500 Auto Fundamentals
parallelogram linkage and rack-and-pinion
linkage. Parallelogram linkage was the most
common arrangement for many years and is
still used on large cars, SUVs, and pickup trucks.
Rack-and-pinion linkage has been used on most
small and midsize vehicles for the past 25 years.
The two types of linkage are discussed in the
following sections.
Rack-and-Pinion Linkage
The rack-and-pinion steering system con-
tains fewer linkage components than the paral-
lelogram system. The steering column shaft is
connected directly to the pinion, or sector shaft.
The pinion operates the rack section, which
operates the tie rods and, therefore, the steering
knuckles. See Figure 25-5.
Inner and Outer Tie Rods
The only rack-and-pinion linkage parts are
inner and outer tie rods. The inner and outer tie
rods are both ball-and-socket connections, such
as those shown in Figure 25-6. Tie rods always
have a ball-and-socket connection on one end
and a threaded connector on the other end. The
threads can be internal or external, depending on
the design of the attaching parts. The ball-and-
socket connection is always held to the attaching
part with a tapered shaft. When the shaft nut is
tightened, the shaft wedges itself into the attach-
ing part and will resist working loose under vibra-
tion. The nut is always secured with a cotter pin
or may be a jam nut with deformed threads that
resists backing off.
The inner tie rod usually includes the round
bar that threads into the outer tie rod. The bar
and tie rod are kept from unthreading by a
Strut mount
Ball joint mount
Upper ball
joint mount
Caliper
mount
Lower ball
joint mount
A B
Steering
arm
Steering arm
Figure 25-3.
Two types of steering knuckles. A—This is a steering knuckle used with a MacPherson strut front suspension. Note
the strut rod mounting at the top and the ball joint opening at the bottom. B—This steering knuckle is used with a
conventional front suspension. The knuckle has mounts for top and bottom ball joints.
Goodheart-Willcox Publisher
Snap ring
Bearing
Dust shield
Dust
shield
bolt
Steering
knuckle
assembly
Figure 25-4.
This front-wheel drive steering knuckle illustration shows
the bearing that supports the axle shaft.
Sterling