Parking Brake
CONDITION CAUSE REMEDY
PARKING BRAKE WON’T
APPLY
Restricted hose or tube Remove restriction or replace.
Defective relay valve Repair or replace
Defective spring brake valve Repair or replace
Defective control valve Repair or replace
PARKING BRAKES WON’T
RELEASE
Insufficient system air
pressure
Allow engine to run to
increase pressure to above
70 p.s.i.
Restricted hose or tube Remove restriction or replace
Insufficient hold off pressure Check for system (or
excessive valve) leaks
Leaking brake actuator
diaphragm
Replace brake actuator
(spring pot).
Defective relay valve Repair or replace relay valve
Defective spring brake valve Repair or replace spring
brake valve
Defective control valve Repair or replace control
valve
RT500
Troubleshooting
214 REVISED:
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