unit.
UNIVERSAL JOINT—A flex joint allowing limited
up-and-down and side-to-side movement.
UNSPRUNG WEIGHT—The weight of the vehicle
parts that are not supported by the springs, such as
the wheels.
VACUUM ADVANCE—A mechanism on the
ignition distributor that uses intake manifold
vacuum to advance the timing of the spark to the
spark plugs.
modulates, or changes, the main-line hydraulic
pressure in an automatic transmission to meet
changing engine loads.
VALVE BODY—Housing that contains most of the
valves used in operation of an automatic
WHEEL BEARING—Ball or roller bearing
assemblies that reduce friction as wheels or axles
VALVE CORE—A threaded air valve that screws
into place in a valve stem.
that use hydraulic pressure to apply friction for
stopping a vehicle.
VALVE STEM—A rubber inflation tube with a
threaded metal core that snaps into a hole on the
rim of a wheel designed for tubeless tires.
actuates braking at each wheel.
VALVE STEM CAP—A cap placed over the end of
the valve stem to prevent stem wear.
VOLTAGE DROP—Reduction of the amount of
current flowing in a circuit.
VOLTAGE REGULATOR—Device used to control
alternator output.
WHEEL SHIMMY—A side-to-side
caused by dynamic imbalance.
VOLTAGE—Electrical pressure that causes current
VOLTGAE DROP TEST—Starting system test that
identifies parts showing high resistance.
WHEEL SPEED SENSORS—Magnetic pickups to
detect wheel speed (used on anti-lock braking
WHEEL WEIGHT—Small pieces of lead that are
clipped to the wheel rim to balance the wheel and
tire combination.
WINDING—Loop or wire on a motor armature that
generates a magnetic field.
WEAR BAR—Solid bars of rubber across the tread
that appears when a tire has worn to an unsafe
relationships of components in an electrical
WET CHARGED—Battery that is filled with
electrolyte and fully charged at the factory.
WIRING HARNESS—A group of primary wires
enclosed in a protective plastic covering.
WHEEL ALIGNMENT—Adjusting wheels of a
vehicle to roll in a straight line.
WORM SHAFT—Input gear in a recirculating ball
Although the following references were current when this TRAMAN
was published, their continued currency cannot be assured. When
consulting these references, keep in mind that they may have been revised to
reflect new technology or revised methods, practices, or procedures. You
therefore need to ensure that you are studying the latest references.
1988 C-K Pick-Up Truck, Service Manual, Chevrolet Motor Division, General
Motors Corporation, Detroit, MI, 1986.
1989 Medium/Heavy-Duty Truck, Shop Manual, Ford Motor Company, Dearborn,
MI, 1988.
Duffy, James E., Modern Automotive Technology, Goodheart-Willcox Company
Inc., South Holland, IL, 1994.
Equipment Operator Basic, NAVEDTRA 12535, Naval Education and Training
Professional Development and Technology Center, Pensacola, FL, 1994.
Fluid Power, NAVEDTRA 12964, Naval Education and Training Professional
Development and Technology Center, Pensacola, FL, 1990.
Fundamental of Service, Electrical Systems, 5th ed., Deere and Company, Moline,
IL, 1984.
Fundamental of Service, Hydraulics. Deere & Company, Moline, IL, 1987.
Fundamental of service, Power Trains, Deere and Company, Moline, IL, 1984.
Navy Electricity and Electronics Training Series (NEETS), Introduction to
Generators and Motors, NAVEDTRA B72-05-00-94, Naval Education and
Training Professional Development and Technology Center, Pensacola, FL,
Navy Electricity and Electronics Training Series (NEETS) Introduction to Matter,
Energy, and Direct Current, NAVEDTRA B72-01-00-94, Naval Education
and Training Professional Development and Technology Center, Pensacola,
FL, 1994.
Nichols, Herbert L., Jr., Heavy Equipment Repair, McGraw-Hill, New York, 1989.
Principles of Automotive Vehicles, TM 9-8000, Department of the Army,
Washington, DC, 1988.
Rough Terrain Forklift Truck Service Manual, Model M4KN (4,000 Pounds), J.I.
Case Company, Racine, WI, 1987.
Rough Terrain Forklift Truck Service Manual, Model LK12000, Lift King
Incorporated, Main Line Construction Equipment, Woodbridge, Ontario, 1991.
Rubber Tired Loader Service Manual, Model 520C, Dresser Industries,
Libertyville, IL, 1990.
Tractor, Full-Tracked Service Manual, Model 1150E, J.I. Case Company, Racine,
WI, 1986.
Accumulators, 3-15
Abnormal noises, 4-10
Adjusting mechanism, 6-16
Aiming headlights, 2-47
Air brake system, 7-33
Air cleaner servicing, 3-34
Air compressor maintenance, 3-33
Air-hydraulic-power cylinder (AIR PAK), 7-45
Air hoses and fittings, 7-43
Air tanks/reservoirs, 7-37
Air-over-hydraulic brake operation, 7-46
Air-over-hydraulic brake system, 7-44
Aftercoolers, 3-33
Alternators, 2-17
Alternator construction, 2-17
Alternator maintenance, 2-20
Alternator operation, 2-19
Alternator output control, 2-20
Alternator testing, 2-21
Amperage, 1-9
Anti-lock brake system, 7-17
Automatic transaxle, 4-42
Automatic transmissions, 4-26
Automatic transmission service, 4-40
Automotive chassis and body, 8-1 - 8-58
Automotive clutches and transmissions, 4-1 - 4-44
Automotive clutches, 4-1
Automotive electrical circuits, 2-1 - 2-64
Automotive wiring, 2-59
Auxiliary transmission, 4-20
Axle bearing service, 5-26
Axle housing, 5-23
Axle seal service, 5-27
Backup light system, 2-49
Ball and Trunnion universal joints, 5-4
Ball joint service, 8-13
Ball joints, 8-6
Ball sockets, 8-17
Basic automotive electricity, 1-1 - 1-17
Basic principles of electricity, 1-1
Basic principles of hydraulics, 3-1
Basic principles of pneumatics, 3-29
Battery capacity, 2-5
Battery charging, 2-5
Battery condition gauge, 2-51
Battery construction, 2-3
Battery maintenance, 2-7
Battery ratings, 2-5
Battery test, 2-9
Bendix-Weiss (CV) joint, 5-6
Belted bias tire, 8-30
Bias-ply tire, 8-30
Blackout lights, 2-48
Body repair, 8-47
Body tools, 8-48
Boyle’s law, 3-29
Brake band, 4-33
Brake chambers, 7-38
Brake disc service, 7-31
Brake pedal action, 7-25
Brake shoe energization, 7-12
Brake system bleeding, 7-31
Brake system inspection, 7-25
Brake system leaks, 7-25
Brake switches and control valves, 7-16
Brake valves, 7-38
Brake warning light switch, 7-17
Brakes, 7-1 - 7-48
Braking ratio, 7-3
Braking temperature, 7-2
Cam and lever, 8-19
Camber, 8-43
Caster, 8-42
Caster-camber gauge, 8-46
Center link, 8-17
Center support bearing service, 5-10
Center support bearings, 5-7
Centrifugal advance, 2-37
Charging circuit, 2-2
Charging system output test, 2-23
Charging system test, 2-22
Charles’s law, 3-30
Check valves, 7-42
Checking brake assemblies, 7-25
Checking master cylinder fluid, 7-25
Checking the fluid, 4-30
Circuit breaker and fuses, 2-51
Circuit configurations, 1-10
Circuit failures, 1-12
Circuit resistance test, 2-23
Cleaning and flushing the system, 3-26
Clutch adjustment, 3-7
Clutch cable adjustment, 4-7
Clutch construction, 4-3
Clutch disc, 4-6
Clutch fork, 4-4
Clutch housing, 4-4
Clutch linkage adjustment, 4-7
Clutch operation, 4-6
Clutch overhaul, 4-11
Clutch pack limited slip differential, 5-16
Clutch release mechanism, 4-3
Clutch start switch, 4-7
Clutch troubleshooting, 4-8
Clutches and bands, 4-31
Combination valve, 7-17
Combined quick-release valve, 7-40
Composition of matter, 1-1
Composition of electricity, 1-2
Compressed air, 3-30
Compressibility and expansion of gas, 3-29
Compressor design, 3-31
Compressor, unloader assembly, 7-33
Computerized advance, 2-37
Computing force, pressure, and area, 3-1
Conductors and insulators, 1-3
Cone clutch limited slip differential, 5-18
Connectors and fittings, 3-30
Constant mesh transmission, 4-17
Constant velocity joint service, 5-10
Constant velocity (CV) joints, 5-3
Construction equipment drive trains, 6-1 - 6-32
Contact point ignition system, 2-35
Contact points ignition system, 2-35
Contamination control, 3-35
Control arms and bushings, 8-6
Control valves, 3-7
Conventional transfer case, 5-28
Corrosion control, 8-54
Cross and Roller universal joints, 5-3
Cylinders, 3-13
Demister or separator element, 3-35
Differential action, 5-14
Differential carrier, 5-11
Differential case, 5-11
Differential construction, 5-11
Differential lubricant service, 5-19
Differential adjustment, 5-20
Differential removal and reassembly, 5-19
Differential service and maintenance, 5-18
Differentials, 5-11
Dimmer switch, 2-46
Diodes, 1-6
Direct-current (dc) generator, 2-11
Disadvantages of drum brakes, 7-12
Disc brake assembly, 7-15
Disc brake pad replacement, 7-30
Disc brake types, 7-15
Disc brakes, 7-14
Distributor service, 2-40
Double Cardan universal joints, 5-4
Double reduction final drive, 5-13
Dragging, 4-10
Drive axles, 5-23
Drive line assembly, 5-1
Drive line maintenance, 5-7
Drive lines, differentials, drive axles, and
power train accessories, 5-1 - 5-35
Drive shaft inspection, 5-8
Drive shaft noises, 5-8
Drive shafts, 5-2
Drive trains, 6-1
Driving straight ahead, 5-14
Driving wheel assembly, 8-36
Drop center wheel, 8-34
Drum brake assemblies, 7-7
Drum brakes, 7-7
Electric current, 1-3
Electrical measurements, 1-9
Electric speedometers and tachometers, 2-57
Electromagnetic induction, 1-15
Electromagnetism, 1-13
Electron theory of electricity, 1-2
Electronic ignition system, 2-35
Electronic ignition system components, 2-36
Electronic ignition system operation, 2-36
Electronic speedometers, 2-57
Electronic tachometers, 2-57
Emergency light system, 2-50
Epoxy fillers, 8-54
Extension housing, 4-13
External cylinder (linkage type), 8-23
Fifth gear, 4-20
Final drive, 5-12
First gear, 4-18
Fluid replacement, 4-40
Flywheel, 4-6
Fourth gear, 4-20
Frame maintenance, 8-3
Frames, 8-1
Front bearing hub, 4-13
Front drive axle, 5-25
Front-wheel drive axle, 5-26
Fuel gauge, 2-52
Full-floating axle, 5-24
Generators, 2-11
Generator maintenance, 2- 14
Generator repair, 2-14
Governor valve, 4-38
Grabbing, 4-9
Hall effect sensor, 2-36
Hard steering, 8-29
Headlight switch, 2-45
Headlights, 2-45
Heavy-duty compressors, 3-31
Horn, 2-58
Hydraulic boosters, 7-22
Hydraulic brake systems, 7-1
Hydraulic clutch adjustment, 4-8
Hydraulic and pneumatic systems, 3-1 - 3-37
Hydraulic systems, 3-1
Hydraulic system components, 3-4
Hydraulic system maintenance, 3-25
Hydraulic system, brake lines and hoses, 7-5
Hydraulic system, master cylinder, 7-3
Hydraulic system, wheel cylinders, 7-5
Hydrostatic drive operation, 6-9
Hydrostatic drive train, 6-7
Hypoid gear, 5-12
Identification marking, 8-54
Idler arm, 8-17
Ignition circuit components, 2-32
Ignition circuit, 2-31
Ignition coil, 2-32
Ignition distributor, 2-33
Igniton switch, 2-32
Ignition system maintenance, 2-38
Ignition timing, 2-42
Ignition timing devices, 2-36
Incompressibility of liquids, 3-2
Inspection of track, 6-17
Instruments, gauges, and accessories, 2-5
Integral piston (linkage type), 8-22
Integrated frame and body, 8-2
Intercoolers, 3-33
Joint, Bendix-Weiss, 5-6
Joint, constant velocity, 5-4
Joint, Rzeppa, 5-4
Joint, slip yoke, 5-1
Joint, tripod, 5-7
Kickdown valve, 4-39
Kinetic theory of gases, 3-29
Lamps, 2-44
Leaf spring, 8-10
Limited slip differentials, 5-14
Linkage and band adjustment, 4-40
Load index and speed ratings, 8-32
Low-air-pressure warning indicator, 7-43
Lug nuts, studs, and bolts, 8-34
Magnetism, 1-12
Main oil filter servicing, 3-34
Maintenance of hydrostatic drives, 6-12
Manual bleeding, 7-31
Manual steering systems, 8-18
Manual steering system service, 8-25
Manual transaxles, 4-42
Manual transmissions, 4-13
Manual valve, 4-36
Mechanical drive train, 6-1
Mechanical speedometers, 2-56
Mechanical tachometers, 2-56
Metering valve, 7-17
Motors, 3-18
Multiple-disc clutch, 4-31
Multiplication of forces, 3-3
Neutral safety switch, 2-29
Nondriving wheel assembly, 8-35
OHM'S Law, 1-9
Oil and filter changes, 3-26
One- and two-wire circuits, 2-59
Overrunning clutch, 1-32
Painting, 8-53
Painting, preparing the surface, 8-52
Parking brakes, 7-22
Pascal’s law, 3-2
Pedal pulsation, 4-10
Petroleum-based fluids, 3-4
Pilot bearing, 4-6
Pinion gear, 5-11
Pitman arm, 8-17
Pivot brakes, 6-7
Placing new batteries in service, 2-6
Planetary gear sets, 4-30, 6-4
Planetary steering, 6-5
Pneumatic gases, 3-30
Pneumatic systems, 3-29
Positive traction transfer case, 5-31
Potential hazards, 3-35
Power brakes, 7-19
Power flow, 4-18
Power rack and pinion, 8-23
Power shift transmission, 6-1
Power steering systems, 8-21
Power steering system service, 8-27
Power takeoffs, 5-32
Pressure and force, 3-1
Pressure bleeding, 7-32
Pressure-control system, 3-33
Pressure gauge, 2-54
Pressure plate, 4-1
Pressure regulator, 4-35
Preventing leaks, 3-26
Preventing overheating, 3-28
Primary and secondary circuits, 2-31
Principles of braking, 7-1
Proportioning valve, 7-17
Pump, 4-35
Pumps, 3-6
Qualities, 3-30
Quick-release valve, 7-40
Rack and pinion, 8-20
Radial ply tire, 8-30
Rear axle service, 5-26
Rear drive axle, 5-24
Receiver tank, 3-33
Recoil spring, 6-17
Refilling the transmission, 4-41
Regulation of generator output, 2-13
Regulator bypass test, 2-23
Regulator voltage test, 2-23
Relay emergency valve, 7-41
Release bearing, 4-4
Removing dents, 8-49
Replacing brake shoe linings, 7-27
Replacing sheet metal, 8-51
Reservoir, 3-5
Resistance, 1-9
Reverse gear, 4-18
Ring and pinion backlash, 5-21
Ring and pinion tooth contact pattern, 5-21
Ring gear, 5-11
Rotating tires, 8-37
Rzeppa joint, 5-5
Safety precautions, 3-35
Safety wheel, 8-34
Sealing materials and devices, 3-23
Second gear, 4-20
Semiconductors, 1-4
Semidrop center wheel, 8-34
Servicing air brakes, 7-44
Servicing brake drums, 7-29
Servicing caliper assemblies, 7-30
Servicing disc brakes, 7-29
Servicing drum brakes, 7-26
Servicing master cylinders, 7-26
Servicing wheel cylinders, 7-27
Shift linkage and levers, 4-16
Shift valves, 4-39
Shock absorber service, 8-15
Shock absorbers and struts, 8-6
Shop repairs, 6-17
Slack adjusters, 7-38
Slipping, 4-9
Slip yoke (joint), 5-1
Spark plug, 2-33
Spark plugs and plug wires, 2-38
Spark plug heat range and reach, 2-34
Spark plug wires, 2-34
Speedometers and tachometers, 2-56
Spider gears, 5-12
Spiral bevel gear, 5-12
Spring terminology, 8-9
Stabilizer bar, 8-9
Starting circuit, 2-25
Starting circuit maintenance, 2-30
Starting motor, 2-25
Starting motor circuit tests, 2-30
Starting motor construction, 2-25
Starting motor current draw test, 2-30
Starting motor voltage drop tests, 2-30
Steering axis inclination, 8-44
Steering geometry, 8-41
Steering linkage, 8-17
Steering linkage service, 8-25
Steering system, 8-16
Steering system maintenance, 8-25
Steering system noises, 8-29
Steering ratio, 8-18
Stoplight switch, 7-17
Stoplight switches, 7-43
Stoplight system, 2-50
Storage battery, 2-2
Strainers and filters, 3-6
Strut service, 8-15
Suspension bushing service, 8-13
Suspension system components, 8-6
Suspensions systems, 8-4
Suspension system service, 8-13
Suspension system springs, 8-9
Synchromesh transmission, 4-18
Synchronizers, 4-15
Synthetic fire-resistant fluids, 3-4
System switches and indicators, 7-43
Temperature gauge, 2-55
Third gear, 4-20
Tie-rod assemblies, 8-18
Tire and wheel-bearing noise, 8-41
Tire construction, 8-30
Tire grades, 8-32
Tire impact damage, 8-40
Tire inflation problems, 8-40
Tire repair, 8-36
Tire size and markings, 8-31
Tire wear patterns, 8-40
Tire vibration problems, 8-41
Tires, wheels, and wheel bearings, 8-29
Toe, 8-43
Torsion bar, 8-12
Torque converters, 4-27
Track adjustment, 6-17
Track and track frames, 6-13
Track assembly, 6-13
Track chain, 6-13
Track frame, 6-15
Track frame rollers, 6-15
Track guiding guards, 6-16
Track lubrication, 6-17
Track shoe, 6-14
Track-frame assemblies, maintenance of, 6-17
Tracking, 8-45
Tractor protection valve, 7-40
Trailer control valve, 7-40
Tram gauge, 8-47
Transaxles, 4-41
Transfer case maintenance and service, 5-31
Transfer cases, 5-28
Transmission case, 4-13
Transmission construction, 4-13
Transmission of forces through liquid, 3-2
Transmission overhaul, 4-23
Transmission service, 3-25
Transmission shafts, 4-13
Transmission troubleshooting, 4-21
Transmission types, 4-16
Transistors, 1-6
Treadle valve, 7-39
Tripod joint, 5-7
Troubleshooting steering systems, 8-28
Truck frame, 8-3
Tube repair, 8-37
Tubes, 8-33
Tubing, piping and hoses, 3-18
Turn-signal systems, 2-49
Turning corners, 5-13
Turning radius gauges, 8-46
Two-speed final drive, 5-14
Two-stroke, 2-1
Types of hydraulic fluids, 3-4
Types of starting motors, 2-29
Universal joint service, 5-8
Universal joints, 5-2
Vacuum advance, 2-37
Vacuum boosters, 7-19
Vacuum modulator valve, 4-36
Vehicle stopping distance, 7-2
Voltage, 1-9
Volume and distance factors, 3-1
Water-based fire-resistant fluids, 3-4
Wheel alignment, 8-41
Wheel alignment tools and equipment, 8-45
Wheel balancing, 8-38
Wheel bearing and hub assembly, 8-35
Wheel bearing service, 8-39
Wheels, 8-33
Winches, 6-19
Winches and wire rope, 6-19
Windshield wipers, 2-58
Wire rope attachments, 6-29
Wire rope failure, 6-24
Wire rope maintenance, 6-28
Wire rope, 6-21
Wire rope, characteristics of, 6-23
Wire rope, composition of, 6-21
Wire rope, grades of, 6-22
Wire rope, handling and care of, 6-24
Wire rope, lays of, 6-22
Wire rope, measuring of, 6-24
Wire rope, safe working load (SWL), 6-24
Wire support and protection, 2-62
Wire terminal ends, 2-61
Wiring assemblies, 2-59
Wiring diagrams, 2-61
Wiring identification, 2-60
Worm and nut, 8-19
Worm and roller, 8-19
Worm and sector, 8-18
Zener diodes, 1-6
Textbook Assignment "Basic Automotive Electricity" and "Automotive Electrical Circuits and
Wiring," chapters 1 and 2, pages 1-1 through 2-40.
All matter is made up of tiny
particles. These particles are known
by what term?
1-2. A group of electrons produce what
type of electrical charge?
1-7. In an electrical circuit, current (or
electron) flow is measured in amps
and is known as
The movement of free electrons
The movement of free protons
The movement of free neutrons
The movement of free quarks
In a semiconductor, what type of
material is doped to yield free
What transistor design is the most
often used in automotive
1-3. Electrical energy is transferred
through conductors by what means?
What type of electrical device is used
in electrical circuits to control the
flow of current and operates by either
allowing or not allowing current to
1-8. Using Ohm’s law, what is the
amperage in a circuit if the voltage is
13.8 and resistance is 2.25 ohms?
What type of automotive circuit
allows the disconnection or burning
out of any individual component
without affecting the operation of the
1-13. How is electromagnetic induction
produced in an ac generator?
1. The wire is moved through a
stationary magnetic field
2. The wire is stationary and the
magnet is moved so the magnetic
field is carried past the wire
3. The wire and electromagnet are
both held stationary and current is
turned on and off
4. Both the wire and electromagnet
are moved, thereby alternating the
magnetic field
1-10. To have a series-parallel circuit, you
must have what minimum number of
resistance units?
1-14. What are the names of the five
automotive electrical circuits?
1. Charging, starting, ignition,
lighting, and accessory
2. Starting, lighting, accessory,
charging, and cranking
3. Lighting, battery, power
generation, accessory, and starting
4. Ignition, power generation,
charging, starting, and accessory
1-11. What type of circuit failure occurs
when the resistance in the wiring
circuit is such that current can NOT
flow between the battery and the unit
it operates?
Short circuit
Open circuit
Ground circuit
Dead circuit
1-15. In a lead-acid battery, current is
produced by what type of reaction?
1-12. When the direction of current flow is
known, what rule can be used to
determine the north pole of an
1-16. A 12-volt lead-acid, automotive
battery consists of how many elements
that are connected in series?
1-21. The capacity of a battery cell is NOT
affected by which of the following
1-17. The positive plates in a charged leadacid battery contain what chemical
Lead phosphate
Lead sulfate
Lead chromate
Lead peroxide
1. The area of the plates in contact
with the electrolyte and the
quantity and specific gravity of the
2. The type of separators and the
final limiting voltage
3. The general condition of the
battery (degree of sulfating, plates
buckled, separators warped,
sediment in the bottom of the
cells, etc.)
4. The number of elements connected
in parallel
1-18. Why are the cell elements of a storage
battery elevated inside the case?
1. To allow the electrolyte to
circulate under the elements
2. To prevent the elements from
shorting against the case
3. To reduce the amount of lead
required for connecting the
elements and terminal posts
4. To prevent shorting of the
elements when material from the
plates settles to the bottom of the
1-22. What are the two methods for rating
lead-acid storage batteries?
1. Reserve capacity rating and
discharge rating
2. Reserve capacity rating and
ampere-hour rating
3. Cold-cranking rating and reserve
capacity rating
4. Cold-cranking rating and
discharge rating
1-19. When the temperature is 80°F, a fully
charged lead-acid battery will produce
what specific gravity reading?
1-23. In battery charging, either the current
or voltage is kept constant.
1-20. When taking a hydrometer reading of
a battery whose temperature is 100 F,
you must make what modification to
the reading to determine the actual
specific gravity of the electrolyte?
1. True
2. False
1-24. When charging a 19-plate battery by
the constant-current method, you
should use what charging rate?
1. 9 amp
2. 10 amp
3. 19 amp
4. 20 amp
1-28. What should you do with a new 12volt battery that registers only 9 volts
on a voltmeter?
1-25. Which of the following factors
produces the value of the charging
current in a constant voltage battery
1. The battery increasingly resists
current as its own charge builds
2. A clock-actuated rheostat adjusts
the current value
3. A rectifier tube automatically
adjusts the current value
4. The operator changes plug-in
positions to lower the charger
output at half-hour intervals
Add electrolyte
Recharge it
Discard it
Place it in service to see whether
its voltage will increase or
1-29. What procedure is considered the only
safe way to mix electrolyte for a leadacid battery?
1. Pour water into acid slowly and
stir gently
2. Pour water into acid slowly and
stir vigorously
3. Pour acid into water slowly and
stir gently
4. Pour acid into water slowly and
stir vigorously
1-26. You are about to connect a battery to a
charger when you notice that the
terminal markings on the battery post
are not readable. To ensure correct
battery-to-charger connections, you
should take what action?
1. Check the battery with an ammeter
to determine the positive post
2. Connect the larger battery post to
the unmarked charger terminal
3. Energize the charger and observe
the reading on the charger gauge
as you touch the battery cables to
the charger
4. Connect the larger battery post to
the marked charger terminal
1-30. When cleaning the top of a lead-acid
battery, you should use a
1. soft bristle brush and a mixture of
water and baking soda
2. soft bristle brush and a mixture of
water and muratic acid
3. stiff bristle brush and a mixture of
water and baking soda
4. stiff bristle brush and a mixture of
water and muratic acid
1-27. When charging batteries, you should
take which of the following actions?
1. Add electrolyte to any cell in
which the fluid level is below the
top of the plates before charging
2. Remove the vent plugs to prevent
an accumulation of gases
3. Take frequent hydrometer readings
to determine if the battery is
functioning properly during
4. Remove each battery for a 10minute break when half charged
1-31. What test allows you to determine the
general condition of a maintenancefree battery?
Cell voltage
Battery leakage
Battery drain
Battery voltage
1-32. When load testing a battery with a
cold-cranking rating of 350 amps, you
should load the battery to what total
number of amps?
1-37. The current regulator functions to
protect the electrical system by
1-38. What condition causes solder globules
to form inside the cover band of a
1-33. The generator converts mechanical
energy into electrical energy and
restores the battery with the energy it
1. True
2. False
1-34. The current generated by an alternator
is converted to direct current by means
of what component?
Changes in the polarity of the field
Slip rings
Excessive current output
Open field circuit
Excessively worn brushes
Internally shorted armature
1-39. A test lamp lights with normal
brilliance when it is connected to the
field lead terminal of a generator.
What condition does this indicate?
Armature coil
Station field coil
1-35. The alternating current in the armature
coil of a dc generator is changed to
direct current in the external circuit by
what component?
limiting battery output
limiting generator output
disconnecting the electrical system
increasing resistance at the
An open field
A normal field
A shorted field
A grounded field
1-40. When a milliammeter reading near
zero is obtained across a pair of
commutator segments on an armature
that is mounted in a growler, the coil
1-36. The output of a dc generator is NOT
determined by which of the following
1. The speed of the armature rotation
2. The number of armature
3. The strength of the magnetic field
4. The weakness of the ions
1-41. What component of an alternator is
mounted on the rotor shaft and
provides current to the rotor
Slip rings
Claw poles
Stator core
1-42. In what manner are stator windings
connected in an alternator?
1. One end is connected to the
positive diodes and the other end
to the negative diodes
2. One end is connected to the stator
assembly and the other end to the
rectifier assembly
3. One end is connected to the
negative diodes and the other end
to the field windings
4. One end is connected to the
electrical terminals and the other
end to the rotor shaft
1-43. What type of stator will provide good
current output at low engine speeds?
rotor windings
1-46. A charging system containing an
alternator can be checked for proper
operation by means of a/an
jumper wire
1-47. To determine if an alternator rotor is
internally shorted, you can test the
rotor windings with what device?
Armature growler
Test lamp
1-48. Testing of an alternator stator is
limited to
1-44. A total of how many diodes are
grounded in an alternator?
1-45. Grounding the field terminal of the
alternator will result in damage to the
shorts and opens
opens and grounds
grounds and continuity
continuity and shorts
1-49. Which of the following charging
system tests allow you to measure the
charging system voltage under low
output, low load conditions?
Regulator bypass
Charging system output
Regulator voltage
Charging system bypass
1-54. Field windings vary according to
application. What is the most popular
configuration used to provide a large
amount of low-speed torque?
1-50. When performing a regulator bypass
test, you should use which of the
following methods to bypass the
voltage regulator?
1. Place a jumper wire from the field
terminals of the alternator to the
engine block
2. Place a jumper wire from the test
tab to the field terminals of the
3. Place a jumper wire across the
battery and field terminals of the
4. Unplug the wire from the regulator
1-55. Which of the following starting circuit
components is common to all vehicles
and equipment having automatic
1-51. What mechanism relies on the
principle of inertial force to make the
drive pinion mesh with the flywheel?
Starter solenoid
Neutral safety switch
Double reduction starter
1-56. When it is necessary to adjust a
neutral safety switch, which of the
following test equipment is required?
Bendix drive
overruning clutch
Dyer drive
reduction drive
1-52. In a starting circuit containing a
solenoid, when is battery current
supplied to the starter motor?
1. When the remote control switch is
2. At the time the ignition switch is
turned to the start position
3. After the starter pinion is engaged
with the flywheel
4. When the plunger closes the
contacts in the solenoid
Inductive ammeter
Test light
1-57. When inspecting a disassembled
starter, you should replace the brushes
if they are less than
1-53. Continued starter operation after
releasing the starter button or ignition
key is often caused by
Six windings, series-parallel
Two windings, parallel
Three windings, series-parallel
Four windings, series
a broken Bendix spring
a worn solenoid plunger
shorted solenoid windings
a faulty pinion and rotor assembly
one half of their original size
one third of their original size
one fourth of their original size
one eighth of their original size
1-58. To determine the operating condition
of the starter circuit, you should use
which of the following tests to
measure the amount of amperage used
by the circuit?
1-60. Which component in the ignition
circuit provides high voltage in the
secondary circuit?
1. Actuate the ON/OFF cycles of
current flow through the primary
windings of the coil
2. Distribute the high voltage surges
of the coil to the spark plugs
3. Change spark timing with changes
in engine load
4. Deactivate the thermostat
Starter circuit resistance
Starter circuit voltage drop
Stator current draw
Starter ground
1-59. The battery-ignition circuit consists of
a total of how many circuits?
1-62. Which of the following actions is
NOT a function of the distributor in
the ignition circuit?
Ignition distributor
Ballast resistor
Ignition coil
1-63. A nonresistor type spark plug is
designed to reduce static in the radio
in a vehicle.
1. True
2. False
1-64. When troubleshooting an ignition
circuit, you should change the
manufacturer's specified heat range of
the spark plugs when what condition
1. Increased resistance is required by
the circuit
2. Abnormal operating conditions are
3. Ignition timing is changed from
the manufacturer’s setting
4. High voltage surges in the primary
circuit are reduced
1-61. In an ignition circuit, high voltage is
directed to the spark plugs in the
correct firing order by what
Ballast resistor
Ignition coil
Distributor rotor
Spark plug wires
1-65. A function of the condenser in a
contact-point ignition system is to
1. stop the flow of the magnetic lines
of flux when the points open
2. regulate the flow of current
through the secondary winding
3. allow for a rapid collapse of the
magnetic field around the primary
4. prevent arcing at the points when
they are first opened
1-66. The distributor contact points and cam
provide a means of opening and
closing the primary circuit.
1-71. In a computerized timing advance
mechanism, what sensor reports piston
position to the computer?
1. True
2. False
1-67. The amount of time that the points
remain closed between openings,
given in degrees of distributor
rotation, is known as
1-72. A grayish tan deposit on the insulator
of a spark plug indicates what
condition exists?
1-68. What component opens and closes the
primary circuit of an electronic
ignition system?
1. Each time the vehicle is serviced
2. At 6,000 mile intervals
3. Any time they are removed for
4. During a "B" PM only
engine cylinders
cam lobes
1-74. Some manufacturers specify spark
plug torque, while others recommend
bottoming the plugs on the seat and
then turning an additional one-quarter
to one-third turn.
1. True
2. False
1-70. What timing advance mechanism
provides additional spark when the
engine load is low and at part throttle?
Normal operation
Carbon fouled
Ash fouled
Preignition damage
1-73. How often should spark plugs be
Electronic module control (EMC)
Electronic primary control (EPC)
Electronic circuit control (ECC)
Electronic control unit (ECU)
1-69.An electronic ignition system is
equipped with a Hall effect sensor. In
this system there are the same number
of shutters as there are
1-75. You have performed a spark plug wire
resistance test. The test should not
show the resistance to be over 5,000
ohms per inch or what total number of
1. 25,000
2. 50,000
3. 100,000
4. 125,000
Textbook Assignment: "Automotive Electrical Circuits and Wiring" (continued) and "Hydraulic
and Pneumatic Systems," chapters 2 and 3, pages 2-40 through 3-37.
Of the following conditions on a
distributor cap, which one will short
coil voltage to ground?
Faulty distributor lead
Broken coil wire
Carbon trace
Broken rotor
When the points in a contact-point
distributor become burnt or pitted, you
should take what action?
1. Clean the points with a special file
2. Remove any burrs or pits with fine
3. Clean the points with a rubbing
block and realign
4. Discard them and install a new set
When setting the dwell on a contactpoint distributor, you should replace
the distributor if the dwell varies more
than what number of degree(s)?
After installing contact points, you
notice that the faces do not make full
contact. What corrective action should
you take?
When testing an electronic distributor,
you conduct what test to check the
resistance of the pickup coil?
Pickup coil ammeter test
Pickup coil ohmmeter test
Pickup coil voltage drop test
Pickup coil ECU test
2-6. What tool should you use to set the
pickup coil air gap?
1. File the faces straight across the
edge that is riding high
2. Bend the movable breaker arm
3. Bend the stationary contact
4. Remove the points and realign the
Multi-blade steel feeler gauge
Nonmagnetic feeler gauge
Dwell meter
12-volt test light
2-12. How far in front of the vehicle should
you locate the aiming screen when
aligning headlights?
To advance timing, you should turn
the distributor housing in the same
direction as the shaft rotation.
1. True
2. False
2-8. Which of the following conditions
results from ignition timing being too
Spark knock
Poor fuel economy
Sluggish acceleration
Overheated exhaust manifold
24 inches
26 inches
28 inches
30 inches
2-14. When headlights are correctly aimed,
the high intensity light beams drop
what distance for every 25 feet away
from the bulb?
1. 6 or 12 volts
2. 12 or 18 volts
3. 12 or 24 volts
4. 18 or 24 volts
2-10. Of the following terms, which one
refers to the luminous intensity of an
incandescent lamp?
Rated size
2-15. The aiming of truck headlights differs
from the aiming of automobile
headlights to compensate for which of
the following conditions?
2-11. A halogen light increases light output
by what percentage?
2-13. When the headlights of a vehicle are
centered 28 inches from the ground,
how high should the reference line on
the aiming screen be above ground
Navy automotive and construction
equipment lighting systems operate on
what voltages?
1. The effect of the variations in
2. The height of the vehicle
3. The width of the vehicle
4. The size of tires used
2-16. On tactical vehicles equipped with
blackout lights, the driving light is
designed to provide light directly in
front of the vehicle out to a distance of
what number of feet?
2-17. The function of what component is to
turn off the turn signal switch?
2-20. What component supplies power for
the small electric motor that rotates
the input shaft of an electric
2-21. An electronic tachometer on a diesel
engine derives its input signal from
1. a pulse signal from the distributor
as it switches the coil on and off
2. a signal from a magnetic pickup
coil that has its field interrupted by
a rotating pole piece
3. alternating current generated by
the stator terminal of the alternator
4. a power signal that is generated
through a magnetic pickup at the
Composite cam
Limiting cam
Canceling cam
Cutoff cam
2-18. A burned-out fuse has a discolored
sight glass. This condition indicates
the existence of what problem?
The rating of the fuse is too low
An overloaded circuit
An open circuit
A short in the wiring
2-22. What component in the windshield
wiper switch provides the operator a
means of delaying windshield wiper
2-19. You are operating a vehicle with a 12volt electrical system. The voltmeter
in the vehicle should indicate a
reading that falls within what voltage
Magnet generator
Thermistor generator
Distribution generator
Resolution generator
Variable speed resistor
2-27. When 50 pounds of force is applied to
piston 1 (as shown in textbook figure
3-4), how many pounds of force is
applied to piston 2?
2-23. On which of the following types of
equipment will you find numbered
tags that identify the wiring circuits?
M-series vehicles
Track-mounted equipment
Wheel-mounted construction
1. 2 5
2. 5 0
3. 7 5
4. 100
2-24. All construction equipment regardless
of manufacturer use the same color
code for each component.
1. True
2. False
2-28. Referring to textbook figure 3-5, when
piston 1 is 4 square inches and is
pushed down 2 inches and piston 2 is
16 square inches, how far will piston 2
2-25. Wires passing through holes in a metal
member of the body or frame should
be protected by which of the following
types of materials?
2-29. What are the three most common
types of hydraulic fluids?
Plastic clamps
Flexible tubing
Rubber grommets
Electrical tape
2-26. A properly constructed hydraulic
system possesses which of the
following characteristics?
1. The use of complicated gears,
cams, and levers is required
2. Provides variable motion only in a
straight-line transmission of power
3. Low temperature changes
4. Motion can be transmitted without
the slack inherent in the use of
solid machine parts
1. Petroleum-based, synthetic fireresistant, petroleum-based fireresistant
2. Water-based, phosphate ester fire
resistant, water-based fire-resistant
3. Silicon-based, petroleum-based
fire-resistant, water-based fireresistant
4. Petroleum-based, synthetic fireresistant, water-based fire-resistant
2-30.A properly designed and constructed
hydraulic reservoir should be capable
separating air from the oil
causing a vortex
dissipating air bubbles
maintaining line pressure
2-35. Which of the following types of
hydraulic pumps is designed to
operate at moderate speeds which
reduces erosion and excessive wear of
the pump?
2-31. Why is the hydraulic reservoir vented?
2-36. Which of the following actions is
NOT a function performed by the
valves in a hydraulic system?
To prevent the loss of fluid
To allow the reservoir to breathe
To separate air from the fluid
To dissipate heat from the fluid
1. Prevents leakage between
precision machined surfaces
2. Controls pressure in the system
3. Directs the flow of fluid
4. Regulates the flow of fluid
2-32. In a standard hydraulic system, the
strainer is at what location?
On the discharge side of the pump
Between the filter and the pump
In the pressure relief line
On the pump suction lines
2-37. In a hydraulic system, what valve is
designed to regulate the flow of the
hydraulic fluid?
2-33. The operating pressure within a
hydraulic system is created by the
1. pumping capacity of the pump
2. opening and closing of the relief
3. resistance encountered by the fluid
4. the displacement of the pump
Directional control
Functional control
Flow control
Pressure control
2-38. In a hydraulic system, the directional
control valve serves which of the
following functions?
2-34. The amount of fluid that a hydraulic
pump can deliver per cycle is known
by what term?
1. Keeps the hydraulic pump
operating at a constant speed
2. Regulates the pressure sent to the
cylinder during operation
3. Sends fluid back to the reservoir
when pressure becomes too great
4. Regulates the speed and operation
of hydraulic cylinders
Pump displacement
Discharge displacement
Volumetric output
Variable output
2-39. Which of the following is NOT a type
of valving element used in the
construction of a directional control
2-43. A fixed displacement hydraulic motor
provides which of the following
Rotary spool
Sliding spool
2-44. What type of hydraulic motor is most
often used in hydraulic systems?
2-40. The double-acting cylinder shown in
textbook figure 3-31 will have more
force applied to the cylinder as it is
1. True
2. False
2-45. In a hydraulic system, which of the
following is NOT an advantage of
tubing over pipe?
2-41. Why are accumulators used in some
hydraulic systems?
1. Handles large volumes of fluid
under high pressure
2. Requires fewer fittings and has a
better appearance
3. Easier to bend, cut, and fit
4. Easier to maintain
1. To increase fluid capacity
2. To absorb and stabilize shock
3. To stabilize the amount of fluid
4. To store fluid for emergency fluid
2-42. What are the three major types of
hydraulic accumulators?
Constant torque and variable speed
Variable torque and constant speed
Variable torque and variable speed
Constant torque and variable speed
2-46. When piping is used in a hydraulic
system, the pipe should be made of
which of the following materials?
1. Weight-loaded, bladder, and
2. Bladder, floating piston, and
3. Spring-loaded, diaphragm, and
4. Pneumatic, weight-loaded, and
Electric welded mild steel
Galvanized mild steel
Seamless rolled mild steel
Seamless cold-drawn mild steel
2-47. The flexible hose you are using has a
designation of – 4. What is the inside
diameter of this hose?
1/16 inch
1/8 inch
1/4 inch
1/2 inch
To reduce resistance
To prevent deterioration
To protect the strength members
To prevent the hose from twisting
2-49. When placing support clamps on a
length of flexible hose, you place the
clamps at intervals of what maximum
12 inches
18 inches
24 inches
30 inches
Pressure drops
Pressure increases
Cooling factor increases
Twisted hose
Back to back
Head to head
Toe to toe
Face to face
2-53. A hydraulic system on a piece of
CESE should be flushed according to
the manufacturer's recommendation.
1. True
2. F a l s e
2-54. The branch of science that pertains to
gaseous pressure and flow is known
by what term?
2-50. Which of the following conditions is a
result of mismatched hoses and
Quad rings
T seals
X rings
O rings
2-52. When more than one U cup is
installed, they are installed in what
2-48. Why is the inner tube (layer) of a
flexible hydraulic hose made of
synthetic material?
2-51. Which of the following is NOT a type
of fluid power seal?
2-55. What law states that a volume of a gas
is proportional to its absolute
temperature if pressure remains
Charles's Law
Boyle's Law
Pascal's Law
Murphy's Law
2-60. What type of air compressor is
equipped with an intercooler?
2-56. Which of the following is NOT a
desired quality of a gas used in a
pneumatic system?
1. Multistage reciprocating
2. Multistage rotary
3. Multistage screw
4. Single-stage screw
Free from acids
Chemically stable
Excellent lubricating power
2-57. Compressed air systems are
categorized by operating pressure. A
medium-pressure air system is rated at
what pressure?
180 to
151 to
175 to
200 to
2-62. On a rotary air compressor, engine
speed is regulated to correspond with
which of the following factors?
1. Capacity of the compressor
2. Volume of air to supply the
3. Discharge pressure of the
4. Temperature of air leaving the
spring tension
oil pressure
air pressure
centrifugal force
2-59. Before the compressed air leaves the
service valves of a rotary air
compressor, the oil in the air is
removed by what component?
1. To remove moisture from the air
2. To eliminate surges in air delivery
3. To prevent overheating of
pneumatic tools
4. To reduce pressure in the
distribution system
1,500 psi
1,000 psi
1,200 psi
2,000 psi
2-58. In the rotary compressor, the sliding
vanes are held against the pump
casing by
2-61. Why are aftercoolers used on some
reciprocating air compressors?
The in-line oiler
The receiver separator
The oil cup
The oil separator
2-63. When using compressed air to clean
the primary element of an air cleaner,
you should not allow the air pressure
to exceed
10 psi
20 psi
30 psi
40 psi
2-64. When should you replace the air
cleaner elements of an air compressor?
1. Each time the compressor oil is
2. After every 500 hours of service
3. When inspections shows an
accumulation of greasy dirt
4. When the red band is visible in the
air cleaner service indicator
2-65. Under normal operating conditions,
compressor oil should be changed
after what number of operating hours?
Textbook Assignment: "Automotive Clutches, Transmissions, and Transaxles," chapter 4, pages
4-1 through 4-44.
What device is designed to disconnect
the engine from the power tram?
Universal joint
Transfer case
Throw-out bearing
Clutch release mechanism
Clutch fork
Pressure plate
The clutch fork transfers motion from
the release mechanism to what
The release bearing is held on the
clutch fork by
spring clips
hydraulic pressure
grooves cut into the release
Which of the following clutch
components prevents the transmission
from wobbling up and down when the
clutch is released?
Facing springs
Cushioning springs
Torsion springs
Friction springs
The flat metal springs, located under
the friction lining of the disc, allow for
smooth engagement of the clutch.
These springs are known by which of
the following terms?
Pressure plate
Release bearing
Clutch housing
Clutch fork
What component of the clutch disc
absorbs vibration and shock produced
by clutch engagement?
1. The clutch linkage and release
2. The clutch slave cylinder and
pressure plate
3. The pressure plate and clutch disc
4. The release bearing and pressure
What clutch component can either
engage or disengage the clutch disc
and flywheel?
What component provides the
operator the means with which to
operate the clutch assembly?
Pilot bearing
Release bearing
Diaphragm pressure plate
Clutch release mechanism
3-9. Which of the following safety devices
prevents the engine from starting
unless the clutch pedal is fully
Clutch start switch
Transmission safety switch
Engine failsafe switch
Neutral safety switch
3-10. How is a hydraulically operated clutch
1. By turning the eccentric cam in the
clutch pedal support
2. By shortening and lengthening the
slave cylinder pushrod
3. By lengthening the effective stroke
of the piston of the master cylinder
4. By bleeding off a small amount of
fluid. at the slave cylinder
3-13. Which of the following conditions
will result in the clutch slipping?
3-14. An operator reports that a vehicle has
a severe vibration when accelerated
from a standstill. What is the most
likely cause of this trouble?
1 inch
2 inches
1 1/2 inches
4 inches
3-12. What is the most common cause of
premature clutch troubles?
Excessive free play
Broken disc facing
Bent release levers
Worn release bearing
3-15. An operator reports hearing rattling
sounds when the clutch is engaged.
This condition is generally due to
which of the following problems?
3-11. You are in the field and no manuals
are available. What amount of clutch
pedal free travel will allow for
adequate clutch operation until the
vehicle reaches the shop?
Loose spring shackles
Bent crankshaft flange
Loose transmission mount
Broken motor mount
1. Worn pilot bearing
2. Worn clutch disc facing
3. A broken clutch disc torsion
4. A broken clutch release
3-16. A pilot bearing that is worn or lacks
lubricant will produce noise in the
clutch when which of the following
conditions exists?
Operator abuse
Misaligned transmission
Over lubrication
Stop-and-go traffic
The transmission is in gear
The clutch is disengaged
The vehicle is standing still
The clutch is engaged
3-17. An operator reports that a vehicle has
"clutch-pedal pulsation." A mechanic
should know that this means that
1. slippage between the clutch disc
facing and the flywheel is being
sensed through the clutch pedal
2. the clutch has a strong jerk that is
being sensed through the clutch
3. a series of slight movements can
be felt on the clutch pedal when
the clutch is being disengaged
4. there must be dirt or grease on the
clutch facings
3-20. When overhauling a clutch, you
should NOT inspect the pressure plate
and flywheel for which of the
following conditions?
3-21. Which of the following tool(s) are
used to measure the amount of wear of
a pilot bearing?
3-18. Clutch-pedal pulsation can NOT be
caused by which of the following
1. Misalignment of the engine and
2. The flywheel not being seated on
the crankshaft flange
3. A warped pressure plate or clutch
4. Excessive clutch pedal free play
3-19.When disassembling a clutch, you
should take what action before
removing the pressure plate?
Inside caliper
Outside caliper
Telescoping gauge and micrometer
Thickness gauge and sliding scale
3-22. A clutch release bearing is running
roughly. What action should the
mechanic take?
1. Clean the bearing with solvent
2. Disassemble the bearing and
smooth any rough areas
3. Repack the bearing with lubricant
4. Replace the bearing
3-23. What is the maximum number of
adjustments on a pressure plate before
1. Relieve the tension on the pressure
plate springs
2. Check the thickness of the clutch
3. Loosen the flywheel mounting
4. Mark the pressure plate cover and
3-24. The pressure plate adjustment that
positions the release levers and allows
the release bearing to contact the
levers simultaneously is known by
which of the following terms?
1. Countershaft gears, input gear,
output gear, and reverse idler gear
2. Main shaft gears, output gear,
synchronized gears, and reverse
idler gear
3. Input gear, countershaft gears,
main shaft gears, and reverse idler
4. Reverse gear, main shaft gears,
countershaft gears, and output gear
Clearance height
Relation height
Finger height
Free height
3-25. You are reassembling a clutch
assembly and a clutch alignment tool
is NOT available. You can center the
clutch disc on the flywheel by using
1. an old clutch shaft from the same
type of vehicle
2. a wooden dowel the same size as
the pilot bearing
3. a pry bar to move the clutch disc
up and down
4. measured spacers to provide exact
3-26. What component provides a selection
of gear ratios so a vehicle can operate
under a variety of operating conditions
and loads?
3-28. What are the four gear groups in a
manual transmission?
The transmission
The differential
The transfer case
The final drive
3-29. Of the following functions, which one
is a function of the synchronizer in a
manual transmission?
1. Provides the operator an easy
means of shifting gears
2. Locks the main shaft gear to the
main shaft
3. Increases torque going to the drive
wheels for quick acceleration
4. Completes the power flow from
the transmission to the drive
3-30. What are the two types of shifting
linkages used on manual
1. External shift cable and internal
shift rod
2. Internal shift rod and external shift
3. Internal shift cable and external
4. External rod and internal shift rail
3-27. In a manual transmission, what shaft
is locked in place within the
transmission case?
Reverse idler
3-31. When the gears are shifted, what type
of transmission locks the gears to their
shafts using sliding collars?
3-34. The reverse gear in a synchromesh
transmission does NOT affect the gear
1. True
2. False
Sliding gear
Constant mesh
3-35. What component of an auxiliary
transmission is splined to the main
shaft and slides backwards or forwards
when shifting into high or low
3-32. What is the function of the
synchronizer in a synchromesh
1. To engage the main drive gear
with the transmission main shaft
2. To engage the first speed main
shaft with the transmission main
3. To equalize the speed of the
driving and driven members
4. To engage the second speed main
shaft with the transmission main
3-36. Which of the following conditions
will result in a transmission being hard
to shift?
1. Excessive countershaft end play
2. Lack of spring tension on the shift
lever detent
3. Defective synchronizer
4. Shift linkage out of adjustment
3-33. The only function of the reverse gear
in a synchromesh transmission is to
1. make the main shaft rotate in the
opposite direction to the input
2. make the countershaft rotate in the
opposite direction to the input
3. make the reverse idler shaft rotate
in the opposite direction to the
input shaft
4. make the main shaft and reverse
idler shaft rotate in the same
direction to the input shaft
Gear type of dog clutch
Over-center dog clutch
High-lo shift fork
3-37. A clutch that is NOT releasing will
cause a transmission to
make noise in neutral
make noise in gear
stick in gear
slip out of gear
3-38. When disassembling a manual
transmission, you find brass-colored
particles. What components are most
likely damaged?
The main drive gears
The thrust washers
The input shaft bearing
The reverse idler shaft sleeve
3-39. When replacing a main shaft gear, you
should also replace the matching gear
on what shaft?
3-42. What action within an automatic
transmission allows the transmission
to shift gear ratios without operator
Reverse idler
1. Locking and releasing of planetary
gearsets in various combinations
and unlocking of
hydraulic actuated multiple-disc
3. Controlling the hydraulic pressure
that locks and releases brake bands
4. Engaging and disengaging of the
torque converter from the engine
3-40. You have completed reassembling a
transmission. Which of the following
actions should you take before
reinstalling the transmission?
1. Fill the case with proper lubricate
2. Ensure the transmission shifts
3. Measure end play clearance of the
4. Lightly coat all components with a
medium-grade lubricating oil
3-41. Operator control of an automatic
transmission is limited to what action?
1. Changing the throttle position to
match the load requirements of the
2. Coupling and uncoupling the
engine and automatic transmission
through the torque converter
3. Moving the control lever to select
the gear range
4. Locking the planetary gearsets to
produce the required forward and
reverse gear ratios
3-43. In a torque converter, what component
is known as the converter pump?
1 . Stator
2. Impeller
3. Turbine
4. Drive fan
3-44. The turbine of a torque converter is
connected to what component?
Clutch housing
3-45. The blades inside a torque converter
are forced to rotate by
1. oil thrown by the pump
2. centrifugal force generated by the
3. engine torque transmitted through
the crankshaft
4. pressure from the flywheel
3-46. In a torque converter, what action
causes torque multiplication to occur?
1. The impeller is spinning faster
than the turbine
2. The impeller is spinning slower
than the stator
3. The turbine is spinning faster than
the impeller
4. The turbine is spinning slower
than the stator
3-50. What component of a lockup torque
converter assists in dampening engine
pulses entering the drive train?
3-51. Of the following gears, which one is
NOT a part of the makeup of the
planetary gearset?
3-47. The condition that exists when the
impeller of a torque converter is at
maximum speed and the turbine is
almost stationary is known by what
Dog clutch
One-way clutch
Over-center clutch
Multi-disc clutch
Planet pinion
Planetary carrier
3-53. What component of an automatic
transmission is used to transmit torque
by locking elements of the planetary
gearsets to rotating members within
the transmission?
3-49. What type of torque converter
eliminates the heat caused by torque
converter slippage which results in
increased fuel economy and
transmission life?
Planetary carrier
3-52. What gear is the center gear in a
planetary gearset?
Torque speed
Engine speed
Acceleration speed
Stall speed
3-48. What component locks the stator of a
torque converter when the impeller is
turning faster than the turbine?
Cushioning springs
Facing springs
Torsion springs
Leaf springs
Over-center clutch
Multiple-disc clutch
One-way clutch
Dog clutch
3-54. What component of a multiple-disc
clutch is used to distribute application
pressure equally on the surfaces of the
clutch discs and plates?
Clutch hub
Pressure plate
Clutch drum
Clutch springs
3-55. What component of a multiple-disc
clutch ensures a rapid release of the
clutch when hydraulic pressure to the
clutch piston is released?
1. To produce pressure to operate the
2. To lubricate the moving parts of
the transmission
3. To keep the torque converter tilled
4. To route excess transmission fluid
to the cooling tank
3-60. What valve in an automatic
transmission is operated by the shift
mechanism, allowing the operator to
select park, neutral, reverse, or
different drive ranges?
Brake band
Multiple-disc clutch
Valve body
3-57. Of the following functions, which one
is NOT a basic function of the
hydraulic system of an automatic
Actuate clutches and bands
Control shifting patterns
Circulate transmission fluid
Control the planetary gearset
Transmission case
Torque converter hub
Engine crankshaft
3-59. Of the following functions, which one
is NOT a function of the hydraulic
pump of an automatic transmission?
Clutch springs
Clutch hub
Clutch drum
Pressure plate
3-56. What component of an automatic
transmission is designed to lock a
planetary gearset element to the
transmission case so the element can
act as a reactionary member?
3-58. So it can be driven by the engine, the
hydraulic pump of an automatic
transmission is keyed to what
3-61. What component works in conjunction
with the vacuum modulator to
determine shift points in an automatic
Manual valve
Kickdown valve
Governor valve
Shift valve
3-62. What valve causes the transmission to
shift into a lower gear during quick
3-63. In addition to giving off a burnt smell,
overheated transmission fluid will turn
what color?
3-66. Water mixed with automatic
transmission fluid will turn the fluid
what color?
3-67. After a vehicle has been operated in
severe service, the transmission will
require a band adjustment.
1. True
2. False
3-68. "Severe service" does NOT include
which of the following conditions?
3-64. Using a transmission fluid that is
incompatible with the unit you are
working on may lead to which of the
following problems?
The transmission overheating
The transmission fluid foaming
A milky appearance of the fluid
An early transmission failure
Construction operations
Trailer towing
Stop-and-go driving
Contingency operations
3-69. Oil drained from an automatic
transmission should be disposed of
according to what instructions?
3-65. Air trapped in the hydraulic system of
an automatic transmission can cause
which of the following problems?
1. High line pressure
2. Slow application of the clutch
3. Low torque output
4. Hard shifting
Federal regulations
Local civilian
Local naval station
3-70. Which of the following factors is NOT
an advantage of a vehicle with a
transaxle and front-wheel drive?
1. Increased passenger compartment
2. Quieter operation
3. Greater sprung weight
4. Improved traction on slippery
3-71. In a manual transaxle the output shaft
transfers torque to which of the
following components?
3-72. The flow of fluid to the pistons and
servos of an automatic transaxle is
controlled by what component?
Drive axles
Hub assembly
Transaxle clutches and bands
Transaxle planetary gearsets
Transaxle differential
Transaxle valve body
Textbook Assignment: "Drive Lines, Differentials, Drive Axles, and Power Train Accessories,"
chapter 5, pages 5-1 through 5-35.
Of the following functions, which one
is NOT a function of a drive line
1. Magnafluxing the drive shaft
2. Welding small weights to the light
side of the shaft
3. Placing weights on the opposite
ends and opposite sides of the
4. Truing the shaft on a lathe
1. Provides a smooth power transfer
2. Allows up-and-down movement of
the rear axle
3. Sends power from the
transmission to the rear axle
4. Maintains proper alignment of the
rear axle and transmission
Flange tube
Torque tube
4-7. What component of a drive train is
used to allow changes in the angle of
the drive line assembly?
Slip yoke
Rear yoke
Drive shaft
Flex shaft
What component of a drive shaft
assembly provides free movement in a
horizontal direction and is capable of
transmitting torque?
What type of drive shaft is enclosed
and rotates within a support bearing to
prevent whipping?
Universal joint
Center support bearing
Drive shaft
Slip yoke
What component of a drive line
assembly transfers turning power from
the front universal joint to the rear
universal joint?
Which of the following drive line
components is used only on long
wheelbase vehicles?
What modification prevents drive
shafts from vibrating at full-engine
Slip yoke
Rear yoke
Front universal joint
Rear universal joint
Support bearing
Companion flange
Slip joint
Universal joint
4-12. The balls of a Rzeppa type constantvelocity joint
4-8. What type of drive shaft design
prevents shaft speed fluctuations?
1. transfers rotating power from the
axle shaft to the hub assembly
2. maintains an equally divided drive
angle between the connected
3. furnishes the only points of
driving contact between the two
halves of the coupling
4. ensures angular displacement of
the shafts are maintained by the
outward movement of the balls
1. A drive shaft containing two
universal joints assembled 90
degrees apart
2. A drive shaft containing one
universal joint and one slip joint
on the same end
3. A drive shaft containing one
universal joint at the transmission
and a slip joint at the differential
4. A drive shaft containing one
universal joint at the differential
and a slip joint at the transmission
4-13. When the driven shaft of a Rzeppa CV
joint is moved 30 degrees, the cage
and balls move what number of
What type of universal joint is most
often used?
Double cardan
Ball and trunnion
Cross and roller
4-10. What type of universal joint has two
cross-and-roller joints in tandem to
form a single joint?
4-14. What component of a tripod CV joint
is splined to the axle shaft?
1. Ball-and-trunnion
2. Double-cardan
3. Rzeppa
4. Tripod
4-11. In a front-wheel drive vehicle, the
outboard CV joint is a sliding joint
that transfers rotating power from the
axle shaft to the hub assembly.
Inner spider
Outer yoke
Outer housing
Axle hub
4-15. Of the following functions, which one
is NOT a function of a pillow block
bearing in an auxiliary power train?
1. To support the drive shaft
2. To maintain drive shaft alignment
3. To prevent whipping under heavy
4. To prevent shimmy and poor
1. True
2. False
4-16. An operator reports hearing a grinding
noise coming from the drive shaft.
This report most likely indicates the
existence of what problem?
4-20. Lubricating universal joints with a
low-pressure grease gun prevents
which of the following types of
A worn center support bearing
Worn splines in the slip yoke
A worn universal joint
A worn transmission housing
4-17. Which of the following conditions
indicates that a center support bearing
is faulty?
1. A whining noise in the drive line
2. Failure of the vehicle to start
moving smoothly
3. Frequent stalling when the clutch
is engaged
4. Vibration from the chassis at low
4-21. You are removing the drive shaft from
a vehicle. What component can be
damaged if you allow the full weight
of the drive shaft to hang from the slip
Rear U-joint
Front bushing
Extension housing
Support bearing
4-22. When reassembling a universal joint,
you should use what type of lubricant
to prevent the bearings from falling
out of the bearing cap?
4-18. When performing a drive shaft
inspection, you take what action to
check the U-joints?
1. Move them by prying with a pry
2. Completely disassemble the joints
3. Measure the play between the
cross and roller
4. Wiggle and rotate each joint back
and forth
High-temperature grease
Wheel bearing grease
Water pump lubricant
4-23. What is the first indication that a
vehicle has a faulty center support
4-19. In what gear is a worn universal joint
most often noticed?
Bearing damage
Seal damage
Bearing seizure
Over lubrication
1. A clunking sound when changing
from acceleration to deceleration
2. A whining sound coming from the
drive shaft
3. Excessive chassis vibration at low
4. The drive shaft begins to wobble
causing abnormal universal joint
4-28. The outer end of the pinion gear is
joined to the rear U-joint companion
flange by
4-24. When replacing the center support
bearing, you should ensure that the
1. bearing shield contains grease
2. grease fitting is in place
3. dust shield is placed in its grooves
4. drive shaft alignment is
4-25. Of the following functions, which one
is a function of the differential in an
automotive vehicle?
1. Connects the rear axles shafts
2. Allows the axles to turn at
different speeds when cornering
3. Permits the driving axles to be
driven as a single unit
4. Transmits power indirectly to the
drive axles
4-29. What component of a differential
drives the ring gear?
4-31. What component of a differential is
splined to the inner ends of the axles?
Side gear
Spider gear
Spiral bevel gear
Pinion gear
1. True
2. False
4-27. What component of a differential
assembly holds the ring gear, the
spider gears, and the inner ends of the
lock rings
snap rings
4-30. When repairing a differential, you
must replace the ring and pinion as a
matched set.
4-26. What type of differential carrier is
constructed as part of the axle
Differential integral gears
Differential idler gears
Differential pinion gears
Differential side gears
4-32. Which of the following gear ratios of a
final drive provides a substantial
increase in acceleration; however, fuel
economy is decreased?
final drive
4-37. A two-speed final drive is limited to
use in those vehicles containing one
driving axle.
4-33. Which, if any, of the following
components is part of a final drive?
Bevel drive pinion
Differential carrier
Saddle yoke
None of the above
1. T r u e
2. False
4-38. In a two-speed final drive, what
component is placed between the
differential drive ring gear and the
differential case?
4-34. What type of final drive designs are
most often used?
Double reduction and two-speed
Spiral bevel gear and hypoid gear
Limited slip and cone clutch
Full-floating and three-quarter
4-35. What type of final drive has the pinion
gear meshing with the ring gear below
the center line and at a slight angle?
4-39. In a clutch pack type limited-slip
differential, clutch packs are applied
by the
1. centrifugal force of the spider
gears and spring pressure
2. friction of the steel disc and spring
3. spring force and the thrust action
of the spider gears
4. side pinion gears walking inside
the side gears
Spiral bevel
Double reduction
Limited slip
A 5-ton military vehicle is equipped
with what type of final drive?
Limited slip
Clutch pack
Cone clutch
Planetary gear train
Sliding pinion gear
4-40. Under rapid acceleration, the
differential pinion gears of a cone
clutch limited-slip differential push
outward on what components?
Side gears
Cone gears
Flange casings
Drive axles
4-41. What condition is generally accepted
as the first hint of differential
4-44. When removing an integral
differential, you should inspect and
mark the individual components as
they are removed.
Loss of traction
Vehicle vibration
Loss of lubricant
Unusual noises
4-42. Which of the following differential
troubles will produce a humming
1. Lack of lubrication
2. Improperly adjusted ring and
pinion gears
3. Improperly adjusted pinion and
side gears
4. Backlash is too great
1. True
2. False
4-45. When replacing the seals in a
differential, you should use which of
the following tools?
4-46. Which of the following methods are
used to adjust pinion gear depth?
4-43. Which of the following conditions
generate a clunking sound in the
1. Faulty differential gears
2. Worn axle support bearings
3. Excessive backlash between the
ring-and-pinion gears
4. Loose carrier bearings
Seal driver
Hammer and a block of wood
Slide hammer
Seal insert
Using a collapsible spacer
Tightening the pinion nut
Replacing the shim pack
Varying shim thickness
4-47. When adjusting the pinion bearing
preload with a collapsible spacer, you
should use which of the following
tools to measure the pinion preload?
Dial indicator
Foot-pound torque wrench
Inch-pound torque wrench
Feeler gauge
4-48. Which of the following problems
results from having a differential case
bearing preload that is too high?
Ring-and-pinion noise
Overheated bearings
Too much backlash
Excessive differential case runout
4-52. A live axle only serves as a support
for part of the vehicle while providing
a mounting for the wheel assembly.
4-49. Ring-and-pinion backlash is required
for which of the following reasons?
To allow for heat expansion
To prevent ring gear runout
To ensure a good contact pattern
To ensure that the pinion gear is
perpendicular to the ring gear
1. True
2. False
4-53. What type of axle housing is most
often used?
4-50. When checking ring-and-pinion tooth
contact pattern, you note that the
pattern is located on the upper edge
(high contact) of the teeth. What
corrective action is required?
1. Move the ring gear away from the
2. Move the ring gear towards the
3. Move the pinion towards the ring
4. Move the pinion away from the
ring gear
4-51. The ideal tooth contact pattern on a
used gear will have considerably more
contact in which area of the gear?
4-54. Why are automotive axle housings
To cool the lubricant
To prevent pressure buildup
To prevent overfilling
To adjust for loads
4-55. The vehicle weight-supporting
bearings in a full-floating axle are
1. at the inner end of the axle
2. on the outer end of the axle shaft
3. on the outer end of the axle
4. at the inner end of the axle shaft
The toe
The heel
The drive side
The coast side
4-56. What type of drive axle allows the
axle shaft to be removed without
removing the wheel?
Three-quarter floating
4-57. To permit the drive shaft of a front
drive axle to pass beside the engine oil
is accomplished by
using a constant velocity joint
using an intermediate drive shaft
using a transfer case
having an off-center differential
4-58. In the front drive axle of a four-wheel
drive vehicle, what component
transfers power from the drive axles to
the drive wheels?
4-62. To help ensure axle bearing problems
do NOT reoccur, you should take what
1. Determine the cause of the part
2. Perform all repairs according to
the manufacturer’s manual
3. Follow the shop supervisor’s
4. Install a higher quality part
Locking hubs
Interconnecting shaft
Outer stub shaft
Sliding hub
4-63. When removing a pressed-on bearing
collar from an axle, you should use
which of the following tools?
4-59. In a front-wheel drive vehicle, what
component of the front-wheel drive
axle is splined to the side gears in the
4-61. Worn or damaged axle bearings
produce what type of sound?
Interconnecting shaft
Outer stub shaft
Inner stub shaft
Rzeppa joint
4-60. What action allows for a change in
distance between the transaxle and the
wheel hub?
Cutting torch
Hand grinder
Slide hammer
Bearing puller
4-64. When removing an axle bearing using
a hydraulic press, you should place the
driving tool so it contacts what area of
the bearing?
1. The plunging action of the outer
CV joint
2. The plunging action of the inner
CV joint
3. The sliding action of the short
shaft spline to the side gears
4. The sliding action of the
interconnecting shaft
The outer race
The inner race
The bearing collar
The bearing sleeve
4-65. What is the proper tool for removing a
housing-mounted axle seal?
Hand grinder
Pry bar
Cutting torch
Slide hammer
4-66. What component is used to divide
engine torque between the front and
rear driving axles?
Excessive end play
Clutch slippage
Bent linkage
Improperly linkage lubrication
4-70. A power takeoff unit is driven by what
shaft of the transmission?
Main shaft
Idler shaft
Accessory drive shaft
4-71. Faulty operation of a power takeoff
unit is caused by which of the
following problems?
Sliding cone clutch
External shifting rail
Sliding dog clutch
4-68. In a vehicle using a positive traction
transfer case, what component is
engaged when the rear wheels lose
traction and provides power to the
front wheels?
Power takeoff
Auxiliary transmission
Transfer case
Power divider
4-67. Shifting is accomplished in a
conventional transfer case by what
4-69. An operator reports that the transfer
case is hard to shift. Which of the
following problems is NOT a possible
1. Damaged linkage
2. Improper spacing between the
meshing gears
3. Excessive end play
4. Worn bearings
4-72. To compensate for PTO wear, you
must take what action?
Sliding cone clutch
Sprag unit
Energizing springs
Add shims
Remove shims
Adjust the linkage
Adjust the control lever
Textbook Assignment: "Construction Equipment Power Trains," chapter 6, pages 6-1 through
What are the two most common types
of drive trains used in modem
construction equipment?
5-5. The pinion gear that is splined to the
bevel pinion shaft is adjusted for
pinion depth by adding shims.
1. True
2. False
Mechanical and hydromechanical
Pneumatic and mechanical
Hydrostatic and mechanical
Pneumatic and hydrostatic
5-2. The power shift transmission is
coupled to the torque converter
1. interconnecting splines
2. a swash plate
3. a universal joint
4. a jack shaft
What power shift transmission shaft
has the reverse drive gear keyed to the
front of the shaft?
Reverse clutch
Forward clutch
Bevel pinion
When the high-lo lever of a power
shift transmission is shifted, a sliding
gear on the spline shaft meshes with
gears on what shaft?
Reverse clutch
Forward clutch
Bevel pinion
Center and knock-off
Accelerator and force
Sintered and backing
Separator and drum
5-7. Upon application of the hydraulic
clutch, main oil pressure is directed
through which of the following
What two pistons are the heart of the
forward and reverse hydraulic clutch
in a power shift transmission?
Clutch shaft
Force piston cavity
Accelerator piston cavity
Drive gear and drum
Before shifting the hi-lo-shifting lever
in the power shift transmission, you
must put the gearshift lever in neutral
while the engine is running.
1. True
2. False
What component is the center gear in
a planetary gearset?
Planet pinion
Ring gear
Sun gear
Planetary carrier
5-10. How many different ways can the
planetary gearset be engaged to either
increase or decrease torque?
5-14. Adjusting the steering brakes of a
planetary steering system is required
because it provides what advantage?
5-15. The actuating disc assembly of the
pivot brakes on tracked equipment is
made up of what components?
5-11. In a planetary gearset, direct drive is
achieved by locking
1. the planetary carrier
2. the planet pinion
3. the ring gear
4. any two members together
1. Three discs that have laminated
2. Two smooth discs held in position
by studs
3. Two steel plates splined to the
sprocket drive
4. Two steel plates with steel balls
between them
5-12. In a planetary steering system, the sun
gear, machined to the steering brake
hub, performs the same function as
what component in a conventional
planetary system?
Even braking
Prevents slippage
Even lining wear
Prevents brake pull
5-16. In a hydrostatic drive train,
mechanical power from the engine is
converted to hydraulic power by what
Pinion gear
Planetary gear
Carrier gear
Ring gear
5-13. In a planetary steering system, braking
prevents what action?
1. The sprocket drive shaft and
steering brake hub from rotating
2. The steering brake hub and sun
gear from rotating
3. Transmitting power from the sun
gear to the sprocket drive shaft
4. The pinion gears from walking
around the sun gear on the steering
brake hub
1. Piston and cylinder
2. Swash plate and displacement
control valve
3. Pump and motor
4. Charge pump and cylinder block
5-21. Which of the following factors has no
bearing on the control of the
operations of a hydrostatic drive?
5-17. A hydrostatic drive is designed to
accomplish the functions of both a
clutch and a transmission.
1. True
2. False
5-18. What component of a hydrostatic
drive train can have its angle varied so
the volume and pressure of oil
pumped by the pistons can be changed
or the direction of the oil reversed?
5-22. Of the following advantages, which
one is NOT provided by a hydrostatic
1. Low torque available for starting
2. Smooth shifting
3. Low maintenance and service
4. Shifts "on-the go"
1. Displacement control valve
2. Low charge pressure control valve
3. Shuttle valve
4.Swash plate
5-19. In a hydrostatic drive train, what
pump-motor combination will provide
variable speed and constant torque?
5-23. In a hydrostatic drive, what design
feature determines the volume of oil
displaced per revolution of the pump?
1. A fixed displacement pump and
fixed displacement motor
2. A variable displacement pump and
fixed displacement motor
3. A fixed displacement pump and
variable displacement motor
4. A variable displacement pump and
variable displacement motor
5-20. In a hydrostatic drive train, what
pump-motor combination is the most
flexible, but is also the most difficult
to control?
Rate of oil flow
Direction of oil flow
Pressure of the oil
Quality of the oil
1. Speed of the engine
2. Angle of the swash plate
3. Alignment of the pump pistons
and the outlet port
4. Action of the high charge pressure
control valve
5-24. What valve, located in the motor
manifold, monitors the pressure of the
forward flow of oil and protects the
system from exceeding the rated psi?
1. A fixed displacement pump and
fixed displacement motor
2. A variable displacement pump and
fixed displacement motor
3. A fixed displacement pump and
variable displacement motor
4. A variable displacement pump and
variable displacement motor
Inlet check
High-pressure relief
Low charge pressure control
5-25. In a hydrostatic drive system the pump
drive shaft and cylinder block always
rotates clockwise; however, the motor
drive shaft and cylinder block may
rotate either clockwise or
5-30. What track frame components
maintains alignment of the track
assembly as it passes over the track
1. True
2. False
5-31. The operation of the recoil springs
depends upon what factor?
5-26. What are the two major components
of the undercarriage on crawlermounted equipment?
Track assembly and front idler
Track frame and drive sprocket
Front idler and drive sprocket
Track frame and track assembly
5-27. The length of a track will gradually
increase during normal use as a result
of wear on the
1. Back off the adjusting nut on the
idler yoke
2. Add shims in front of the recoil
3. Loosen the vent screw on the track
4. Loosen and slide the carrier rollers
track assembly and track frame
track links
sprocket and idler
pins and bushings
Bushing diameter and track pitch
Pin diameter and track pitch
Link width and bushing diameter
Chain length and link width
5-33.What track guiding guards reduce the
wear on the roller flanges and track
5-29. How many track links should you
measure across when checking track
Amount of tension on the idler
Amount of tension on the sprocket
Amount of tension on the track
Amount of tension on the track
5-32. To relieve tension on the track of a
modem crawler tractor, you should
take what action?
5-28. Which of the following measurements
are used to determine the wear of a
track assembly?
Track rollers
Guiding guards
Front idler
Carrier rollers
5-34. Friction in a tight track robs the
crawler tractor of needed horsepower.
5-39. Before replacing any components of
the track or track frame, you should
consult what publication?
1. T r u e
2. False
5-35. When the track on a crawler tractor is
too loose, it will have a tendency to
cause the idler to wear rapidly
come off when the tractor is turned
damage track rollers
increase pin and bushing wear
5-40. In the NCF, what publication contains
the guidelines for the maintenance and
use of wire rope?
INST 11200.1
2. NAVFAC P-404
3. NAVFAC P-458
4. NAVFAC P-306
5-36. When it becomes necessary to adjust
the track in the field, you should
remove all the slack in the track and
release the pressure until the front
idler moves back a 1/2 inch.
5-41. The typical front-mounted winch is
classified as what type of winch?
1. True
2. False
5-37. When inspecting a piece of tracked
equipment, you notice that the track is
out of alignment. What person
determines what action should be
The manufacturer's service manual
5-42. What component protects a winch
from being overloaded?
Crew leader
Operator of the track
Shop supervisor
5-38. When removing a track, you can
easily identify the master pin because
Sliding-clutch worm gear
Sliding-collar worm gear
Jaw-clutch worm gear
Sliding-jaw worm gear
Clutch key
Worm-gear key
Shear pin
Handle pin
5-43. What brake prevents the drum from
overrunning the cable when the cable
is being unreeled?
1. is larger than the other pins
2. has a locking device or a hole
drilled in its end
3. has a capital "M" cast into the end
4. has three stripes engraved on it
Winch support
Shift lever
5-48. What type of strand construction has
alternating large and small wires that
provide a combination of great
flexibility with a strong resistance to
5-44. Failure of the winch to operate is
usually the result of what component
being broken or damaged?
Drive shaft
Shear pin
Universal joint
PTO gear
5-45. A wire rope that has strands or wires
that are shaped to conform to the
curvature of the finished rope is
known as
5-49. What type of wire rope core is a
separate wire rope over which the
main strands of the rope are laid?
non-preformed wire rope
non-conformed wire rope
preformed wire rope
conformed wire rope
5-46. Which of the following components is
NOT part of the construction of a wire
5-47. Wire rope is designated by the number
of strands per rope and what other
Length of the strand
Diameter of the strand
Number of wires per strand
Number of strands per wire
Wire strand
5-50. Each square inch of improved plow
steel wire rope can withstand a strain
that is within what range, in pounds of
5-51. What type of wire rope lays has the
wires in the strands laid to the right,
while the strands are laid to the left to
form the wire rope?
Left lang lay
Right regular lay
Right lang lay
Left regular lay
5-57. Too large of a fleet angle can cause a
wire rope to climb the flange of a
5-52. Because it is very flexible, what type
of wire rope is acceptable for use on
1. True
2. False
6 x 37
6 x 24
6 x 19
6 x 12
5-53. What wire rope characteristic includes
a reserve of strength as a safety factor?
Crushing strength
Fatigue resistance
Tensile strength
Wear resistance
5-54. When measuring the diameter of wire
rope, you should measure what
number of places at what minimum
distance apart?
5 places
2 places
3 places
4 places
5-60. Which of the following conditions
will shorten the service life of wire
Dragging over obstacles
Improper coiling
Cross winding on drums
Using an excessive fleet angle
5-56. What type of wire rope damage starts
with the formation of a loop?
5-59. What total number of seizing is
required for seizing a 7/8-inch wire
least 4 feet apart
least 10 feet apart
least 5 feet apart
least 2 feet apart
5-55. Which of the following mistakes is
NOT a common cause of wire rope
5-58. In wire rope rigging, the diameter of
the sheave should never be less than
how many times the diameter of the
wire rope?
Crush spots
Wear spots
Broken wires
Excessive fleet angle
Lack of lubrication
Improper lay
Reverse bends
5-65. Wire rope eyes with thimbles and wire
rope clips can hold approximately
what percentage of the strength of a
wire rope?
5-61. When you are working in the field,
what wire rope lubricant ratio is
1. 70-percent diesel fuel to 30percent new motor oil
2. 70-percent used motor oil to 30percent diesel fuel
3. 70-percent gasoline to 30-percent
used motor oil
4. 70-percent new motor oil to 30percent diesel fuel
5-62. Speltering is the technique of
attaching a socket to a wire rope by
pouring hot zinc around it.
5-66. At a swaged connection, what is the
maximum amount of broken wires
allowed before the fitting should be
1. True
2. False
5-63. What type of wire rope attachment is
used to make eyes in wire rope?
Wedge socket
Wire rope clips
Speltered socket
5-67. When a swaged connection is made
properly, it will provide what
percentage of the capacity of the wire
5-64. To form an eye with a 3/4-inch wire
rope requires what total number of
wire rope clips?
5-68. A bent hook should be straightened by
heating it with a torch.
1. True
2. False
5-69. Hooks should always be inspected
before lifting a full-rated load.
1. True
2. False
5-70. What are the two types of shackles
used in rigging?
Screw pin and round pin
Mousing and bow
Anchor and chain
Ring and thimble
Textbook Assignment: "Brakes," chapter 7, pages 7-1 through 7-40.
What term is used to describe the
energy an object possesses due to its
relative motion?
Potential energy
Kinetic energy
Static energy
Perpetual motion
When the speed of a vehicle is
doubled, the amount of kinetic energy
that must be overcome by braking
action is multiplied by
6-3. The time frame between the instant
the operator decides that the brakes
should be applied and the moment the
brake system is activated is known by
what term?
Total reaction time
Decision reaction time
Operator reaction time
Stopping reaction time
The distance during the operator’s
reaction time and the distance during
which the brakes are applied before
the vehicle stops is known by what
Extreme weather conditions
Operator abuse
Load on the vehicle
Speed of the vehicle
On a typical rear-wheel drive vehicle
the front brakes will handle what
percentage of the braking power?
6-6. Which of the following factors will
NOT increase braking temperatures?
1. 10 times
2. 2 times
3. 3 times
4. 4 times
In answering this question, refer to
figure 7-3 in the text. You are driving
an average vehicle with brakes that are
in good condition. What is the vehicle
braking distance for the vehicle when
you are traveling at 60 miles per hour?
60 to 70
70 to 80
30 to 40
40 to 50
Of the following functions, which one
is NOT a function of the master
cylinder in a hydraulic brake system?
1. Develops pressure
2. Assists in equalizing the pressure
required for braking
3. Keeps the system full of fluid
4. Prevents fluid from seeping past
the cups of the wheel cylinders
Vehicle travel distance
Total stopping distance
Overall reaction distance
Braking travel distance
6-14. What brake system component
changes hydraulic pressure into
mechanical force?
6-9. Which of the following factors is an
advantage of having a dual master
cylinder in a hydraulic brake system?
1. It enables the brakes to be applied
with less effort
2. There is less chance of the brakes
3. It causes the brake shoes to wear
4. It makes for a safer brake system
6-15. What type of wheel cylinder is used to
compensate for a faster rate of wear on
the front brake shoe?
6-10. The front piston in a dual master
cylinder is known as the primary
1. True
2. False
Latitudinal split
Longitudinal split
Diagonal split
Equidistant split
6-12. A dual master cylinder with a large
front reservoir is an indication of what
type of brake system?
6-16. Brake lines are constructed from what
type of material?
6-11. What dual master cylinder system
operates the brake assemblies on
opposite comers?
Wheel cylinder
Master cylinder
Combination valve
Brake drum
Latitudinal split
Longitudinal split
Diagonal split
Equidistant split
Seamless aluminum tubing
Seamed aluminum tubing
Single-wall steel tubing
Double-wall steel tubing
6-17. What component is used to feed twowheel cylinders from a single brake
Poppet valve
Counterbalance valve
Junction block
Pressure-control block
6-18. Which of the following properties is
NOT a characteristic of brake fluid?
6-13. Where are the residual check valves
located in a diagonally split system?
1. In the rear reservoir of the master
2. At the wheel cylinder
3. At the tees that split the system
front to rear
4. In the combination valve
Moisture absorbent
Low freezing point
High boiling point
6-19. The primary brake shoe is the front
shoe and normally has a slightly
shorter lining than the secondary shoe.
6-24. Of the following components, which
one is NOT part of a disc brake
1. True
2. False
6-20. What type of brake lining does NOT
wear the brake drum excessively?
6-25. What component of a caliper acts as a
spring to retract the piston?
6-21. What type of brake shoe adjusting
system is operable in both forward and
reverse directions?
Dust boot
Piston seal
Boot seal
Caliper clip
6-26. Metal tabs are built into some disc
brake pads for the purpose of
1. notifying the operator of worn
2. allowing easy installation and
removal from the caliper
3. preventing the pads from coming
out of the caliper during operation
4. identifying the type of lining
material used on the pads
6-22. Which of the following actions is a
disadvantage of drum brakes?
Brake pads
Brake hub
No means of adjustment
Brake fade
Decreased braking distances
Allows excessive cooling air to
enter the assembly
6-27. What are the three type of disc brakes?
6-23. Which of the following actions is an
advantage of disc brakes?
1. Reduces braking distances
2. Increases brake fade
3. Collects asbestos dust in the brake
4. Dissipates heat through the brake
1. Semi-fixed caliper, fixed caliper,
and sliding caliper
2. Semi-floating caliper, fixed
caliper, and floating caliper
3. Sliding caliper, semi-floating
caliper, and semi-fixed caliper
4. Fixed caliper, floating caliper, and
sliding caliper
6-28. What type of caliper is designed to
permit equal braking force to be
applied to both sides of the rotor?
6-29. On a dual brake system, what switch
warns the operator of a pressure loss
on one of the sides?
1. True
2. False
6-34. To develop the additional force
required to apply the brakes, most
power brake systems use the
difference between
1. exhaust manifold vacuum and
hydraulic pressure
2. exhaust pressure and pneumatic
3. intake manifold vacuum and
atmospheric pressure
4. manifold air vacuum and exhaust
gas pressure
Master cylinder
Brake warning light
6-30. In a combination valve, what valve
holds off front disc braking until the
rear brakes makes contact with the
6-33. When antilock brakes are in use, you
may feel a vibration in the brake
6-35. What are the two types of vacuum
Pressure differential
Pressure reducing
1. Atmospheric suspended and
vacuum suspended
2. Hydraulic suspended and
pneumatic suspended
3. Vacuum suspended and hydraulic
4. Pneumatic suspended and
atmospheric suspended
6-31. In an antilock brake system (ABS),
what component modulates the
amount of braking pressure (PSI)
going to a specific wheel circuit?
Trigger wheels
Hydraulic actuator
Wheel speed sensors
ABS computer
6-36. What component is designed to make
vacuum available for a short time to
the booster unit should the vehicle
have to stop quickly with a stalled
6-32. During the operation of an antilock
brake system, what component
measures trigger wheel rotation?
Hydraulic actuator
ABS computer
Frequency reducer
Wheel speed sensor
6-37. Which of the following actions will
occur when you check a vacuum
power booster for proper operation?
6-40. The parking/emergency brake must
hold a vehicle on any grade.
1. The brake pedal will move
upwards slightly
2. The brake pedal move downward
slightly then upwards
3. The brake pedal will move
downward slightly
4. There is NO brake pedal
6-38. Which of the following conditions
will cause a vacuum failure in the
power booster, resulting in a hard
brake pedal?
6-41. Emergency brake requirements are
listed in what publication?
1. NAVFAC P-300
3. Code of Federal Regulations
4. Federal Motor Carrier Safety
Regulation Pocketbook
6-42. You are checking the fluid level in a
master cylinder. How far should the
fluid be from the top of the reservoir?
1. A collapsed vacuum hose at the
exhaust manifold
2. A broken air valve spring
3. A broken power piston linkage
4. A faulty check valve
6-39. Should the power steering system fail,
what component of a hydraulic power
booster retains enough fluid and
pressure for at least two brake
1 . True
2. False
1/4 inch
1/8 inch
1/2 inch
1/16 inch
6-43. The distance from the floor to the
brake pedal with the brake applied is
known as the brake pedal
Hydraulic reservoir
Pressure regulator
Booster valve
free play
reserve distance
performance distance
6-44. Disc brake pads should be replaced
when the lining is approximately how
1/32 inch
1/16 inch
1/8 inch
1/4 inch
6-45. When reconditioning a master
cylinder, you should take what action
if the bore is NOT badly pitted or
6-49. Why should you install a wheel
cylinder clamp before removing the
brake shoes?
1. To facilitate removal of the brake
shoe retracting springs
2. To prevent the loss of brake fluid
should someone accidentally
depress the brake pedal
3. To keep dirt out of the cylinder
when cleaning the backing plate
4. To hold the pistons in the wheel
Install a sleeve in the bore
Hone the cylinder
Machine the bore oversize
Sand the bore using emery cloth
6-46. Which of the following tools is NOT
used to determine if a master cylinder
bore is worn excessively?
6-50. When the rivet holes in a brake shoe
become enlarged, you should take
what action?
Outside micrometer
Inside caliper
Feeler gauge
Telescoping gauge
6-47. Before installing a master cylinder on
a vehicle, you should take what
1. Lubricate all parts with denatured
2. Remove the inlet ports and check
for obstructions
3. Install the master cylinder clamp
4. Bench bleed the master cylinder
6-51. When riveting the lining to a brake
shoe, you should start
1. at one end of the lining, then
alternately work towards the other
2. by first riveting both ends, then
work alternately toward the center
of the lining
3. at one end and work down one
side then the other
4. in the center and work alternately
toward each end of the lining
6-48. What action should be taken when you
find any pitting, scoring, or scratching
in the bore of a wheel cylinder?
Replace the wheel cylinder
Hone the cylinder bore
Install a cylinder sleeve
Sand the cylinder bore with emery
Install oversize rivets
Weld the holes closed and re-drill
Discard the brake shoe
Drill new holes in the shoe
6-52. Normally, what is the maximum
amount of surface material that can be
removed from a brake drum and still
provide adequate braking?
.006 inch
.060 inch
.003 inch
.030 inch
6-57. Which of the following defects is the
most likely cause of soft, spongy
action of the brake pedal in a
hydraulic brake system?
6-53. What tool should you use to measure
the diameter of a brake drum?
Brake drum caliper
Brake drum telescoping gauge
Brake drum micrometer
Brake drum circumference gauge
6-54. When replacing disc brake shoes, you
force the caliper pistons into the bores
of the caliper to
1. determine if the pistons are free to
move in the caliper
2. open the caliper wide enough for
the new thicker pads
3. inspect for hydraulic leaks around
the piston seal
4. open the caliper wide enough for
the removal of the rust ridge on
the disc
6-58. When removing air from the hydraulic
brake system, you should bleed one
brake at a time starting with the wheel
cylinder located
nearest to the master cylinder
farthest from the master cylinder
on the left front
on the right front
6-59. When you pressure bleed a hydraulic
brake system, the bleeder ball should
be charged with what amount of air
6-55. What tool should you use to check a
brake disc for runout?
1. Micrometer
2. Outside caliper
3. Thickness gauge
4. Dial indicator
1. 5 to 10 psi
2. 15 to 20 psi
3. 20 to 25 psi
4. 10 to 15 psi
6-56. When the disc brake runout is beyond
the manufacturer's specifications, you
should take what action?
Faulty pedal return spring
Sticking wheel cylinder
Air trapped in the brake lines
A clogged master cylinder
Resurface the disc
Tighten the wheel bearings
Replace the caliper
Discard the disc
6-60. The function of the governor in an air
brake system is to maintain the air
pressure in the reservoir.
1. True
2. False
6-65. In a type D governor, at what pressure
range will the spring loading within
the governor overcome the developed
force of the air pressure under the
1. 80-85 psi
2. 90-95 psi
3. 100-105 psi
4. 110-115 psi
6-61. The governor maintains the proper
pressure required for safe operation by
controlling what component?
6-66. To increase the pressure setting of the
type D governor, you must perform
which of the following tasks?
1. The compressor unloader
2. The pilot valves
3. The pressure differential valve
4. The spring tube
1. Turn the adjusting nut counterclockwise
2. Turn the adjusting screw
3. Add shims to the inlet valve guide
4. Remove shims from the inlet valve
6-62. What gauge should you use to adjust
the type O-1 governor accurately?
Thickness gauge
Vacuum gauge
Depth gauge
Air pressure gauge
6-67. What is the function of the unloader
6-63. To decrease the pressure range in the
type O-1 governor, you may
1. To cool, store, and remove
moisture from the air
2. To protect the brake system
against excessive pressure
3. To stop and start compression in
the compressor
4. To control the air pressure that is
delivered to the brake chambers
1. add shims beneath the upper valve
2. remove shims from the upper
valve guide
3. turn the adjusting screw clockwise
4. turn the adjusting screw counterclockwise
6-64. At what pressure range, within the
type D governor, will the air pressure
allow the exhaust stem to close the
exhaust valve and to open the inlet
6-68. What component is used to cool, store,
and remove moisture from the air and
give a smooth flow of air to the brake
1. 80-90 psi
2. 90-100 psi
3. 100-110 psi
4. 110-120 psi
Unloader mechanism
Air pressure diaphragm
Pressure differential mechanism
6-73. After cleaning a treadle valve, you
should apply which of the following
lubricants to the internal parts of the
valve during reassembly?
6-69. What is the function of the safety
valve located on top of the first
1. To prevent moisture buildup in the
2. To protect the system against
excessive back pressure
3. To prevent air pressure from
reaching it’s maximum setting
4. To protect the system against
excessive air pressure
6-70. What component is designed to
convert the energy of compressed air
into mechanical force and motion?
Brake camshaft
Adjusting screw
Pushrod adjuster
Slack adjuster
Quick release
Trailer control
6-75. In a quick-release valve, as air
pressure above the diaphragm is
released, the air pressure below raises
the diaphragm off the exhaust port.
This action allows air in the brake
chamber to exhaust at the quickrelease valve.
1. True
2. False
6-72. What valve controls the air pressure
delivered to the brake chambers?
Engine oil
Chassis lube
Bearing grease
6-74. What valve is designed to exhaust
brake chamber air pressure and speed
up brake release of the air brake
6-71. What component provides a quick and
easy way to adjust air brakes to
compensate for wear?
Tractor protection
Quick release
Textbook Assignment: "Automotive Chassis and Body" (continued), chapter 8, pages 8-29
through 8-58.
What are the two basic functions of a
1. To support the weight of the
vehicle and provide adequate
2. To act as a cushion between the
road and the wheel and provide
adequate traction on any road
3. To prevent road shock from being
felt in the passenger compartment
and provide adequate traction.
4. To provide a means to control the
vehicle and to provide traction
1. The strength of the plies decrease
2. It provides a rough ride on smooth
3. The body of the tire is too rigid
4. It increases rolling resistance
Body plies
Tire bead
Tire beads
What type of tire has the plies running
at an angle from bead to bead?
Stabilizer cord
Stabilizer ply
Stabilizer belt
Stabilizer liner
A radial tire has plies running
1. straight across from bead to bead
with stabilizer belts directly
beneath the tread
2. from the sidewall at different
angles than the stabilizer belts
3. at an angle from bead to bead with
a stabilizer belts between each ply
4. straight across from the sidewall
with the stabilizer belts at a
different angle
What part of the tire is used to stiffen
the tread and strengthen the plies?
In a belted bias tire, what part is added
to increase tread stiffness?
What part of the tire has two steel
rings encased in rubber that holds the
sidewalls against the rim?
What is a major disadvantage of a
bias-ply tire?
What is the major disadvantage of a
radial tire?
1. It produces a softer ride at high
2. It produces a harder ride at high
3. It produces a harder ride at low
4. It produces a softer ride at low
Bias ply
Belted bias
Belted radial
8-9. Which of the following types of
information will you NOT locate on
the sidewall of a tire?
1. Load range and speed index
2. Load index and aspect ratio
3. Load range and the grade of the
4. Load index and proper inflation
8-15. For every 10 degrees Fahrenheit
change in ambient temperature, the
inflation pressure of a tire will change
Temperature rating
Aspect ratio
Load index
Speed rating
8-12. A tire has a P-metric tire size-rating
system. What does the letter "P"
Ply rating
section width
aspect ratio
load index
treadwear rating
8-14. What factors determine how much of
a load a tire can safely carry?
Tire size
Treadwear rating
Speed rating
Load index
8-11. A tire has an alphanumeric tire size
rating. What does the first number
Tire size
Mileage range
Treadwear rating
Inflation pressure
8-10. What information is presented in a
letter-number sequence on the
sidewall of a tire?
8-13. The comparison of the height of the
tire to the width of the tire is known as
1 psi
2 psi
3 psi
4 psi
8-16. What government agency requires
each tire manufacturer to grade its
tires under the Uniform Tire Quality
Grade (UTQG) labeling system?
1. National Transportation Safety
Board (NTSB)
2. Department of Highway and
Motor Vehicle Safety (HMVS)
3. Department of Transportation
4. Federal Highway Administration
8-20.Uniform Tire Quality Grade (UTQG)
ratings are not required for light truck
and commercial tires.
8-17. When you are comparing tires of the
same brand, what rating factor
provides the most accurate
1. True
2. False
Load rating
Temperature resistance rating
Traction rating
Treadwear rating
8-21. For easy identification, a butyl type
synthetic rubber tube has a stripe on it
that is what color?
8-18. In 1997, what traction rating was
introduced to indicate a greater wet
braking traction?
8-22. Of the following wheel designs, which
one is NOT a common design?
8-19. What temperature resistance grade is
the minimum level of performance for
all passenger vehicle tires?
Drop center
Semidrop center
8-23. What is the most common type of
wheel used on passenger vehicles?
Semidrop center
Drop center
8-24. A lug nut has the letter "M" stamped
into it, what does the "M" indicate?
Military thread
Multipurpose thread
Metric thread
Machine thread
8-25. In a nondriving wheel bearing and hub
assembly, what component extends
outward from the steering knuckle?
1. 20 psi
2. 15 psi
3. 10 psi
4. 5 psi
Outer drive axle
Bearing support
8-30. What are the two methods used to
patch an inner tube?
8-26. In a driving wheel bearing and hub
assembly, what component extends
through the wheel bearings and is
splined to the hub?
1. Cold-patch and chemical
2. Chemical-vulcanizing and heat
3. Hot-patch and chemical fusion
4. Cold-patch and hot-patch
Outer drive axle
Steering knuckle
Axle locknut
8-31. How often should tires be rotated?
8-27. Using a plug to attempt a tire repair
without dismounting the tire is
effective only what percentage of the
8-28. You should NOT attempt to repair a
tubeless tire that has a puncture that is
larger than
8-29. When removing an object from a tire,
you should reduce the air pressure to
at least
Once a month
Once a quarter
3,000 to 5,000 miles
8-32. Refer to figure 8-41 in the textbook.
what pattern is used when you are
rotating the tire on a vehicle that has
directional tires?
8-33. What type of tire imbalance will cause
the tire to vibrate up and down and
from side to side?
1. Tears
2. Punctures
3. C u t s
4. Splits
8-34. A wheel and tire assembly that has its
weight evenly distributed around the
axis of rotation is known to be in
8-37. Of the following types of tire damage,
which one is NOT considered impact
8-38. What is the most probable cause for
the center of a tire to wear faster than
the outer area?
static balance
radius balance
dynamic balance
spiral balance
8-35. If a large amount of weight is required
to static balance a wheel and tire
assembly, you should distribute the
weight in what manner?
1. Add half to the outside and half to
the inside
2. Add a quarter to the outside and
the rest to the inside
3. Add a quarter to the inside and the
rest to the outside
4. Add exactly where needed
8-39. What type of tread wear pattern is
caused by excessive camber?
One-side wear
Cornering wear
8-40. The vehicle you are driving has a
tendency to pull to the left. What is
the most probable cause of this
8-36. What is the most common type of
balancer used by the NCF?
Erratic scrubbing against the road
Over inflation
Excessive camber
Faulty ball joints
Spin balancer
On-the-vehicle balancer
Bubble balancer
Computerized balancer
Right tire ply separation
Under inflated left tire
Over inflated left tire
Imbalanced right tire
8-41. Maximum tire life depends mainly on
what factor?
8-45. As a general rule, vehicles with power
steering should have positive caster.
1. True
2. False
Regular rotation
Proper inflation
Operating conditions
8-46. Negative caster tilts the top of the
steering knuckle towards the
8-42. Correct wheel alignment is essential to
vehicle safety, handling, extending tire
life, and achieving maximum fuel
1. True
2. False
8-47. Of the following functions, which one
is NOT a function of camber?
8-43. What type of alignment ensures that
the wheels are "squared" to each
1. To aid steering by placing vehicle
weight on the inner end of the
2. To prevent tire wear on the inner
or outer tread
3. To load the larger inner wheel
4. To offset road crown pull
Front-end alignment
Frame alignment
Thrust angle alignment
Steering alignment
8-44. Of the following steering angles,
which one is NOT a tire wear angle?
Toe-out on turns
rear of the vehicle
front of the vehicle
right side of the vehicle
left side of the vehicle
8-48. When performing a wheel alignment,
you make a slight positive camber
setting. As a general rule, the setting
you make should be between
1/16 to 1/8
1/8 to 1/4
1/4 to 1/2
1/2 to 3/4
8-49. What wheel alignment angle is
determined by the difference in the
distance between the front and the rear
of the left and right wheels?
8-52. Steering axis inclination is NOT
adjustable because it is designed into
the suspension of the vehicle.
1. True
2. False
Steering axis inclination
Toe-out on turns
8-53. When performing a wheel alignment,
you should take what action to correct
the steering axis inclination angle?
8-50. Of the following alignment angles,
which one is considered to be the most
1. Adjust the suspension system
2. Replace damaged or worn
suspension components
3. Change the angle of the steering
control arm
4. Adjust the steering mechanism
8-51. When you are performing a wheel
alignment on a front-wheel drive
vehicle, what amount of toe-out is
8-54. You are performing a wheel alignment
and discover that the toe-out on turns
angle is incorrect. This condition is a
good indication that what problem
1. 1/16 inch
2. 1/8 inch
3. 1/4 inch
4 .1/2 inch
Wrong size tires
Worn ball joints
Misadjusted steering mechanism
Damaged steering components
8-55. What steering geometry angle
maintains a right angle between the
center line of the vehicle and both
front and rear axles?
Toe-out on turns
Steering axis inclination
8-60. You should use what tools to remove
surface defects on dolly blocks?
8-56. Which of the following conditions
will cause improper tracking?
Bent rear axle mount
Bent control arm
Broken shock mount
Loose sway bar
8-57. When checking toe-out on turns using
a turning radius gauge, you must turn
one of the front wheels until the gauge
1. 10
2. 15
3. 20
4. 25
8-61. When repairing a damaged vehicle,
you force the damaged area to return
to a near original shape by using a
8-58.When performing a front-end
alignment, you must align both caster
and camber together because one
affects the other.
1. work from the point of impact to
the center
2. work the ridge farthest from the
point of impact
3. work from the center to the point
of impact
4. work the ridge closest to the point
of impact
8-59. You are making a toe adjustment to
the tires of a vehicle. To compare the
distance between the front and rear of
the tires, you should use what tool?
Tape measure
Tram gauge
Philadelphia rod
body straightener
portable hydraulic jack
8-62. When using a hammer and dolly to
remove a body dent, you should
1. True
2. False
Grinder and crocus clothe
Rasp and course grit sandpaper
File and tine grit sandpaper
Sanding block and medium grit
8-63. Body hammers with crowned faces
should only be used to make repairs to
what type of surfaces?
8-68. What action should be taken to
prevent deterioration of exposed sheet
metal due to an accident?
8-64. What is the most important factor to
be considered before a heavily
damaged body panel is repaired?
1. Overall time and labor cost
2. Damaged area of the body panel
3. Direction of force that caused the
4. Amount of materials on hand
8-65. When welding a new piece of sheet
metal on a damaged vehicle, you can
ensure a reduction in distortion by
1. using a small torch tip
2. working from the bottom up
3. allowing the metal to cool between
4. staggering the welds
8-66. You are prepping a vehicle that is in
good condition for painting. To
remove any scratches, you should use
abrasive paper that is what size?
1. 50 grit
2. 150 grit
3. 280 grit
4. 320 grit
8-69. When you are refinishing a vehicle,
what type of problem will highviscosity paint create?
Improper flow-out
Orange peel
Poor adherence to the surface
8-70. What distance should the spray gun be
held from the surface to be painted to
obtain optimum coverage?
6 inches
8 inches
10 inches
12 inches
8-71. What is the recommended thickness
for a layer of epoxy filler?
8-67.What is the preferred method for
removing paint from the entire surface
of a vehicle?
Refinish the entire vehicle
Refinish the damaged side
Refinish the damaged panel
Spot paint only
Chemical removal
Acid bath
Heat guns
1/16 inch
1/8 inch
1/4 inch
3/8 inch
8-72. What publication contains information
on the placement of registration
numbers on a piece of CESE?
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