Lesson 2/Learning Event 1
On the top of the axle, the springs are mounted on flat, smooth surfaces or pads. The
mounting surfaces are called spring seats and usually have five holes. The four holes on
the outer edge of the mounting surface are for the U-bolts which hold the spring and axle
together. The center hole provides an anchor point for the center bolt of the spring. The
head of the center bolt, seated in the center hole in the mounting surface, ensures proper
alignment of the axle with the vehicle frame.
A hole is located in each end of the I-beam section. It is bored at a slight angle and
provides a mounting point for the steering knuckle or kingpin. A small hole is drilled
from front to rear at a right angle to the steering knuckle pinhole. It enters the larger
kingpin hole very slightly. The kingpin retaining bolt is located in this hole and holds the
kingpin in place in the axle.
The steering knuckle is made with a yoke at one end and a spindle at the opposite end.
Bronze bushings are pressed into the upper and lower arms of the yoke, through which
the kingpin passes. These bushings provide replaceable bearing surfaces. A lubrication
fitting and a drilled passage provide a method of forcing grease onto the bearing surfaces
of the bronze bushings. The spindle is a highly machined, tapered, round shaft that has
mounting surfaces for the inner and outer wheel bearings. The outer end of the spindle is
threaded. These threads are used for installing a nut to secure the wheel bearings in
position. A flange is located between the spindle and yoke. It has drilled holes around its
outer edge. This flange provides a mounting surface for the brake drum backing plate
and brake components.
The kingpin acts like the pin of a door hinge as it connects the steering knuckles to the
ends of the axle I-beam. The kingpin passes through the upper arm of the knuckle yoke,
through the end of the I-beam and a thrust bearing, and then through the lower arm of the
knuckle yoke. The kingpin retaining bolt locks the pin in position. The ball-type thrust
bearing is installed between the I-beam and lower arm of the knuckle yoke so that the end
of the I-beam rests upon the bearing. This provides a ball bearing for the knuckle to pivot
on as it supports the vehicle's weight.
When the vehicle is not in motion, the only job that the axle has to do is hold the wheels
in proper alignment and support part of the weight. When the vehicle goes into motion,
the axle receives the twisting stresses of driving and braking. When the vehicle operator
applies the brakes, the brake shoes are pressed against the moving wheel drum. This
action tries to make the axle turn.