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 240 of 1313
COMPRESSED AIR AND BRAKE SYSTEM OPERATION
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:
1.
Medium Wrecker Automatic Brake Lock System Operation.
2.
Air Pressure Supply System Operation.
3.
Secondary Service Airbrake System Operation.
4.
Spring Airbrake System Operation.
5.
Primary Service Airbrake System Operation.
6.
Auxiliary Air-Powered System Operation.
7.
Air Venting System Operation.
8.
Central Tire Inflation System (CTIS) (M939A2 series vehicles).
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
PTO lever is engaged. Major components of the automatic brake lock system are:
A. TRANSFER CASE PTO 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.
AIR SUPPLY LINE
AIR CONTROL LINE
AIR SIGNAL LINE
MECHANICAL LINKAGE
A
B
D
C
TO
VARIABLE
SPEED
GOVERNOR
FUEL PUMP
TO
SECONDARY
AIR RESERVOIR
TO FRONT AND REAR,
AND REAR-REAR RELAY VALVE
G0037DAA
Figure 25.
Medium Wrecker Automatic Brake Lock System Components.
TM 9-2320-272-23-1
0003
0003-35
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