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 51 of 481

TM 9-2320-272-10
1-34
f. Transfer Case Control System Operation.
The transfer case control system converts four-wheel driving power into six-wheel
driving power, provides smooth shifting of transfer case into high or low driving
rangs while vehicle is in motion, prevents transfer case from being shifted with
transmission in gear, and provides hydraulic power for auxiliary equipment through
a Power Takeoff (PTO).
(1) Six-wheel drive is achieved two different ways depending on the drive
range (high or low) desired. In low range, the transfer case shift linkage
automatically moves a cam-actuated valve which dumps air into the front
drive cylinder. This forces a piston against the transfer case clutch to
engage front-wheel drive. In high range, front-wheel drive is engaged in
the same manner except that the front-wheel drive valve is manually
actuated by the front-wheel drive lock-in switch on the instrument panel.
(2) In order to shift the transfer case from one driving range to another, an
interlock system working in conjunction with the 5th-gear lock up solenoid
is used. This system prevents the transfer case form being shifted unless
the transmission is in neutral.
(3) With the automatic transmission, several actions must occur in order to
shift the transfer case from one driving range to another. Because of the
interlock system, the transmission must be placed in neutral. The transfer
case shift lever switch must also be depressed.
(4) The transfer case control system, through the use of a PTO driven by the
transfer case, also provides hydraulic power to operate the crane and rear
winch on the M936/A1/A2 wreckers.
(5) Major components of this system are:
1-17. CONTROL SYSTEM OPERATION (Contd)


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