Brakes
Directory
Previous
Previous
Next
Search
Exit
Brakes
Table of Contents
Sub-Headings
Safety
5
Warnings
5
Cautions
5
Notes
5
Introduction
5
Description of Operation
7
Description of Components
9
Safety Valve
9
Governor
9
Air Dryer
9
Low Pressure Indicator
9
Dual Circuit Brake Valve
10
Automatic Slack Adjuster
10
Service Quick Release Valve 10
Brake Chamber
11
Double Check Valves
12
Stop Lamp Switches
12
Parking Quick Release Valve 12
Relay Valve
12
Spring Brake Valve
13
Push Pull Control Valves
13
Pressure Protection Valve
13
Air Compressor
13
Unloading
14
Loading
14
Air Compressors Major Difference
Unloading
15
Antilock Systems Component
15
Wheel Speed Sensor
15
Wheel Speed Sensor Operation
15
Antilock Modulator Assembly
16
Antilock Traction Controller
16
Physical
17
Dual Brake Valve Operation
17
Normal Operation-Primary 17
Normal Operation-Secondary 17
Loss of Air-Secondary
18
Loss of Air-Primary
18
Balanced Primary Circuit
18
All American Brakes
Balanced Secondary Circuit
Releasing Primary Circuit
Releasing Secondary Circuit
Air Dryer Operation
Operation of the AD-9 Air Dryer
Charge Cycle
Purge Cycle
Turbo Cut-Off Feature
Relay Valve Operation Application
Balance
Exhaust or Release
Air Compressor
Intake and Compression of Air
(Loaded)
Non-Compression of Air
Lubrication
Air Induction
Cooling
Compressor Turbo Charging
Parameters
Crankshaft Maximum Compressor
Troubleshooting and Diagnostics
Brake System Troubleshooting
Preventative Maintenance
Air Dryer
Relay Valve
Dual Circuit Brake Valve
Automatic Slack Adjuster
Brake Chamber
Push Pull Control Valves
Air Compressor
Intake Adapter
Compressor Cooling
Lubrication
Compressor Drive
Antilock Systems Preventative
Maintenance
Wheel Speed Sensor
Antilock Modulator
Assembly
18
18
18
18
18
19
19
19
20
20
20
20
20
21
22
22
22
22
23
23
24
61
61
62
62
63
63
63
63
63
64
64
64
64
64
65
1
Directory
Previous
Previous
Next
Service Checks
65
Air Dryer
65
Relay Valve
66
Dual Circuit Brake Valve
67
Automatic Slack Adjuster
67
Brake Chamber
67
Push Pull Control Valves
67
Air Compressor
68
Unloader Piston Leak
68
Antilock Systems
69
Wheel Speed Sensor
69
Antilock Modulator Assembly
69
Operation Testing
69
Electrical Testing
69
Diagnosing and Locating a System
Fault
70
Diagnostic Communication Interface 71
Optional Diagnostic LED and
RESET
71
EC-17 Controller Configuration
74
EC-17 Controller Display
74
EC-17 Self Configuring Process
75
Speed Sensors
75
Electronic Engine Control
75
Antilock Traction Relay Valve
75
Traction Disable Switch
75
Self Configuration Process
76
Troubleshooting
77
General
77
Troubleshooting Help
77
Diagnostic Display
77
Hydraulic Brakes
94
General
94
Routine Maintenance
94
Theory of Operation
97
Hydraulic Booster
Configuration
97
Hydro-Max Power Brake System
Components
98
Hydraulic Pump Operating
Components
98
Electrical
99
Operation of Flow and Warning
Switch
102
Operation of Electronic Monitor
Module
102
2
Search
Exit
Brake Warning System
Remove Hydro-Max Booster
Replace Hydro-Max Booster
Refilling and Bleeding Hydro-Max
Check Brake System
Hydraulic Brake Components
Electrical Components
Park Brake Components
Repairing the Hydro-Max Brake
Booster
Hydro-Max Brake Booster
Disassembly
Threaded Contact Disassembly
Snap Ring Contact Disassembly
Cleaning
Inspection
Actuator Installation
Threaded Contact Assembly
Snap Ring Contact Assembly
102
103
103
104
104
104
105
105
110
111
111
111
112
112
113
114
114
List of Figures
Figure 1—Safety Valve
9
Figure 2—Governor
9
Figure 3—Air Dryer
9
Figure 4—Low Pressure Indicator 10
Figure 5—Dual Circuit Brake Valve 10
Figure 6—Service Quick Release
Valve
10
Figure 7—Spring Brake Chamber 11
Figure 8—Double Check Valve
12
Figure 9—Stop Lamp Switches
12
Figure 10—Parking Quick Release
Valve
12
Figure 11—Relay Valve
12
Figure 12—Spring Brake Valve
13
Figure 13—Push-Pull Control Valve 13
Figure 14—Air Compressor Bendix 14
Figure 15A—Air Compressor Major
Assemblies
14
Figure 15B—Air Compressor
Major Assemblies
14
Figure 16—Nameplate
14
Figure 17—Wheel Speed Sensor
Output
16
Figure 18—Antilock Modulator
Assembly
16
All American Brakes
Directory
Previous
Previous
Next
Figure 19—Antilock Traction
Controller
16
Figure 20—Dual Brake Valve
17
Figure 21—Dual Brake Valve Cross
Section
18
Figure 22—Turbo Cut-Off Feature 20
Figure 23—Relay Valve Ports
20
Figure 24—Operational-Loaded
(Intake)
21
Figure 25—Operational Loaded
21
Figure 26—Operational-Unloaded 21
Figure 27—Lubrication
22
Figure 28—Cooling
22
Figure 29—Hydraulic Brakes ISB,
TC
33
Figure 30—Ignition Voltage and
Ground
35
Figure 31—Diagnostic T1587 Serial
Circuits
37
Figure 32—ABS Signal Circuit for
Cummins Engine w/ WT (TC)
39
Figure 33—ABS Signal Circuit w/
AT/ MT Transmission
39
Figure 34—Ground Circuit
41
Figure 35—Chassis Option Solenoid
Circuit
43
Figure 36—ABS Signal Circuit for
Engines
45
Figure 37—ABS Signal Circuit for
Engines
45
Figure 38—Ignition Switch Circuit 47
Figure 39—Vehicle Speed in Circuit
with AT/MT Transmissions 49
Figure 40—Vehicle Speed in Circuits
with WT Transmissions
51
Figure 41—Vehicle Sped in Circuits
with AT/MT Transmission 51
Figure 42—Serial Comm Interface
Circuits w/ Throttle
Diagnostic & Master Chassis 53
Figure 43—Transmission Retarder
Circuit (1 of 2)
55
Figure 44—Transmission Retarder
Circuit (2 or 2)
57
Figure 45—Relay Circuit w/ ISB
All American Brakes
Search
Exit
& AT/MT Transmission
59
Figure 46—Air Dryer Connection 66
Figure 47—Modulator Test
70
Figure 48—DCI Tool
71
Figure 49—Diagnostic Connector 71
Figure 50—DCI Tool with PC
71
Figure 51—Diagnostic Display
Quick Response
78
Figure 52—EC-17 Configuration
79
Figure 53—Antilock Dash Lamp
Testing
80
Figure 54—Inspection for
Illuminated Leeds
81
Figure 55—Power to EC-17
84
Figure 56—Testing Modulator
85
Figure 57—Testing the Wheel Speed
Sensor
87
Figure 58—Testing for False
Indication Caused by Dash
Light Relay
89
Figure 59—Testing for False
Indication Caused by Wheel
Speed Components
90
Figure 60—Testing Traction
Control Dash Lamp
91
Figure 61—Testing Traction Control
Modulator
92
Figure 62—Testing Engine Control
Module Wire Harness
93
Figure 63—Hydraulic System
Configuration
98
Figure 64—Hydro-Max Connections 99
Figure 65—Performance Curve
100
Figure 66—Master Cylinder
Operation
101
Figure 67—Brake Booster Electrical
Components
106
Figure 68—Power Piston
Installation
111
List of Tables
Table 1—Compressor
Troubleshooting
Table 2—Lamp Configuration
Table 3—Brake Booster and
26
74
3
Directory
Previous
Previous
Warning System
Troubleshooting
Table 4—Troubleshooting and
Diagnostic Hydro-Max
Power Brake System
4
Next
Search
Exit
95
107
All American Brakes
Directory
Previous
Previous
Next
Brakes
Safety
The purpose of this safety summary is
twofold. First, it is to help ensure the safety
and health of individuals performing service
on, or operation of, the Blue Bird All
American Series bus. Second, it is to help
protect equipment. Before performing any
service or operating procedure on the All
American bus, individuals should read and
adhere to the applicable warnings, cautions
and notes located throughout this Blue Bird
Service Manual.
Warnings
Warnings apply to a procedure or practice
that, if not correctly adhered to, could result
in injury or death. Particular attention
should be paid to sections of this manual
where warnings appear.
Cautions
Cautions apply to a procedure or practice
that, if not correctly adhered to, could result
in destruction of equipment.
Notes
Notes are used to explain, clarify or
otherwise give additional insight for a given
subject, product or procedure. Please note
that on occasion, notes, too, may advise of
potential safety issues.
Introduction
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
All American Brakes
Search
Exit
contained in this section has been republished 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 IM-298 (Supercedes
IM-494).
Webb® Wheel Products, Inc. Torque
Specifications and Publication Number SD012: 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.
MGM Brakes Model TR – Tamper Resistant
Spring Brakes, © MGM 12/92, Form
Number 5026-MGM.
Midland™ EL1300 and EL1600 Air
Compressor Service Procedures, Publication
Number L30002, Rev 9-93, © MidlandGrau Heavy Duty Systems.
Allied Signal Bendix® Brakes Air Hand
Brake Handbook, Components,
Maintenance and Troubleshooting, © Allied
Signal TBS Co 9/1996, Publication Number
BW5057.
Allied Signal Bendix® Brakes TU-FLO 550
Compressor Service Data SD-01-333,
©Allied Signal 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 Number BW1662.
Allied Signal Bendix® Brakes M-21 and M22 Antilock Modulator Assembly Service
5
Directory
Previous
Previous
Next
Data SD-13-4793, ©Allied Signal TBS Co
11/1996, Publication Number BW1664.
Allied Signal Bendix® Brakes EC-17
Antilock Traction Controller Service Data
SD-13-4788, © Allied Signal TBS Co
2/1998, Publication Number BW1910.
Allied Signal Bendix® Brakes AD-9 Air
Dryer Service Data SD-08-2412, © Allied
Signal TBS Co 5/1996, Publication Number
BW1627.
Allied Signal Bendix ® Brakes Push-Pull
Type Control Valves Service Data SD-033611, © Allied Signal TBS Co 4/1996,
Publication Number BW1578.
Allied Signal Bendix® Brakes E-6 and E-10
Dual Brake Valves Service Data SD-03-817,
© Allied Signal 6/1996, Publication Number
BW1427.
Allied Signal Bendix® Brakes R-12 and R14 Relay Valves Service Data SD-03-1064,
© Allied Signal 6/1996, Publication Number
BS1431.
Note
For the AD-9 Air Dryer, please refer to
Bendix Service Data Sheet SD-08-2412.
For the AD-SP System Purge Air Dryer and
SC-PR Single Check Protection Valve,
please refer to Bendix Service Data Sheet
SD-08-2415. These publications can be
obtained from the Bendix website.
Caution
Always block vehicle's 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
6
Search
Exit
recommended procedures. Some
components contain powerful springs; injury
can result if component is not properly
disassembled.
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. Equipment damage can result if
the caution instructions are not followed.
Hydraulic Brake Systems are powerassisted. Braking capacity is reduced
without engine assist. Do not move the bus
with dead engine.
Warning
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.
Caution
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. The 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
proper fluids could result in loss of braking
or steering.
All American Brakes
Directory
Previous
Previous
Next
Warning
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.
Caution
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.
Warning
Search
Exit
moisture-laden air is passed through an air
dryer that removes moisture before being
utilized in the system. The compressed dry
air is temporarily 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 warning 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:
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 until appropriate measures have been
taken to prevent vehicle movement.
Successive stops would deplete the air
supply directly from the compressor if a
storage tank were not used.
Description of Operation
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.
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 this friction. As the friction
increases, heat increases. Therefore,
rotating brake components are designed with
cooling fins to dissipate heat rapidly.
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,
All American Brakes
Using two storage tanks provides a margin
of safety in the event one of the two-brake
circuits malfunction.
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
7
Directory
Previous
Previous
Next
Search
Exit
between rotating and stationary components
to slow and stop the vehicle.
Air Brake System
A—Primary or Rear Service Tank
B—E-6 (Brake Valve)
C—Front Air Chamber
D—Slack Adjusters (4 used)
E—M-22 (ABS Antilock Modulator
Assembly (4 used))
F—QR-1C (Quick Release Valve) (3 used)
G—Air Compressor
H—Check Valve
I—Air Dryer
J—Governor
K—Pressure Protection Valve
L—Drain Valve (3 used)
M—Schrader Valve
N—Low-Pressure Indicator Switch
8
O—Safety Valve
P—Wet Tank
Q—Rear Brake Chamber (2 used)
R—Quick Release Valve
S—R-12 Relay valve with Double Check
T—Double Check Valve
U—Pressure Gauge (2 used)
V—Brake Light Switch (2 used)
W—PP-1 (Push Pull Control Valve)
X—SR-1 (Spring Brake Valve)
Y—Second or Front Tank
Description
Safety Valve
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
The safety valve protects the air brake
system against excessive air pressure
buildup. It must be installed in the same
reservoir to which the compressor discharge
line is connected. Safety valves are
available in both adjustable and nonadjustable styles, in various pressure
settings, and with either 1/4inch or 3/8 inch
NPT. Figure 1.
Figure 2—Governor
Air Dryer
The air dryer 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 3. (See note at end of this Section.)
Figure 1—Safety Valve
Governor
The governor 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.
Figure 2.
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 is
absorptive properties are renewed each time
the compressor is unloaded.
The air dryer en 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.
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.
Figure 3—Air Dryer
All American Brakes
9
Directory
Previous
Previous
Next
Search
Exit
Low Pressure Indicator
Low-pressure indicators 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 low-pressure 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 4.
Figure 5—Dual Circuit Brake Valve
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.
Figure 4—Low Pressure Indicator
Service Quick Release Valve
Dual Circuit Brake Valve
Dual circuit brake valves 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 function of the quick release valve is to
speed up the exhaust of air from the air
chambers. It is mounted close t 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.
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. Figure 5.
Figure 6—Service Quick Release
Valve
10
All American Brakes
Directory
Previous
Previous
Next
Brake Chamber
The brake chamber 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. Figure 7.
Search
Exit
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
End Cap
Release Tool
Steel Head
Sealed Spring Chamber
Power Spring
Push Rod
Piston and Guide
Service Piston Seal
Push Rod Seal
Stroke Alert Indicator
Center Hole Shield
Figure 7—Spring Brake Chamber
All American Brakes
11
Directory
Previous
Previous
Next
Search
Double Check Valves
A double check valve 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. Figure 8.
Exit
release valve. In addition, it functions as an anticompound device. The double check valve prevents
a service and emergency brake application from
occurring simultaneously. Figure 10.
Figure 10—Parking Quick Release Valve
Relay Valve
Figure 8—Double Check Valve
Stop Lamp Switches
The stop lamp switches are pressure sensitive
electro-pnuematic switches installed in the service
application system. They operate the vehicle stop
lamps, completing an electrical circuit and lighting
the stop lamps weach time a brake application is
made. Figure 9.
Relay valves 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 to
which they are connected. 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.
Figure 9—Stop Lamp Switches
Parking Quick Release Valve
The parking quick release valve is a dual function
valve. The valve's primary function is to serve the
emergency side of a spring brake actuator as a quick
12
Figure 11—Relay Valve
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Spring Brake Valve
Pressure Protection Valve
The spring brake valve 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 would provide a modulated spring brake
application proportional to service braking pressure
delivered to the front axle. Figure 12.
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.
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.
Air Compressor
Figure 12—Spring Brake Valve
Push Pull Control Valves
Push-Pull control valves 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 above 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. Figure 13.
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. 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 consists of two major
subassemblies, the cylinder head and the crankcase.
The cylinder head is an iron casting the houses the
inlet, discharge and unloader valves. 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 14, Figure
15A and Figure 15B.
Figure 13—Push-Pull Control Valve
All American Brakes
13
Directory
Previous
Previous
Next
Search
Exit
Figure 16—Nameplate
A nameplate identifying the compressor piece
number and serial number is attached to the side of
the crankcase. Figure 16.
Figure 14—Air Compressor Bendix
The Holset air compressor is an engine driven,
piston-type compressor that supplies compressed air
to operate the service brakes and other air powered
devices. The compressor operates or turns
continuously but has loaded and unloaded operating
modes. Operations are controlled by a pressureactivated governor and compressor unloading
assembly.
Unloading
Figure 15A—Air Compressor Major
Assemblies
When the air system reaches "cut-out" pressure, the
governor applies an air signal to the air compressor
unloader assembly, causing the unloaded 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.
Loading
Figure 15B—Air Compressor Major
Assemblies
14
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.
All American Brakes
Directory
Previous
Previous
Next
Search
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.
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.
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.
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
All American Brakes
Exit
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 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 simply 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.
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.
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.
15
Directory
Previous
Previous
Next
Search
Exit
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 sensor is installed in a mounting block that
is affixed to the axle housing. Figure 19. A springloaded retainer bushing provides a friction fit
between the mounting block bore and the WS-20.
The friction fit allows the WS 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 is inserted all the way into the
mounting block and the wheel is installed on the
axle, the hub exciter contacts the sensor that pushed
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
running clearance or air gap between the sensor and
exciter. Figure 17.
Figure 18—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 19 shows the basic controller.
Figure 19—Antilock Traction Controller
Figure 17—Wheel Speed Sensor Output
Antilock Modulator Assembly
The antilock system modulators are high capacity,
on/off air valves the 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. Figure
18.
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.
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
16
All American Brakes
Directory
Previous
Previous
Next
Search
improve vehicle traction during acceleration in
adverse road conditions.
Integrated with antilock logic, traction control
monitors wheel speed information from the sensor
during acceleration, as well as braking. The system
helps maintain vehicle stability on hazardous road
surfaces and improves drive ability and safety.
The controller containers 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 on which it is
installed.
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 sensor
Four air pressure modulator valves
One dash mounted antilock condition lamp
One service brake relay valve
When programmed to provide traction control in
addition to antilock, the following components are
added:
•
•
•
•
One traction solenoid (incorporated into the
relay valve)
One dash mounted traction condition lamp
Serial connection to engine control module
for vehicles programmed for torque limiting
feature
Traction disable wiring and switch
Exit
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 EC17 to antilock and traction system components: one
30 pin and on 18 pin connector.
Dual Brake Valve Operation
Normal Operation—Primary Circuit Portion
When the brake treadle 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.
Because of the small volume of air required to move
the relay piston, action of the secondary circuit of
the valve is almost simultaneously with the primary
circuit portion. Figure 20.
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.
All American Brakes
Figure 20—Dual Brake Valve
17
Directory
Previous
Previous
Next
Search
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 Portion".
Loss of Air in the Primary Circuit
Should air be lost in the primary circuit, the function
will be as followings: As the brake treadle is
depressed an 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. Figure
21.
Exit
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.
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
to the exhaust port.
Air Dryer Operation
See Note concerning Bendix Air Dryer at end of
Brake Section, page 116.
Operation of the AD-9 Air Dryer
Figure 21—Dual Brake Valve Cross
18
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.
All American Brakes
Directory
Previous
Previous
Next
Search
Charge Cycle
When the compressor is loaded compressing air
along with oil, oil vapor, water and water vapor flow
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 and
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.
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.
Exit
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.
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 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.
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.
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.
All American Brakes
Turbo Cut-Off Feature
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.
19
Directory
Previous
Previous
Next
Search
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 cut-off 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. Figure 22.
Exit
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 22—Turbo Cut-Off Feature
Air Compressor
Relay Valve Operation
Application
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.
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.
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 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)
Figure 23—Relay Valve Ports
20
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.
All American Brakes
Directory
Previous
Previous
Next
Search
Note
The discharge valve remains on its seat.
Atmospheric air is drawn through the air strainer
and the open inlet valve into the cylinder.
Exit
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 24—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
discharge valve off its seat and air flows by the open
discharge valve, into the discharge line and to the
reservoirs. Figure 25.
Figure 26—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. The
unloader pistons move down, holding the inlet
valves off their seats. 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.
Figure 25—Operational-Loaded
All American Brakes
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. The unloader springs force the pistons
upward and the inlet valves return to their seats.
Compression is then resumed.
21
Directory
Previous
Previous
Next
Search
Lubrication
The vehicle's engine provides a continuous supply of
oil to the compressor. 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.
Exit
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
27.
Figure 28—Cooling
Figure 27—Lubrication
Air Induction
There are different methods or 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.
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.
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. Figure 28.
22
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.
Note
The following compressor crankshaft rotational
speed and inlet pressure relationships may not be
exceeded.
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Crankshaft Maximum
Compressor
RPM Inlet Pressure
o
•
2200 RPM 21.0 PSI (145kPa)
2600 RPM 25.0 PSI (172.5 kPa)
Troubleshooting and
Diagnostics
If governor cut-out is higher or lower than
specified by Blue Bird:
o
o
•
o
Test 1—Governor Cut-Out/Low Pressure
Check List
o
•
o
o
On some vehicles with anti-lock, a warning light will
also come on shortly when ignition is turned on.
Make all necessary repairs before proceeding to Test
2. See Check List 1 for common corrections.
Governor Cut-Out/Low Pressure
Check List 1
•
If the low pressure warning light or buzzer
does not come on:
o
o
Check wiring
Check bulb
All American Brakes
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:
Note
5. Low pressure warning light should go off at
approximately 60 PSI
6. Build up time pressure should build from 85-100
PSI within 40 seconds
7. Governor cut-out stops compressor at correct
pressure. Check manufacturer's
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.
Adjust the governor using a gauge of
known accuracy
Repair or replace governor as necessary
after being sure compressor unloader
mechanism is operating correctly
If low pressure warning occurs below 60 PSI:
Brake System Troubleshooting
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
Repair or replace buzzer, bulb or low
pressure warning switch(es)
o
o
o
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
Note
Retest to check out all items repair 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
3. Pressure Drop (A 2 PSI drop within 2 minutes is
allowable for either service reservoir)
23
Directory
Previous
Previous
Next
Search
Note
Make all necessary repairs before proceeding to
Test 3. See Check List 2 for common corrections.
Check List 2
Exit
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)
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:
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.)
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
Note
Supply lines and fittings (tighten)
Wet tank
Front air tank
Rear air tank
Single check valves
Double check valves
PP-1 (push pull control valve)
E-6 brake valve
SR-1 spring brake valve
QR-1C Quick release valve
M-22 ABS antilock modulator assemblies
Front air chambers
Rear brake chambers
Safety valve
Low pressure indicator switch
Schrader valve
Drain valves
Pressure gauges
Governor
Compressor discharge valve
Note
A leak detector or soap solution will aid in locating
the faulty component.
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:
1.
2.
3.
4.
5.
Service lines and fittings (tighten)
E-6 brake valve
ST-1 spring brake valve
Brake light switch
R-12 relay valve with double check valve
If the angle between the brake chamber push rod and
slack adjuster arm is less than 90°, 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.
Warning
Warning
Retest to check out all items repaired or replaced.
Retest to check out all items repaired or replaced.
Test 3—Leak (Service Air Delivery) Full
Pressure, Engine Stopped, and 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.)
24
Test 4—Automatic Emergency System Full
Pressure, Engine Stopped
Drain front axle reservoir to 0 PSI.
Rear axle reservoir should not lose pressure
With no air pressure in the front axle reservoir, make
a brake application
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Rear axle brakes should apply and release
The stop lamps should light
Test 5—Brake Balance Test
Front axle reservoir should not lose pressure
1. Test drive vehicle approximately 10-15 minutes,
applying brakes frequently
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
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
With no air pressure in the rear axle reservoir, make
a brake application
If temperature range is within limits, vehicle is in
proper brake balance.
Front axle brakes should apply and release
If temperature is out of range, see Check List 5 for
common corrections.
1. Slowly drain rear axle reservoir pressure.
2. Spring brake push pull valve should pop out
between 35 and 45 PSI
3. Close drain cocks, recharge system and drain
rear axle reservoir to 0 PSI
Check List 4
If the vehicle fails to pass the tests outlined, then
check the following components for leak and proper
operation
Check List 5
1.
2.
3.
4.
5.
1.
2.
3.
4.
5.
Fittings
Kinked hose or tubing
PP-1 push pull control valve
E-6 brake valve
SR-1 spring brake valve
If the brake balance test failed, one or more of the
following devices could be causing the problem.
Worn brake shoes
Worn return springs
Brake actuating components binding
Incorrect adjustment of slack adjuster
Inoperative self-adjusting slack adjuster
Retest to check all items repaired or replaced
function properly.
All American Brakes
25
Directory
Previous
Previous
Next
Search
Exit
Compressor Troubleshooting
Symptom
Cause
Compressor passes excessive Restricted air intake
oil as evidenced in system or
by presence of oil at exhaust
ports of valves or seeping
from air strainer.
Remedy
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 Oil return to the engine should not be in anyway
engine)
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 Contaminants not being Check reservoir drain valves to insure that they
oil as evidenced in system or regularly drained from are functioning properly. It is recommended that
the vehicle should be equipped with functioning
by presence of oil at exhaust system reservoirs.
automatic drain valves, or have all reservoirs
ports of valves or seeping
drained to zero (0) psi daily, or optimally to be
from air strainer.
equipped with a desiccant-type air dryer prior to
the reservoir system.
Table 1—Compressor Troubleshooting
26
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Symptom
Cause
Remedy
---
Compressor runs loaded Vehicle system leak should not exceed industry
an excessive amount of standards of 1 psi pressure drop per minute
time.
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 Test for excessive engine crankcase pressure and
crankcase pressure.
replace or repair ventilation components as
necessary. (An indication of crankcase pressure is
a loose or partially lifted dipstick.)
---
Excessive
pressure.
engine
oil 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,
Troubleshooting.
see
Engine
---
Malfunction of the turbo Warn or defective turbo cutoff piston. Replace
cutoff piston in the air end cover check valve assembly of AD-9 Air
dryer, resulting in a loss Dryer.
of back pressure on the
compression
exhaust
port
of
compressor
during unload mode
(Holset Only).
---
Malfunctioning
check Replace check valve.
valve in wet tank air
supply
line
to
compressor exhaust port
causing a lack of back
pressure during the
unload mode (Holset
Only)
---
Faulty compressor.
Replace or repair the compressor only after none
of the preceding installation defects exist.
Table 1—Compressor Troubleshooting (continued)
All American Brakes
Directory
Symptom
Previous
Previous
Next
Search
Cause
Exit
Remedy
Noisy
compressor Loose drive gear or Pulley.
operations.
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
couplings or gears.
drive Inspect drive gear, couplings, and engine for
excessive wear.
Replace as necessary.
(Nonmetallic gears should be replaced when the
compressor is changed.)
---
Compressor cylinder head or Inspect the compressor discharge port and
discharge line restrictions.
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)
28
Directory
Previous
Previous
Next
Search
Exit
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.
The vehicle
manufacturer certifies
minimum compressor
performance to meet
federal requirements.
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 Inspect the compressor discharge port and line for
compressor discharge cavity. 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 Check and clean the operation of the unloading
valves.
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)
All American Brakes
Directory
Symptom
Previous
Previous
Next
Search
Cause
Exit
Remedy
Compressor fails to Faulty governor or governor Test the governor for proper operation and inspect air
unload.
installation.
lines to and from the governor for kinks or
restrictions. Replace or repair the governor or its
connecting air lines.
---
Faulty or worn unloader Inspect for worn, dirty or corroded unloader pistons,
pistons, valves or bores.
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 Visually inspect the compressor exterior for cracked
cover.
or broken components. Loose mounting bolts can
cause cracked or broken crankcases or mounting
flanges. The end cover can be cracked by overtorque 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 Check the torque of external oil line fittings and
line fittings.
tighten as necessary.
Porous compressor casting.
Replace the compressor if porosity is found.
Mounting flange or end Replace as necessary.
cover, O-ring or gasket
missing, cut or damaged.
Compressor
Leaking
compressor
constantly
cycles unloader pistons or valves.
(compressor remains
unloaded for a very
Faulty Governor.
short time).
Excessive system leak.
Excessive
Contaminants.
Remove the compressor inlet air strainer or fitting.
With the compressor unloaded (not compressing air),
check for air leak. Repair or Replace as necessary.
Test the governor for proper operation and repair or
replace as necessary
Test for excessive system leak, (See Test 2). Reduce
leak wherever possible.
reservoir Drain reservoirs.
Table 1—Compressor Troubleshooting (continued)
30
Directory
Previous
Previous
Next
Search
Exit
Symptom
Cause
Remedy
---
Air dryer check valve leak.
Replace check valve with appropriate AD-9 End
Cover Check Valve Replacement Kit.
Compressor
coolant.
leak Improperly installed plugs Check torque of fittings and plugs and tighten as
and coolant line fittings.
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
gasket failure.
head Restricted discharge line.
---
Loose head bolts.
Clear restriction or replace line.
Tighten evenly to proper torque specifications.
Table 1—Compressor Troubleshooting (continued)
All American Brakes
Directory
Previous
Previous
Next
This page intentionally left blank.
32
Search
Exit
Directory
Previous
Previous
Next
Search
Exit
Figure 29—ISB Hydraulic Brakes
All American Brakes
33
Directory
Previous
Previous
Next
Search
Exit
This page intentionally left blank.
34
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Figure 30—Ignition Voltage and Ground
All American Brakes
35
Directory
Previous
Previous
Next
Search
Exit
This page intentionally left blank.
36
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Figure 31—Diagnostic T1587 Serial Circuits w/ Cummins Engine
All American Brakes
Directory
Previous
Previous
Next
Search
This page intentionally left blank.
38
Exit
Directory
Previous
Previous
Next
Search
Exit
Figure 32—ABS Signal Circuit for Cummins Engine w/ WT
Figure 33—ABS Signal Circuit w/ AT/MT Transmission
All American Brakes
Directory
Previous
Previous
Next
Search
This page intentionally left blank.
40
Exit
Directory
Previous
Previous
Next
Search
Exit
Figure 34—Ground Circuit
All American Brakes
Directory
Previous
Previous
Next
Search
This page intentionally left blank.
42
Exit
Directory
Previous
Previous
Next
Search
Exit
Figure 35—Chassis Option Solenoid Circuit
All American Brakes
43
Directory
Previous
Previous
Next
Search
Exit
This page intentionally left blank.
44
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Figure 36—ABS Signal Circuit for Engine ISB
Figure 37—ABS Signal Circuit for Engine ISB
All American Brakes
45
Directory
Previous
Previous
Next
Search
Exit
This page intentionally left blank.
46
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Figure 38—Ignition Switch Circuit
All American Brakes
47
Directory
Previous
Previous
Next
Search
Exit
This page intentionally left blank.
48
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Figure 39—Vehicle Speed in Circuit w/ AT/MT Transmission
All American Brakes
49
Directory
Previous
Previous
Next
Search
Exit
This page intentionally left blank.
50
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Figure 40—Vehicle Speed in Circuits w/ WT Transmission
Figure 41—Vehicle Speed in Circuits w/ AT/MT Transmission
All American Brakes
51
Directory
Previous
Previous
Next
Search
Exit
This page intentionally left blank.
52
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Figure 42—Serial Comm Interface Circuits w/ Throttle Diagnostic and Master Chassis
All American Brakes
53
Directory
Previous
Previous
Next
Search
Exit
This page intentionally left blank.
54
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Figure 43—Transmission Retarder Circuit (1 of 2)
All American Brakes
55
Directory
Previous
Previous
Next
Search
Exit
This page intentionally left blank.
56
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Figure 44—Transmission Retarder Circuit (2 of 2)
All American Brakes
57
Directory
Previous
Previous
Next
Search
Exit
This page intentionally left blank.
58
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Figure 45—Relay Circuit w/ ISB and AT/MT Transmission
All American Brakes
59
Directory
Previous
Previous
Next
Search
Exit
This page intentionally left blank.
60
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Preventative Maintenance
remove a component or plug unless you are
certain all system pressure has been depleted.
Note
Never exceed recommended pressures and
always wear safety glasses.
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.
Warning
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 brake 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 recommended procedures,
deactivate the electrical system in a manner
that removes all electrical power from the
vehicle.
Warning
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 as it may whip. Never
All American Brakes
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 be
repaired. Repairs requiring machining or
welding should not be attempted unless
specifically approved as stated by Blue Bird or
the component manufacturer.
Before returning the vehicle to service, be sure
all component 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
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.
Directory
Previous
Previous
Next
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 due
to accessory air demands or some unusual
air requirement that does not allow the
compressor to load and unload (compressing
and non-compressing cycle) in a normal
mode
4. Check for high air system leak
Note
If the air dryer has been installed in a system
that has been previously used without an air
dryer, this 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. Retorque to 270-385 inch-pounds.
6. Perform the Operation and Leak Tests in
this publication.
62
Search
Exit
Every 36 months, 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.
Relay Valve
Every 3 months, 25,000 miles, or 900
operating hours
Check for proper operation
Every 12 months, 100,000 miles, or 3,600
operating hours
1. Disassemble valve
2. Clean parts with mineral spirits
3. Replace all rubber parts and any 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 threadle, 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
Directory
Previous
Previous
Next
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
Automatic Slack Adjuster
Search
Exit
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.
Intake Adapter
When the engine air cleaner is replaced
Some compressors are fitted with compressor
intake adapters that allow the compressor intake
to be connected to the engine air induction
system.
1. Lubricate automatic slack adjuster in
accordance with maintenance schedule.
2. Visually inspect for cracks and loose or
missing hardware.
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.
Brake Chamber
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.
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.
Air Compressor
Every 2 months, 800 operating hours or
20,000 miles
All American Brakes
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.
Every 6 months, 1,800 operating hours or
after each 50,000 miles
Compressor Cooling
Caution
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
Directory
2.
3.
4.
5.
6.
Previous
Previous
Next
is found, thoroughly clean or replace the
affected parts.
Re-inspect the compressor cooling system.
Check all compressor coolant lines for kinks
and restrictions to flow
Check coolant lines for internal clogging
from rust scale, if coolant lines appear
suspicious.
Check the coolant flow and compare to the
tabulated technical data.
Inspect the air induction system for
restrictions.
Search
Exit
Every 24 months, 7,200 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 genuine Blue
Bird remanufactured unit.
Every 6 months, 1,800 operating hours or
50,000 miles
Antilock Systems Preventative
Maintenance
Lubrication
Wheel Speed Sensor
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.
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.
Every 6 months, 1,800 operating hours or
50,000 miles
Compressor Drive
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.
2. If the compressor is belt driven, check for
proper belt and pulley alignment and belt
tension.
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.
64
Every 3,000 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 Modular 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 outlet.
Every 3 months, 25,000 miles or 900
operating hours
Directory
Previous
Previous
Next
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.
Search
Exit
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.
Service Checks
Air Dryer
Operation and Leak Test
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 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 govern cut-out and note
that AD-9 purges with an audible escape of
All American Brakes
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 during 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
7. Turn off the ignition switch and cool the end
cover assembly to below 40° Fahrenheit.
8. Check the resistance between the electrical
pins in the female connector with an
ohmmeter. The resistance should be 1.5 to
3.0 ohms.
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
limits, the thermostat and heater assembly is
operating properly.
Directory
Previous
Previous
Next
If the resistance values obtained are outside the
limits, replace the purge valve housing
assembly, which includes the heater and
thermostat assembly.
Figure 46—Air Dryer Connections
A two lead, 12 inch, wire harness with attached
weather resistant connector is supplied with all
retrofit and replacement AD-9 Air Dryers.
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.
11. A fuse should be installed in the power
carrying wire; install a 10 amp fuse.
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.
Relay Valve
Operation and Leak Test
1. Chock the wheels, fully charge air brake
system and adjust the brakes.
66
Search
Exit
2. Make several brake applications and check
for prompt application and release at each
wheel.
3. Check for inlet valve and O-ring leak.
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 acceptable.
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.
8. Make this check with the spring brakes fully
applied if the R-14 is used to control the
spring brakes.
9. Coat the exhaust port with a soap solution; a
1 inch bubble in 3 seconds is acceptable.
10. Coat the outside of the valve where the
cover joins the body to check for seal ring
leak; no leak is acceptable.
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,
replace the park control in the release 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
acceptable.
If the valves do not function as described above,
or if leaks are excessive, it is recommended that
the valves be replaced. Blue Bird parts are
available at any authorized Blue Bird parts
outlet.
Directory
Previous
Previous
Next
Dual Circuit Brake Valve
Operating Check
1. Check the delivery pressure of both primary
and secondary circuits using accurate test
gauges.
2. Depress the treadle to several positions
between the fully released and fully applied
positions.
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. 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.
Warning
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.
Always check the vehicle brake system for
proper operation after performing brake work
and before returning the vehicle to service.
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
acceptable. If the brake valve does not
function or leak is excessive, replace with a
All American Brakes
Search
Exit
new or remanufactured unit, or repair 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 section in this Blue
Bird Service Manual on Automatic Slack
Adjuster.
Brake Chamber
Apply brakes and observe movement of all
brake chamber rods.
Push Pull Control Valves
Operation 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.
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.
2. There should be no leak between upper and
lower body.
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
3 seconds.
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 PP1s.)
Directory
Previous
Previous
Next
Air Compressor
Operation Tests
Vehicles manufactured after the effective date of
FMVSS 121, with a 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.
Blue Bird must certify this performance on new
vehicles with appropriate allowances for air
systems with greater than the minimum required
reservoir volume.
Air Leak Test
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, its engine not running,
the entire air system completely drained to 0 psi
and the inlet check valve detail parts removed, if
applicable.
Unloader Piston Leak
The unloader pistons leak check
1. Remove the cylinder head from the
compressor
2. Cover securely the inlet flange, apply 120
psi of air pressure to the governor port
3. Listen for an escape of air at the inlet valve
area. An audible escape of air should not be
detected.
68
Search
Exit
Discharge Valve Leak
Unloader piston leak must be repaired before
this test is performed. Leak past the discharge
valves can be detected.
1. Remove the discharge line and apply shop
air back through the discharge 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, we recommend
it be returned to the nearest authorized Blue Bird
distributor for a factory remanufactured
compressor.
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 Test
1. Park the vehicle on a level surface and block
or chock the wheels. Release the parking
Directory
2.
3.
4.
5.
6.
Previous
Previous
Next
brakes and build the air system to full
pressure.
Turn the engine OFF, make four or five
brake applications, and note that the service
brakes apply and release promptly.
Build system pressure to governor cut out
and turn the engine OFF.
Hold a full service brake application.
Apply a soap solution to the exhaust port of
the modulator. Leak should not exceed a
one inch bubble in less than 3 seconds. If
leak exceeds the specified maximum,
replace the modulator.
Apply a soap solution around the solenoid
assembly (top and bottom). Leak should not
exceed a one inch bubble in less than 3
seconds.
If leak exceeds specified maximum, tighten the
solenoid cap screws and re-test. If the leak
remains excessive after re-testing, replace the
modulator.
Search
Exit
4. Apply brakes and hold.
5. Post a service technician 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. Figure 47.
7. Apply a soap solution around each
diaphragm cover. Leak should not exceed a
one inch bubble in less than 3 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.
Operation Testing
Note
To properly test the function of the modulator
will require two 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.
All American Brakes
Figure 47—Modulator Test
Directory
Previous
Previous
Next
Search
Exit
EXHAUST to HOLD: Read 7 to 10 OHMS
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.
Individually test the resistance of each pin to
vehicle ground and note there is no continuity.
The fault condition is truly stored and is not
cleared by loss of power to the antilock system.
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.
The optional LEDs will illuminate when power
is restored and it will remain illuminated until
the failure is corrected.
HOLD to SOURCE: Read 3.5 to 5 OHMS
EXHAUST to SOURCE: Read 3.5 to 5 OHMS
If the resistance values are not as shown above,
replace the modulator.
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.
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. Figure 48.
The EC-17 is programmed at the factory to
accommodate the needs of the vehicle and the
customer's desires.
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.
70
Figure 48—DCI Tool
Diagnostic Communication
Interface
The Diagnostic Communication Interface (DCI)
is a dual level electronic diagnostic tool for the
EC-17 antilock controller. It can be used either
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 the figure below. This connector
is generally located on the driver's side, in the
Directory
Previous
Previous
Next
lower portion of the dash or under the dash
panel. Figure 49.
Search
Exit
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 Allied Signal Bendix
parts outlet, or call 1-800-AIR-BRAK (1-800247-2725).
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.
Figure 49—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.
This is particularly useful when attempting to
determine the source of intermittent fault
indication from the antilock dash condition
lamp.
No special tool or equipment is 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 on 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.
Figure 50—DCI Tool with PC
When using the DCI's LED display for system
diagnosis or controller self configuration, the
descriptions and procedures presented in this
All American Brakes
•
•
•
•
FRT Red LED
MID Red LED
RER Red LED
RHT Red LED
Directory
•
•
•
•
•
•
Previous
Previous
Next
LFT Red LED
TRC Red LED
MOD Red LED
SEN Red LED
ECU Red LED
VLT Green LED
RESET + No LED
Search
Exit
It will light in conjunction with either the
FRONT or REAR LED and the MOD or SENS.
LEFT (Left) 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.
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.
72
TRC (Traction) 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.
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
Directory
Previous
Previous
Next
positioning LEDs (RHT/LFT +
FRT/MID/RER).
ECU (Electronic Control Unit) LED
The 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.
Monetarily 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.
All American Brakes
Search
Exit
Directory
Previous
Previous
Next
Search
Exit
Table 2—Lamp Configuration
EC-17 Controller
Configuration
Note
The following information and procedure
applies to the EC-17 controller equipped with
the optional LED diagnostic display and magnet
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 and then go out.
74
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 (front) and + RER (rear) = A four
sensor configuration (all systems must have at
least a four sensor configuration)
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
Directory
Previous
Previous
Next
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.
EC-17 Self-Configuring
Process
Note
The self-configuring feature of the EC-17
influences three aspects of the antilock and
traction system.
Speed Sensors
The number of speed sensors connected to the
EC-17 will be detected during the selfconfiguration 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).
Search
Exit
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.
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:
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 TR valve is
connected to the EC-17, the differential braking
All American Brakes
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
Directory
Previous
Previous
Next
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
pre-programmed 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 complete the self-configuring process
successfully, 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).
76
Search
Exit
If the vehicle has an electronic engine and
traction control torque limiting is desired, the
engine control module must be connected (B2
and B3 o 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.
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.
Turn the ignition ON, toggle the traction control
enable/disable switch back and forth, and then
hold a magnet on the RESET position of the EC17 diagnostic display until the LEDs begin to
flash, and then remove the magnet.
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.
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.
Directory
Previous
Previous
Next
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).
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 EC-17 diagnostic display.
Search
Exit
Troubleshooting
Caution
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 diagnostics LED is used
only on 6 x 4 vehicles.
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.
General
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.
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.
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.
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.
All American Brakes
Troubleshooting Help
Begin by observing the dash condition lamp(s)
and performing the Initial Startup Procedure.
The troubleshooting technician should record all
findings and action taken during the
troubleshooting process.
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 EC17 toward an antilock traction system
component (modulator, wheel speed sensor, etc.)
Directory
Previous
Previous
Next
Diagnostic Display
This index is troubleshooting Bendix fullvehicle wheel control antilock with traction
control. It provides a quick reference to specific
Search
Exit
section that provides testing procedures and
values.
Figure 51—Diagnostic Display Quick Reference
78
Directory
Previous
Previous
Next
Search
Exit
Figure 52—EC-17 Configuration
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Figure 53—Antilock Dash Lamp Testing
80
Directory
Previous
Previous
Next
Search
Exit
Figure 54—Inspection for Illuminated LEDs
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Figure 54—Inspection for Illuminated LEDs (continued)
82
Directory
Previous
Previous
Next
Search
Exit
Figure 54—Inspection for Illuminated LEDs (continued)
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Figure 55—Power to EC-17
84
Directory
Previous
Previous
Next
Search
Exit
Figure 56—Testing Modulator
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Figure 56—Testing Modulator (continued)
86
Directory
Previous
Previous
Next
Search
Exit
Figure 57—Testing the Wheel Speed Sensor
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Figure 57—Testing the Wheel Speed Sensor (continued)
88
Directory
Previous
Previous
Next
Search
Exit
Figure 58—Testing for False Indication Caused by Dash Light Relay
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Figure 59—Testing for False Indication Caused by Wheel Speed Components
90
Directory
Previous
Previous
Next
Search
Exit
Figure 60—Testing Traction Control Dash Lamp
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Figure 61—Testing Traction Control Modulator
92
Directory
Previous
Previous
Next
Search
Exit
Figure 62—Testing Engine Control Module Wire Harness
All American Brakes
Directory
Previous
Previous
Next
Hydraulic Brakes
General
The dual hydraulic brake system receives
hydraulic boost from the vehicle's power
steering system, incorporating an electric motor
back-up boost in the event of a main system or
engine failure.
Caution
Do not mix fluids in either the brake system or
the boost system because premature brake
system failure will occur.
The dual brake system gives the driver
reasonable braking capacity in the event that
either the front or rear brakes circuit should fail.
The brake system utilizes a glycol based
hydraulic fluid (DOT), and the boost system
utilizes power steering system fluid (DEXTRON
III).
The parking brake is a drum type brake installed
on the output shaft of the transmission. It is
94
Search
Exit
activated by a hand lever and cable mechanism
that applies the brake shoes to the parking brake
drum
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
2. Check the Hydro-Max exterior and all the
connecting lines for fluid leak. Remove dirt
from the exterior of the Hydro-Max.
3. Check for loose or disconnected electrical
connections and damaged wiring.
4. Check the vehicle brake warning system
(Reference Brake Booster and Warning
System Troubleshooting) comparing the
reaction of warning lights and buzzers to the
vehicle's handbook.
5. Check brake fluid level. Brake fluid must
be maintained to the correct level.
Directory
Previous
Previous
Next
Search
Exit
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
Brake Off
Warning Light /Buzzer Off
Normal
Warning Light/Buzzer On
Ignition diode bad
Off- Motor On
Motor Off
Normal
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
All American Brakes
Directory
Previous
Previous
---
Next
Search
Exit
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
closed.
differential
switch
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
closed
differential
switch
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
closed
differential
switch
Difference in front and rear
system pressure.
Switch failure
Relay fault
Table 3—Brake Booster and Warning System Troubleshooting (continued)
96
Directory
Previous
Previous
Next
Search
Exit
---
Warning Light/Buzzer Off
Normal
---
Warning Light/Buzzer On
Low fluid flow
Flow switch failed
Motor
failed
disconnected
or
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
module
booster
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.
All American Brakes
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 either by 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.
The mini master cylinder is a split system type
with a separate brake fluid reservoir and pistons.
Directory
Previous
Previous
Next
The output ports for the front and rear brakes
systems, or a single system master cylinder, may
be used where regulations are not applicable.
Search
Exit
2. A reserve electric motor pump
3. A hydraulic master cylinder
4. An integral flow sensing switch and warning
system
Hydraulic Pump Operating Components
Hydro-Max Power Brake System
Components
The Hydro-Max booster is positioned in the
vehicle's hydraulic circuit integrated with the
power steering gear.
1. A hydraulically powered booster
Figure 63—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). Figure 63.
have an internal bypass to allow manual steering
during reserve system operation.
The power steering gear must be balanced so
that it can handle the pressures generated in the
steering gear return line. It must 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
The pressure line must be 1/2 inch flexible or
rigid pressure line conforming to SAE J188 and
be designed to run from the steering gear to the
Hydro-max inlet.
98
The fluid flow path depicted is required to
minimize the interaction between the power
steering gear and the hydraulic booster.
Directory
Previous
Previous
Next
Search
Exit
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 pump electrical circuit during normal
operation.
Figure 64—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.
Figure 64.
Electrical
1. A relay
2. A 12 VDC battery
3. A warning light for the pressure differential
valve
4. Electrical connectors and wiring
5. Pedal activated brake light switch
6. A buzzer
7. A warning light for reserve motor
8. An (optional) electronic monitor module
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.
Force applied to the brake pedal by the vehicle
operator is multiplied by the lever ratio of the
All American Brakes
A separate check valve in the motor pump
prevents back flow through the motor pump
during normal applications.
In the even 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.
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 by 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 below.
Directory
Previous
Previous
Next
Search
Exit
Figure 65—Performance Curve
Each pressure chamber has a piston/actuator
subassembly containing a preload (caged) spring
and a return spring. In the released position,
actuators of both the primary and secondary
pistons are in contact with their respective
compensating valve stems, that project into the
cylinder bore. This maintains the valves in an
open position that allows hydraulic fluid in the
reservoir to replenish any fluid displayed from
the cylinder bore.
100
Initial forward travel of the primary piston
moves the primary actuator away from its
compensating valve counterpart permitting the
valve to seat. Closure of this valve shuts off the
passage between the primary pressure chamber
and the reservoir section serving the primary
chamber.
Directory
Previous
Previous
Next
Search
Exit
Figure 66—Master Cylinder Operation
Further movement of the primary piston creates
a pressure in the primary chamber, causing the
secondary piston and actuator to move. As the
secondary piston and actuator move, the
secondary compensating valve closes, shutting
off the passage between the secondary pressure
chamber and the reservoir section serving the
secondary chamber. Additional movement of
the primary piston causes both chambers to build
pressure.
When the load on primary piston is removed,
fluid pressure in each chamber, combined with
return spring force, causes the primary and
secondary pistons to return to their initial
released positions. Each actuator opens its
respective compensating valves, reopening the
passage between the individual reservoir
All American Brakes
sections and its associated pressure chamber.
Should the rate or release be great enough to
cause a partial vacuum in a chamber, the
compensating valve will open to allow
replenishment of fluid in the cylinder bore.
Any excess fluid remaining at the end of the
stroke due to "pumping", and/or volume change
due to temperature fluctuation, is released as the
compensating valve ports open.
Directory
Previous
Previous
Next
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
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.
102
Search
Exit
The second source of power for the module is
received fro 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.
The relay is controlled, in turn, 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, 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 turned 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 because of the following:
Directory
Previous
Previous
Next
Engine is running, brakes not applied with a loss
of electrical power to the electric backup pump
motor.
Engine is running, brakes are applied and either
the front or the 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.
Search
Exit
steel brake lines connected to the master
cylinder.
Do not apply the brakes after removal of 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.
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
Hydro-Max to the bus and remove the
Hydro-Max.
Note
When the engine is not running and ignition
OFF, a depressed brake pedal will cause the
backup to run with no light and buzzer.
To check that the backup pump system is not
working, the engine should be running, brakes
applied and ignition in the ON or START
position. The backup system should go off when
the pedal is released.
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.
5. Disconnect the electrical lead from the flow
switch.
6. Disconnect the wires at the relay.
Caution
The master cylinder must be supported in some
fashion so that the weight is not exerted on the
All American Brakes
Replace Hydro-Max Booster
1. Mount the Hydro-Max on the vehicle using
four bolts.
2. Torque the mounting bolts to 18-25 poundsft (24.4-33.9 Nm)
3. Install the bus master cylinder on the HydroMax.
4. Torque the four cap nuts to 25-30 pounds-ft
(33.9-40.7 Nm).
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 Nm).
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.
8. Perform Refilling and Bleeding Hydro-Max.
9. Perform Check Out Brake System.
Directory
Previous
Previous
Next
Search
Exit
Refilling and Bleeding HydroMax
The hydraulic components consist of a fluid
reservoir, master cylinder, Hydro-Max booster,
and brake calipers.
Caution
The electrical components consist 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.
Do not use brake fluid. Use only clean power
steering fluid. (Refer to Approved Hydraulic
Fluids location in Section 120— Steering.)
1. Check hydraulic pump or power steering
pump reservoir supplying Hydro-Max.
2. Fill with clean power steering fluid. (Refer
to Approved Hydraulic Fluids located in
Section 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, buzzer, or electric motor should
come on. Check for leak.
Refer to Routine Maintenance (see procedure in
this section) 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 Section 120—Steering.)
Hydraulic Brake Components
The hydraulic brake system is comprised of
hydraulic, electrical and mechanical
components.
104
The mechanical components are comprised of
the parking brake system.
Remote Reservoir
The remote reservoir is connected to the master
cylinder with two fed 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.
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, which press
the brake pads against the rotor.
Directory
Previous
Previous
Next
Search
Exit
Electrical Components
Brake Warning Buzzer activates a warning
when hydraulic pressure is low.
Brake Booster Module supplies power to the
relay.
Electrical Wire Harness connects electrical
components.
Brake System Relay transfer power from the
brake booster module to the electric booster
pump motor.
Electrical Connectors connect electrical wire
harness to electrical components.
Electric Booster Pump Motor supplies
hydraulic fluid to the Hydro-Max booster in case
of hydraulic failure.
Park Brake Components
Flow Switch senses hydraulic pressure.
Stoplight switch senses pressure going to the
brake calipers and closes the circuit to illuminate
stoplights.
All American Brakes
A hand level that is attached to a cable activates
the parking brake system. 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.
Directory
Previous
Previous
Next
Search
Exit
Figure 67—Brake Booster Electrical Components
106
Directory
Symptom
Previous
Previous
Next
Search
Exit
Cause
Remedy
Fluid leak between booster and Worn or damaged master Repair
or
master cylinder.
cylinder primary pressure seal or cylinder.
back-up ring.
replace
master
Worn or damaged seals or O- Repair or replace booster.
rings in booster end cap
assembly.
Fluid leak on booster or booster Damaged or missing seals at Replace seals.
pump. (Power steering pump)
booster and electric motor pump
mating surface.
Loose pump belt.
Tighten belt to specified tension.
Excessive output pressure at Replace pump.
pump. (Gauge at inlet line to
booster pump reads 5515 kPa
(800 psi) at least before pedal is
hard.
Binding pedal rod linkage
Repair cause of restriction.
Replace components as required.
Worn or wet brake linings.
Repair or replace brake linings
Sluggish booster operation with Slipping belt.
little or no assist.
Replace belt if required. Tighten
belt to specified tension.
Table 4—Troubleshooting and Diagnostics – Hydro-Max Power Brake System
---
Low fluid level in booster pump Refill to specified level.
reservoir.
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 Replace booster pump.
booster pump.
Motor pump check valve leaking Check booster pump pressure at
in booster.
inlet with full brake application.
Replace electric motor pump if
low pressure is noted.
All American Brakes
Directory
Previous
Previous
Next
Search
Exit
Electric motor pump does not Brake switch out of adjustment.
operate with engine off, ignition
Brake switch worn or damaged.
off and brake pedal depressed.
Adjust.
Replace switch.
Electric motor pump does not Ignition switch or connecting Check condition of switch and
operate with engine off and wires.
wiring replace as necessary.
ignition on.
Loose, disconnected or broken Repair or replace.
power lead wire at motor pump.
Loose, disconnected or broken Repair or replace.
flow switch wire.
Inoperative motor pump relay.
Repair or replace.
Inoperative booster flow switch.
Repair or replace.
Inoperative electronic monitor Replace monitor module.
module.
Inoperative electric motor pump
Electric motor pump runs Brake light switch.
continuously with ignition off
Inoperative, damaged
and brake pedal NOT depressed.
pump relay.
Check operation and replace as
required.
Adjust, repair or replace.
motor Replace.
Inoperative electronic monitor Replace monitor module.
module.
Table 4—Troubleshooting and Diagnostics – Hydro-Max Power Brake System (continued)
Premature lining wear/dragging Brake drag and associated If binding, repair or replace brake
brakes
premature lining wear is caused pedal mechanism and/or brake
either by the brakes being light switch.
applied when they should not be,
or the brakes not fully releasing
after an application.
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.
108
Directory
---
Previous
Previous
Next
Search
Exit
On sliding-caliper disc brakes, Replace piston seals.
make sure the calipers are free to
slide on their pins or rails.
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 If brake drag is present, it is likely
they are free.
With wheels that the booster is defective,
spinning, start the engine but do repair or replace booster.
not apply the brakes. When
the wheels stop spinning, check
for brake drag. If present, it's
likely that the booster is
defective
Low or sinking pedal
Common cause is air in the If air in system bleed system.
hydraulic system. The fix may
be as easy as bleeding the
brakes.
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)
All American Brakes
Directory
---
Previous
Previous
Next
Search
Exit
If you cannot 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 occur, 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, and
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 (continued)
Repairing the Hydro-Max
Brake Booster
Max assemblies, rather than local repair. Use
genuine Blue Bird maintenance parts.
If it is determined that the Hydro-Max booster is
not functioning properly after troubleshooting
the brake system, replace the defective Hydro-
Blue Bird seal bullet is used to install the power
piston in the boost housing on units found on
1981 and earlier year vehicles.
110
Directory
Previous
Previous
Next
The bullet to install the power piston in the end
cap and filter assembly on all Hydro-Max units
must be fabricated. Disassembly and assembly
should not be attempted without a kit.
Search
Exit
5. Push in on input push rod to force power
piston assembly from booster. (Rotate end
cap to ease piston removal.)
Caution
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.
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 that the
flow switch contact assembly is retained.
Threaded Contact Assembly
Figure 68—Power Piston Installation
Tool
Hydro-Max Brake Booster
Disassembly
1. Remove the cap screws securing the relay to
the booster housing, if equipped.
2. Remove the two cap screws that secure the
pump motor.
Warning
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.
All American Brakes
1. Remove the contact assembly
2. Remove and discard the O-ring from the
contact assembly
3. Extract the flow switch piston and spring
using 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
4. Remove and discard the O-ring
5. Extract the flow switch piston and spring
using a small magnet
Caution
Do not clamp onto power piston.
Directory
Previous
Previous
Next
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.
Caution
Do not over tighten 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
Caution
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.
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.
14. Pry the actuator seal retainer from the input
plug and discard.
15. Remove actuator pin and discard actuator
seal.
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
using 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
pulling the input push rod out of the input
112
Search
Exit
plug. A load up to 100 pounds may be
required to pull the rod from the plug.
Note
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.
2. Inspect the large piston seal surface to
ensure it is smooth, and without excessive
wear.
3. If any defects are found, replace the power
piston assembly.
4. Confirm that the check ball is in place and is
cleaned free to move.
5. Confirm that the reaction piston bore and
poppet seat surface inside the piston are
clean and undamaged.
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.
Directory
Previous
Previous
Next
Using the proper rebuild kit:
1. Replace the filter end cap assembly if
cracked or damaged. The 12 rib cage is
interchangeable with the four rib cage.
2. Remove the three largest O-rings from the
kit.
Note
Two of the three are identical in thickness with
the third O-ring being noticeably thicker.
If the cap is the four rib version, discard the
thickest O-ring of the three.
3. 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.
4. Install the O-ring in the OD groove closest
to the end cap ribs and the thin O-ring in the
other OD groove.
5. Remove the one inch OD O-ring and the
smallest of the three lip seals in the kit.
6. Lubricate and install the O-ring and lip seal
in the appropriate grooves in the ID of the
filter and end cap assembly.
Caution
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.
7. Install the grommet on the input push rod.
8. 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.
Caution
If the input push rod is not properly installed,
the push rod could become disconnected from
the input plug. Complete brake failure will
All American Brakes
Search
Exit
result. Do not clean parts with brake fluid. Use
only fresh clean steering fluid.
Actuator Installation
1. Lubricate and install actuator seal (smallest
seal in kit) in the recess inside of the input
plug.
2. Lubricate and insert the actuator pin in the
seal.
3. Install the actuator seal retainer in the input
plug with its flat side toward the input plug.
Of the O-rings remaining in the kid, 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 O-ring
and discard the remaining O-ring. The correct
one is the thicker of the two.
4. Remove the two remaining lip seals from
the kit.
5. Lubricate and install both seals in the small
ID of the booster housing bore. The lip of
both seals should 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.
6. Lubricate and install one of the small
diameter O-rings in the groove of the inlet
check valve.
7. Install the inlet check ball in the inlet port of
the booster housing.
8. Lubricate and install the assembled inlet
check valve and O-ring in the inlet port.
9. Push the inlet check valve in until it comes
to rest.
Directory
Previous
Previous
Next
10. Install the flow switch spring and then the
flow switch piston in the booster housing.
11. Determine the type of flow switch contact
assembly that is in use.
Threaded Contact Assembly
1. Install the larger diameter of the two
remaining O-rings on the contact assembly
2. Install the contact assembly in the booster
housing and torque to 20-40 pound-inch (2.4
Nm)
Caution
Do not over tighten the contact assembly. A
failed and leaking assembly will result.
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.
Snap Ring Contact Assembly
1. If the contact assembly requires a snap ring
to secure in the booster housing, lubricate
and install the smaller 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.
114
Search
Exit
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 a way that is 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.
11. Install the poppet valve.
Note
Be sure the poppet valve is installed with coneshaped end toward the return spring.
12. Install the valve rod and reaction piston
assembly in the hollow end of the power
piston.
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 not use tools to
tighten.
15. Lubricate the exterior of the input plug and
power piston input shaft.
Directory
Previous
Previous
Next
Search
Exit
16. Insert the power piston in the booster
housing with a gentle twisting motion.
Proceed to Step 21 of the assembly
instructions.
Note
Note
26. Secure the pump to the housing using two
cap screws.
27. Torque the cap screws 18-25 foot-pounds
(24-33 Nm).
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.
21. Ensure that the tape is not wrapped on any
portion of the major diameter of the plug or
shaft.
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.
All American Brakes
Before installing the electric pump motor
assembly on the booster housing, check to be
sure that the motor pump check ball and
retainer are present in the delivery port.
Caution
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
Nm).
Directory
Previous
Previous
Next
Search
Exit
Note
Information contained in this Service Manual was obtained, either whole or in part, from the following
ArvinMeritor publications.
•
•
•
•
•
•
•
•
•
•
•
•
Manual 1, Lubrication – Revised 02-01
Manual 4, Cam Brakes – Revised 10-98
Manual 4B, Automatic Slack Adjuster – Revised 03-98
Manual 5A, Single Reduction Rear Differential Carriers – Revised 09-00
Manual 8 – Drive Axle Housings – Revised 08-00
Manual 23 – Bus and Coach Front Axles – Issued 07-98
Manual 23A – Bus and Coach Rear Axles – Revised 09-97
Manual 23B – Bus and Coach Brakes – Revised 11-96
Manual 39 – Hydraulic ABS for Medium-Duty Trucks, Buses and Motor Home Chassis – Rev 09-00
Manual MM-2075, Four Piston Quadraulic Disc Brake Caliper – Issued 01-01
Manual 2 – Parts 1 & 2, Front Non-Drive Steering Axles – Rev 05-01 (supersedes MM-99120)
Manual TP-9955, Failure Analysis for Drive Axle Components – Issued 08-00
Please note that you can access current maintenance and service information in the Tech Library at
arvinmeritor.com. Click Products & Services/Truck & Trailer Products/Sales and Service tab/Tech
Library icon. The screen will display a list of publications by type. You can also contact ArvinMeritor's
Customer Service Center at 800-535-5560 to order publications or to verify current editions.
For information on the AD-9 Air Dryer, see Bendix Service Data SD-08-2414. For information on the
AD-SP System Purge Air Dryer and SC-PR Single Check Protection Valve, see Bendix Service Data
SD-08-2415. These publications can be accessed from the Bendix website. See
www.Bendix.com/Products/AirDryers.shtml.
Back to Top
116
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement