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 258 of 1313
REAR WINCH HYDRAULIC SYSTEM OPERATION
A rear winch is installed only on the M936/A1/A2 medium wrecker. It is used primarily to rescue vehicles that have
become deeply mired. The rear winch hydraulic system converts mechanical power of the engine into fluid power
through use of the hydraulic pump and back into mechanical power at the winch drive motor. The major components
of the rear winch hydraulic system are:
A. PTO DRIVESHAFT
- Transmits mechanical driving power from PTO to the hydraulic pump.
B. HYDRAULIC PUMP
- Draws oil from hydraulic oil reservoir and directs it to the rear winch control valve
and winch drive motor.
C. OIL FILTER
- Filters used or bypassed oil from the control valve before it returns to the hydraulic
oil
reservoir.
D. HYDRAULIC OIL RESERVOIR
- Storage tank for hydraulic oil.
E. TORQUE CONTROL LEVER
- Controls the operating gear ratio of the winch drive motor. Lever is pulled
outward to HIGH for heavy loads or pushed inward to LOW for light loads.
F. WINCH DIRECTIONAL CONTROL LEVER
- Manually-operated lever that controls the wind and unwind
direction of the rear winch drum. Lever does this by opening and closing the directional control valve to the
winch motor, and reversing the direction of pressurized hydraulic fluid. Lever is pushed inward to wind and
pulled outward to unwind winch cable.
G. DIRECTIONAL CONTROL VALVE
- Receives pressurized hydraulic oil from the hydraulic pump and
directs it to the winch motor. The flow of hydraulic oil to and from this control valve provides forward or
reverse driving power to the winch motor. Valve also returns used oil back to the hydraulic oil reservoir from
the winch.
H. TORQUE CONTROL VALVE
- Hydraulically controls the hydraulic oil pressure to engage rear winch
drum clutch in high or low gear range.
I. WINCH MOTOR
- Converts hydraulic power back into mechanical power needed to turn the rear
winch
drum.
J. CONTROL LINKAGE
- Connects transfer case PTO control to transfer case PTO.
K. TRANSFER CASE PTO CONTROL
- A manually-operated control lever located inside the cab that
permits engagement or disengagement of the PTO.
L. TRANSFER CASE PTO
- Uses driving power of the transfer case to provide mechanical driving power
for the hydraulic pump.
J
K
L
A
B
C
D
E
F
G
H
I
G0047DAA
Figure 35.
Rear Winch Hydraulic System Components.
TM 9-2320-272-23-1
0003
0003-53
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