Lesson 2/Learning Event 2
front of the vehicle and to the side away from the ring gear. A spiral bevel pinion may be
pulled inward toward the differential as it tries to drive the ring gear. At the same time,
the ring gear will try to move to the side away from the driving pinion. Some axle
assemblies include a thrust pad mounted on the case to the rear of the ring gear to limit
the amount the gear can move sideways. As the ring gear is forced away from the pinion,
a twisting force is received by the differential carrier bearings. Also, as the ring gear
drives the differential, the resistance from the wheels causes the assembly to drive against
thrust washers between the gear and the case. When a sudden heavy force is applied to
the axle shafts, they tend to twist or wind up. The entire axle assembly tries to twist the
mounting springs as it drives the wheels. The vehicle's springs or torque rods are
designed to control the twisting effort of the axle assembly.
CONSTRUCTION OF LIVE FRONT AXLES
One of the requirements for tactical military vehicles is all-wheel drive. To provide this,
the front axle must be similar to a live rear axle assembly. The main difference between
the live front and live rear axles is that the front wheels must be able to pivot for steering
purposes. This also means that the driving axle shafts must be able to deliver torque at an
angle to the wheels when they are turned. There is very little difference in the final drive
and differential assemblies of most front and rear live axles. On some models of
vehicles, the differential assemblies are made the same in both the front and rear so that
they may be interchanged. This section, therefore, will cover the construction of parts
not found in the rear axle.
The axle housing is a large steel hollow casting that acts as the base or mount for all the
other parts. On the front axle housing, the final drive and differential assembly are often
mounted off-center. This is to allow the driving propeller shaft to bypass the engine oil
pan. The axle housing extends all of the way across the front of the vehicle. Each end of
the housing contains components for the steering mechanism. As with the dead axle,
these are the parts of the axle that are hinged to turn and provide steering. On the live
axle, the steering knuckle appears to be a large ball joint with each end of the axle
housing shaped like a ball.
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