TROUBLESHOOTING GUIDE
5-5
TABLE OF CONTENTS
ALL BRAKES DO NOT RELEASE Air system improperly connected to
tractor
Tighten or adjust connections.
Brake valve on tractor is applied Release brake.
Relay emergency valve in emergency
position
Check line pressure and check valve.
Restricted tubing or line Locate restriction and remove.
Defective tractor protection valve Troubleshoot tractor air system.
Parking brakes locked Troubleshoot air system.
Moisture in air system Check air system.
Tractor pressure too low Adjust to provide 105 psi min.
INSUFFICIENT BRAKES Brakes need adjusting Adjust brakes
(See “Brake System
Maintenance” on page 4-16.)
Brakes need lubricating Lubricate brakes.
Brakes need relining Reline brakes.
Low air pressure Troubleshoot air system.
Defective relay emergency valve Repair or replace.
Brakes overheated Stop and allow brakes to cool, locate
cause of overheating.
BRAKES GRABBING Grease on brake linings Reline brakes.
Brake rigging binding Align brakes or replace bent parts.
Defective brake valve on tractor Repair or replace valve.
Defective relay emergency valve Repair or replace valve.
EXCESSIVE LEAKAGE WITH BRAKES
RELEASED
Relay emergency valve leaking Repair or replace valve.
Leaking tubing or hose Replace defective part.
EXCESSIVE LEAKAGE WITH BRAKES
APPLIED
Relay emergency valve leaking Repair or replace valve.
Leaking brake chamber diaphragm Replace diaphragm.
Call Factory or see qualified Trailer/Brake Technician
Leaking tubing or hose Replace defective part.
EXCESSIVE LEAKAGE WITH
EMERGENCY SYSTEM ONLY
APPLIED - NO LEAKAGE WITH
NORMAL BRAKING
Defective relay emergency valve Repair or replace valve.
EXCESSIVE WATER PRESENT IN
BRAKE SYSTEM
Reservoir not drained often enough Drain reservoir daily.
EXCESSIVE OIL PRESENT IN BRAKE
SYSTEM
Compressor on tractor passing
excessive oil
Repair compressor.
BRAKE WILL NOT APPLY PROPERLY Flat spot on cam roller or camshaft Replace and lubricate.
BRAKES WILL NOT APPLY WHEN
EMERGENCY LINE IS
DISCONNECTED
Initial air pressure too low Allow air system to build up to
minimum 90 PSI and stabilize.
Defective relay valve Repair or replace valve.
Air line leak Locate leak and repair.
Brake chamber leak Locate leak and repair or replace.
ABS WARNING LIGHT STAYS
ON
Refer to Rockwell WABCO ABS maintenance manual supplied with semitrailer, for
system function and use of blink code diagnostics.
PROBLEM PROBABLE CAUSE SOLUTION
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