TM 9-2320-272-24-1
1-24. HYDRAULIC SYSTEM OPERATION
Oil pressure (hydraulics) is used to provide operating power for the auxiliary equipment on the vehicles
covered in this manual. The components that provide hydraulic power are discussed in the following order:
a . Front Winch Hydraulic System Operation (page 1-71).
b . Rear Winch Hydraulic System Operation (page 1-72).
c. Dump Body Hydraulic System Operation (page 1-73).
d . Medium Wrecker Crane Hydraulic System Operation (page 1-74).
a. Front Winch Hydraulic System Operation.
A front winch is installed on M925/A1/A2, M928/A1/A2, M930/A1/A2, M932/A1/A2, and M936/A1/A2
series vehicles. The front winch hydraulic system converts mechanical power at the winch drive motor. The
basic operating principles are the same for each model. Major components of this system are:
Key Item and Function
1 CLUTCH LEVER - Manual control that engages winch drum gear to drive gear of winch motor.
2 TRANSMISSION PTO CONTROL - A manually-operated control lever located inside the cab that
permits engagement or disengagement of the transmission PTO.
3 WINCH CONTROL LEVER -An operator control that determines the hydraulic oil pressure flow
from the control valve to the winch motor. The flow of this oil determines the direction the winch
drum will turn.
4 TRANSMISSION PTO - Uses transmission driving power to provide mechanical driving power for
the hydraulic pump.
5 PTO DRIVESHAFT - Transmits mechanical power from PTO to the hydraulic pump.
6 HYDRAULIC PUMP - Driven by PTO driveshaft, it draws oil from the oil reservoir through
hydraulic hoses, then pressurizes and directs this oil to the control valve.
7 OIL FILTER - Filters used or bypassed oil from the control valve before it returns to the hydraulic
oil reservoir.
8 HYDRAULIC OIL RESERVOIR - Storage tank for hydraulic oil.
9 CONTROL VALVE - Four-port valve accepts pressurized oil from the hydraulic pump and directs
this oil to the winch motor. It also directs oil returning from the winch back to the oil reservoir. The
flow of this oil from the valve determines the directional drive of the winch motor.
10 WINCH MOTOR - Converts hydraulic power into mechanical power as hydraulic oil is forced
through the winch motor.
1-71
