Section V POWER TRANSFER CASE AND REAR AXLE
The power transfer cases on M916 thru M920 trucks provide a means of engaging or disengaging front
wheel drive. The instrument panel control for this feature also allows the driver to lock up the rear
inter-axle differential so that all differentials on rear axle tandem turn the same speed. (The instru-
ment panel control engages or disengages the front propeller shaft to the front driving axle (M916 thru
M920) and the inter-axle differential located in all the forward rear tandem axles.) On M916 and
M920 models only, an oil cooler is used to keep the transfer case lubricant within the proper tempera-
ture range during warm weather operation. It is disconnected in cold weather to prevent cooler dam-
age (see para 7-9).
The M915 is a 6 x 4, activating the differential lockout control locks the inter-axle differential there-
by connecting the transmission to front tandem and rear tandem axles solidly together.
The forward rear tandem axle is equipped with a no-spin differential which automatically locks, elim-
inating differential action independent of the manual control, at least three wheels on the rear tandem
must turn when the inter-axle differential lock is engaged.
2-14. POWER TRANSFER CASE.
ENGINE RUN SWITCH. Energizes 12-volt electrical system, including differential lockup
LOCKUP INDICATOR. Illuminates when lockup switch is closed.
ClRCUIT BREAKER (CB-6). Protects electrical components of differential lockup circuit by
opening when load exceeds 20 amps, Automatically recycles until overload is removed.
AIR MANIFOLD. Routes air from reservoir to control valve.
CONTROL VALVE. Provides control to engage or disengage front wheel drive on M916 thru
M920. When front wheel drive is engaged, air pressure is applied to lockup rear axle differen-
tial. When front wheel drive is disengaged, air pressure is vented through lockup valve. On
M915, this control locks up the rear differential only.
OIL COOLER LINE. Carries cooled oil to top of power transfer case. (M916 and M920 only).
OIL COOLER. By means of fresh air flow thru fins and tubing, cools warm oil from power
transfer case (M916 and M920 only); suspended under winch platform.
OIL COOLER LINE. Brings warm oil from power transfer case to oil cooler (M916 and M920
OIL PUMP. Driven from upper shaft of power transfer case, draws warm oil from bottom of
case, pumps thru cooler, and returns to top of case (M916 and M920 only).
OIL PUMP LINE. Carries warm oil from bottom of case to pump (M916 and M920 only).
TEE. Replaces drain plug (plug is reinserted in end of tee; provides connection for line (10).
(M916 and M920 only).