Chapter 5 Front Suspension Systems 87
the nut holds the rod to the bushing. Another washer is
held in place at the bottom of the lower bushing assembly
by a shoulder formed in the rod.
Since the entire strut assembly turns with the wheels,
the upper mounting must allow the strut to move in
relation to the body. The upper mounting of many struts
contains a ball or needle bearing, while others use a flat
washer, sometimes called a thrust bearing, that moves in
relation to the fixed mounting plate. A few upper
mountings have a rubber bushing that flexes enough to
allow the strut to move during turns. See Figure 5-3.
The upper strut mounting is usually fastened to the
body at the inner fender, Figure 5-4. The inner fender is
reinforced to absorb the suspension shocks. The strut
mounting point is carefully selected to produce a strut
angle that causes the wheel position to move upward in a
curve, or arc, when the wheel rises over bumps. Moving
the wheel up and down in an arc instead of straight up and
down keeps the entire tire tread in contact with the road,
Figure 5-5.
Most upper strut mounting plates have pressed-in
studs that pass through holes in the body and are secured
under the hood with jam nuts. Most mounting plates have
three or four studs, although smaller cars may have only
two studs. A few upper mounting plates are drilled and
threaded to accept bolts. The holes in the vehicle body are
sometimes elongated so the strut can be moved for align-
ment adjustment. A gasket may be used between the upper
mounting plate and the body to help absorb noise and
vibration.
Lower Strut Mounting
The lower strut mounting has sheet metal plates that
fit tightly around a matching flat spot in the steering
knuckle. The steering knuckle may have ridges or knurling
to help keep the strut in position. The lower mounting is
usually held to the knuckle with bolts. Figure 5-6 illustrates
a typical lower strut mounting. The mounting holes on
some struts are elongated to allow the strut and wheel
position to be adjusted. On other struts, an adjusting cam
may be installed.
On some struts, there is no separate steering knuckle.
Instead, the bottom of the strut forms a support for the
wheel bearing assembly and is attached to the lower ball
joint.
The steering arm may be built into the lower portion
of the strut body as shown in Figure 5-7. A bracket for
attaching the brake hose may be welded to the lower strut
tube. The entire lower strut assembly is a single piece
containing the shock absorber. On some vehicles, a
separate strut cartridge can be removed from the lower
strut assembly after the spring and upper mount are
removed.
Other MacPherson Strut Parts
In addition to the parts discussed above, the
MacPherson strut assembly usually has a bumper installed
on the piston rod at the upper mount. The strut bumper is
a round rubber bushing with a hole through its center. The
bumper keeps the strut piston assembly from compressing
completely when the vehicle hits a severe road irregularity.
If the strut piston were completely compressed, usually
called bottoming out, the piston rod or the tube could be
bent. A typical bumper is shown in Figure 5-8.
To keep the rod from being pulled out of the upper
strut mount if the suspension drops too far, an upper stop
is built into the mount. The most common type of stop, as
Self-locking nut
Washer
Damper mounting
collar
Mounting bushing
Upper strut
mounting base
(steel)
Mounting bushing
Spring mounting
rubber
Self-locking
nut
Strut rod
Washer
Figure 5-2. A MacPherson upper mounting. Note the mounting
bushings and the mounting base. (Honda)