Troubleshooting guide

60
www.bendix.com 1-800-AIR-BRAKE (1-800-247-2725)
Air Brake System Troubleshooting Tests (continued)
2. Manually operate the system park control (usually
yellow diamond button) and note all parking brakes
(tractor and trailer) apply promptly.
If sluggish performance is noted in either test, check
for:
1. Dented or kinked lines
2. Improperly installed hose fitting
3. A faulty relay emergency valve
4. A faulty modulator(s)
If the trailer brakes do not actuate and the trailer supply
line remains charged, check the:
1. Tractor protection control
2. Trailer spring brake valve
Retest to check out all items repaired or
replaced.
Make all necessary repairs before proceeding to
Test Five.
TEST FIVE
Automatic Emergency System
Check with air system at full pressure, with the
engine stopped.
1. Drain front axle reservoir to 0 PSI.
A. Rear axle reservoir should not lose pressure
B. On combination vehicles, the trailer air system
should remain charged
C. Tractor and trailer brakes should not apply
automatically
2. With no air pressure in the front axle reservoir
make a brake application.
A. Rear axle brakes should apply and release
B. On combination vehicles the trailer brakes
should also apply and release
C. The stop lamps should illuminate
3. Slowly drain rear axle reservoir pressure.
A. With the button out, supply either supply port
with 120 psi of air. Then push the button in.
The air pressure should rise in the delivery
volume equivalent to supply pressure. Pull the
button out. The delivery pressure should
exhaust to 0 psi. Build each supply source to
120 psi and decrease supply pressure at the
secondary service reservoir supply port at a
rate of 10 psi per second. Primary supply
pressure and delivery pressure should not
drop below 100 psi. Repeat the test for
decreasing primary service reservoir pressure.
Build each supply source to 120 psi. Then
decrease both supply pressures to below 20
to 30 psi. The button should automatically
"pop" out when pressure drops within that
range.
B. The tractor protection valve should close
between 45 PSI and 20 PSI and the trailer
supply hose should be exhausted
C. Trailer brakes should apply after tractor
protection closes
4. Slowly drain the rear axle reservoir pressure.
5. Close drain cocks, recharge the system and drain
the rear axle reservoir to 0 PSI.
A. Front axle reservoir should not lose pressure
B. On combination vehicles the trailer air system
should remain charged
6. With no air pressure in the rear axle reservoir,
make a brake application.
A. The front axle brakes should apply and release
B. On combination vehicles the trailer brakes
should also apply and release
C. If the vehicle is equipped with an inverting relay
spring brake control valve, the rear axle brakes
should also apply and release
If the vehicle fails to pass the tests above, then
check the following components for leakage and
proper operation:
1. Fittings
2. Check for kinked hoses or tubing
3. Single check valves
4. Double check valves
5. Tractor protection valve
6. Tractor protection control valve
7. Parking control valve
8. Relay valves (antilock modulators)
9. Trailer spring brake control valve
10. Inverting relay spring brake control valve (optional
on straight trucks and buses)
Retest to check out all items repaired or
replaced.