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

  TM-9-2320-272-23-1 - Page 259 of 1313

DUMP BODY HYDRAULIC SYSTEM OPERATION
The dump body is installed on M929/A1/A2 and M930/A1/A2 model vehicles. These models are used to transport
and deposit cargo. The dump body hydraulic system converts mechanical power from the engine into fluid power
through use of the hydraulic pump. The pump draws fluid from the oil reservoir and then forces it into the control
valve. This hydraulic pressure raises and lowers the dump body. Major components of the dump body hydraulic
system are:
A. PTO DRIVESHAFT
- Transmits mechanical driving power from the PTO to the hydraulic pump.
B. HYDRAULIC PUMP
- Driven by the PTO driveshaft, it draws oil from oil reservoir through hydraulic hoses,
then pressurizes and directs it to the control valve.
C. HYDRAULIC OIL RESERVOIR
- Storage tank for hydraulic oil.
D. DUMP BODY SAFETY LATCH
- Hydraulically-operated in conjunction with the dump body control lever,
the safety latch locks dump body in the lowered position and releases it when the control lever is pulled back
to the raised position.
E. DUMP BODY CYLINDER ASSEMBLY
- Consists of two piston-type hydraulic cylinder hoists. Assembly
raises and lowers dump body with hydraulic oil, forcing the cylinder upward or downward.
F. OIL FILTER
- Filters used or bypassed oil from the control valve before it returns to the hydraulic
oil
reservoir.
G. CONTROL VALVE
- Four-port valve accepts pressurized oil from the hydraulic pump and directs oil
pressure flow from control valve to the hydraulic cylinders. It also directs oil returning from the hydraulic
cylinders back to the hydraulic oil reservoir.
H. DUMP BODY CONTROL LEVER
- An operator control that determines the hydraulic oil pressure flow
from control valve to the hydraulic cylinders. The route this oil takes will determine whether the dump will
raise or lower.
I. CONTROL LINKAGE
- Connects dump body control lever inside cab to the control valve.
J. TRANSMISSION PTO CONTROL
- A manually-operated control lever located inside the vehicle cab that
permits engagement or disengagement of the transmission PTO.
K. TRANSMISSION PTO
- Uses driving power of the transmission to provide mechanical driving power for
the hydraulic pump.
TM 9-2320-272-23-1
0003
0003-54


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