TM-9-2320-272-23-1
TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)
TECHNICAL MANUAL; FIELD MAINTENANCE MANUAL; VOLUME 1 OF 5
SEPTEMBER 2012
TM-9-2320-272-23-1 - Page 247 of 1313
SPRING AIRBRAKE SYSTEM OPERATION
The spring airbrake system applies rear brakes when vehicle parking brake is applied or in event of a major brake
failure. The spring brake is located on one of the two service brake chambers at each rear wheel. Major components
of the spring airbrake system are:
A. SPRING BRAKE WARNING LIGHT SWITCH
- Activates warning light when spring brakes are engaged.
B. SPRING BRAKE RELEASE CONTROL VALVE
- Pushed in to release spring brakes independently of
mechanical parking brake. Control is also used to release spring brakes in order to test and adjust
mechanical brake.
C. DOUBLE CHECK VALVE NO. 4
- Allows spring brake air pressure to come from either release control
valve or spring parking brake valve directly to double check valve No. 3.
D. INTERMEDIATE FRONT SPRING BRAKE CHAMBER
- Contains a large spring which applies rear
brakes when spring brake air pressure is released.
E. ONE-WAY CHECKVALVE
- Allows air pressure to flow into spring brake reservoir, but prevents it from
coming out if constant pressure system or primary system fails.
F. SPRING BRAKE AIR RESERVOIR
- Stores enough air pressure to release spring brakes for emergency
operation in event of primary or secondary air system failure.
G. QUICK-RELEASE VALVE
- Releases spring brake air pressure directly to vent if parking brake has been
set or brake system fails.
H. SPRING BRAKE VALVE
- Automatically sets spring brakes when parking brake is set. Valve can be
released independently of parking brake when spring brake control valve is pushed in.
I. SPRING BRAKE RESERVOIR DRAIN VALVE
- Provides a drain for moisture and air from spring
brake
reservoir.
J. DOUBLE CHECK VALVE NO. 3
- Allows spring brake air pressure to come from either release control
valve or spring parking brake valve directly to double check valve No. 4.
K. REAR-BEAR SPRING BRAKE CHAMBER
- Contains a large spring which applies rear brakes when
spring brake air pressure is released.
TM 9-2320-272-23-1
0003
0003-42
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