BENDIX BW2872 Scheda Tecnica

BW2872  ©  2010 Bendix Commercial Vehicle Systems LLC, a member of the Knorr-Bremse Group •  6/2010 •  All Rights Reserved

vehicle.  

If the vehicle is equipped with a Bendix

®

 AD-IS

®

 air dryer 

system or a dryer reservoir module, be sure to drain the purge 
reservoir.

5.  Following the vehicle manufacturer’s recommended procedures, 

deactivate the electrical system in a manner that safely removes all 
electrical power from the vehicle.

6.  Never exceed manufacturer’s recommended pressures.  
7.  Never connect or disconnect a hose or line containing pressure; it 

may whip. Never remove a component or plug unless you are certain 
all system pressure has been depleted.

8.  Use only genuine Bendix

®

 brand replacement parts, components 

and kits. Replacement hardware, tubing, hose, fi ttings, etc. must be 
of equivalent size, type and strength as original equipment and be 
designed specifi cally for such applications and systems.

9.  Components with stripped threads or damaged parts should be 

replaced rather than repaired.  Do not attempt repairs requiring 
machining or welding unless specifi cally stated and approved by the 
vehicle and component manufacturer.

10. Prior to returning the vehicle to service, make certain all components 

and systems are restored to their proper operating condition.

11.  For vehicles with Automatic Traction Control (ATC), the ATC function 

must be disabled (ATC indicator lamp should be ON) prior to 
performing any vehicle maintenance where one or more wheels on 
a drive axle are lifted off the ground and moving.

When working on or around a vehicle, the following general 
precautions should be observed at all times.

1.  Park the vehicle on a level surface, apply the parking brakes, and 

always block the wheels.  Always wear safety glasses.  

2.  Stop the engine and remove ignition key when working under or 

around the vehicle.  When working in the engine compartment, the 
engine should be shut off and the ignition key should be removed. 
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.

3.  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.

4.  

If the work is being performed on the vehicle’s air brake system, 
or any auxiliary pressurized air systems, make certain to drain the 
air pressure from all reservoirs before beginning ANY work on the 

www.foundationbrakes.com

The color coding of the brake system schematic follows TMC Recommended Practice #423.  Air 
disc & drum brake actuation combined on a single axle are shown for pictorial purposes only.

School Bus Air Brake Systems (Small version of BW2872)

BW1114 Bendix

 

Quick Reference Catalog

Air Brake System Troubleshooting Wallchart

BW1555   

Brake Balance Procedure

BW2780   

Troubleshooting Bendix

®

 ESP

®

 Stability System Wallchart

Troubleshooting Bendix

®

 ESP

®

 Stability System

BW5057   

Air Brake Handbook

BVA-85

™

 Brake Valve Actuator

SD-13-4815   EC-30

™

 ABS Controller

SD-13-4863   EC-60

™

 ABS Controller

C

Bendix

C





Make and hold a brake application. When ignition power is applied, each 
pressure modulator valve (PMV) solenoid is briefl y energized. If the air 
system is fully charged and the service brake pedal is depressed during 
ignition, the modulator creates a single, sharp audible “chuff” of air pressure. 
The modulators are energized in a certain pattern, as follows: right front, 
left front, right rear, left rear. This test is performed only when the vehicle is 
stationary (if the vehicle moves the chuff test will not be performed).

NOTE:  The Bendix

®

 EC-60

™

 electronic controller will perform a pressure modulator valve 

(PMV) chuff test on all installed modulators in the following order:

1. Steer Axle Right PMV
2. Steer Axle Left PMV
3. Drive Axle Right PMV
4. Drive Axle Left PMV
5. Additional Axle Right PMV
6. Additional Axle Left PMV
7. Drive Axle Traction Control Valve (TCV)
The pattern will then repeat itself.
See appropriate Service Data Sheet for repairs.





1. Make and hold an 80-90 psi brake application. This can be accomplished 

by using the Bendix

®

 BVA-85

™

 brake valve actuator.  If the vehicle is not 

equipped with a BVA-85

™

 brake valve actuator, an assistant should be 

used to maintain a constant brake application during these tests.

2. Allow pressure to stabilize for 1 minute; then begin timing for 2 minutes 

while watching the dash gauges for a pressure drop.  A 4 psi drop within 
2 minutes is allowable for either service reservoir.

3. Check brake chamber push rod travel (refer to chart for allowable 

tolerances).  With the parking brakes released and service brakes 
applied with 80 to 90 psi of air pressure to the service chambers.
 

__________________________________________________    
12 1-3/8” 

1-3/4” 

 16 

1-3/4” 

2” 

   

20 1-3/4” 

2” 

 

 

24 1-3/4” 

2” 

 

 

24 (Max Stroke) 

- 

2-1/2” 

 

 30 

2” 

2-1/2”

4. Check the angle formed between the brake chamber push rod and slack 

adjuster arm. It should be approximately 90° in the applied position 
(80-90 psi) and the same across the axle.





1. Drain all the reservoirs to 0 psi.
2. Start the engine and run at fast idle.  The low pressure warning should 

be on.  Note: on vehicles equipped with ABS, the warning lamp will also 
come on momentarily when the ignition is turned on.  On some systems, 
such as the Bendix

®

 AD-IS

®

 dryer system (illustrated), reservoirs may 

not fi ll simultaneously and one reservoir may fi ll to 110 psi before the 
other starts to fi ll.  

3. Low pressure warning; dash warning lamp should go off above 60 psi.

4. Build up time; pressure should build from 85-100 psi within 40 seconds.

5. Governor cut-out; cuts-out at the correct pressure, 135 psi (maximum).

6. Governor cut-in; reduce the service air pressure to governor cut-in. The 

difference between cut-in and cut-out pressure must not exceed 30 psi.

1.  Check the warning lamp wiring.
2.  Check the warning lamp bulb.
3.  Repair or replace the buzzer, bulb or low pressure warning switch(es).

1. Repair, replace or adjust the governor as necessary after ensuring the compressor 

unloader mechanism is operating correctly.

1.  Check the dash gauge with test gauge known to be accurate.
2.  Repair or replace the faulty low pressure indicator switch.

1.  Examine the compressor air inlet fi lter and inlet line checking for restrictions, damage or 

wear.  Clean or replace the fi lter or inlet line as necessary.

2.  Check the compressor discharge port and line for excessive carbon. Clean or replace the 

discharge line as necessary.  If carbon is present, fi nd the cause of the excessive heat.

3. With the system fully charged and governor in the unloaded mode, listen at the 

compressor inlet for leakage. If leakage can be heard, remove the unloaders and repair 
or replace as necessary.

System Air Leakage (Bendix

® 

 part number BW2327 - CD)





1. Allow the air pressure to stabilize for at least 1 minute.

2. Observe the dash gauge pressures for 2 minutes and note any pressure 

drop. A 4 psi drop within 2 minutes is allowable for either service 
reservoir.

NOTE:  A leak detector or soap solution will aid in locating the faulty component.

1.  Supply lines and fi ttings
2.  Low pressure indicator(s)
3.  Service brake relay valve(s) 
4.  Spring brake relay valve (where applicable)
5.  Dual brake valve
6.  Park control valve
7.  System safety valve(s) in the supply reservoir and/or air dryer 
8.  Governor (may be mounted on the air dryer as illustrated, on the compressor, or remotely)
9.  Compressor discharge line 





3.  “Pop” Pressure Vehicle Test Procedure (Continued)

Install an accurate “shop standard” pressure gauge in the secondary 
service reservoir.  Build pressure in the service reservoirs until the 
compressor cut-out is reached, shut the engine off.  Fully open the 
manual drain valve on the primary service reservoir allowing the 
reservoir to drain completely.  Open the secondary reservoir’s manual 
drain valve creating a bleed rate of approximately 20-50 psi/min.  
Monitor the pressure gauge noting the pressure at which the parking 
control automatically “pops”.  This is not a Federal requirement - See 
Note in previous column.

4.  Close the drain cocks, recharge the system and drain the rear axle 

primary reservoir to 0 psi.  The front axle reservoir should retain most 
of its pressure.

5. With no air pressure in the rear axle reservoir, make and release a 

brake application. 

A. Front axle brakes should apply and release.

B. If the vehicle is equipped with a spring brake modulating valve, the 

rear axle brakes should also apply and release by exhausting spring 
brake air.

1. Fittings
2.  Kinked hose or tubing
3.  Pressure protection valves
4.  Double check valves
5.  Parking control valve
6.  Relay valves (antilock modulators)
7.  Inverting relay spring brake control valve (optional) 

NOTE: A leak detector or soap solution will aid in locating the faulty component.

1.  Loose service lines and fi ttings 
2.  Park control valve
3. Stoplight switch
4.  Spring brake chamber, service chamber and/or brake chamber diaphragms
5.  Service brake relay valves 
6.  Dual brake valve
7.  Inverting relay spring brake control valve (where applicable – usually found on the spring 

brake relay valve) straight trucks and buses

8.  Double check valve

CAUTION:  If the brake chamber push rod travel exceeds the allowable stroke, identify and 
correct the root cause of the excess stroke.  Do not make manual adjustments of an automatic 
slack adjuster once it can no longer automatically adjust the brakes.  Manual adjustment DOES 
NOT fi x the underlying wheel-end adjustment.  As soon as possible, have the vehicle inspected 
by a qualifi ed technician or consult the manufacturer’s troubleshooting guidelines to fi nd and fi x 
the problem.





Manually operate the park control, yellow button valve, and note that 
parking brakes apply and release promptly as the control valve button is 
pulled out and pushed in.

1.  Dented or kinked lines
2.  Improperly installed hose fi tting
3.  A faulty quick release valve or spring brake control valve
4.  Damaged or improperly installed spring brake chamber and/or service chambers
5.  Foundation brake component binding, improper installation and/or lack of lubrication





1.  Drain the front axle or secondary reservoir to 0 psi.  The rear axle or 

primary reservoir should retain most of its pressure.

2.  With no air pressure in the front axle reservoir, make a brake application.

A.  The rear axle brakes should apply and release when the application 

is released.

B. The stop lamps should light and go off when the application is 

released.

3. “Pop” Pressure Vehicle Test Procedure

Note: Bendix is not aware of any federal legislation that specifi es the pressure at which the 
YELLOW parking brake control valve must automatically “trip” to apply the vehicle parking 
brakes.  This includes the Federal Motor Carrier Safety Regulations (FMCSR) for in-use 
vehicles, the CVSA out-of-service criteria, and the Federal Motor Vehicle Safety Standards 
(FMVSS) for newly manufactured vehicles.  Although the “trip” pressure for the parking brake 
control valve is not stipulated for in-use or newly manufactured vehicles, a parking brake control 
valve “trip” pressure of 20-40 psi is currently (02/2009) specifi ed as part of the Commercial 
Driver License in the CDL Manual.  The CDL Manual is not consistent with the regulations cited 
above.  See Bulletin TCH-003-051.       

                                                             

continued . . .

Note:  The optional Bendix

®

 BVA-85

™

 actuator for Bendix

®

 E-6

®

-, E-8P

™

-, and E-10

™

-

based brake valve confi gurations, plus the door interlock kit (Pc. No. K036675), is 
intended to provide an approximately 40 psi service brake application to all wheels 
when the following conditions are met;

•  Passenger door is open
•  RED crossing fl ashers are ON
•  Vehicle speed is below 3 mph

Indication is provided to the operator in the event that the control pressure to the 
BVA-85

™

 actuator drops below the minimum pressure required to hold the bus.   

•    All genuine Bendix

®

 brand replacement parts are 

manufactured to meet original OE specifications to 
guarantee quality,  reliability and proper operating 
performance.

•    Rely on genuine Bendix

®

 brand replacement parts to keep 

your Air Brake System operating efficiently.

•    With thousands of authorized Bendix Parts Outlets across 

North America, you’re never far from quality genuine Bendix

®

 

brand replacement parts.

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