TM-9-2320-272-10
TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)
TECHNICAL MANUAL; OPERATOR'S MANUAL
SEPTEMBER 2004
CHANGE 2
TM-9-2320-272-10 - Page 82 of 481
TM 9-2320-272-10
1-65
1-20. COMPRESSED AIR AND BRAKE SYSTEM OPERATION (Contd)
D
INTERMEDIATE FRONT SPRING BRAKE CHAMBER
–
Contains a
large spring which applies rear brakes when spring brake air pressure is
released.
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.
K
REAR-REAR SPRING BRAKE CHAMBER
– Contains a large spring
which applies rear brakes when spring brake air pressure is released.
I
SPRING BRAKE RESERVOIR DRAINVALVE
– Provides a drain for
moisture and air from spring brake reservoir.
J
DOUBLECHECK VALVE #3
–
Allows spring brake air pressure to come
from either release control valve or spring parking brake valve directly to
doublecheck valve #4.
G
QUICK-RELEASE VALVE
–
Releases spring brake air pressure directly to
vent if parking brake has been set or brake system fails.
E
ONE-WAY CHECK VALVE
– Allows air pressure to flow into spring brake
reservoir but prevents it from coming out if constant pressure system or
primary system fails.
e. Primary Service Airbrake System Operation.
(1) The primary service airbrake system is made up of two subsystems:
(a) Primary constant pressure system provides continuous air pressure to:
• Pedal valve.
• Rear relay valve.
• Spring brake air reservoir.
• Spring parking brake valve.
(b) Primary signal system serves three functions:
• Contains pressure only when operator steps on brake pedal.
• Is regulated by various valves to give operator control over
amount of braking.
• Provides pressure to apply front service brakes and the front two
service brakes on the intermediate and rear axles stamped with
an A. Service brakes on the intermediate axle are piggybacked to
spring brakes but operate independently of them.
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.
Back to Top
