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 50 of 481
TM 9-2320-272-10
1-33
1-17. CONTROL SYSTEM OPERATION (Contd)
e. Transmission Control System Operation.
The transmission control system permits shifting of transmission, prevents
starting of engine with transmission in gear, and prevents shifting of transfer case
unless transmission is in neutral. This system also permits engagement of the
Transmission Power Takeoff (PTO) to provide hydraulic power for auxiliary
equipment on M925/A1/A2, M928/A1/A2, M929/A1/A2, M930/A1/A2, M932/A1/A2
and M936/A1/A2 vehicles. Major components of the transmission control system are:
TRANSMISSION SELECTOR LEVER
– Is used to select vehicle driving
gear range.
POWER TAKEOFF CONTROL LEVER
– Engages transmission power
takeoff to provide power for auxiliary equipment.
TRANSMISSION CONTROL SWITCH
– Actuates transmission lock-up
solenoid valve when transmission selector lever is placed in neutral and
transfer case shift lever lock-out switch is pressed.
TRANSMISSION sNEUTRAL START SWITCH
– The neutral start switch,
wired to the starter switch, prevents the engine from being started with
transmission in gear.
TRANSMISSION 5TH-GEAR LOCKUP SOLENOID VALVE
– Activated
by transmission control switch and transfer case switch, the 5th-gear lockup
solenoid valve directs main oil pressure of transmission to the transmission
governor system. This puts the transmission in 5th-gear, creating less drag on
the transfer case synchronizer which permits smoother shifting from one
transfer case drive range to another. Refer to paragraph 1-17f, Transfer Case
Control System Operation, for further details.
TRANSMISSION POWER TAKEOFF (PTO)
– Driven by the transmission,
the PTO drives the hydraulic pump which provides hydraulic pressure to
power the front winch on M925/A1/A2, M928/A1/A2, M930/A1/A2,
M932/A1/A2, and M936/A1/A2 vehicles, and to power the dump body on
M929/AVA2 and M930/A1/A2 vehicles. The PTO is mounted on the right front
side of the transmission.
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