TM-9-2320-272-24-1
TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)
TECHNICAL MANUAL; UNIT, DIRECT SUPPORT, AND GENERAL SUPPORT MAINTENANCE MANUAL; VOLUME 1 OF 4
JUNE 1998
TM-9-2320-272-24-1 - Page 43 of 1015
TM 9-2320-272-24-l
l-20. CONTROL SYSTEM OPERATION (Contd)
Key
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Item and Function
TRANSFER CASE SHIFT LEVER SWITCH
- When depressed with transmission in NEUTRAL,
signals interlock solenoid valve to exhaust air pressure from interlock air cylinder and actuates
lockup solenoid.
TRANSFER CASE SHIFT LEVER
- Is pushed down to HIGH for light load operations, and up to
LOW for heavy load operations. Six-wheel drive is achieved automatically when transfer case shift
lever is placed in LOW.
TRANSFER CASE PTO CONTROL LEVER
- Manual control for engaging PTO.
TRANSFER CASE PTO
- Mounted and mechanically driven at rear of transfer case, the PTO
drives a pump to supply hydraulic pressure to power the rear winch and crane on the M936/A1/A2
wreckers.
FRONT-WHEEL DRIVE LOCK-IN SWITCH
- Manual control for activating front-wheel drive
valve to provide front-wheel drive with transfer case in HIGH drive range.
6
INTERLOCK AIR CYLINDER
- Under air pressure, a piston in the interlock air cylinder forces a
shaft against one of three grooves in transfer case shift lever, This prevents transfer case from being
shifted with transmission in gear.
7
INTERLOCK SOLENOID VALVE
- Releases air from interlock air cylinder when transmission is
in NEUTRAL and transfer case shift lever switch is depressed. This permits the transfer case
high/low shift shaft to move.
8
FRONT-WHEEL DRIVE AIR CYLINDER
- When under pressure, it moves transfer case clutch
forward to engage front-wheel drive.
9
FRONT-WHEEL DRIVE VALVE
- When tripped by a cam on transfer case shift shaft, the front-
wheel drive valve routes air to front-wheel drive air cylinder.
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