86 Auto Suspension and Steering
Introduction
This chapter is devoted to the front suspension. In the
past, the front suspension was the primary focus of the
steering and suspension technician. Today, although rear
suspensions have become more complex, the so-called
front end is still the source of most suspension and steering
complaints. Lighter vehicles, front-wheel drive systems,
and radial tires will magnify any problems that occur. In
this chapter you will learn about parts of MacPherson strut
front suspensions, conventional front suspension systems,
and solid and twin I-beam suspensions. You will also learn
how these parts work together to produce a smooth ride. In
addition, you will learn how to identify the load-carrying
and follower ball joints in any type of suspension.
The Job of the Front Suspension
The primary job of any front suspension is to absorb
road shock and maintain tire-to-road contact as the vehicle
is driven straight ahead and through turns. Additionally, the
suspension must not interfere with the turning ability of the
vehicle.
Modern front-wheel drive vehicles must have a
suspension that can absorb both acceleration and braking
forces. Modern suspensions must be as light and compact
as possible, but they must be strong enough to maintain
wheel alignment for thousands of miles. Finally, the
suspension parts must survive for a reasonable amount of
time without requiring major repairs.
The suspensions discussed in the following sections
make use of many of the parts that were described in
Chapter 4, Common Suspension System Components.
Keep in mind that to perform its job properly, the
suspension needs help from the steering system, wheel
bearings, and tires.
MacPherson Strut Front
Suspensions
A MacPherson strut assembly consists of a strut,
which contains the shock absorber, and a coil spring. The
top of the strut assembly is attached to the vehicle’s body.
The bottom of the strut assembly is attached to the steering
knuckle and turns with the wheel. In addition to
containing the spring and shock absorber, the strut assem-
bly supplies the structural support for the suspension
system. Most MacPherson strut suspensions have the coil
spring installed around the strut assembly as in Figure 5-1.
The spring is compressed between the upper and lower
seats in the strut assembly. The strut is a self-contained unit
and must generally be removed from the vehicle for
disassembly and parts replacement. The following sections
discuss the major components of the MacPherson strut.
Coil spring and shock absorber designs were discussed in
Chapter 4.
Upper Strut Mounting
The upper strut mounting, or strut top, is a steel plate
that is contoured to fit a matching spot on the vehicle’s
body. The top of the piston rod passes through a hole in the
center of the plate. Bushings isolate the piston rod from the
plate and hold it in position, Figure 5-2. The top of the rod
is threaded to accept a jam nut (a nut with the top few
threads deformed to lock to the rod threads) or a self-
locking nut with a plastic retaining insert. A washer under
Coil spring
Insulator/
dust shield
Shock
absorber
Bumper
Strut
Figure 5-1. The shock absorber is inside a MacPherson strut
assembly. Note how the coil spring is mounted around the strut.
(Chrysler)