Table 9-1. Compressed Air and Brake System Troubleshooting Procedures (Continued).
TEST OR INSPECTION.
3. PARK BRAKES WILL NOT RELEASE (Continued):
(M915, M916 and M920 only). Inspect intervehicle air hoses for proper connections.
Connect hoses properly.
Check the air line between the two rear quick-release valves for damage or leaks using
a soap solution.
Replace the line if damaged and tighten connections.
Replace the park brake quick-release valve (para 9-22).
4. TRAILER OR TOWED VEHICLE BRAKES WILL NOT RELEASE:
Check intervehicle air hoses for proper connections. Close the trailer supply valve and
disconnect the hoses.
Reconnect the hoses and open the supply valve.
Check for trailer air leaks or defective brakes.
5. SERVICE BRAKES WILL NOT RELEASE (ONE WHEEL ONLY) :
Refer to brake malfunctions 3 and 4, above.
SERVICE BRAKES WILL NOT APPLY:
Check the pressure gages in the cab.
Operate the engine to build up proper pressure.
Check position of park brake and trailer supply valves.
(M915, M916 and M920 only). Check intervehicle connections.
Connect air hoses correctly and open trailer supply valve.