Chapter 5 Front Suspension Systems 93
Solid and I-Beam Axle Front
Suspensions
The suspensions used on some pickup trucks, vans,
and sport utility vehicles (SUV) are variations on the solid
axle design. Others are twin I-beam suspensions. These axle
designs are more rugged than independent suspensions, but
they reduce handling ability. Although these designs are no
longer used on automobiles, they have been retained on
some pickup trucks, vans, and SUVs for two reasons:
The severe service that pickup trucks, vans, and
sport utility vehicles are subjected to require a
simple, strong axle design.
Four-wheel drive components, when used, are
easier to install into this type of axle.
Types of solid and twin I-beam front suspensions are
discussed in the following sections.
Ball Joints or Kingpins?
Most modern vehicles use ball joints to transfer vehi-
cle weight at the steering knuckle. However, the technician
may encounter a truck or SUV with a solid or twin I-beam
front axle that uses kingpins, Figure 5-24. Kingpins perform
the same basic function as upper and lower ball joints—
they allow the steering knuckle to pivot on the axle during
turns. However, their design allows them to move only left
and right, and they cannot adapt to any changes in
suspension angle. A wheel with kingpins instead of ball
joints is less able to move in an arc when a bump is
encountered. This makes kingpins unsuitable for indepen-
dent front suspensions.
Kingpin suspensions use a thrust bearing and a shim
between the axle and the steering knuckle. The thrust bear-
ing is installed between the bottom of the axle and the
knuckle. The weight of the vehicle passes from the axle,
through the thrust bearing, and into the steering knuckle.
The shim is installed between the top of the axle and the
steering knuckle. The shim is often used to control vertical
play between the axle and steering knuckle. Replacement
shims are available in different sizes. Some larger vehicles
have a combination kingpin and tapered roller bearing
suspension. The tapered roller bearing may be installed at
the top or bottom of the axle, depending on the vehicle.
Shock absorber
Spring
Stabilizer bar
Lower control arm
Steering knuckle
Upper control arm
Figure 5-16. A late-model front suspension with coil spring placed between lower control arm and the vehicle frame.
Upper control arm
Control arm
shaft
Coil spring
Bumper
Lower control arm
Lower
ball joint
Bushing
Insulator
Bumper
Upper
ball
joint
Figure 5-17. The bumper helps to prevent damage to suspen-
sion parts if the suspension bottoms out (is fully compressed).
(General Motors)