TM-9-2320-338-10

TRUCK, CARGO, 8X8, M977A4

TECHNICAL MANUAL; OPERATOR'S MANUAL

OCTOBER 2008

TM-9-2320-338-10 - Page 128 of 1120

Power from the transmission is transferred to the transfer case (3) and on to front and rear

axles (4) through a series of drive shafts and universal joints (5).

AUTOMATIC TRANSMISSION

HEMTT series vehicles use an Allison HD4000 series transmission model 4500SP.

This hydrokinetic type transmission has an integral-locking torque converter, lock-up clutch,

constant mesh planetary gearing, the GEN IV, a speedometer, and control valve module

assembly.

The primary components of the GEN IV system are the Transmission Control Module

(TCM), transmission range selector in the vehicle cab, a control valve module beneath the

transmission gearing section which contains solenoid valves for clutch control, an engine

speed sensor, a turbine speed sensor, and an output speed sensor that relays the

transmission output speed to the TCM for shifting and control functions.

TM 9-2320-338-10

0012

0012-2