030—Brakes - Central States Bus Sales, Inc.

030—Brakes - Central States Bus Sales, Inc.
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TC Series Brakes
TC Series Brakes
Table of Contents
Blue Bird Corporation assumes sole responsibility for
ensuring that the information provided herein is
accurate to the best of its knowledge at the time of
printing. In keeping with its policy of continual
product improvement, Blue Bird reserves the right to
change product information without notice and
without incurring obligation. Some information
contained in this section has been re-published from
the following publications:
Eaton® Axle and Brake Service Manual, EB and ES
Models, Publication number BRSM-0033: April 1997.
© Eaton Corporation, 1997. All rights reserved.
Webb® Wheel Products, Inc. Installation, Service and
Safety Instructions Manual, Publication number IM298 (Supercedes IM-494).
Webb® Wheel Products, Inc. Torque Specifications,
and Publication number SD-012: Revised April 1997.
Multiple loose-leaf instruction pages provided by
Crewson Brunner®, Inc. on installing and maintaining
Automatic Slack Adjusters, no publication number.
Holset® Air Compressor Field Service Manual, no
publication numbers or dates.
Allied Signal Bendix® Brakes TU-FLO 550
Compressor Service Data SD-01-333, © AlliedSignal
4/1996, Publication number BW1639.
Allied Signal Bendix® Brakes WS-20 Antilock Wheel
Speed Sensor Service Data SD-13-4754, © Allied
Signal TBS Co. 11/1996, Publication numbers
BW1662.
Allied Signal Bendix® Brakes M-21 and M-22
Antilock Modulator Assembly Service Data SD-134793, © AlliedSignal TBS Co. 11/1996, Publication
numbers BW1664.
Allied Signal Bendix® Brakes EC-17 Antilock
Traction Controller Service Data SD-13-4788, ©
AlliedSignal TBS Co. 2/1998, Publication number
BW1910.
Allied Signal Bendix® Brakes AD-9 Air Dryer
Service Data SD-08-2412, © AlliedSignal TBS Co.
5/1996, Publication numbers BW1627.
Allied Signal Bendix® Brakes Push-Pull Type Control
Valves Service Data SD-03-3611, © AlliedSignal TBS
Co. 4/1996, Publication numbers BW1578.
MGM Brakes Model TR – Tamper Resistant Spring
Brakes, © MGM 12/92, Form Number 5026-MGM.
Allied Signal Bendix® Brakes E-6 and E-10 Dual
Brake Valves Service Data SD-03-817, © AlliedSignal
6/1996, Publication numbers BW1427.
Midland™ EL1300 and EL1600 Air Compressor
Service Procedures, Publication Number L30002, Rev.
9-93, © Midland-Grau Heavy Duty Systems.
Allied Signal Bendix® Brakes R-12 and R-14 Relay
Valves Service Data SD-03-1064, © AlliedSignal
6/1996, Publication number BW1431.
Allied Signal Bendix® Brakes Air Brake Handbook,
Components, Maintenance and Troubleshooting, ©
AlliedSignal TBS Co. 9/1996, Publication numbers
BW5057.
030-1
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TC Series Brakes
Table of Contents ............................................2
Safety.....................................................................5
Warnings and Cautions .......................................5
Description of Operation .....................................6
Safety Valve ..........................................................8
Governor...............................................................8
Air Dryers .............................................................8
Low Pressure Indicator .......................................9
Dual Circuit Brake Valve ....................................9
Automatic Slack Adjuster ...................................9
Service Quick Release Valve ...............................9
Brake Chamber ....................................................10
Double Check Valves ...........................................11
Stop Lamp Switches.............................................11
Parking Quick Release Valve..............................11
Relay Valve ...........................................................11
Spring Brake Valve..............................................11
Push Pull Control Valves.....................................12
Pressure Protection Valve ...................................12
Air Compressor ....................................................12
Air Compressor-Bendix.......................................12
Antilock Systems ..................................................14
Wheel Speed Sensor .............................................14
Antilock Modulator Assembly ............................15
Antilock-Traction Controller..............................15
Dual Brake Valve Operation...............................16
Air Dryer Operation ............................................17
Relay Valve Operation.........................................21
Air Compressor ....................................................21
Brake System Troubleshooting...........................22
Compressor Troubleshooting..............................25
Individual Circuit Diagrams ...............................31
Preventative Maintenance...................................49
Air Dryer...............................................................49
Relay Valve ...........................................................50
Dual Circuit Brake Valve ....................................50
Automatic Slack Adjuster ...................................51
Brake Chamber ....................................................51
Push Pull Control Valves.....................................51
Air Compressor ....................................................51
Antilock System Preventative
Maintenance ....................................................52
Antilock Modulator Assembly ............................52
Service Checks......................................................52
Air Dryer...............................................................52
Relay Valve ...........................................................54
Dual Circuit Brake Valve ....................................54
Automatic Slack Adjuster ...................................55
Brake Chamber ....................................................55
Push Pull Control Valves.....................................55
Air Compressor ....................................................55
Air Leak Tests ......................................................55
Antilock Systems Service Checks .......................56
Antilock Modulator Assembly............................ 56
Operation Testing................................................ 56
Diagnosing and Loading a System EC-17 ......... 58
Diagnosing the Communication
Interface .......................................................... 58
Optional Diagnostic LED and Reset .................. 59
EC-17 Controller Configuration ........................ 61
EC-17 Self Configuration Process...................... 62
Troubleshooting................................................... 63
Troubleshooting Help.......................................... 64
Diagnostic Display ............................................... 64
Initial Startup Procedure.................................... 65
Section I - Antilock Dash Lamp Testing............ 66
Section II - Inspection for Illuminated
LED.................................................................. 67
Section III - Inspection for Illuminated
LED.................................................................. 68
Section IV - Inspection for Illuminated
LED.................................................................. 69
Section V - Testing for Power to
the EC-17......................................................... 70
Section VI A - Testing the Modulator................ 71
Section VI B - Testing the Modulator................ 72
Section VII A - Testing the Modulator .............. 72
Section VII B - Testing the
Wheel Speed Sensor ....................................... 73
Section VIII - Testing for False Indication
Caused by Dash Light Relay ........................ 75
Section IX - Testing for False Indication
Caused by Wheel Speed Components .......... 75
Section X - Testing Traction Control
Dash Lamp...................................................... 77
Section XI - Testing Traction Control
Modulator ....................................................... 78
Section XII - Testing Engine Control
Module Wire Harness .................................... 79
Hydraulic Brakes................................................. 80
Routine Maintenance .......................................... 80
Theory of Operation............................................ 83
Hydro-Max General Description ....................... 83
Hydro-Max Power Brake System
Components .................................................... 83
Hydraulic Pump Operating Components.......... 83
Brakes ................................................................... 84
Electrical............................................................... 85
Operation of the Hydro-Max Booster
and Reserve Electric Motor Pump ............... 85
Operation of the Mini Master Cylinder ............ 87
Operation of the Flow Switch and
Warning Switch.............................................. 88
Operation of the Electric Monitor
Module............................................................. 88
Brake Warning System ....................................... 88
030-2
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TC Series Brakes
Parking Brake ...................................................... 89
Remove Hydro-Max Booster............................... 89
Replace Hydro-Max Booster............................... 89
Refilling and Bleeding Hydro-Max .................... 89
Check Brake System ............................................ 90
Hydraulic Brake Components ............................ 90
Electrical Components......................................... 90
Park Brake Components ..................................... 91
Mechanical Components ..................................... 92
Troubleshoot and Diagnostics HydroMax Power Brake System .............................. 93
Repair the Hydro-Max Brake Booster............... 97
Hydro-Max Brake Booster Disassembly............ 97
Threaded Contact Assembly ............................... 97
Snap Ring Contact Assembly.............................. 97
Cleaning ................................................................ 98
Inspection.............................................................. 98
Snap Ring Contact Assembly.............................. 100
List of Figures
Figure 1—Safety Valve.......................................... 8
Figure 2—Governor ............................................... 8
Figure 3—Air Dryer............................................... 8
Figure 4—Low Pressure Indicator ......................... 9
Figure 5—Dual Circuit Brake Valve
Automatic Slack Adjuster ................................. 9
Figure 6—Service Quick Release Valve................ 9
Figure 7—Brake Chamber ................................... 10
Figure 8—Double Check Valve........................... 11
Figure 9—Stop Lamp Switches ........................... 11
Figure 10—Parking Quick Release Valve ........... 11
Figure 11—Relay Valve ...................................... 11
Figure 12—Spring Brake Valve........................... 12
Figure 13—Push-Pull Control Valve ................... 12
Figure 14—Air Compressor Bendix .................... 12
Figure 15A and B—Air Compressure
Major Assemblies ........................................... 13
Figure 16—Name Plate........................................ 13
Figure 18—Wheel Speed Sensor ......................... 14
Figure 19—Wheel Speed Sensor Output ............. 15
Figure 20—Antilock Modulator Assembly.......... 15
Figure 21—Antilock Traction Controller ............ 15
Figure 22—Dual Brake Valve.............................. 16
Figure 23—Dual Brake Valve Cross
Section ............................................................ 17
Figure 25—Turbo Cutoff Feature ........................ 19
Figure 26—Relay Valve Ports ............................. 19
Figure 28—Operational Loaded (Intake)............. 20
Figure 29—Operational Loade
(Compression)................................................. 20
Figure 30—Operational Unloaded ....................... 20
Figure 31—Lubrication........................................ 21
Figure 32—Cooling ............................................. 21
Figure 33—ISD Hydraulic Brakes
ISB/TCFE ....................................................... 33
Figure 34—Ignition Voltage and Ground ............ 34
Figure 35—Traction Control Lamp Circuit ......... 35
Figure 36—Traction Enable Switch Circuit......... 35
Figure 37—Diagnostic T1586 Serial
Circuits With Cummins Engine ...................... 36
Figure 38—ABS Signal Circuit for
Cummins Engine w/WT ................................. 37
Figure 39—ABS Signal Circuit
w/AT/MT Transmission.................................. 37
Figure 40—Ground Circuit .................................. 38
Figure 41—Chassis Option Solenoid
Circuit ............................................................. 39
Figure 42—ABS Signal Circuit for Engine ISB .. 40
Figure 43—ABS Signal Circuit for Engine ISB . 40
Figure 44—Ignition Switch Circuit...................... 41
Figure 45—Vehicle Speed in Circuits
w/AT/MT Transmission.................................. 42
030-3
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TC Series Brakes
Figure 46—Vehicle Speed in Circuits
w/WT Transmission ....................................... 43
Figure 47—Vehicle Speed in Circuits
w/AT/MT Transmission ................................. 43
Figure 48—Serial Comm-Interface
Ciruits w/Throttle Diagnostic and
Master Chassis................................................ 44
Figure 49—Transmission Retarder
Circuits (1 of 2) .............................................. 45
Figure 50—Transmission Retarder
Circuits (2 of 2) .............................................. 46
Figure 51—Relay Circuit w/ISB/ISC and
AT/MT Transmission ..................................... 47
Figure 52—ABS Module Interface...................... 48
Figure 53—Air Dryer Connections ..................... 53
Figure 54—Modulator Test ................................. 57
Figure 55—DCI Tool .......................................... 58
Figure 56—Diagnostic Connector ....................... 58
Figure 57—DCI Tool with PC............................. 58
Figure 58—Diagnostic Display Quick
Reference........................................................ 64
Figure 59—EC-17 Configuration ........................ 65
Figure 60—Antilock Dash Lamp Testing............ 66
Figure 61—Inspection for Illuminated
LEDs............................................................... 67
Figure 62—Inspection for Illuminated
LEDs............................................................... 68
Figure 63—Inspection for Illuminated
LEDs ............................................................... 69
Figure 64—Power to EC-17................................. 70
Figure 65—Testing Modulator............................. 71
Figure 66—Testing the Wheel Speed
Sensor.............................................................. 73
Figure 67—Testing for False Indication
Caused by Dash Light Relay........................... 75
Figure 68—Testing for False Indication
Caused by Wheel Speed Components ............ 76
Figure 69—Testing Traction Control
Dash Lamp ...................................................... 77
Figure 70—Testing Traction Control Modulator. 78
Figure 71—Testing Engine Control
Modulator Wire Harness................................. 79
Figure 72—Hydraulic System
Configuration .................................................. 84
Figure 73—Hydro-Max Connection .................... 84
Figure 74—Booster Operation ............................. 85
Figure 75—Performance Curve ........................... 86
Figure 76—Master Cylinder Operation ............... 87
Figure 77—Brake Booster .................................. 91
Figure 78—Park Brake Configuration ................. 92
Figure 79—Power Piston Installation
Tool ................................................................. 97
030-4
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TC Series Brakes
Safety
Safety is always a primary concern. Remember to
bleed system pressure, chock wheels and disable
starting system prior to performing maintenance
procedures to the vehicle.
When working with fluid under pressure, make sure
you wear a face shield or protective goggles and
clothing that covers exposed parts of the body.
Pressurized fluid that escapes can penetrate exposed
areas of the body. Be sure to relieve pressure before
disconnecting pressurized lines.
Use only genuine Blue Bird replacement
components. Only components, devices and
mounting and attaching hardware specifically
designed for use in hydraulic brake systems should
be used. Replacement hardware, tubing hose,
fittings, etc. should be the same size, type and
strength as the original equipment.
Devices with stripped threads or damaged parts
should be replaced. Repairs requiring machining
of components should not be attempted.
Warnings and Cautions
You must adhere to the WARNINGS and Cautions to
work safely.
Equipment damage can result if the caution
instructions are not followed.
DEATH OR SERIOUS PERSONAL
INJURY CAN RESULT IF THE WARNING
INFORMATION INSTRUCTIONS ARE
NOT FOLLOWED.
Always block vehicle wheels. Stop engine when
working under vehicle. Keep hands away from
chambers as they may activate when system
pressure drops.
Never connect or disconnect a hose or line
containing pressure; it may whip. Never remove
component, pipe or plug unless all system pressure
has been depleted.
Never exceed recommended pressure and always
wear safety glasses.
Never attempt to disassemble a component until
you have read and understand recommended
procedures. Some components contain powerful
springs and injury can result if component is not
properly disassembled.
Hydraulic Brake Systems are power assisted.
Braking capacity is reduced without engine assist.
Do not move the bus with dead engine.
DO NOT DRIVE THE BUS WHEN THE
ELECTRICAL BACKUP PUMP DOES
NOT OPERATE. IN THE CASE OF A
LOSS OF POWER ASSIST, THERE WILL
BE REDUCED BRAKE CAPACITY
WITHOUT THE ELECTRICAL BACKUP.
When one circuit of the dual system fails, the
following conditions will exist:
Bus stopping distance will increase. (Drive the bus
only with extreme caution. Service immediately).
The brake pedal will be softer to push.
030-5
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TC Series Brakes
this friction. As the friction increases, so does heat, so
rotating brake components are designed with cooling
fins to dissipate heat rapidly.
The brake pedal will travel further, even as far as
the floorboard. These conditions exist because only
one axle will be stopping the bus.
Put only brake fluid in the brake fluid reservoir
and power steering fluid in the power steering
system. Failure to use the proper fluids could
result in loss of braking or steering.
IMPROPER ADJUSTMENT OF THE
PARKING BRAKE CAN SIGNIFICANTLY
REDUCE THE HOLDING ABILITY OF
THE PARKING BRAKE SYSTEM. THIS
COULD RESULT IN THE VEHICLE
MOVING WHEN UNATTENDED.
The parking brake is designed to hold on a 20 %
grade, clean , dry and smooth road surface.
Parking on wet, ice or snow covered grades is not
recommended. Chocking of the wheel(s) is
recommended when parking on any grade.
The air brake system utilizes modulated air under
pressure to overcome spring force, which, in the
absence of air pressure, forces the rotating and
stationary members together. Compressed air is
developed by an engine driven, twin piston air pump
(G).
As the air is compressed and cools, moisture
condenses and must be removed from the system.
Moisture is removed to prevent system contamination
and components from rusting and binding. The
compressed, moisture laden air is passed through an
air dryer that removes moisture before being utilized
in the system. The compressed dry air is temporally
stored in the wet tank (P) and can be diverted for use
by additional accessories. Several valves and sensors
are added to the wet tank to monitor system pressure
and warn the operator in case of a system malfunction.
Air pressure is then routed through two single check
valves and into the front and rear storage tanks (A, and
Y). The storage tanks store air pressure for their
respective front or rear circuits as needed. These air
tanks are required to store air pressure for two reasons:
Successive stops would deplete the air supply directly
from the compressor if a storage tank were not used.
Using two storage tanks provides a margin of safety in
the event one of the two-brake circuits malfunction.
The double check valve (T) provides spring brake
valve (W) and spring break (Q) with the highest
pressure from either front or rear storage tank.
EXTREME CAUTION SHOULD BE
EXERCISED WHEN THE DRIVE SHAFT
IS REMOVED ON A UNIT EQUIPPED
WITH HYDRAULIC BRAKES. THE
PARKING BRAKE BECOMES
INOPERATIVE WHEN THE DRIVE
SHAFT IS DISCONNECTED. DO NOT
LEAVE THE BUS UNATTENDED UNTIL
APPROPRIATE MEASURES HAVE BEEN
TAKEN TO PREVENT VEHICLE
MOVEMENT.
Description of Operation
The basic principle in automotive brake systems is to
develop friction between rotating and stationary
components to stop a vehicle. The friction developed
between the brake pad and rotor or brake shoe and
brake drum are the primary elements used to develop
The brake valve (B) is controlled by the operator and
modulates the air pressure to both the front and rear
brake circuits. Provisions for monitoring brake
pressure (U) and mounting location for brake light
switch (V) is facilitated at the brake valve.
Modulated air from the brake valve is directed to the
quick release valve (F) and the antilock modulator
assembly. The brake chambers (Q) are spring applied
pressure released, sealed, dual chambers.
The modulated air pressure enters the chamber and
works against spring pressure to combine spring force
and modulated air pressure to a longitudinal force.
The automatic slack adjusters (D) convert the
longitudinal force to a rotational force. A cam action
is then used to apply friction between rotating and
stationary components to slow and stop the vehicle.
030-6
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TC Series Brakes
Air Brake System Diagram with ABS (Bluebird Specific)
Legend
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K.
Primary or Rear Service Tank
E-6 (Brake Valve)
Front Air Chamber
Slack Adjusters (4 used)
M-22 (ABS Antilock Modulator Assembly) (4
used)
QR-1C (Quick Release Valve) (3 used)
Air Compressor
Check Valve
Air Dryer
Governor
Pressure Protection Valve
L.
M.
N.
O.
P.
Q.
R.
S.
T.
U.
V.
W.
X.
Y.
Drain Valve (3 used)
Schrader Valve
Low Pressure Indicator Switch
Safety Valve
Wet Tank
Rear Brake Chamber (2 used)
Quick Release Valve
R-12 Relay Valve with Double Check
Double Check Valve
Pressure Gauge (2 used)
Brake Light Switch (2 used)
PP-1 (Push Pull Control Valve)
SR-1 (Spring Brake Valve)
Secondary or Front Tank
030-7
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TC Series Brakes
Description
Safety Valve
The safety valve (Figure 1) protects the air brake
system against excessive air pressure buildup. It must
be installed in the same reservoir that the compressor
discharge line is connected to. Safety valves are
available in both adjustable and non-adjustable styles,
in various pressure settings, and with either 1/4" or
3/8" NPT.
Figure 2—Governor
Air Dryers
The air dryer (Figure 3) is a desiccant type in-line
filtration system that removes both liquid and water
vapor from the compressor discharge air before it
reaches the air brake reservoirs. This results in only
clean, dry air being supplied to the air brake system,
aiding in the prevention of airline freeze ups.
Figure 1—Safety Valve
Governor
The governor (Figure 2) operates in conjunction with
the compressor unloading mechanism and maintains
reservoir air pressure between a predetermined
maximum and minimum pressure. The governor is an
adjustable piston-type valve available in various
pressure settings. A non-adjustable pressure range
between specified cut-in and cutout pressures is
designed into the governor.
Provisions are made for direct mounting to the
compressor, or for remote mounting, if desired. The
governor is available in weatherproof and high
temperature versions for special installations.
The air dryer uses a replaceable desiccant material,
that has the unique ability to strip water vapor from
moisture laden air.
The desiccant material is regenerative in that its
adsorptive properties are renewed each time the
compressor is unloaded.
The air dryer end cover is equipped with an automatic
drain valve, controlled by the air system governor, and
is equipped with an integral heating element, and is
available for either 12 or 24-volt systems.
The air dryer is equipped with an integral storage of
dry air for the purge cycle.
Figure 3—Air Dryer
030-8
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Low Pressure Indicator
Low pressure indicators (Figure 4) are pressure
operated electro-pneumatic switches. These switches
are designed to complete an electrical circuit and
activate a warning light and buzzer for the driver in the
event air pressure in the service brake system is below
a safe minimum for normal operation. The lowpressure indicator is available in various pressure
settings, is not adjustable, and is generally used in
conjunction with a dash mounted warning lamp or
warning buzzer, or both.
Figure 5—Dual Circuit Brake Valve
Figure 4—Low Pressure Indicator
Dual Circuit Brake Valve
Dual circuit brake valves (Figure 5) use two separate
supply and delivery circuits for service and secondary
braking. The first circuit is mechanically operated
through the action of the treadle/pedal and plunger.
The second circuit normally operates similar to a relay
valve, with control air delivered from the first, or
primary circuit. In the emergency mode (failure of the
primary supply), the secondary inlet valve is
mechanically opened by a push through mechanical
force (from the driver’s foot via the treadle/pedal,
plunger and primary piston). The brake valve provides
the driver with graduated control for applying and
releasing the vehicle brakes. A rubber spring provides
the driver with the correct feel.
Automatic Slack Adjuster
Automatic slack adjusters function the same as manual
adjusters, except that the automatic slack adjusters
compensate for lining wear. The entire slack adjuster
operates as a unit (rotating as a lever with the brake
camshaft) as the brakes are applied or released.
Service Quick Release Valve
The function of the quick release valve (Figure 6) is to
speed up the exhaust of air from the air chambers. It is
mounted close to the chambers it serves. In its
standard configuration, the valve is designed to deliver
within one psi of control pressure to the controlled
device; however, for special applications the valve is
available with greater differential pressure designed
into the valve. The quick release valve has a die cast
body and diaphragm but does not employ a spring or
spring seat.
Figure 6—Service Quick Release Valve
030-9
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TC Series Brakes
Brake Chamber
The brake chamber (Figure 7) is a sealed nonrepairable unit designed to receive modulated air
pressure to apply the service brakes. Both sides of the
diaphragm are connected via porting to allow internal
air from the chamber being compressed to enter the
chamber expanding.
5. Power Spring
1. End Cap
10. Stroke Alert Indicator
2. Release Tool
11. Center Hole Shield
6. Push Rod
7. Piston and Guide
8. Service Piston Seal
9. Push Rod Seal
3. Steel Head
4. Sealed Spring Chamber
Figure 7—Brake Chamber
030-10
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TC Series Brakes
Double Check Valves
A double check valve (Figure 8) is used in the air
system when a single function or component must
be controlled by either of two sources of pressure.
The double check valve will always transmit the
higher of the two pressure sources to the outlet port.
Double check valves are available in both disc and
shuttle types and in various configurations for
various applications. It is recommended that double
check valves be mounted so that the shuttle operates
horizontally.
The double check valve prevents a service and
emergency brake application from occurring
simultaneously.
Figure 10—Parking Quick Release Valve
Figure 8—Double Check Valve
Stop Lamp Switches
The stop lamp switches (Figure 9) are pressure
sensitive electro-pneumatic switches installed in the
service application system. They operate the vehicle
stop lamps, completing an electrical circuit and
lighting the stop lamps each time a brake application
is made.
Figure 9—Stop Lamp Switches
Parking Quick Release Valve
The parking quick release valve (Figure 10) is a dual
function valve. The valve's primary function is to
serve the emergency side of a spring brake actuator
as a quick release valve. In addition, it functions as
an anti-compound device.
Relay Valve
Relay valves (Figure 11) are primarily used on long
wheel base vehicles to apply and release rear axle(s)
service or parking brakes. The valve is air operated,
graduating control valves of high capacity and fast
response. Upon signal pressure from the service
brake valve, hold or release air pressure from the
chambers they are connected to. The valve is
generally mounted close to the chambers they serve.
Relay valves are available in both remote and
reservoir mount designs and feature inlet/exhaust
valve cartridge replacement without line removal.
Figure 11—Relay Valve
Spring Brake Valve
The spring brake valve (Figure 12) is used in
FMVSS 121 dual circuit brake systems and serves
two functions. During normal operation, it limits
hold-off pressure to the spring brakes to 90 or 95 psi.
Should a loss of pressure occur in the rear service
brake service supply, it will provide a modulated
spring brake application proportional to service
braking pressure delivered to the front axle.
030-11
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Pressure protection valves allow air to be "shared"
between two reservoirs above the closing setting of
the valve. The sharing ceases when pressure drops
below the closing pressure off valve and the
reservoirs are then isolated from each other.
Figure 12—Spring Brake Valve
Push Pull Control Valves
Push-Pull control valves (Figure 13) are most often
mounted on the vehicle dashboard and are used for a
variety of control applications. The valves are
pressure sensitive, normally closed, on/off control
valves, that automatically return to the exhaust
(button out) position when supply pressure is below
the required minimum. They may be manually
operated to either position when pressure is above
the required minimum. Pressure settings and button
configuration and lettering may vary, depending on
application. The valves are commonly used to
control parking and emergency brakes.
Air Compressor
The function of the air compressor (Figure 14) is to
provide and maintain air under pressure to operate
devices in the air brake and/or auxiliary air systems.
The Tu-Flo 550 compressor is a two cylinder single
stage, reciprocating compressor with a rated
displacement of 13.2 cubic feet per minute at 1250
RPM.
The compressor assembly (Figure 15) consists of
two major subassemblies, the cylinder head and the
crankcase. The cylinder head is an iron casting that
houses the inlet, discharge, and unloader valves.
(See Figure 14) The cylinder head contains the air
inlet port and is designed with both top and side air
discharge ports.
Three water coolant ports provide a choice of
coolant line connections. Governor mounting
surfaces are provided at both the front and the rear of
the cylinder head.
The head is mounted on the crankcase and is secured
by six cap screws. The Tu-Flo 550 compressor is
designed so the cylinder head can be installed in one
of two positions 180° apart.
The crankcase houses the cylinder bores, pistons,
crankshaft and main bearings, and provides the
flange or base mounting surface.
Figure 13—Push-Pull Control Valve
Pressure Protection Valve
The pressure protection valve is normally a closed
pressure sensitive control valve. These valves can
be used in many different applications but are
typically used to protect or isolate one reservoir from
another, by closing automatically at a preset
pressure. The valve is also commonly used to delay
the filling of auxiliary reservoirs until a preset
pressure is achieved in the primary or braking
reservoirs.
Figure 14—Air Compressor Bendix
030-12
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TC Series Brakes
to operate the service brakes and other air powered
devices. The compressor operates or turns
continuously but has loaded and unloaded operating
modes. Operation is controlled by a pressureactivated governor and compressor unloading
assembly.
•
Figure 15A—Air Compressor Major Assemblies
Unloading
When the air system reaches “cut-out” pressure, the
governor applies an air signal to the air compressor
unloader assembly, causing the unloader valve to
close and stopping compressed air from flowing into
the system.
The unloader intake valve remains closed during the
unloaded mode. This, in conjunction with back
pressure on the exhaust valve, causes air inside the
compressor cylinder to become trapped.
As the compressor rotates, the energy developed
during the compression stroke is in turn released
during the down stroke. The compressor effectively
becomes an air spring.
This action nearly eliminates pumping losses during
non-demand operation. Additional benefits include
reduced oil passage, cooler exhaust air temperatures
and unlimited turbo boosting capability.
•
Figure 15B—Air Compressor Major Assemblies
Loading
As the air in the air system is depleted, system
pressure drops. At cut-in pressure, the governor
exhausts the air signal to the compressor unloader
assembly, allowing the compressor to again pump
compressed air into the system.
Due to the unique unloading technique of the Holset
compressor, a positive pressure must be maintained
at the exhaust port or excessive oiling will occur.
This can be checked at the air dryer inlet line.
Figure 16—Nameplate
A nameplate identifying the compressor piece
number and serial number is attached to the side of
the crankcase. Reference Figure 16 Nameplate.
The Holset air compressor is an engine driven,
piston-type compressor that supplies compressed air
Air Compressors Major Difference Unloading
In the unloading mode, the Holset unloads as the
governor applies a pressure to CLOSE the intake
valve, creating an air spring, effect while the Bendix
and Midland compressors OPEN the intake valve.
Due to the unique unloading technique of the Holset
compressor, a positive pressure must be maintained
at the exhaust port or excessive oiling will occur.
This is a result of a vacuum being created on the
down or intake stroke. Oil is then drawn past the
rings of the piston and into the compressed air
system.
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TC Series Brakes
Antilock Systems Component Description
Antilock Systems
Brake antilock systems and components are
designed to provide improved vehicle stability by
reducing wheel lock during aggressive braking.
The sensor is mounted in a fixed position, while the
exciter is installed on a rotating member so that its
teeth move, in close proximity, past the tip of the
sensor.
While all antilock systems provide this basic benefit,
there are several different systems and components
offered. Each is designed to meet the specific needs.
Each modulator controller assembly model
represents a different method of vehicle control and,
in most cases, a different level of system
performance.
All antilock controllers feature digital electronics
with self-test and diagnostic circuitry that
continuously monitors operation of the entire
antilock system, including wiring continuity.
The condition of specific antilock components is
provided to maintenance personnel by a series of
labeled, Light Emitting Diodes (LEDs) displayed
through a diagnostic window in the controller
housing.
No special tools or equipment is required to read or
interpret the diagnostics window. It should be noted
that the diagnostics display is separate from the
antilock condition lamp on the dash.
Feature conditions are stored in the controller
memory and are not cleared by loss of power to the
unit.
Wheel Speed Sensor
The wheel speed sensor (Figure 18) is an
electromagnetic device used to obtain vehicle speed
information for the antilock controller. The sensor is
mounted on the axle and works in conjunction with
an exciter, or tone wheel, mounted in the wheel hub.
When the wheel rotates, the exciter with its notched
surface rotates across the face of the sensor,
generating a simple AC signal.
The sensor is connected to the antilock controller
that analyzes the signal and issues antilock
commands accordingly. Specifically, the speed
sensor consists of a coil, pole piece and magnet.
The exciter is a steel ring, or gear-like device, that
has regularly spaced high and low spots called teeth.
Figure 18—Wheel Speed Sensor
Wheel Speed Sensor Operation
The sensor magnet and pole piece form a magnetic
field. As an exciter tooth passes by the sensor, the
magnetic field is altered, generating AC voltage in
the sensor coil. Each time an exciter tooth and its
adjacent space move past the tip of the sensor, an
AC voltage cycle is generated.
The number of AC cycles per revolution of the
vehicle's wheel depends on the number of teeth in
the exciter that is programmed into the antilock
controller. Using the programmed data, the
controller can calculate vehicle speed by analyzing
the frequency of AC cycles sent by the speed sensor.
(The frequency of AC cycles is directly proportional
to wheel speed.) AC voltage is also proportional to
speed, but voltage is not used to determine speed. It
is only an indication of AC signal strength.
The amount of AC voltage generated by a specific
speed sensor depends on the distance, or gap,
between the tip of the sensor and the surface of the
exciter. Voltage increases as the sensor gap
decreases.
The WS-20 is installed in a mounting block that is
affixed to the axle housing. See Figure 19. A spring
loaded retainer bushing provides a friction fit
between the mounting block bore and the WS-20.
The friction fit allows the WS-20 to slide back and
forth under force but to retain its position when force
is removed. This feature allows the WS-20 to self
adjust after it has been installed in the mounting
block and the wheel is installed.
When the WS-20 is inserted all the way into the
mounting block and the wheel is installed on the
axle, the hub exciter contacts the sensor, that pushes
the sensor back. In addition, normal bearing play
will bump the sensor away from the exciter. The
combination of these two actions will establish a
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TC Series Brakes
running clearance or air gap between the sensor and
exciter.
Figure 21—Antilock Traction Controller
Designed to minimize the potential of brake lock up
on all wheels during aggressive braking, the
controller based antilock system provides the vehicle
with a high degree of stability and steer-ability
during braking. In most cases, vehicle stopping
distance is also reduced.
Figure 19—Wheel Speed Sensor Output
Antilock Modulator Assembly
The antilock system modulators (Figure 20) are high
capacity, on/off air valves that incorporate a pair of
electrical solenoids for control. The solenoids
provide the electro-pneumatic interface or link
between the antilock controller and the air brake
system.
The antilock portion of the controller based system
minimizes wheel skid during hard or aggressive
braking. By controlling wheel skid at all wheels on
the vehicle, optimum steering control and stopping
distance is obtained.
Traction control, an optional feature in the full
vehicle wheel control antilock system, helps
improve vehicle traction during acceleration in
adverse road conditions.
Integrated with antilock logic, traction control
monitors wheel speed information from the sensors
during acceleration, as well as braking. The system
helps maintain vehicle stability on hazardous road
surfaces and improves drive-ability and safety.
The controller contains a self configuring or learning
feature that allows it to be configured by the user
when installed on the vehicle. Because of this
feature, all controllers contain all the features and
options available, and will activate the specific
features required for the vehicle it is installed on.
Figure 20—Antilock Modulator Assembly
Antilock-Traction Controller
The EC-17 is an electronic antilock controller. It is
the base component in a family of full vehicle wheel
control antilock systems. In addition to the antilock
function, the EC-17 can be assembled and
programmed to provide an optional traction control
feature. Figure 21 shows the basic controller.
The controller is installed on vehicles with only
antilock or vehicles using the traction control
feature. The procedure for activating the selfconfiguring feature is contained in the section
entitled Configuring the EC-17.
To provide full vehicle wheel control antilock, the
controller is used in combination with the following
components:
•
•
•
•
Four or six wheel speed sensors
Four air pressure modulator valves
One dash mounted antilock condition lamp
One service brake relay valve
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When programmed to provide traction control in
addition to antilock, the following components are
added:
- One traction solenoid (incorporated into the relay
valve)
Because of the small volume of air required to move
the relay piston, action of the secondary circuit of
the valve is almost simultaneous with the primary
circuit portion.
- One dash mounted traction condition lamp
- Serial connection to engine control module for
vehicles programmed for torque limiting feature
- Traction disable wiring and switch
Physical
The EC-17 electronics are contained in a nonmetallic housing and are environmentally protected
by an epoxy compound.
The design of the digital electronics is intended to
provide a high degree of protection from radio,
electromagnetic and environmental interference.
The patented optional light emitting diode (LED)
display and magnetically actuated reset switch is
incorporated in the housing for troubleshooting and
diagnostic purposes.
Two electrical connectors, located in the controller
housing opposite the diagnostic display (if so
equipped), connect the EC-17 to antilock and
traction system components: one 30 pin and one 18
pin connector.
Dual Brake Valve Operation
Normal Operation – Primary Circuit Portion
When the brake treadle (Figure 22 and Figure 23) is
depressed, the plunger exerts force on the spring
seat, graduating spring and primary piston. The
primary piston that contains the exhaust valve seat
closes the primary exhaust valve. As the exhaust
valve closes, the primary inlet valve is moved off its
seat, allowing primary air to flow out the primary
delivery port.
Normal Operation – Secondary Circuit
When the primary inlet valve is moved off its seat,
air is permitted to pass through the bleed passage
and enters the relay piston cavity. The air pressure
moves the relay piston that contains the exhaust seat
and closes the secondary exhaust valve. As the
secondary exhaust valve closes, the secondary inlet
valve is moved off its seat allowing the secondary
air to flow out the secondary delivery port.
Figure 22—Dual Brake Valve
Loss of Air in the Secondary Circuit
Should air be lost in the secondary circuit, the
primary circuit will continue to function as described
above under “Normal Operation—Primary Circuit
Portion.”
Loss of Air in the Primary Circuit
Should air be lost in the primary circuit, the function
will be as follows: As the brake treadle is depressed
and no air pressure is present in the primary circuit
supply and delivery ports, the primary piston will
mechanically move the relay piston.
This allows the piston to close the secondary exhaust
valve and open the Secondary inlet valve, and allows
air to flow out the secondary delivery port.
Balanced Primary Circuit
When the primary delivery pressure acting on the
piston equals the mechanical force of the brake pedal
application, the primary piston will move and the
primary inlet valve will close, stopping further flow
of air from the primary supply line through the
valve. The exhaust valve remains closed preventing
any escape of air through the exhaust port.
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Releasing Primary Circuit
With the brake treadle released, mechanical force is
removed from the spring seat, graduating spring and
primary piston. Air pressure and spring load moves
the primary piston, opening the primary exhaust
valve, allowing air pressure in the primary delivery
line to exhaust out the exhaust port.
Releasing Secondary Circuit
With the brake treadle released, air is exhausted
from the primary circuit side of the relay piston. Air
pressure and spring load move the relay piston,
opening the secondary exhaust valve allowing air
pressure in the secondary delivery line to exhaust out
the exhaust port.
Air Dryer Operation
Operation of the AD-9 Air Dryer
The AD-9 air dryer alternates between two
operational modes or cycles during operation: the
charge cycle and the purge cycle. The following
description of operation is separated into these
cycles of operation.
Figure 23—Dual Brake Valve Cross Section
Balanced Secondary Circuit
When the air pressure on the secondary side of the
relay piston approaches that being delivered on the
primary side of the relay piston, the relay piston
moves, closing the Secondary inlet valve and
stopping further flow of air from the supply line
through the valve.
The exhaust remains closed as the secondary
delivery pressure balances the primary delivery
pressure.
When applications in the graduating range are made,
a balanced position in the primary circuit pressure on
the delivery side of the primary piston equals the
effort exerted by the driver's foot on the treadle.
A balanced position in the secondary portion is
reached when air pressure on the secondary side of
the relay piston closely approaches the air pressure
on the primary side of the relay piston.
When the brake treadle is fully depressed, both the
primary and secondary inlet valves remain open and
full reservoir pressure is delivered to the actuators.
Charge Cycle
When the compressor is loaded compressing air
along with oil, oil vapor, water and water vapor
flows through the compressor discharge line to the
supply port of the air dryer end cover.
As air travels through the end cover assembly, its
direction of flow changes several times, reducing the
temperature, causing contaminants to condense and
drop to the bottom or sump of the air dryer end
cover.
After exiting the end cover, the air flows into the
desiccant cartridge. Once in the desiccant cartridge,
air first flows through an oil separator, that removes
water in liquid form as well as oil, oil vapor and
solid contaminants.
Air exits the oil separator and enters the desiccant
drying bed. Air flowing through the column of
desiccant becomes progressively dryer as water
vapor adheres to the desiccant material in a process
known as adsorption. The desiccant cartridge using
the adsorption process typically removes 95% of the
water vapor from the pressurized air.
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The majority of dry air exits the desiccant cartridge
through its integral single check valve to fill the
purge volume between the desiccant cartridge and
outer shell. Some air will also exit the desiccant
cartridge through the purge orifice adjacent to the
check valve.
Dry air flows out of the purge volume through the
single check valve assembly and out the delivery
port to the first (supply) reservoir of the air system.
The air dryer will remain in the charge cycle until air
brake system pressure builds to the governor cutout
setting.
Purge Cycle
When air brake system pressure reaches the cutout
setting of the governor, the compressor unloads (air
compression stopped) and the purge cycle of the air
dryer begins. See Figure 24—Air Dryer Operation
Cycle.
When the governor unloads the compressor, it
pressurizes the compressor unloader mechanism and
line connecting the governor unloader port to the
AD-9 end cover control port.
Contaminants in the end cover sump are expelled
immediately when the purge valve opens. Also, air
that was flowing through the desiccant cartridge
changes direction and begins to flow toward the
open purge valve. Oil and solid contaminants
collected by the oil separator are removed by air
flowing from the desiccant drying bed to the open
purge valve.
The initial purge and desiccant cartridge
decompression lasts only a few seconds. The actual
reactivation of the desiccant drying bed begins as
dry air flows from the purge volume through the
desiccant cartridge purge orifice and into the
desiccant drying bed. Pressurized air from the purge
volume expands after passing through the purge
orifice; its pressure is lowered and its volume
increased. The flow of dry air through the drying
bed reactivates the desiccant material by removing
the water vapor adhering to it. Generally 15-30
seconds are required for the entire purge volume of a
standard AD-9 to flow through the desiccant drying
bed.
The purge piston moves in response to air pressure
causing the purge valve to open to atmosphere and
(partially) closing off the supply of air from the
compressor. This will be further discussed in the
section covering the turbo cut-off feature.
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TC Series Brakes
The end cover single check valve assembly prevents
air pressure in the brake system from returning to the
air dryer during the purge cycle. After the 30second purge cycle is complete, the air dryer is ready
for the next charge cycle to begin.
The purge valve will remain open after the purge
cycle is complete and will not close until air brake
system pressure is reduced and the governor signals
the compressor to charge.
Turbo Cut-Off Feature (Figure 25)
The primary function of the turbo cut-off valve is to
prevent loss of engine turbocharger air pressure
through the AD-9 in systems where the compressor
intake is connected to the engine turbocharger. The
turbo cut-off valve also reduces the “puffing” of air
out the open exhaust when a naturally aspirated,
single cylinder compressor equipped with an inlet
check valve is in use. At the onset of the purge
cycle, the downward travel of the purge piston is
stopped when the turbo cut-off valve (tapered
portion of purge piston) contacts its mating metal
seat in the purge valve housing. With the turbo cutoff valve seated (closed position), air in the
discharge line and AD-9 inlet port is restricted from
entering the air dryer. While the turbo cut-off
effectively prevents loss of turbo charger boost
pressure to the engine, some seepage of air may be
detected under certain conditions of compressor
engine and turbo charger operation.
Relay Valve Operation
Application (Figure 26)
Air pressure delivered to the service port enters the
small cavity above the piston and moves the piston
down. The exhaust seat moves down with the piston
and seats on the inner or exhaust portion of the
inlet/exhaust valve, sealing off the exhaust passage.
At the same time, the outer or inlet portion of the
inlet/exhaust valve moves off its seat, permitting
supply air to flow from the reservoir, past the open
inlet valve and into the brake chambers.
Figure 26—Relay Valve Ports
Balance
The air pressure being delivered by the open inlet
valve also is effective on the bottom area of the relay
piston. When air pressure beneath the piston equals
the service air pressure above, the piston lifts
slightly and the inlet spring returns the inlet valve to
its seat. The exhaust remains closed as the service
line pressure balances the delivery pressure. As
delivered air pressure is changed, the valve reacts
instantly to the change, holding the brake application
at that level.
Exhaust or Release
When air pressure is released from the service port
and air pressure in the cavity above the relay piston
is exhausted, air pressure beneath the piston lifts the
relay piston and the exhaust seat moves away from
the exhaust valve, opening the exhaust passage.
With the exhaust passage open, the air pressure in
the brake chambers is then permitted to exhaust
through the exhaust port, releasing the brakes.
Figure 25—Turbo Cut-Off Feature
Air Compressor
The function of the air compressor is to provide and
maintain air under pressure to operate devices in the
air brake and/or auxiliary air systems.
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TC Series Brakes
The compressor assembly consists of two major
subassemblies, the cylinder head and the crankcase.
The cylinder head is an iron casting which houses
the inlet, discharge, and unloader valving. The
cylinder head contains the air inlet port and is
designed with both top and side air discharge ports.
Three water coolant ports provide a choice of
coolant line connections. Governor mounting
surfaces are provided at both the front and the rear of
the cylinder head. The head is mounted on the
crankcase and is secured by six cap screws. The
crankcase houses the cylinder bores, pistons,
crankshaft and main bearings, and provides the
flange or base mounting surface.
Intake and Compression of Air (Loaded)
During the down stroke of the piston, a slight
vacuum is created between the top of the piston and
the cylinder head, causing the inlet valve to move off
its seat and open.
Note
The discharge valve remains on its seat.
Atmospheric air is drawn through the air
strainer and the open inlet valve into the
cylinder (See Figure 28).
discharge valve off its seat and air flows by the open
discharge valve, into the discharge line and to the
reservoirs (see Figure 29).
Figure 29—Operational-Loaded
As the piston reaches the top of its stroke and starts
down, the discharge valve spring and air pressure in
the discharge line returns the discharge valve to its
seat.
This prevents the compressed air in the discharge
line from returning to the cylinder bore as the intake
and compression cycle is reseated.
Non-Compression of Air (Unloaded)
Figure 28—Operational-Loaded (Intake)
As the piston begins its upward stroke, the air that
was drawn into the cylinder on the down stroke is
being compressed. Air pressure on the inlet valve,
plus the force of the inlet spring, returns the inlet
valve to its seat and closes. The piston continues the
upward stroke and compressed air pushes the
Figure 30—Operational-Unloaded
When air pressure in the reservoir reaches the cutout setting of the governor, the governor allows air
to pass from the reservoir, through the governor and
into the cavity above the unloader pistons.
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The unloader pistons move down holding the inlet
valves off their seats (see Figure 30.) With the inlet
valves held off their seats by the unloader pistons,
air is pumped back and forth between the two
cylinders, and the discharge valves remain closed.
Cooling
Air flowing through the engine compartment from
the action of the engine’s fan and the movement of
the vehicle assists in cooling the compressor. (See
Figure 32)
When air pressure from the reservoir drops to the
cut-in setting of the governor, the governor closes
and exhausts the air from above the unloader
pistons.
Coolant flowing from the engine’s cooling system
through connecting lines enters the head and passes
through internal passages in the cylinder head and is
returned to the engine.
The unloader springs force the pistons upward and
the inlet valves return to their seats. Compression is
then resumed.
Lubrication
The vehicle's engine provides a continuous supply of
oil to the compressor (see Figure 32). Oil is routed
from the engine to the compressor oil inlet. An oil
passage in the compressor crankshaft allows oil to
lubricate the connecting rod crankshaft bearings.
Note
Proper cooling is important in maintaining
discharge air temperatures below the
maximum recommended 400° Fahrenheit.
Connecting rod wrist pin bushings and crankshaft
ball bearings are spray lubricated. An oil return line
connected from the compressor drain outlet to the
vehicle engine crankcase allows for oil return.
On flange mounted models the oil drains back
directly to the engine through the mounting flange.
Figure 32—Cooling
Figure 31—Lubrication
Air Induction
There are three methods of providing clean air to the
compressor:
1. Naturally aspirated - Compressor utilizes its own
attached air strainer (polyurethane sponge or
pleated paper dry element).
2. Naturally aspirated - Compressor inlet is
connected to the engine air cleaner or the
vacuum side (engine air cleaner) of the
supercharger or turbocharger.
3. Pressurized induction - Compressor inlet is
connected to the pressure side of the
supercharger or turbo-charger.
4. If a previously non-turbocharged compressor is
being turbo-charged, it is recommended that the
inlet cavity screen (238948) be installed with an
inlet gasket (291909) on both sides of the screen.
Compressor Turbo Charging Parameters
Air entering the compressor inlet during the loaded
cycle must not exceed 250° F (121° C). A metal
inlet line is recommended.
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• Check wiring.
Note
• Check bulb.
The following compressor crankshaft
rotational speed and inlet pressure
relationships may not be exceeded.
Crankshaft Maximum Compressor
• Repair or replace the buzzer, bulb or low
pressure warning switch(s).
•
If governor cut-out is higher or lower than
specified by the vehicle manual
RPMInlet Pressure
2200 RPM 21.0 PSI (145 kPa)
• Adjust the governor using a gauge of known
accuracy.
2600 RPM 25.0 PSI (172.5 kPa)
• Repair or replace governor as necessary after
being sure compressor unloader mechanism
is operating correctly.
Troubleshooting and Diagnostics
Brake System Troubleshooting
Test 1-Governor Cut-Out/Low Pressure Check
List
1. Warning/Pressure Build-Up Vehicle Parked,
Wheels Chocked.
2. Drain all reservoir to 0 PSI.
3. Start engine (run at fast idle)
4. Low pressure warning should be on.
Note
On some vehicles with anti-lock, a warning
light will also come on momentarily when
ignition is turned on.
5. Low pressure warning dash warning light should
go off at or above 60 PSI.
6. Build up time pressure should build from 85-100
PSI within 40 seconds.
7. Governor cut-out, cuts out at correct pressure
check manufacturers recommendations; usually
between 100-130 PSI.
8. Governor cut-in reduce service air pressure to
governor cut-in. The difference between cut-in
and cut-out pressure must not exceed 25 PSI.
Make All Necessary Repairs Before
Proceeding To Test 2; See Check List 1 For
Common Corrections.
Governor Cut-Out/Low Pressure Check List
• If the low pressure warning light or buzzer
does not come on
•
If low pressure warning occurs below 60 PSI
• Check dash gauge with test gauge known to
be accurate.
• Repair or replace the faulty low pressure
indicator.
•
If build up time exceeds 40 seconds or is
considerably greater than the permanent
record figure:
• Examine the compressor air strainer and
clean or replace.
• Check for restricted inlet line if compressor
does not have strainer, repair or replace as
necessary.
• Check compressor discharge port and line for
excessive carbon. Clean or replace as
necessary.
• With system charged and governor
compressor in unloaded mode, listen at the
compressor inlet for leak.
• If leak can be heard apply a small amount of
oil around unloader pistons. If no leak is
indicated, then leak is through the
compressor discharge valves.
• Check the compressor drive for slippage.
Note
Retest To Check Out All Items Repaired Or
Replaced
Test 2-Leak Reservoir Air Supply Full Pressure,
Engine Stopped, Parking Brakes Applied
1. Allow pressure to stabilize for at least 1 minute.
2. Observe the dash gauge pressures for 2 minutes
and note any pressure drop.
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3. Pressure Drop: (A 2 PSI drop within 2 minutes
is allowable for either service reservoir)
Note
Make All Necessary Repairs Before
Proceeding To Test 3; See Check List 2 For
Common Corrections.
Check List 2
If there is excessive leak in the supply side of the
pneumatic system, one or more of the following
devices could be causing the problem:
Allow pressure to stabilize for 1 minute; then begin
timing for 2 minutes while watching the dash gauges
for a pressure drop.
Pressure Drop: (A 4 PSI drop within 2 minutes is
allowable for either service reservoir)
Check the angle formed between the brake chamber
push rod and slack adjuster arm. (It should be at
least 90° in the fully applied position)
Note
5. Single check valves
Make All Necessary Repairs Before
Proceeding To Test 4; See Check List 3 For
Common Corrections
Check List 3
If there is excessive leak in the service side of the
pneumatic system, one or more of the following
devices could be causing the problem.
6. Double check valve
1. Service lines and fittings (tighten)
7. PP-1 (push pull control valve)
2. E-6 brake valve
8. E-6 brake valve
3. SR-1 spring brake valve
9. SR-1 spring brake valve
4. Brake light switch
10. QR-1C Quick release valves
5. R-12 relay valve with double check valve
11. M-22 ABS antilock modulator assemblies
If the angle between the brake chamber push rod and
slack adjuster arm is less than 90°, then adjust slack
adjuster arm to obtain desired setting. If brake
chamber push rod travel exceeds the allowable
tolerance, then adjust adjuster arm to obtain desired
setting.
1. Supply lines and fittings (tighten)
2. Wet tank
3. Front air tank
4. Rear air tank
12. Front air chambers
13. Rear brake chambers
14. Safety valve
15. Low pressure indicator switch
Note
16. Schrader valve
Retest To Check Out All Items Repaired
Or Replaced
17. Drain valves
Test 4-Automatic Emergency System Full
Pressure, Engine Stopped
Drain front axle reservoir to 0 PSI.
18. Pressure gauges
19. Governor
20. Compressor discharge valve
Note
A leak detector or soap solution will aid in
locating the faulty component.
Retest To Check Out All Items Repaired Or
Replaced
Test 3-Leak (Service Air Delivery) Full Pressure,
Engine Stopped, Parking Brakes Released
Make and hold 80-90 PSI brake application. (A
block of wood can be used to hold the foot valve
down during these tests)
•
Rear axle reservoir should not lose pressure.
With no air pressure in the front axle reservoir make
a brake application.
•
Rear axle brakes should apply and release
•
The stop lamps should light
1. Slowly drain rear axle reservoir pressure.
2. Spring brake push pull valve should pop out
between 35 and 45 PSI.
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3. Close drain cocks, recharge system and drain
rear axle reservoir to 0 PSI.
Front axle reservoir should not lose pressure
Test 5-Brake Balance Test
1. Test drive vehicle approximately 10-15 minutes
applying brakes frequently.
With no air pressure in the rear axle reservoir, make
a brake application.
2. Park in a safe suitable location to perform brake
test.
•
3. Take a temperature reading at each wheel drum
using a thermocouple and note reading.
•
Front axle brakes should apply and release
Check List 4
If the vehicle fails to pass the tests outlined, then
check the following components for leak and proper
operation.
1. Fittings
2. Kinked hose or tubing
3. PP-1 push pull control valve
4. E-6 brake valve
5. SR-1 spring brake valve
6. Retest To Check All Items Repaired Or
Replaced Function Correctly.
4. Compare the two front wheel drum temperature
readings and compare the two rear wheel drum
temperature readings.
5. Temperature range must be within ±50° for each
two front drums and each two rear drums.
If temperature range is within limits, vehicle is in
proper brake balance.
If temperature is out of range, see Check List 5 for
common corrections.
Check List 5
If the brake balance test failed, one or more of the
following devices could be causing the problem.
1. Worn brake shoes.
2. Worn return springs.
3. Brake actuating components binding.
4. Incorrect adjustment of slack adjuster.
5. Inoperative self-adjusting slack adjuster.
030-23
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TC Series Brakes
Compressor Troubleshooting
Symptom
Cause
Remedy
Compressor passes
excessive oil as
evidenced in system or
by presence of oil at
exhaust ports of valves
or seeping from air
strainer.
Restricted air intake
Check engine or compressor air cleaner and
replace if necessary. Check compressor air inlet
for kinks, excessive bends and be certain inlet
lines have the minimum specified inside diameter.
---
Restricted oil return (to
engine)
Oil return to the engine should not be in anyway
restricted. Check for excessive bends, kinks and
restrictions in the oil return line. Return line
must constantly descend from the compressor to
the engine crankcase. Make sure oil drain
passages in the compressor and mating engine
surfaces are unobstructed and aligned. Special
care must be taken when sealant is used with, or
instead of gaskets.
---
Poorly filtered inlet air.
Check for damaged, defective or dirty air filter on
engine or compressor. Check for leaking,
damaged or defective compressor air intake
components (e.g. induction line, fittings, gaskets,
filter bodies, etc.). The compressor intake should
not be connected to any part of the exhaust gas recirculation (EGR) system on the engine.
Compressor passes
excessive oil as
evidenced in system or
by presence of oil at
exhaust ports of valves
or seeping from air
strainer.
Contaminants not being
regularly drained from
system reservoirs.
Check reservoir drain valves to insure that they
are functioning properly. It is recommended that
the vehicle should be equipped with functioning
automatic drain valves, or have all reservoirs
drained to zero (0) psi daily, or optimally to be
equipped with a desiccant-type air dryer prior to
the reservoir system.
Table 1—Compressor Troubleshooting
030-25
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TC Series Brakes
Symptom
Cause
Remedy
---
Compressor runs loaded
an excessive amount of
time.
Vehicle system leak should not exceed industry
standards of 1 psi pressure drop per minute
without brakes applied and 3 psi pressure drop per
minute with brakes applied.
If leak is excessive, check for system leak and
repair.
---
Excessive engine
crankcase pressure.
Test for excessive engine crankcase pressure and
replace or repair ventilation components as
necessary. (An indication of crankcase pressure is
a loose or partially lifted dipstick.)
---
Excessive engine oil
pressure.
Check the engine oil pressure with a test gauge
and compare the reading to the engine
specifications. If not to specification check the
following:
Check oil level and condition. Replace if
necessary (see specifications for engine oil
viscosity).
Defective oil pump. Replace oil pump.
For further diagnostics, see Engine
Troubleshooting.
---
Malfunction of the turbo
cutoff piston in the air
dryer, resulting in a loss
of back pressure on the
compression exhaust
port of compressor
during unload mode
(Holset Only).
Warn or defective turbo cutoff piston. Replace
end cover check valve assembly of AD-9 Air
Dryer.
---
Malfunctioning check
valve in wet tank air
supply line to
compressor exhaust port
causing a lack of back
pressure during the
unload mode (Holset
Only)
Replace check valve.
---
Faulty compressor.
Replace or repair the compressor only after none
of the preceding installation defects exist.
Table 1—Compressor Troubleshooting continued
030-26
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TC Series Brakes
Symptom
Cause
Remedy
Noisy compressor
operations.
Loose drive gear or Pulley.
Inspect the fit of the drive gear on pulley on the
compressor crankshaft. The pulley on gear must
be completely seated and the crankshaft nut must
be tight. If the compressor crankshaft surface or
the keyway is damaged, it is an indication of loose
drive components. If damage to the compressor
crankshaft is detected, replace the compressor.
When installing the drive gear or pulley, torque
the crankshaft nut to the appropriate torque
specifications. Do not back off the crankshaft nut
to align the cotter pin and castellated nut. (Some
compressors do not use castellated nuts.) Do not
use impact wrenches.
---
Excessively worn drive
couplings or gears.
Inspect drive gear and couplings and engine for
excessive wear. Replace as necessary.
(Nonmetallic gears should be replaced when the
compressor is changed.)
---
Compressor cylinder head or
discharge line restrictions.
Inspect the compressor discharge port and
discharge line for carbon build-up. If carbon is
detected, check for proper cooling to the
compressor. (See Symptom number 1. For
Insufficient compressor cooling.) Inspect the
discharge line for kinks and restrictions. Replace
discharge line as necessary.
---
Worn or burned out bearings.
Check for proper oil pressure in the compressor.
Check for excessive oil temperature; should not
exceed 240° Fahrenheit.
---
Faulty compressor.
Replace or repair the compressor after
determining none of the preceding installation
defects exist.
Table 1—Compressor Troubleshooting continued
030-27
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TC Series Brakes
Symptom
Cause
Remedy
Excessive build-up and
recover time.
Compressor should be
capable of building air
system from 85-100 psi
in 40 seconds with
engine at full governed
rpm. Minimum
compressor
performance is certified
to meet federal
requirements by the
vehicle manufacturer.
Do not downsize the
original equipment
compressor.
Dirty induction air filter
Inspect engine or compressor air filter and replace
if necessary.
Restricted induction line.
Inspect the compressor air induction line for kinks
and restrictions and replace as necessary.
Restricted discharge line or
compressor discharge cavity.
Inspect the compressor discharge port and line for
restrictions and carbon build-up. If a carbon
build-up is found, check for proper compressor
cooling. Replace faulty sections of the discharge
line.
Slipping drive components.
Check for faulty drive gears and couplings and
replace as necessary. Check the condition of drive
belts and replace or tighten, whichever is
appropriate.
Excessive air system leak.
Test for excessive system leak and repair as
necessary. Use the following as a guide:
Build system pressure to governor cutout and
allow the pressure to stabilize for one minute.
Using the dash gauge, note the system pressure
and the pressure drop after two minutes.
The pressure drop should not exceed 2 psi in each
reservoir.
Sticking unloader pistons or
valves.
Check and clean the operation of the unloading
mechanism. Lube mechanism with high
temperature grease. Check the proper operation
of the compressor air governor. If the governor is
operating properly, replace the unloader
mechanism. Inspect for bent, kinked or blocked
tubing leading to or from the governor.
Gauge defective
Replace gauge.
Faulty compressor.
Replace or repair the compressor after
determining none of the preceding installation
defects exist.
Table 1—Compressor Troubleshooting continued
030-28
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TC Series Brakes
Symptom
Cause
Remedy
Compressor fails to
unload.
Faulty governor or governor
installation.
Test the governor for proper operation and inspect
air lines to and from the governor for kinks or
restrictions. Replace or repair the governor or its
connecting air lines.
---
Faulty or worn unloader
pistons, valves or bores.
Inspect for worn, dirty or corroded unloader
pistons, valves and their bores. Replace as
necessary.
---
Gauge defective.
Replace gauge.
Compressor leak oil.
Damaged mounting gasket.
Check the compressor mounting bolt torque. If
the mounting bolt torque is low, replace the
compressor mounting gasket before re-torque of
the mounting bolts.
Cracked crankcase or end
cover.
Visually inspect the compressor exterior for
cracked or broken components. Cracked or
broken crankcases or mounting flanges can be
caused by loose mounting bolts. The end cover
can be cracked by over-torque fitting or plugs
installed in the end cover. Replace or repair the
compressor as necessary.
Loose end cover cap.
Check the cap screw torque and tighten as
necessary.
Loose oil supply or return
line fittings.
Check the torque of external oil line fittings and
tighten as necessary.
Porous compressor casting.
Replace the compressor if porosity is found.
Mounting flange or end
cover, O-ring or gasket
missing, cut or damaged.
Replace as necessary.
Leaking compressor unloader
pistons or valves.
Remove the compressor inlet air strainer or fitting.
With the compressor unloaded (not compressing
air), check for air leak. Repair or Replace as
necessary.
Faulty Governor.
Test the governor for proper operation and repair
or replace as necessary
Excessive system leak.
Test for excessive system leak, (See Test 2).
Reduce leak wherever possible.
Excessive reservoir
Contaminants.
Drain reservoirs.
Compressor constantly
cycles (compressor
remains unloaded for a
very short time).
Table 1—Compressor Troubleshooting continued
030-29
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TC Series Brakes
Symptom
Cause
Remedy
---
Air dryer check valve leak.
Replace check valve with appropriate AD-9 End
Cover Check Valve Replacement Kit.
Compressor leak
coolant.
Improperly installed plugs
and coolant line fittings.
Check torque of fittings and plugs and tighten as
necessary. Over-torque fittings and plugs can
crack the head or block casting.
Freeze cracks due to improper Test antifreeze and strengthen as necessary.
antifreeze strength.
Check coolant flow through compressor to assure
the proper antifreeze mixture reaches the
compressor.
Compressor head
gasket failure.
Restricted discharge line.
Clear restriction or replace line.
---
Loose head bolts.
Tighten evenly to proper torque specifications.
Table 1—Compressor Troubleshooting continued
030-30
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TC Series Brakes
Electrical Circuits - ABS and Traction Control
Figure 33–ISB Hydraulic Brakes
Figure 34–Ignition Voltage and Ground
Individual Circuit Diagrams
Figure 35–Traction Control Lamp Circuit
Figure 36–Traction Enable Switch Circuit
Figure 37–Diagnostic T1586 Serial Circuits with Cummins Engine
Figure 38–ABS Signal Circuit for Cummins Engine w/WT
Figure 39–ABS Signal Circuit w/AT/MT Transmission
Figure 40–Ground Circuit
Figure 41–Chassis Option Solenoid Circuit
Figure 42–ABS Signal Circuit for Engine ISB
Figure 43–ABS Signal Circuit for Engine ISB continued
Figure 44–Ignition Switch Circuit
Figure 45–Vehicle Speed in Circuits w/AT/MT Transmission
Figure 46–Vehicle Speed in Circuits w/WT Transmission
Figure 47–Vehicle Speed in Circuits w/AT/MT Transmission
Figure 48–Serial Comm. Interface Circuits w/Throttle Diagnostic and Master Chassis
Figure 49–Retarder Circuit (1 of 2)
Figure 50–Retarder Circuit (2 of 2)
Figure 51–Relay Circuit w/ISB and AT/MT Transmission
Figure 52–ABS Module Interface
030-31
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TC Series Brakes
030-31
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TC Series Brakes
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030-31
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TC Series Brakes
Figure 33—Hydraulic Brakes ISB, TC
030-33
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TC Series Brakes
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030-33
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TC Series Brakes
Ignition Voltage and Ground Circuits w/WT and AT/MT Transmission
Figure 34—Ignition Voltage and Ground
030-34
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TC Series Brakes
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030-35
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TC Series Brakes
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030-35
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TC Series Brakes
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030-35
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TC Series Brakes
Diagnostic T1587 Serial Circuits with Cummins Engine
Figure 37—Diagnostic T1587 Serial Circuits with Cummins Engine
030-36
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TC Series Brakes
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030-39
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TC Series Brakes
ABS Signal Circuit for Cummins Engine w/WT
Figure 38—ABS Signal Circuit for Cummins Engine w/WT (TC)
ABS Signal Circuit w/AT/MT Transmission
Figure 39—ABS Signal Circuit w/AT/MT Transmission
030-37
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TC Series Brakes
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030-41
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TC Series Brakes
Ground Circuit
Figure 40—Ground Circuit
030-38
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TC Series Brakes
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030-43
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TC Series Brakes
Option Solenoid Circuit
Figure 41—Chassis Option Solenoid Circuit
030-39
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TC Series Brakes
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030-45
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TC Series Brakes
Figure 42—ABS Signal Circuit for Engine ISB
Figure 43—ABS Signal Circuit for Engine ISB
030-40
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TC Series Brakes
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030-40
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TC Series Brakes
Ignition Switch Circuit
Figure 44—Ignition Switch Circuit
030-41
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TC Series Brakes
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030-49
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TC Series Brakes
Vehicle Speed In Circuits w/AT/MT Transmission
Figure 45—Vehicle Speed In Circuits w/AT/MT Transmission
030-42
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TC Series Brakes
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030-51
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TC Series Brakes
Vehicle Speed in Circuits w/WT Transmission
Figure 46—Vehicle Speed in Circuits w/WT Transmission
Vehicle Speed in Circuits w/AT/MT Transmission
Figure 47—Vehicle Speed in Circuits w/AT/MT Transmission
030-43
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TC Series Brakes
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030-53
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TC Series Brakes
Serial Comm. Interface Circuits w/Throttle Diagnostic and Master Chassis
Figure 48—Serial Comm. Interface Circuits w/Throttle Diagnostic and Master Chassis
030-44
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TC Series Brakes
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030-55
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TC Series Brakes
Retarder Circuit (1 of 2)
Figure 49—Transmission Retarder Circuit (1 of 2)
030-45
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TC Series Brakes
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030-57
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TC Series Brakes
Retarder Circuit (2 of 2)
Figure 50—Transmission Retarder Circuit (2 of 2)
030-46
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TC Series Brakes
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030-59
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TC Series Brakes
Relay Circuit w/ISB/ISC and AT/MT Transmission
Figure 51—Relay Circuit w/ISB and AT/MT Transmission
030-47
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Preventative Maintenance
Note
Review the warranty policy before performing
any intrusive maintenance procedures. An
extended warranty may be voided if intrusive
maintenance is performed during this period.
Because no two vehicles operate under
identical conditions, maintenance and
maintenance intervals will vary. Experience
is a valuable guide in determining the best
maintenance interval for any one particular
operation.
Note
When working on or around a vehicle, the
following general precautions should be
observed.
1. Park the vehicle on a level surface, apply the
parking brakes, and always block the wheels.
2. Stop the engine when working around the
vehicle.
3. If the vehicle is equipped with air brakes, be
sure to drain the air pressure from all reservoirs
before beginning any work on the vehicle.
4. Following the vehicle manufacturer’s
recommended procedures, deactivate the
electrical system in a manner that removes all
electrical power from the vehicle.
Exit
Never exceed recommended pressures and always
wear safety glasses.
Do not attempt to install, remove, disassemble or
assemble a component until you have read and
thoroughly understand the recommended
procedures. Use only the proper tools and
observe all precautions pertaining to use of those
tools.
Use only genuine Blue Bird replacement parts,
components, and kits. Replacement hardware,
tubing, hose, fittings, etc. should be of equivalent
size, type, and strength as original equipment and
be designed specifically for such applications and
systems.
Components with stripped threads or damaged
parts should be replaced rather than repaired.
Repairs requiring machining or welding should
not be attempted unless specifically approved and
stated by the vehicle or component manufacturer.
Prior to returning the vehicle to service, be sure
all components and systems are restored to their
proper operating condition.
Air Dryer
Every 900 operating hours or 25,000 miles or
every three (3) months:
1. Check for moisture in the air brake system by
opening reservoirs, drain cocks, or valves and
checking for presence of water.
Note
When working in the engine compartment the
engine must be shut off. Where circumstances
require that the engine be in operation, extreme
caution should be used to prevent personal injury
resulting from contact with moving, rotating,
leaking, heated or electrically charged
components.
Never connect or disconnect a hose or line
containing pressure; it may whip. Never remove
a component or plug unless you are certain all
system pressure has been depleted.
030-52
If moisture is present, the desiccant may
require replacement; however, the following
conditions can also cause water accumulation
and should be considered before replacing the
desiccant.
2. An outside air source has been used to charge
the system. This air did not pass through the
drying bed.
3. Air usage is exceptionally high and not normal
for a highway vehicle. This may be due to
accessory air demands or some unusual air
requirement that does not allow the compressor
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to load and unload (compressing and noncompressing cycle) in a normal mode
4. Check for high air system leak.
Note
The air dryer has been installed in a system
that has been previously used without an air
dryer. This type system will be saturated with
moisture and several weeks of operation may
be required to dry it out.
Location of the air dryer is too close to the air
compressor.
In areas where more than a 30 degree range of
temperature occurs in one day, small amounts of
water can accumulate in the air brake system due to
condensation.
Under these conditions, the presence of small
amounts of moisture is normal and should not be
considered as an indication that the dryer is not
performing properly.
A small amount of oil in the system may be normal
and should not, in itself, be considered a reason to
replace the desiccant; oil stained desiccant can
function adequately.
5. Check mounting bolts for tightness. Re-torque
to 270-385 inch-pounds.
6. Perform the Operation and Leak Tests in this
publication.
Every 36 months or 300,000 miles or 10,800
hours:
• Rebuild the air dryer including the desiccant
cartridge.
Note
The desiccant change interval may vary from
vehicle to vehicle. Typical desiccant cartridge
life is three years.
030-52
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Relay Valve
Every 3 months or 25,000 miles or 900 operating
hours:
Check for proper operation.
Every 12 months or 100,000 miles or 3,600
operating hours:
1. Disassemble valve.
2. Clean parts with mineral spirits.
3. Replace all rubber parts and any part worn or
damaged.
4. Check for proper operation before placing
vehicle in service.
Dual Circuit Brake Valve
Every 3 months, or 25,000 miles or 900 operating
hours:
1. Clean any foreign material away from the heel
of the treadle, plunger boot and mounting plate.
2. Lubricate the treadle roller, roller pin and hinge
pin with light oil.
3. Check the rubber plunger boot for cracks, holes
or deterioration and replace if necessary.
4. Check mounting plate and treadle for integrity.
5. Apply 2 to 4 drops only of oil between plunger
and mounting plate.
Every year, or 100,000 miles, or 3,600 operating
hours:
1. Disassemble parts.
2. Clean parts with mineral spirits.
3. Replace all rubber parts or any part worn or
damaged.
4. Check for proper operation before placing
vehicle in service.
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Automatic Slack Adjuster
1. Lubricate automatic slack adjuster in accordance
with maintenance schedule.
2. Visually inspect for cracks and loose or missing
hardware.
Brake Chamber
1. Visually inspect brake chamber for cracks and
loose or missing hardware.
2. Check air lines for cracks and loose fittings.
Push Pull Control Valves
Every 6 Months, or 50,000 miles or 1,800
operating hours:
• Disassemble, clean and replace parts as
necessary.
•
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Every 6 months, 1,800 operating hours or after
each 50,000 miles:
• Compressor Cooling
Note
Minimum coolant line size is 3/8 inch ID.
1. Inspect the compressor discharge port, inlet
cavity and discharge line for evidence of
restrictions and carbon. If excessive buildup is
found, thoroughly clean or replace the affected
parts.
2. Re-inspect the compressor cooling system.
3. Check all compressor coolant lines for kinks and
restrictions to flow.
4. Check coolant lines for internal clogging from
rust scale. If coolant lines appear suspicious,
5. Check the coolant flow and compare to the
tabulated technical data.
6. Inspect the air induction system for restrictions.
Air Compressor
Every two months, 800 operating hours or 20,000
miles:
• Compressor Inlet Line
1. Air induction for the compressor comes from the
engine intake.
2. Inspect hose from engine to compressor intake
for kinks, abrasions, worn spots, and cracks.
Replace as necessary.
Every six months, 1800 operating hours or 50,000
miles:
• Lubrication
1. Check external oil supply and return lines for
kinks, bends or restrictions to flow.
2. Supply lines must be a minimum of 3/16 inch ID
and return lines must be a minimum of 1/2 inch
ID.
When the engine air cleaner is replaced.
3. Oil return lines should slope as sharply as
possible back to the engine crankcase and should
have as few fittings and bends as possible.
Some compressors are fitted with compressor intake
adapters that allow the compressor intake to be
connected to the engine air induction system.
Every six months, 1,800 operating hours or
50,000 miles:
• Compressor Drive
The compressor receives a supply of clean air from
the engine air cleaner. When the engine air filter is
changed, the compressor intake adapter should be
checked.
1. Listen for noisy compressor operation that could
indicate a worn drive gear coupling, a loose
pulley or excessive internal wear. Adjust and/or
replace as necessary.
If it is loose, remove the intake adapter, clean the
strainer plate, if applicable, and replace the intake
adapter gasket, and reinstall the adapter securely.
2. If the compressor is belt driven, check for proper
belt and pulley alignment and belt tension.
•
Intake Adapter
3. Check line connections both at the compressor
intake adapter and at the engine.
4. Inspect the connecting line for ruptures and
replace it if necessary.
030-52
3. Check all compressor mounting bolts and
retighten evenly if necessary.
4. Inspect for leak and proper unloader mechanism
operation. Repair or replace parts as necessary.
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Every 24 months, 7,200 operating hours, or after
each 200,000 miles:
1. Inspect and, depending upon the results of
inspection or experience, disassemble the
compressor.
2. Clean and inspect all parts thoroughly
3. Replace all worn or damaged parts using only
genuine Blue Bird replacements or replace the
compressor with a genuine Blue Bird
remanufactured unit.
Antilock Systems Preventative Maintenance
Wheel Speed Sensor
Every 3 months, 25,000 miles, 900 operating
hours, or during the vehicle chassis lubrication
interval:
Inspect speed sensor visually. Refer to Wheel Speed
Sensor Service Check.
Every 12 months, 100,000 miles, or 3,600
operating hours:
Perform Wheel Speed Sensor Service Check in this
manual.
Antilock Modulator Assembly
Perform the tests and inspections at the maintenance
intervals.
If the modulator fails to function as described, or
leaks are excessive, replace with a new or genuine
Blue Bird remanufactured unit, available at any
authorized parts outlet.
Every 3 Months, 25,000 Miles or 900
operating hours
1. Inspect visually the exterior for excessive
corrosion and physical damage.
2. Remove any accumulated contaminates.
3. Inspect all air lines and wire harnesses
connected to the modulator for signs of wear or
physical damage. Replace as necessary.
4. Test air line fittings for excessive leak and
tighten or replace as necessary.
5. Perform the antilock modulator assembly
Operational and Leak Test described in this
manual.
030-52
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Service Checks
Air Dryer
Operation and Leak Tests
Test the outlet port check valve assembly by
building the air system to governor cut-out and
observing a test air gauge installed in the number 1
reservoir.
A rapid loss of pressure could indicate a failed outlet
port check valve.
This can be confirmed by bleeding the system down,
removing the check valve assembly from the end
cover, subject air pressure to the unit and apply a
soap solution to the check valve side. Leak should
not exceed a 1 inch bubble in 1 second.
Check for excessive leaking around the purge valve.
With the compressor in loaded mode (compressing
air), apply a soap solution to the purge valve housing
assembly exhaust port and observe that the leak does
not exceed a 1 inch bubble in 1 second.
If the leak exceeds the maximum specified, service
the purge valve housing assembly.
1. Close all reservoir drain cocks. Build up system
pressure to governor cut-out and note that AD-9
purges with an audible escape of air. Fan the
service brakes to reduce system air pressure to
governor cut-in.
2. Check the operation of the safety valve by
pulling the exposed stem while the compressor
is loaded (compressing air). There must be an
exhaust of air while the stem is held and the
valve should reseat when the stem is released.
3. Check all lines and fittings leading to and from
the air dryer for leaks and integrity.
4. Check the operation of the end cover heater and
thermostat assembly during cold weather
operation
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Electric Power to the Dryer
5. With the ignition or engine kill switch in the ON
position, check for voltage to the heater and
thermostat assembly using a voltmeter or test
light.
6. Unplug the electrical connector at the air dryer
and place the test leads on each of the pins of the
male connector.
If there is no voltage, look for a blown fuse, broken
wires, or corrosion in the vehicle wiring harness.
Check to see if a good ground path exists.
•
Thermostat and Heater Operation
Note
Some early models of the AD-9 will have
resistance readings of 1.0 to 2.5 ohms for the
12 volt heater assembly and 4.8 to 7.2 ohms
for the 24 volt heater assembly. If the
resistance is higher than the maximum stated,
replace the purge valve housing assembly,
that includes the heater and thermostat
assembly.
7. Turn off the ignition switch and cool the end
cover assembly to below 40° Fahrenheit.
A two lead, 12 inch, wire harness (Figure 53) with
attached weather resistant connector is supplied with
all retrofit and replacement AD-9 Air Dryers.
8. Check the resistance between the electrical pins
in the female connector with a ohmmeter. The
resistance should be 1.5 to 3.0 ohms for the 12
volt heater assembly and 6.8 to 9.0 ohms for the
24 volt heater assembly.
11. A fuse should be installed in the power carrying
wire; install a 10 amp fuse for a 12 volt heater
and a 5 amp fuse for a 24 volt heater.
9. Warm the end cover assembly to over 90°
Fahrenheit and again check the resistance. The
resistance should exceed 1000 ohms. If the
resistance values obtained are within the limits,
the thermostat and heater assembly is operating
properly.
If the resistance values obtained are outside the
limits, replace the purge valve housing assembly,
that includes the heater and thermostat assembly.
030-54
Figure 53—Air Dryer Connections
10. Connect one of the two leads of the wire harness
to the engine kill or ignition switch. The
remaining lead of the wire harness must be
connected to a good vehicle ground.
12. Use 14 AWG wire if it is necessary to lengthen
the wire harness provided.
13. Make sure all wire splices are waterproofed.
14. Tie wrap or support all electrical wire leading to
the AD-9.
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Relay Valve
Operational and Leak Test
1. Chock the wheels, fully charge air brake system
and adjust the brakes.
Dual Circuit Brake Valve
Operating Check
1. Check the delivery pressure of both Primary and
Secondary circuits using accurate test gauges.
2. Make several brake applications and check for
prompt application and release at each wheel.
2. Depress the treadle to several positions between
the fully released and fully applied positions.
3. Check for inlet valve and O-ring leak.
3. Check the delivered pressure on the test gauges
to see that it varies equally and proportionately
with the movement of the brake pedal.
4. Make this check with the service brakes released
when the R-12 or R-14 is used to control the
service brakes.
5. Make the check with the spring brakes applied
(PARK) when the R-14 is used to control the
spring brakes. Coat the exhaust port and the
area around the retaining ring with a soap
solution; a one inch bubble leak in 3 seconds is
permitted.
4. After a full application is released, the reading
on the test gauges should fall off to zero
promptly.
It should be recorded that the Primary circuit
delivery pressure will be about 2 PSI greater than the
Secondary circuit delivery pressure with both supply
reservoirs at the same pressure.
6. Check for exhaust valve leak.
7. Make this check with the service brakes fully
applied if the R-12 or R-14 controls the service
brakes.
9. Coat the exhaust port with a soap solution; a 1
inch bubble in 3 seconds leak is permitted.
A change in vehicle braking characteristics or a
low pressure warning may indicate a malfunction
in one or the other brake circuit. Although the
vehicle air brake system may continue to
function, the vehicle should not be operated until
the necessary repairs have been made.
10. Coat the outside of the valve where the cover
joins the body to check for seal ring leak; no
leak is permitted.
Always check the vehicle brake system for proper
operation after performing brake work and
before returning the vehicle to service.
8. Make this check with the spring brakes fully
released if the R-14 is used to control the spring
brakes.
Note
If the anti-compound feature is in use, the line
attached to the balance port must be
disconnected to perform this test.
If the R-14 is used to control the spring brakes, place
the park control in the released position and coat the
balance port with a soap solution. Check the
diaphragm and seat. A leak equivalent to a one inch
bubble in 3 seconds is permitted.
If the valves do not function as described above, or
if leaks are excessive, it is recommended that the
valves be replaced with new or remanufactured units
or repaired with genuine Blue Bird parts, available at
any authorized Blue Bird parts outlet.
030-54
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Leak Check
1. Hold a high pressure 80 psi application.
2. Coat the exhaust port and body of the brake
valve with a soap solution.
3. A one inch bubble leak in 3 seconds is permitted
If the brake valve does not function or leak is
excessive, replace with a new or remanufactured
unit, or repaired with genuine Bendix parts
available at authorized Blue Bird parts outlets.
Automatic Slack Adjuster
Check the free stroke, push rod power stroke, and
back torque. Refer to Group 030.2 Wheel End
Components (Automatic Slack Adjuster).
Brake Chamber
Apply brakes and observe movement of all brake
chamber rods.
Push Pull Control Valves
Operational and Leak Test
An accurate test gauge should be installed into the
supply line and a means of controlling the supply
pressure should be provided. Apply a 120 psi air
source to the supply port. A small volume reservoir
(e.g. 90 cu. in.) with a gauge should be connected
to the delivery port.
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Air Compressor
Operating Tests
Vehicles manufactured after the effective date of
FMVSS 121, with the minimum required reservoir
volume, must have a compressor capable of raising
air system pressure from 85-100 psi in 25 seconds or
less.
This test is performed with the engine operating at
the maximum recommended governed speed. The
vehicle manufacturer must certify this performance
on new vehicles with appropriate allowances for air
systems with greater than the minimum required
reservoir volume.
Air Leak Tests
Compressor leak tests are not performed on a regular
schedule. These tests should be performed when it
is suspected that discharge valve leak is substantially
affecting compressor build-up performance, or when
it is suspected that the compressor is “cycling”
between the load and unloaded modes due to an
unloader piston leak.
These tests must be performed with the vehicle
parked on a level surface, the engine not running, the
entire air system completely drained to 0 PSI and the
inlet check valve detail parts removed, if applicable.
1. Apply 120 psi supply pressure and pull button
for exhaust position. A leak at the exhaust port
should not exceed a one inch bubble in five
seconds. Likewise,a leak at the plunger stem
should not exceed a one inch bubble in five
seconds.
Unloader Piston Leak
• The unloader pistons leak check
2. There should be no leak between upper and
lower body.
3. Listen for an escape of air at the inlet valve area.
An audible escape of air should not be detected.
3. Push the button in (applied position). Any leak
at the exhaust port or at the plunger should not
exceed a one inch bubble in 3 seconds; at the
plunger a one inch bubble in three seconds.
Discharged Valve Leak
Unloader piston leak must be repaired before this
test is performed. Leak past the discharge valves
can be detected.
4. Reduce the supply pressure. At a pressure from
60 to 20 psi, depending on the spring installed,
the button should pop out automatically,
exhausting the delivery volume. (This does not
apply to some PP-1’s).
1. Remove the discharge line and apply shop air
back through the discharge port.
1. Remove the cylinder head from the compressor.
2. Cover securely the inlet flange, apply 120 psi of
air pressure to the governor port.
2. Listen for an escape of air at the compressor
inlet cavity. A barely audible escape of air is
generally acceptable.
If the compressor does not function as described
above, or if the leak is excessive, it is recommended
that it be returned to the nearest authorized Blue
Bird distributor for a factory remanufactured
compressor.
030-56
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If a return to an authorized Blue Bird distributor is
not possible, the compressor can be repaired using a
genuine Blue Bird cylinder head maintenance kit.
Retest the cylinder head after installation of the kit.
Antilock Systems Service Check
Wheel Speed Sensor Service Check
Check all wiring and connectors. Make sure
connections are free from visible damage.
Examine the sensor. Make sure the sensor,
mounting bracket, and foundation brake components
are not damaged. Repair or replace as necessary.
Antilock Modulator Assembly
Operational and Leak Test
• Leak Testing
1. Park the vehicle on a level surface and block or
chock the wheels. Release the parking brakes
and build the air system to full pressure.
2. Turn the engine OFF and make 4 or 5 brake
applications and note that the service brakes
apply and release promptly.
3. Build system pressure to governor cut out and
turn the engine OFF.
4. Hold a full service brake application.
5. Apply a soap solution to the exhaust port of the
modulator. Leak should not exceed a one inch
bubble in less than 3 three seconds. If leak
exceeds the specified maximum, replace the
modulator.
6. Apply a soap solution around the solenoid
assembly (top and bottom). Leak should not
exceed a one inch bubble in less than 3 three
seconds.
If leak exceeds the specified maximum, tighten the
solenoid cap screws and re-test. If the leak remains
excessive after re testing, replace the modulator.
7. Apply a soap solution around each diaphragm
cover. Leak should not exceed a one inch
bubble in less than three seconds.
If leak exceeds the specified maximum, tighten the
diaphragm cap screws and re test. If the leak
remains excessive after re testing, replace the
modulator.
030-56
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Operation Testing
Note
To properly test the function of the modulator
will require 2 service technicians.
1. Park the vehicle on a level surface and block or
chock the wheels.
2. Release the parking brakes and build the air
system to governor cut out.
3. Turn the engine ignition key to the OFF position
then make and hold a full brake application.
4. Apply brakes and hold.
5. Post a service technicians posted at one of the
modulators, turn the vehicle ignition key to the
ON position.
6. One or two short bursts of air pressure should be
noted at the modulator exhaust.
7. Repeat the test for each modulator on the
vehicle. If at least a single burst of exhaust is
not noted or the exhaust of air is prolonged and
not short, sharp and well defined, perform the
Electrical Tests below.
•
Electrical Tests
Before testing the solenoid assembly of a suspect
modulator, its location on the vehicle should be
confirmed.
Proceed to the modulator in question and inspect its
wiring connector. Disconnect the connector and test
the resistance between the pins on the modulator.
Refer to Figure 54.
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HOLD to SOURCE: Read 3.5 to 5 OHMS
EXHAUST to SOURCE: Read 3.5 to 5 OHMS
EXHAUST to HOLD: Read 7 to 10 OHMS
Individually test the resistance of each pin to vehicle
ground and note there is no continuity.
If the resistance readings are as shown, the wire
harness leading to the modulator may require repair
or replacement.
Before attempting repair or replacement of the wire
harness, refer to Troubleshooting procedures
specified for the antilock controller.
If the resistance values are not as shown above,
replace the modulator.
Figure 54—Modulator Test
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Diagnosing and Locating a System
Fault
General
The EC-17 contains self test and diagnostic circuitry
that continuously checks for proper operation of the
entire antilock/traction system, including wiring
continuity.
The EC-17 is programmed at the factory to
accommodate the needs of the vehicle and the
customer's desires.
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Diagnostic Communication Interface
The DCI is a dual level electronic diagnostic tool for
either the EC-17 antilock controller. It can either be
used as a stand alone diagnostic tool or with
AlliedSignal’s A Com For Windows software.
In order to use the DCI, the vehicle must be
equipped with a J1587 diagnostic link connector as
illustrated in Figure 56. This connector is generally
located on the driver’s side, in the lower portion of
the dash or under the dash panel.
The EC-17 controller can be reconfigured by the end
user to include traction control. A vehicle equipped
with traction control can generally be identified by
noting the presence of a dash mounted condition
lamp, a disable switch (for the traction control
system) and a traction solenoid located above the
relay valve.
Separate dash lamps, controlled by the EC-17,
advise the driver of the condition of the entire
antilock/traction system.
When the controller senses an erroneous condition, it
stores the condition in memory, illuminates the dash
mounted condition lamp and, after certain criteria
are met, it disables the antilock or traction control
function.
The fault condition is truly stored and is not cleared
by loss of power to the antilock system.
The optional LEDs will illuminate when power is
restored and remain illuminated until the failure is
corrected.
After the actual issue is corrected, maintenance
personnel can clear or reset the EC-17 diagnostics
through the SAE J1587 diagnostic link or the
optional magnetic RESET point in the diagnostics
display (Figure 55).
Figure 56—Diagnostic Connector
Used with its Microsoft Windows based software
and a personal computer, the DCI is able to provide
the technician with a high level of diagnostic
information and antilock fault history (Figure 57).
This is particularly useful when attempting to
determine the source of intermittent fault indication
from the antilock dash condition lamp.
Figure 57—DCI Tool with PC
Figure 55—DCI Tool
030-58
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When using the DCI’s LED display for system
diagnosis or controller self configuration, the
descriptions and procedures presented in this manual
can be used. When connected to a PC, use the
instructions and documentation packaged with the
DCI to troubleshoot or reconfigure the EC-17
controller.
For more information on the Allied Signal Bendix,
Diagnostic Communication Interface, see your local
authorized AlliedSignal Bendix parts outlet or call 1800-AIR-BRAK (1-800-247-2725).
Optional Diagnostic LED and RESET
The condition of specific components is provided by
a series of labeled, light emitting diodes (LEDs) in
the EC-17 housing.
No special tools or equipment are needed to read or
interpret the EC-17 diagnostic display. It should be
noted that the EC-17 diagnostics display is separate
from the antilock and traction condition lamps on the
dash Table 1.
With this separation, the driver is aware of any
issues that occur but is not confused by diagnostic
information.
There are ten LEDs plus a magnetically actuated
reset switch.
The first six LEDs locate an issue to a specific area
of the vehicle, and the next three indicate the
component or its wiring. The LEDs are software
driven and are either ON or OFF, depending upon
their monitor function.
Note
Right and left, front and rear are determined
from the driver’s seat.
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•
RESET + No LED
Note
The MID LED is used with some but not all
vehicles.
When six speed sensors are not installed this
LED is not used in the diagnostic process.
However, it will light when a magnet is
placed on the RESET switch in the diagnostic
display.
•
FRT (Front) LED
This Red LED illuminates in order to indicate the
location of a faulted component or its wiring. It will
light in conjunction with either the RIGHT or LEFT
LED and the MOD or SENS LED.
•
MID (Middle Axle) LED
This Red LED is not used in all installations. On
those vehicles that have six speed sensors installed,
this Red LED illuminates to indicate the location of
a faulted speed sensor or its wiring. The "MID"
LED should not illuminate with the "MOD" LED.
•
RER (Rear) LED
This Red LED illuminates in order to indicate the
location of a faulted component or its wiring. It will
light in conjunction with either the RIGHT or LEFT
LED and the MOD or SENS LED
•
RHT (Right) LED
This Red LED illuminates in order to indicate the
location of a faulted component or its wiring. It will
light in conjunction with either the FRONT or
REAR LED and the MOD or SENS
•
LFT (Left) LED
•
FRT Red LED
•
MID Red LED
•
RER Red LED
This Red LED illuminates in order to indicate the
location of a faulted component or its wiring. It will
light in conjunction with either the FRONT or
REAR LED and the MOD or SENS LED.
•
RHT Red LED
•
•
LFT Red LED
•
TRC Red LED
•
MOD Red LED
This Red LED illuminates to indicate a permanent
fault in the traction control system. It may be
illuminated with the MOD LED or may illuminate
by itself.
•
SEN Red LED
•
ECU Red LED
•
VLT Green LED
030-60
TRC (Traction) LED
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Note
If a fault exists with the wiring to the engine
control module (ECM ), this LED will go on.
•
MOD (Modulator) LED
This Red LED illuminates to indicate an open or
short circuit in the solenoids of one of the four
modulators or the wiring connecting them to the
system. When indicating a fault with a modulator
this LED will be illuminated with two positioning
LEDs (RHT/LFT + FRT/RER).
Note
The MID positioning LED should not be
illuminated with this LED. This LED is also
used to indicate a fault with an ATR 1,
antilock Traction Relay, solenoid. When
illuminated for attraction system fault, the
TRC LED will also be on.
•
SEN (Speed Sensor) LED
This Red LED illuminates to indicate an open or
short circuit in one of the speed sensors or the wiring
connecting them to the system. The "SEN" LED
will be illuminated with two positioning LEDs
(RHT/LFT + FRT/MID/RER).
030-60
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ECU (Electronic Control Unit) LED
This Red LED, when illuminated, indicates that the
controller itself has failed. Before controller
replacement is considered, always check vehicle
voltage to the controller.
•
VLT LED
This Green LED illuminates and remains ON during
vehicle operation to indicate that vehicle power is
reaching the controller. If vehicle power is out of
range (below 10 VDC or above 18.0 VDC) this LED
will flash until power is brought into range.
•
RESET
Beneath the RESET area of the display is a
magnetically sensitive switch that is used to reset the
diagnostic system. The device will respond to a
magnet that has strength sufficient to lift a three
ounce weight.
Momentarily holding a magnet against the RESET
will cause ALL LEDs to light during the time the
magnet is against it.
Holding a magnet against the RESET longer than 20
seconds will cause the EC-17 to initiate the self
configuration feature.
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Table 2—Lamp Configuration
EC-17 Controller Configuration
SEN + FRT (front) + RER (rear) = A four sensor
con figuration (all systems must have at least a 4
sensor configuration)
The following information and procedure applies
to the EC-17 controller equipped with the
optional LED diagnostic display and magnetic
RESET switch.
Controllers without this option (EC-17N) must
use the J1587 diagnostic link and the DCI with its
related computer programs to reconfigure the
controller.
EC-17 Configuration Display
Turn the ignition ON.
All LEDs will illuminate, then go out.
The number of active sensors will be displayed by
the momentary illumination of the red SEN (sensor)
LED and two or more of the red locating LEDs. No
other LEDs will be on.
SEN + FRT + MID (middle) + RER = A six sensor
configuration
The red TRC LED will momentarily illuminate by
itself if traction control torque limiting is active. If
not, then the display will go to the condition
described in number 5.
The red TRC and MOD LEDs will momentarily
illuminate if traction control differential braking is
active. If not, then the display will go to the
condition described in number 6. No other LEDs
will be on.
The diagnostic display will return to its normal
operational status. Assuming no faults exist in the
antilock or traction system, all red LEDs will be off
and the single, green, VLT LED is illuminated.
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EC-17 Self Configuring Process
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Any disconnected speed sensor(s) will register as a
failure on the diagnostic display at the end of the
EC-17 self test.
All or part of traction control can be lost during self
configuration by;
Three aspects of the antilock and traction system
are influenced by the self configuring feature of
the EC-17.
•
Speed Sensors
The number of speed sensors connected to the EC17 will be detected during the self configuration
process. The EC-17 will check the MID SEN (mid
axle speed sensor) locations on its connector to
determine if a sensor is connected to it and will
default to a six sensor configuration if it detects even
one sensor connected. If mid axle speed sensors are
not detected, the EC-17 will default to a four sensor
configuration. (Two front and two rear)
•
Electronic Engine Control
If the EC-17 is connected to the control module of
an electronic engine, the torque limiting feature of
traction control will be activated during the self
configuring process.
•
Antilock Traction Relay Valve
If the solenoid assembly in the ATR valve is
connected to the EC-17, the differential braking
feature of traction control will be activated during
the self configuring process.
•
Traction Disable Switch
The traction disable switch must be in the correct
position for the Self Configuration process.
No method is available to disable the Self
Configuration Process feature.
Due to the extended period of time the magnet must
be held on the RESET to initiate the self
configuration process (20 seconds), it is unlikely that
a self configuration would occur accidentally.
Basic, four speed sensor, antilock operation can not
be removed during the self configuration process.
This is a minimum configuration for all EC-17
controllers.
If a speed sensor is connected to either wheel on the
mid axle, the EC-17 will configure for six sensors.
If no mid axle speed sensor is detected, the EC-17
will configure for four sensors.
030-62
Not connecting one of the wire harnesses (engine
control module for torque limiting and ATR valve
solenoid for differential braking)
A missing or inoperative traction control enable
disable switch.
Not toggling the traction control enable/disable
switch in the “traction enabled” after power up, but
prior to the self configuration.
The operator can tell that the traction features are
lost by noting the absence of the traction lamp flash
upon power up. The operator should note the
flashing of the antilock condition lamp, and the
traction lamp if traction equipped, upon every power
up. Observing the dash lamps is one method the
operator has to verify the system operation.
The EC-17 can be reprogrammed up to 10,000
times.
When a replacement EC-17 is installed on a vehicle
that does not have one or more of the preprogrammed features, a failure will be registered on
the dash lamp(s) and on the EC-17 diagnostic
display. For this reason it is necessary to perform
the Self Configuration Process.
Some configuration information is available by
observing the reaction of the dash condition lamps
on vehicles configured with traction control and
equipped with the self configuring EC-17.
When the ignition is switched ON, the EC-17 self
test is begun. During the self test the dash lamps
will flash on and off together as indicated in the
chart, depending upon the type and amount of
traction control configured into the EC-17.
Self Configuration Process
In order to successfully complete the self
configuring process follow the steps presented.
Connect all antilock and traction control wire
harnesses.
Make sure that all the speed sensors present on the
vehicle are connected (H2, H3, J1, J2 on the 30 pin
connector and E2, E3, F2, F3, B2, B3, C2, C3 on the
18 pin connector).
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If the vehicle has an electronic engine and traction
control torque limiting is desired the engine control
module must be connected (B2 and B3 on the 30 pin
connector for J1922 or C3, D2, and D3 on the 30 pin
connector for J1939).
If the vehicle is equipped with either an ATR 1 or
ATR 2 valve, the solenoid connection must be made
to the EC-17 (D2 and D3 on the 18 pin connector) in
order to obtain traction control differential braking.
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Place the traction control enable/disable switch in
the traction control enabled position (traction control
operative), the traction control dash lamp should be
off.
Before placing the vehicle in service, verify the
configuration and the system condition by turning
the ignition OFF then ON while observing the EC17 diagnostic display.
If the vehicle is to be configured with traction
control, it must have a traction control dash lamp
and a traction control enable/disable switch. Both
the lamp and switch must be functional.
The diagnostic display should indicate the desired
configuration as described under the section entitled
EC-17 CONFIGURATION DISPLAY and no red
LEDs should be illuminated at the end of the self
test.
Turn the ignition ON, toggle the traction control
enable/disable switch back and forth then hold a
magnet on the RESET position of the EC-17
diagnostic display until the LEDs begin to flash then
remove the magnet.
If the configuration appears correct but the
diagnostic LEDs indicate a failure somewhere in the
system, refer to the EC-17 Controller Configuration
section and use the Troubleshooting section of this
manual to locate and repair the fault.
If the magnet is not removed during the LED
flashing a second self configuration may be initiated.
The magnet may have to be held on the RESET for
as long as 20 seconds.
If the configuration is incorrect, the process can be
repeated as required. One common error is
performing the self configuration without toggling
the traction control enable/disable switch. This will
prevent any traction features from being activated.
When the self configuration process is complete the
EC-17 will automatically go through a self test.
During the self test the diagnostic display will
indicate the new configuration as described under
the section entitled EC-17 CONFIGURATION
DISPLAY.
Note
If the EC-17 is being configured with Traction
Control (either torque limiting, differential
braking or both), the traction control condition
dash lamp, will be illuminated as well as the
appropriate LEDs on the EC-17 diagnostic
display.
The traction control dash lamp will be
illuminated until the traction control
enable/disable switch is placed in the traction
control enabled position (traction control
operative).
Note
The traction switch must be toggled to
configure traction, but must be placed in the
enable position to allow the traction lamp to
flash.
Troubleshooting
Determine if the vehicle is equipped with traction
control. The presence of a traction condition
lamp on the dash can be used.
Some vehicles are equipped with a traction control"
disabling switch." If so equipped, enable the traction
system before beginning the Troubleshooting. The
traction control must be disabled for dynamic
testing.
If the vehicle is equipped with traction control and is
a tandem axle unit, note the number of drive axles.
The "MID" diagnostic LED is used only on 6x4
vehicles.
030-62
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General
While the EC-17 diagnostic display locates a
specific fault area, it is still necessary to confirm
whether the fault resides in the component itself or
the wiring. All troubleshooting should begin by first
performing the "Initial Start up Procedure" and
following the directions contained in it.
Troubleshooting Help
Begin by observing the dash condition lamp(s) and
performing the Initial Startup Procedure.
The troubleshooting technician should record all
findings and the action taken during the
troubleshooting process.
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No voltage or resistance tests are performed into the
EC-17. All voltage and resistance tests are
performed by beginning at the wire harness half of
the connector and moving away from the EC-17
toward an antilock traction system component
(modulator, wheel speed sensor, etc.)
Diagnostic Display
This index (Figure 58) is troubleshooting Bendix
full-vehicle wheel control antilock with traction
control. It provides a quick reference to specific
sections that provide testing procedures and values.
Figure 58—Diagnostic Display Quick Reference
030-64
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Initial Startup Procedure
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Figure 59—EC-17 Configuration
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Section I – Antilock Dash Lamp Testing
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030-66
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Figure 60—Antilock Dash Lamp Testing
030-66
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Section II – Inspection for Illuminated LEDs
Figure 61—Inspection for Illuminated LEDs
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Section III – Inspection for Illuminated LEDs
Figure 62—Inspection for Illuminated LEDs continued
030-68
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Section IV – Inspection for Illuminated LEDs
Figure 63—Inspection for Illuminated LEDs continued
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Section V – Testing for Power to the EC-17
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030-70
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Figure 64—Power to EC-17
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Section VI A - Testing the Modulator
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Figure 65—Testing Modulator
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Section VI B - Testing the Modulator
030-72
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Figure 65—Testing Modulator continued
030-72
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Section VII A - Testing the Wheel Speed Sensor
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Figure 66—Testing the Wheel Speed Sensor
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Section VII B - Testing the Wheel Speed Sensor
030-74
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030-74
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Figure 66—Testing the Wheel Speed Sensor continued
030-74
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Section VIII - Testing for False Indication Caused by Dash Light Relay
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Figure 67—Testing for False Indication Caused by Dash Light Relay
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Section IX - Testing for False Indication Caused by Wheel Speed Components
030-76
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030-76
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Figure 68—Testing for False Indication Caused by Wheel Speed Components
030-76
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Section X - Testing Traction Control Dash Lamp
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Figure 69—Testing Traction Control Dash Lamp
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Section XI - Testing Traction Control Modulator
030-78
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030-78
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Figure 70—Testing Traction Control Modulator
030-78
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TC Series Brakes
Section XII - Testing Engine Control Module Wire Harness
Figure 71—Testing Engine Control Module Wire Harness
030-89
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TC Series Brakes
Hydraulic Brakes
General
Dual hydraulic brake system receiving hydraulic
boost from the vehicles power steering system
incorporating an electric motor back-up boost in the
event of a main system or engine failure.
FAILURE TO TIGHTEN HAND BRAKE
LEVER LOCK SCREW MAY RESULT
IN FAILURE OR DAMAGE TO THE
PARK BRAKE. INCORRECT
ADJUSTMENT COULD RESULT IN
UNINTENTIONAL VEHICLE
MOVEMENT.
Do not mix fluids in either the brake system or
the boost system because premature brake
system failure will occur.
Do not allow the cable to become twisted.
The dual brake system gives the driver reasonable
braking capacity in the event that either the front or
rear brake circuit should fail. The brake system
utilizes a glycol based hydraulic fluid (DOT), and
the boost system utilizes power steering system fluid
(DEXTRON).
The parking brake is a drum type brake installed on
the output shaft of the transmission. Activated by a
foot pedal and cable mechanism that rotates the
bellcrank assembly that rotates the parking brake
lever assembly that applies the brake shoes to the
parking brake drum, that in turn locks the driveshaft
preventing any further rear tire rotation. At this
point, the parking brake is fully applied.
Routine Maintenance
Every three months, 25,000 miles or 900
operating hours whichever occurs first:
1. Check the brake fluid level of the master
cylinder reservoir and replenish if necessary.
Note
Ensure that vehicle is on level ground with the
wheels blocked to prevent rolling.
6. Loosen the lock screw located on the hand brake
lever and relieve all tension on the cable by
rotating the hand brake lever counter-clockwise.
7. Move the hand brake lever to the fully lowered
position.
8. Disconnect and remove clevis from parking
brake bellcrank assembly.
9. Perform maintenance (such as replacing shoes,
drum, cable, or connecting linkage) as
necessary.
10. Reconnect the cable to the bellcrank assembly
and hold the brake lever in the full upright
position bringing the shoes in contact with the
drums.
2. Check the Hydro-Max exterior and all the
connecting lines for fluid leak. Remove dirt
from the exterior of the Hydro-Max.
11. Adjust the clevis on the cable to align the clevis
holes with the brake lever hole. Insure
minimum thread engagement.
3. Check for the loose or disconnected electrical
connections and damaged wiring.
12. Install clevis pin and cotter pin.
4. Check the vehicle brake warning system
(Reference Brake Booster and Warning System
Troubleshooting) comparing the reaction of
warning lights and buzzers to the vehicles
handbook.
14. Adjust the cable at the hand brake handle. Turn
the lever clockwise to obtain a peak resistance in
the hand brake movement of 90 to 110 pounds
(400 to 489N•m).
5. Check brake fluid level. The Bosch disc brakes
self-adjust for lining wear. Brake fluid must be
maintained to the correct level.
030-80
13. Raise the hand brake lever.
15. Tighten the lock screw located on the hand
brake lever.
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TC Series Brakes
Brake Booster and Warning System Troubleshooting
Conditions
Status
Fault
Key Off-Brake Off
Motor Off
Normal
Motor On
Relay stuck closed
Stop light switch failed or out of
adjustment.
Pedal return spring out of
adjustment or broken.
Key Off-Brake On
Motor On
Normal
Motor Off
Blown stop light fuse
Motor failed or disconnected
Flow switch failed
Stop light switch failed or out of
adjustment
Stop light switch diode bad.
Key On-Engine Off-Brake Off
Warning Light /Buzzer Off
Normal
Warning Light/Buzzer On
Ignition diode bad
Motor On
Normal
Motor Off
Motor faulty or disconnected.
Relay faulty.
Flow switch failed.
Open in fusible link or relay feed
from starter ignition diode bad.
Warning Light/Buzzer On
Normal
Warning Light/Buzzer Off
Booster module fault
Buzzer and light both bad
Buzzer fuse and light both
blown.
Ignition circuit fuse blown
Light On/Buzzer Off
Buzzer bad
Blown fuse
Short in low coolant or Kysor®
heater circuits.
Table 3—Brake Booster and Warning System Troubleshooting
030-82
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TC Series Brakes
---
Light Off/Buzzer On
Bulb burn out.
KEY On-Engine On-Brake Off
Motor Off
Troubleshoot instrument cluster
Normal
---
Motor On
Low fluid flow
Flow switch failed
Pressure differential switch
closed.
Difference in front and rear
system pressures.
Switch failure.
Relay faulty
Warning Light /Buzzer Off
Normal
Warning Light/Buzzer On
Low fluid flow
Flow switch failed
Motor failed or disconnected
Open in fusible link or relay feed
from starter.
Pressure differential switch
closed
Difference in front and rear
system pressure.
Switch failure
Open in wire or fusible link
between pin E of booster module
and relay.
Bad brake booster module
Key On-Engine On-Brake On
Motor Off
Normal
---
Motor On
Low fluid flow
Flow switch failed
Pressure differential switch
closed
Difference in front and rear
system pressure.
Switch failure
Relay fault
Table 3—Brake Booster and Warning System Troubleshooting continued
030-82
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TC Series Brakes
---
Warning Light/Buzzer Off
Normal
---
Warning Light/Buzzer On
Low fluid flow
Flow switch failed
Motor failed or disconnected
Pressure differential switch
closed
Difference in front and rear
system pressure.
Switch failure
Open in wire or fusible link
between pin E of booster module
and relay.
Bad brake booster module
Table 3—Brake Booster and Warning System Troubleshooting continued
Note
Where failed components are indicated, check the integrity before replacing that component. Check
continuity of the circuitry (wires, connectors, etc.) leading to and from that component.
Theory of Operation
Hydro-Max General Description
The Hydro-Max is a hydraulically powered booster
in conjunction with a mini master cylinder that
provides a power assist for applying hydraulic
brakes. Together, they form the hydraulic brake
actuation unit. The unit reduces the pedal effort and
the pedal travel required to apply the brakes as
compared to a non-power system.
The mini master cylinder is a split system type with
a separate brake fluid reservoir and pistons. The
output ports for the front and rear brakes systems, or
a single system master cylinder, may be used where
regulations are not applicable.
•
3. A hydraulic master cylinder
The hydraulic booster configuration
An open center valve and reaction feed back
mechanism, a large diameter boost power piston. A
reserve electric motor pump, and an integral flow
switch. It is powered by either the bus power
steering pump or by a pump dedicated solely to the
booster.
A reserve electric motor pump provides a redundant
source for the hydraulic booster. The pump’s use is
signaled by the integral flow switch.
030-82
Hydro-Max Power Brake System Components
1. A hydraulically powered booster
2. A reserve electric motor pump
4. An integral flow sensing switch and warning
system
Hydraulic Pump Operating Components
The Hydro-Max booster is positioned in the
vehicle’s hydraulic circuit integrated with the power
steering gear.
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TC Series Brakes
Figure 72—Hydraulic System Configuration
The Hydro-Max hydraulic booster operates in series
with the power steering gear. The pressure demands
during simultaneous steering and braking are additive
(i.e., if steering requires 1200 psi and pump relief is
2100 psi, the booster will get 900 psi). See Figure
72—Hydraulic System Configuration.
The power steering gear must be balanced so that it
can handle the pressures generated in the steering gear
return line. It must also have an internal relief valve
setting lower than pump relief. To allow the steering
gear to relieve before the hydraulic pump does, it must
also have an internal bypass to allow manual steering
during reserve system operation.
The fluid flow path depicted is required to minimize
the interaction between the power steering gear and
the hydraulic booster.
The pressure line must be ½ inch flexible or rigid
pressure line conforming to SAE J188 and be designed
to run from the steering gear to the Hydro-max inlet.
030-84
Figure 73—Hydro-Max Connections
The connections for the hose will consist of an
adapter for the return side of the gear and the tube
O arrangement for the Hydro-Max inlet. See
Figure 73.
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TC Series Brakes
Electrical
1. A relay.
5. Pedal activated brake light switch.
2. A 12 VDC battery.
7. A warning light for reserve motor.
3. A warning light for the pressure differential
valve.
8. A (optional) electronic monitor module.
6. A buzzer.
4. Electrical connectors and wiring.
Operation of the Hydro-Max Booster and Reserve Electric Motor Pump
Figure 74—Booster Location
During normal system operation, fluid flow from a
hydraulic power source (in the instance of the power
steering pump), enters the inlet (pressure) port of the
Hydro-Max booster, flows through the throttle valve
and power piston, then through the flow switch and
exits from the outlet (return) port (Figure 74).
Force applied to the brake pedal by the vehicle
operator is multiplied by the lever ratio of the pedal
mechanism to move the input pedal rod of the
booster.
This movement activates the throttle valve,
restricting flow through the power piston. The
resulting pressure, acting on the power piston,
applies a boosted force to the master cylinder
primary piston.
A reaction piston, inside the power piston
subassembly, provides the driver pedal feel during
an application of the brake pedal.
Fluid flow through the flow switch opens the reserve
motor pump electrical circuit during normal
operation.
A separate check valve in the motor pump prevents
back flow through the motor pump during normal
applications.
In the event normal flow from the power steering is
interrupted, the electric motor pump provides the
power for reserve stops. Upon flow interruption, the
integral flow switch closes, energizing a power
relay, thereby providing electrical power to the
motor pump.
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TC Series Brakes
During the reserve operation, fluid is retained within
the booster by the inlet port check valve. The motor
pump re-circulates fluid within the booster assembly
with pressure built on demand via the throttle valve.
The number of applications is limited only the
electrical capacity of the vehicle.
Manual braking is also available in the event both
the power and reserve systems are inoperative. Note
the performance curve shown in Figure 75.
Figure 75—Performance Curve
030-86
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TC Series Brakes
Operation of the Mini Master Cylinder
Figure 76—Master Cylinder Operation
between the secondary pressure chamber and the
Each pressure chamber has a piston/actuator
reservoir section serving the secondary chamber.
subassembly containing a preload (caged) spring and
Additional movement of the primary piston causes
a return spring (Figure 76). In the released position,
both chambers to build pressure.
actuators of both the primary and secondary pistons
are in contact with their respective compensating
When the load on primary piston is removed, fluid
valve stems, that project into the cylinder bore. This
pressure in each chamber, combined with return
maintains the valves in an open position that allows
spring force, causes the primary and secondary
hydraulic fluid in the reservoir to replenish any fluid
pistons to return to their initial released positions.
displayed from the cylinder bore.
Each actuator opens its respective compensating
valve, reopening the passage between the individual
Initial forward travel of the primary piston moves
reservoir sections and its associated pressure
the primary actuator away from its compensating
chamber.
valve counterpart permitting the valve to seat.
Closure of this valve shuts off the passage between
Should the rate or release be great enough to cause a
the primary pressure chamber and the reservoir
partial vacuum in a chamber, the compensating
section serving the primary chamber.
valve will open to allow replenishment of fluid in
the cylinder bore.
Further movement of the primary piston creates a
pressure in the primary pressure chamber, causing
Any excess fluid remaining at the end of the stroke
the secondary piston and actuator to move. As the
due to “pumping”, and/or volume change due to
secondary piston and actuator move, the secondary
temperature fluctuation, is released as the
compensating valve closes, shutting off the passage
compensating valve ports open.
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TC Series Brakes
Operation of Flow Switch and Warning Switch
The Hydro-max hydraulic booster has a reserve
electric motor pump that will provide hydraulic
boost for emergency operation.
The basic signal for operation of the electric motor
pump comes from the integral flow switch (Figure
86) in the Hydro-max booster itself.
The interface of this electric motor with the vehicle’s
existing electrical system can be accomplished in at
least two different ways.
The electric motor pump receives its power from the
reserve system relay. The relay is in turn controlled
by two dependent conditions.
First, the positive or power lead to the coil of the
reserve system relay comes from the brake switch.
Second, the ground path for the coil of the relay is
supplied by the Hydro-Max booster flow switch.
When this switch is closed, a ground path is supplied
to the relay coil. The flow switch senses flow
through the booster. When the flow drops below a
set point, the flow switch closes.
When power to the relay coil is available and the
flow switch is closed, the relay energizes and
supplies power to the reserve electric motor pump.
Therefore, when the flow switch is closed and the
brake pedal is depressed, the electric motor pump is
operating and the reserve system is operational.
Operation of the Electronic Monitor Module
The electronic module receives power from two
sources. The module is powered by the ignition
switch; power is supplied when the ignition switch is
in the run and start positions.
The second source of power for the module is
received from the brake light switch. When the
brake pedal is depressed and the brake switch closes,
power flows to the brake lights and to the electronic
module. Therefore, the module is powered anytime
the vehicle ignition is turned on or anytime the brake
pedal is depressed.
The Hydro-Max reserve system is powered by an
electric motor pump. This electric motor receives its
power from the reserve system relay.
030-88
The relay is in turn controlled by two dependent
conditions. First, the positive or power lead to the
coil of the reserve system relay from the electronic
module. Second, the ground path for the coil of the
relay is supplied by the Hydro-Max booster flow
switch.
When this switch is closed, a ground path is supplied
to the relay coil. This flow switch senses flow
through the booster. When the flow drops below a
set point, the flow switch closes.
Current is available to the coil of the relay whenever
the module is powered.
When power to the relay coil is available and the
flow switch is closed, the relay energizes and
supplies power to the reserve electric motor pump.
Therefore, when the flow switch is closed and either
the brake pedal is depressed or the ignition is on, the
electric motor pump is operating and the reserve
system is operational.
Brake Warning System
The brake warning system includes a buzzer and a
dash mounted indicator. The light and buzzer will
operate as a result of the following:
Engine is running, brakes not applied with a loss of
electrical power to the electric backup pump motor.
Engine is running, brakes not applied with a loss of
power assist from the power steering pump
Engine is running, brakes are applied and either the
front or rear section of the system has failed. The
backup pump buzzer and light will remain on even
after the brake pedal has been released.
Engine is not running, brakes not applied, but
ignition key is ON. This condition should happen
every time the driver starts the bus. The bus should
not be driven if the backup pump system is not
working. The backup system should go off when
the engine starts.
Note
With engine not running and ignition OFF, a
depressed brake pedal will cause the backup
to run with no light and buzzer.
Engine is running, brakes are applied, ignition is in
ON or START position. This is a method for
checking that the back-up pump system is not
working. The backup system should go off when
the pedal is released.
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TC Series Brakes
Without the assist of the power steering pump and
without the assist of the backup pump, the master
cylinder will allow the brakes to be applied.
However, brake capacity will be very limited and the
bus should not be driven under these conditions.
Parking Brake
The parking brake is designed to hold the loaded bus
up to a 20% grade. The parking brake is not to be
used as a normal service brake, but can be used to
help stop in an emergency situation.
When the parking brake is applied, and the ignition
switch is ON, a dash mounted yellow light labeled
PARK will warn the driver that the brake is applied.
The bus should not be driven when the parking
brake is applied.
Driving the bus when the parking brake is applied
will prematurely wear the parking brake or damage
other drive train components.
Remove Hydro-Max Booster
1. Park the bus on a level surface and prevent
movement by means other than brakes.
2. Disconnect the negative terminal on battery.
3. Disconnect the Hydro-max input push rod from
the brake pedal.
4. Detach the electrical power lead from the
Hydro-Max pump motor.
8. Plug the ends of both hoses and the open ports
of the Hydro-Max.
9. Remove the four cap nuts that secure the master
cylinder to the Hydro-Max.
10. Support the master cylinder.
11. Remove the four bolts that secure the HydroMax to the bus and remove the Hydro-max.
Replace Hydro-Max Booster
1. Mount the Hydro-Max on the vehicle using four
bolts.
2. Torque the mounting bolts to 18-25 pounds-ft
(24.4-33.9 N⋅m).
3. Install the bus master cylinder on the HydroMax
4. Torque the four cap nuts to 25-30 pounds-ft
(33.9-40.7 N⋅m).
5. Reconnect the vehicle inlet and return hoses to
the Hydro-Max. Torque the inlet hose fitting to
16-25 pounds-ft (21.7-33.9 N⋅m). Do not over
tighten the inlet hose. Stripping of the
aluminum booster housing will result.
6. Reconnect the bus electrical power lead to the
pump motor. Reconnect the vehicle electrical
lead to the flow switch contact assembly.
Reconnect the wires at the relay.
7. Reconnect the bus negative lead to battery.
5. Disconnect the electrical lead from the flow
switch.
8. Perform Refilling and Bleeding Hydro-Max.
(See procedure in this group).
6. Disconnect the wires at the relay.
9. Perform Check Out Brake System. (See
procedure in this group).
Refilling and Bleeding Hydro-Max
The master cylinder must be supported in some
fashion so that the weight is exerted on the steel
brake lines connected to the master cylinder.
Do not apply the brakes after removal of the
input hose unless the reserve system is
disconnected. Reserve boost pressure will blow
the inlet check valve out of the booster.
7. Identify and remove the inlet and return hoses
from the Hydro-Max.
030-88
Do not use brake fluid. Use only clean power
steering fluid. (Refer to Approved Hydraulic
Fluids located in Group 120 Steering.)
1. Check hydraulic pump or power steering pump
reservoir supplying Hydro-Max.
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TC Series Brakes
2. Fill with clean power steering fluid. (Refer to
Approved Hydraulic Fluids located in Group
120 Steering.)
3. Crank engine several revolutions. (Do not start
engine.) Check pump reservoir and refill if
necessary.
Check Brake System
Before moving the vehicle, check the system for
correct operation.
With engine off depress the brake pedal. The
warning light and/or buzzer should come on and the
electric motor should run, giving you some brake
assistance.
Start the engine. Depress the brake pedal. No
warning lights or buzzer or electric motor should
come on. Check for leak.
Refer to Routine Maintenance (see procedure in this
group) to perform a more comprehensive check of
the systems integrity.
Stop the engine, check the fluid level in the power
steering pump reservoir. Add fluid if necessary.
(Refer to Approved Hydraulic Fluids located in
Group 120 Steering).
Hydraulic Brake Components
The hydraulic brake system is comprised of
hydraulic, electrical and mechanical components.
The hydraulic components consist of a fluid
reservoir, master cylinder, Hydro-Max booster, and
brake calipers.
The electrical components consists of a brake
booster module, brake system relay, electric booster
pump motor, flow switch, stoplight switches, engine
brake warning buzzer, electrical wire harness, and
electrical connectors.
The mechanical components are comprised of the
parking brake system.
Remote Reservoir – The remote reservoir is
connected to the master cylinder with two feed lines.
When the brake pedal is activated, hydraulic fluid is
compressed and activates the pistons in the brake
calipers. The reservoir replenishes the displaced
fluid.
030-90
•
Master Cylinder
The master cylinder utilizes brake pedal effort to
develop fluid pressure to activate the wheel
cylinders.
•
Hydro-Max Booster
The Hydro-Max booster assists the operator in
providing reduced brake pedal effort and reduced
travel required to apply the brakes. The friction
developed between the rotor and brake pads
provides the brake force required to stop the vehicle.
•
Brake Calipers
When the operator presses on the foot pedal,
hydraulic pressure is applied by the master cylinder
to the pistons in the caliper, that press the brake pads
against the rotor.
Electrical Components
• Brake Booster Module
Supplies power to the relay.
•
Brake System Relay
Transfers power from the brake booster module to
the electric booster pump motor.
•
Electric Booster Pump Motor
Supplies hydraulic fluid to the Hydro-Max booster
in case of hydraulic failure.
•
Flow Switch
Senses hydraulic pressure
•
Stoplight Switch
The stoplight switch senses pressure going to the
brake calipers, and closes the circuit to illuminate
stoplights.
•
Brake Warning Buzzer
Activates a warning when hydraulic pressure is low.
•
Electrical Wire Harness
Connects electrical components.
•
Electrical Connectors
Connects electrical wire harness to electrical
components.
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TC Series Brakes
Park Brake Components
The parking brake system is activated by a foot
pedal that is attached to a cable. The cable is
attached to the bellcrank assembly.
That attaches to the parking brake lever by a parking
brake yoke. The parking brake lever pushes the
brake shoes against the parking brake drum.
Electrical Components
Figure 77—Brake Booster Electrical Components
030-90
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TC Series Brakes
Mechanical Components
Figure 78—Park Brake Configuration
030-92
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TC Series Brakes
Troubleshooting and Diagnostics – Hydro-Max Power Brake System
Symptom
Cause
Remedy
Fluid leak between booster and
master cylinder.
Worn or damaged master
cylinder primary pressure seal or
back-up ring.
Repair or replace master
cylinder.
Worn or damaged seals or Orings in booster end cap
assembly.
Repair or replace booster.
Damaged or missing seals at
booster and electric motor pump
mating surface.
Replace seals.
Loose pump belt.
Tighten belt to specified tension.
Excessive output pressure at
pump.(Gauge at inlet line to
booster pump reads 5515 kPa
(800 psi) at least before pedal is
hard.
Replace pump.
Binding pedal rod linkage
Repair cause of restriction.
Replace components as required.
Worn or wet brake linings.
Repair or replace brake linings
Slipping belt.
Replace belt if required. Tighten
belt to specified tension.
Fluid leak on booster or booster
pump. (Power steering pump)
Sluggish booster operation with
little or no assist.
Table 4—Troubleshooting and Diagnostics – Hydro-Max Power Brake System
030-94
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---
Low fluid level in booster pump
reservoir.
Refill to specified level.
Binding pedal rod linkage.
Remove restriction. Replace
components as required.
Restricted hose or line.
Remove restriction in hose or
line.
Worn or damaged booster.
Repair or replace booster.
Air in fluid.
Bleed system.
Internal wear or damage in
booster pump.
Replace booster pump.
Motor pump check valve leaking
in booster.
Check booster pump pressure at
inlet with full brake application.
Replace electric motor pump if
low pressure is noted.
Electric motor pump does not
operate with engine off, ignition
off and brake pedal depressed.
Brake switch out of adjustment.
Adjust.
Brake switch worn or damaged.
Replace switch.
Electric motor pump does not
operate with engine off and
ignition on.
Ignition switch or connecting
wires.
Check condition of switch and
wiring replace as necessary.
Loose, disconnected or broken
power lead wire at motor pump.
Repair or replace.
Loose, disconnected or broken
flow switch wire.
Repair or replace.
Inoperative motor pump relay.
Repair or replace.
Inoperative booster flow switch.
Repair or replace.
Inoperative electronic monitor
module.
Replace monitor module.
Inoperative electric motor pump
Check operation and replace as
required.
Brake light switch.
Adjust, repair or replace.
Inoperative, damaged motor
pump relay.
Replace.
Inoperative electronic monitor
module.
Replace monitor module.
Electric motor pump runs
continuously with ignition off
and brake pedal NOT depressed.
Table 4—Troubleshooting and Diagnostics – Hydro-Max Power Brake System continued
030-94
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TC Series Brakes
Premature lining wear/dragging
brakes
Brake drag and associated
premature lining wear is caused
either by the brakes being
applied when they shouldn't be,
or the brakes not fully releasing
after an application.
If binding repair or replace brake
pedal mechanism and/or brake
light switch.
Check the brake pedal to be sure
it is fully released and is not
binding. Check the position of
the brake light switch. It should
not interfere with brake pedal
travel.
---
On sliding-caliper disc brakes,
make sure the calipers are free to
slide on their pins or rails.
Replace piston seals.
On any type of disc brake, check
the condition of the piston seals.
A damaged, swollen or
deformed seal can cause the
piston(s) to hang up and not
allow the pads to clear the rotor.
---
Spin the front wheels to be sure
they are free. With wheels
spinning, start the engine but
don't apply the brakes. When
the wheels stop spinning, check
for brake drag. If present, it's
likely that the booster is
defective
If brake drag is present, it's likely
that the booster is defective,
repair or replace booster.
Low or sinking pedal
Common cause is air in the
hydraulic system. The fix may
be as easy as bleeding the
brakes.
If air in system bleed system.
Check the hydraulic system:
Pump the brakes several times
with the engine off. Then hold
steady pressure on the brake
pedal. If the pedal sinks
gradually.
Table 4—Troubleshooting and Diagnostics – Hydro-Max Power Brake System continued
030-96
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TC Series Brakes
---
If you can't find any signs of
external leak anywhere, the
internal seals in the master
cylinder have failed.
Check wheel cylinders, lines,
hoses and connections for
external leak. Any detected repair
or replace as needed.
Replace seals in master cylinder.
Pulsing pedal
In any brake, friction material
needs a smooth, flat rotor to rub
against. Unfortunately, no rotor
stays flat. Remember, a brake is
a heat machine. It turns the
energy of slowing a vehicle into
heat, by way of friction. Heat, in
turn, rearranges the molecules in
metal, and warps occurs, making
proper brake adjustment
impossible. In a hydraulic
system, the first indication of
warping is a pulsing sensation
felt through the brake pedal as
the brakes are applied while the
vehicle is moving (not to be
confused with the pulsing
induced by anti-lock brakes
during a panic stop). The
pulsing is generated as the
linings or pads settle into a low
spot in the drum or rotor, then
are intermittently forced away by
high spots as the wheel turns.
Brake fluid is intermittently
compressed and released in the
wheel cylinder or caliper. The
resulting pressure waves are
transmitted back to the master
cylinder and, ultimately, to the
driver's foot.
The fix is to machine or replace
the rotor. Remember, though,
once a rotor is machined, valuable
heat-absorbing metal has been
removed and warping is likely to
re-occur.
Table 4—Troubleshooting and Diagnostics – Hydro-Max Power Brake System
030-96
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Repairing the Hydro-Max Brake Booster
After troubleshooting the brake system and if it is
determined that the Hydro-Max booster is not
functioning properly, replace the defective HydroMax assemblies with new or remanufactured
assemblies rather than local repair. Use genuine
Blue Bird maintenance kits.
5. Push in on input push rod to force power piston
assembly from booster. (Rotate end cap to ease
piston removal).
Blue Bird seal bullet is used to install the power
piston in the booster housing on units found on 1981
and earlier model year vehicles.
During piston removal, pull straight out on piston
to avoid scratching rear piston on external bore
surface area. Handle piston with care.
Aluminum surface will scratch easily.
The bullet to install the power piston in the end cap
and filter assembly on all Hydro-Max units must be
fabricated. (Refer to Figure 79). Disassembly and
assembly should not be attempted without a kit.
6. Remove and discard the two power piston input
seals from the rear of the booster housing.
7. Disassemble the flow switch. There are two
types of flow switch assemblies. The flow
switches are different in the method which the
flow switch contact assembly is retained.
Threaded Contact Assembly
1. Remove the contact assembly.
2. Remove and discard the O-ring from the contact
assembly.
3. Extract the flow switch piston and spring use a
small magnet.
Snap Ring Contact Assembly
1. Press in on the contact assembly until tension is
removed from the snap ring that retains the
contact assembly.
2. Remove and discard the snap ring.
3. Remove the contact assembly.
Figure 79—Power Piston Installation Tool
Hydro-Max Brake Booster Disassembly
1. Remove the cap screws securing the relay to the
booster housing (if equipped). See Figure 80
and Figure 81.
2. Remove the two cap screws that secure the
pump motor.
Note
Approximately three cups of oil will drain out
of the booster when the pump is removed
Avoid damaging the mating surfaces when
removing the pump motor.
3. Remove and discard the two pump motor oval
O-rings.
4. Remove the boot from the input push rod.
030-98
4. Remove and discard the O-ring.
5. Extract the flow switch piston and spring use a
small magnet.
Do not clamp onto power piston.
6. Clamp input push rod in vice.
7. Push against the filter and end cap assembly
compressing the return spring ¼ - ½ inch.
8. Remove the snap ring, filter and end cap
assembly and return spring.
9. Discard the snap ring.
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Note
Do not overtighten the vise.
10. Clamp the flat of the input plug in a vise.
11. Remove the input plug assembly, grasp the large
diameter of the power piston by hand.
12. Rotate counterclockwise.
Note
Do not grip the piston surface with any tool.
If additional leverage is required, a drift may
be inserted through the flow holes in the
output shaft.
If the input plug is the blue plastic type,
special care should be taken in clamping not
to damage it. All rubber debris from the
smeared grommet must be completely
removed from the input rod and plug.
23. Remove and discard the grommet from the input
push rod.
Cleaning
Use clean power steering fluid for cleaning and
lubricating parts and seals.
Inspection
1. Inspect the piston input and output shaft surfaces
for scratches or nicks.
Do not disassemble the valve rod and reaction
piston assembly.
13. Remove the valve rod and reaction assembly,
poppet valve and valve return spring from the
power piston.
2. Inspect the large piston seal surface is smooth
without excessive wear.
14. Pry the actuator seal retainer from the input plug
and discard.
4. Confirm that the check ball is in place and is
cleaned free to move.
15. Remove actuator pin and discard actuator seal.
5. Confirm that the reaction piston bore and poppet
seat surface inside the piston are clean and
undamaged.
16. Remove and discard input plug and O-ring.
17. Remove and discard the O-ring and lip seal from
the ID of the filter and end cap assembly.
18. Remove and discard both O-rings from the OD
of the filter and end cap assembly.
19. Remove the inlet check valve and O-ring from
the inlet port of the booster housing use a
hooked piece of wire.
20. Discard O-ring and the inlet check ball.
21. Clamp the input plug flats in a vise.
22. Insert a 5/8-inch rod as a lever carefully pull the
input push rod out of the input plug. A load up
to a 100 pounds may be required to pull the rod
from the plug.
3. If any defects are found, replace the power
piston assembly.
6. Inspect housing for grooves, scratches or nicks
in the input bore area. If any are found replace
the entire Hydro-Max assembly.
7. Inspect the input plug for wear in the actuator
pin hole. Replace plug if wear is evident.
Note
The blue plastic input plug is not available for
service replacement and is not
interchangeable with the aluminum input
plug.
8. Replace the filter end cap assembly if cracked or
damaged. The 12 rib cage is interchangeable
with the 4 rib cap.
9. Remove the three largest OD O-rings from the
kit.
030-98
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Note
Two of the three are identical in thickness
with the third O-ring being noticeably thicker.
17. Lubricate and insert the actuator pin in the seal
18. Install the actuator seal retainer in the input plug
with its flat side toward the input plug.
•
Does the filter end cap assembly have four or
twelve ribs? If the cap is the four rib version,
discard the thickest O-ring of the three.
10. Install the two identical O-rings in their
respective grooves on the OD of the cap.
•
If the cap is the 12 rib version as illustrated,
discard one of the two thin O-rings.
11. Install the thick O-ring in the OD groove closest
the end cap ribs and the thin O-ring in the other
OD groove.
12. Remove the one inch OD O-ring and the
smallest of the three lip seals in the kit.
13. Lubricate and install the O-ring and lip seal in
the appropriate grooves in the ID of the filter
and end cap assembly.
Make sure that the lip of the lip seal faces the
power piston when the filter and end cap
assembly is installed on the power piston shaft.
Incorrect orientation of the seal will allow
pressurized fluid to leak from the interior of the
Hydro-Max booster. Refer to Figure 66 for
proper assembly.
14. Install the grommet on the input push rod.
15. Insert the input push rod into the plug. Ensure
the grommet is completely seated in the input
plug and is capable of retaining the input push
rod.
Of the O-rings remaining in the kit remove the
two with the largest diameter.
Note
If the input plug assembly is aluminum, install
the 1-3/16 inch OD O-ring and discard the
remaining O-ring. The correct one is the
thinner of the two. If the input plug assembly
is blue plastic, install the 1-5/32 inch OD Oring and discard the remaining O-ring. The
correct one is the thicker of the two.
19. Remove the two remaining lip seals from the kit.
20. Lubricate and install both seals in the small ID
of the booster housing bore. The lip of both
seals should be face the interior of the booster
housing.
Note
Of the three remaining O-rings in the kit two
are identical in size with the third slightly
larger in diameter.
21. Lubricate and install one of the small diameter
O-rings in the groove of the inlet check valve.
22. Install the inlet check ball in the inlet port of the
booster housing.
23. Lubricate and install the assembled inlet check
valve and O-ring in the inlet port.
24. Push the inlet check valve in until it comes to
rest.
25. Install the flow switch spring and then the flow
switch piston in the booster housing.
26. Determine the type of flow switch contact
assembly that is in use.
•
Threaded Contact Assembly
•
If the input push rod is not properly installed, the
push rod could become disconnected from the
input plug. The result will be no brake condition.
Do not clean parts with brake fluid. Use only
fresh clean steering fluid.
16. Lubricate and install the actuator seal (smallest
seal in kit) in the recess inside of the input plug.
030-100
If the contact assembly in use is threaded,
lubricate.
27. Install the larger diameter of the two remaining
O-rings on the contact assembly.
28. Install the contact assembly in the booster
housing and torque to 20-40 pound-inch (2.-4
N•m).
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11. Install the poppet valve.
Note
Do not overtighten the contact assembly. A failed
and leaking assembly will result.
Be sure the poppet valve is installed with
coned shaped end toward the return spring.
Refer to Figure 81 for proper assembly.
Discard the remaining small diameter O-ring and
the plain wire C type snap ring. Do not confuse
the C ring with the Tru-Arc type snap ring that
will be installed later on the power piston shaft.
12. Install the valve rod and reaction piston
assembly in the hollow end of the power piston.
Snap Ring Contact Assembly
1. If the contact assembly requires a snap ring to
secure in the booster housing, lubricate and
install the smallest of the two remaining O-rings
on the contact assembly.
2. Install the contact assembly in the booster
housing.
3. Install the C type snap ring to secure it. Be sure
that the type snap ring is fully seated in its
groove.
4. Discard the last remaining O-ring.
5. Install the return spring on the output shaft of the
power piston, small end first.
6. Lubricate the lip seal and O-ring in the ID of the
filter and end cap assembly.
7. Install on the piston shaft to prevent damage to
the lip seal in the end cap assembly.
8. Install a fabricated seal bullet on the end of the
shaft and depress the end cap onto the shaft until
the snap groove on the piston shaft is exposed.
9. Install the Tru-Arc type snap ring on the piston
shaft and make sure the snap ring is fully seated
in its groove.
Note
It is strongly recommended that a fabricated
seal bullet tool be used to install the filter and
end cap assembly.
The tape must be applied in such away that it
covers the snap ring groove and forms a
smooth forcing surface for the lip of the seal.
10. Re-lubricate with clean power steering fluid.
Install the poppet valve return spring in the
hollow end of the power piston.
030-100
13. Insert the reaction piston end in the power piston
first.
Note
The next phase of assembly will depend upon
the type of input plug in use on the power
piston. If the aluminum plug is in use,
proceed to step 17. If the input plug is blue
plastic, proceed to step 19. The plastic and
aluminum plugs are not interchangeable.
14. Screw the input plug and push rod assembly into
the power piston and hand tighten. Clamp the
input plug flats in a vise and firmly hand tighten
the power piston and plug until seated. Do use
tools to tighten.
15. Lubricate the exterior of the input plug and
power piston input shaft.
16. Insert the power piston in the booster housing
with a gentle twisting motion. Proceed to Step
21 of the assembly instructions.
Note
While it is strongly recommended that a seal
bullet be used to install the power piston, in
an emergency, the following alternate method
may be of use.
17. Install a seal bullet (Bendix tool 74015) over the
open end of the power piston input shaft and
lubricate the bullet and shaft.
18. Install the power piston using the seal bullet to
start the piston shaft through the two lip seals in
the booster housing.
19. Install the blue plastic input plug in the hollow
end of the power piston and tighten by hand.
20. Wrap plastic electrical tape around the input
plug so that a smooth forcing surface is formed
for the two lip seals in the booster housing.
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21. Ensure that the tape is not wrapped on any
portion of the major diameter of the plug or
shaft.
27. Torque the cap screws 18-25 foot-pounds (24-33
N•m).
22. Install the power piston.
23. Inspect the tape. If fragments of the tape are
missing, remove the power piston from the
booster housing. Remove all tape fragments and
use a seal bullet to reinstall.
24. Install the blue plastic input plug and firmly
hand tighten until seated. Do not use tools to
tighten.
25. Lubricate and install the two oval face seals in
the grooves of the electric motor pump
assembly.
Note
Before installing the electric pump motor
assembly on the booster housing, check to be
sure that the motor pump check ball and
retainer is present in the delivery port.
26. Secure the pump to the housing using two cap
screws.
Back to Top
030-100
The electrical pump motor assembly can be
incorrectly installed. The pump motor must be
installed with its delivery port closest to the input
push rod end of the booster housing.
The position of the inlet and return ports on the
booster housing should have the same
relationship to the delivery and return of electric
pump motor assembly.
A check ball is visible in the delivery port of the
electric pump motor. Do not mar the mating
surfaces when installing the pump motor on the
booster housing. Install the boot on the input
push rod.
If the optional electrical relay is in use, secure to the
booster housing using two cap screws. Torque
the cap screws to 35-50 pound-inch (4-5 N•m).
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