Lesson 2/Learning Event 1
When the brakes are applied suddenly, the axle twists against the springs and actually
twists out of its normal upright position. In addition to twisting during braking, the front
axle also moves up and down as the wheels move over rough surfaces.
Steering controls and linkages provide the means of turning the steering knuckles to steer
the vehicle. As the vehicle makes a turn while moving, a side thrust is received at the
wheels and transferred to the axle and springs. These forces act on the axle from many
different directions. You can see, therefore, that the axle has to be quite rugged to keep
all parts in proper alignment.
Trailer Axles
The axles used on trailers are designed to mount the wheels and support the weight of the
vehicle. Since trailer wheels are not powered, the axles used are all of the dead type.
Larger trailer axles are equipped with service brakes to assist in stopping. Host smaller
trailers use a single axle, while larger ones normally have two-axle assemblies. The size
of trailers varies from the small 1/4-ton models to the large 50-ton transporters.
The axle used on most military trailers is usually a straight, round, steel shaft or tube.
Smooth, machined surfaces at the ends of the shaft provide mounting surfaces for the
wheel bearings and the wheel bearing seals. The threads on the ends of the axle shaft
hold the wheel bearing retaining nuts. A locking plate for the wheel bearing nuts fits into
a keyway or slot to prevent the nuts from working loose. Two steel pads welded to the
axle shaft provide seating surfaces to connect the axle to the leaf-type springs. A
machined flange with holes located around the outer edge is located just inside the wheel
bearing surfaces. It provides a mount for the brake backing plates.
On semitrailers with tandem or two axles (one behind the other), the axles are not usually
bolted directly to the leaf-type spring. The springs are mounted on a central trunnion
shaft with spring seats so that they aid in holding the axle in line. The spring ends rest
upon spring bearing plates welded to the axle shafts. The tip of the springs can slide
forward and backward on the bearing plate. Torque rods are used to hold the axles in
proper position.
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