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 74 of 481
TM 9-2320-272-10
Change 2
1-57
1-20. COMPRESSED AIR AND BRAKE SYSTEM OPERATION
NOTE
When vehicles are equipped with antilock
brake system (ABS), they will have different
front and rear relay valves, double check
valves, LQ-2 valve replaces limiting valve,
new air dryer with heater, and inversion valve
installed.
The compressed air and brake system takes filtered air, compresses it, and supplies it
to various components that enable the operator to slow down or stop the vehicle. This
system also supplies compressed air to air-actuated accessories throughout the vehicle.
These components and accessories will be described as part of the following systems:
a. Medium Wrecker Automatic Brake Lock System Operation (page 1-57).
b. Air Pressure Supply System Operation (page 1-58).
c. Secondary Service Airbrake System Operation (page 1-62).
d. Spring Airbrake System Operation (page 1-64).
e. Primary Service Airbrake System Operation (page 1-65).
f. Auxiliary Air-Powered System Operation (page 1-68).
g. Air Venting System Operation (page 1-70).
h. Central Tire Inflation System (CTIS) (M939A2 series vehicles)
(page 1-72).
a. Medium Wrecker Automatic Brake Lock System Operation.
The M936/A1/A2 Medium Wrecker Automatic Brake Lock System locks the service
airbrakes when the transfer case power takeoff lever is engaged. Major components of the
automatic brake lock system are:
A
TRANSFER CASE POWER TAKEOFF LEVER
– Opens the brake lock
control valve through mechanical linkage when engaged.
B
BRAKE LOCK CONTROL
– Allows air pressure to flow from secondary air
reservoir to pressure regulator and activate variable speed governor.
C
PRESSURE REGULATOR
– Reduces and regulates system air pressure to
70 psi (483 kPa) for automatic brake lock application.
D
TREADLE VALVE
– Connects pressure regulator and service airbrakes.
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