INTRODUCTION TO THE HMMWV - OD1615 - LESSON 2/TASK 1
drives, differentials, live axles, devices for resisting drive torques and
a. Components of the Drive Train.
The drive train on the HMMWV
consists of seven components that work together to transmit power to the
In the paragraphs that follow, each of these components will be
b. Engine. The first component in the HMMWV drive train is the engine.
However, since the engine was discussed previously in lesson one, task two
beginning on page 7, it will not be discussed here.
The HMMWV family of vehicles are equipped with a
series 400 hydromatic automatic transmission (THM 400), manufactured by
General Motors, with some parts from the 475 hydromatic transmission. The
transmission holds six quarts of Dexron II transmission fluid and maintains
The transmission contains a three element torque convertor, compound
planetary gear set, three multiple disc clutches, one sprag and one roller,
and two friction bands. The torque convertor couples the engine smoothly to
the planetary gear through oil, and provides additional hydraulic torque
multiplication when required. The compound planetary gear set gives three
forward ratios and one reverse.
automatic in relation to vehicle speed and engine torque input. The torque
from the engine is transmitted to the transmission through the flex plate.
Vehicle speed and engine torque signals are constantly fed to the
transmission to provide the appropriate gear ratio for maximum efficiency
and performance at all throttle openings.
d. Transfer Case.
The transfer case directs engine-to-transmission
power to the front and rear differentials simultaneously.
means the vehicle is always in four-wheel drive. The transfer case allows
for selection of three driving ranges and a neutral position. The transfer
case used on the HMMWV is a New Process 218 (MOD), two speed, locking,
The transfer case holds 3.5 quarts of Dexron II