504 Auto Fundamentals
and tie rod assemblies will be moving through
almost identical arcs. This similarity of arcs keeps
the tie rods and spindle in the same relative posi-
tion when driving over rough roads.
Parallelogram Component Arrangement
The center link and the tie rods should be as
close to parallel as possible (when viewed from
front). This will help eliminate toe-in and toe-
out changes as the frame moves up and down,
Figure 25-14.
Four-Wheel Steering Systems
Some vehicles have four-wheel steering
systems. On a four-wheel steering system, the
rear wheels turn with the front wheels. Four-
wheel steering decreases the turning radius
and makes parking and other close maneuvers
easier. Early four-wheel steering systems used
hydraulic pressure developed by the power
steering pump to turn the rear wheels. The lat-
est four-wheel steering systems use an electric
motor to operate a rear rack-and-pinion steer-
ing gear. The motor is controlled by an on-board
computer based on inputs from sensors installed
on the front steering linkage. See Figure 25-15.
Steering Wheel, Steering Shaft, and
Steering Gear
The steering wheel, steering shaft, and
steering gear are important parts of the steer-
ing system. Steering effort begins at the steering
wheel and shaft. The steering gear transforms
the turning motion of the shaft to the linear
movement of the linkage.
Steering Wheel
Besides the steering wheel’s obvious job of
allowing the driver to input steering motion, it
contributes to steering ease by its size. The larger
the steering wheel, the less effort required to
make turns. This is important on vehicles with-
out power steering.
Steering Shaft
The steering shaft connects the steering
wheel and the steering gear. In the past, it con-
sisted of an upper shaft made of hardened steel, a
fl exible coupling, and a lower shaft, or stub shaft,
splined to match the input shaft of the steering
gear. The modern steering shaft has a two-piece
upper shaft, which is designed to collapse if the
driver is thrown against the steering wheel dur-
ing an accident. The steering shaft often has one
or more universal joints to allow steering effort
to be transmitted through an angle. A modern
steering shaft is shown in Figure 25-16.
Steering Shaft Coupling
The steering shaft coupling absorbs road
vibrations that get past the other steering sys-
tem linkage. It consists of a rubber disc and is
Turn
downward
to increase
rod length
Turn
downward
to decrease
rod length
Turn upward
to decrease
rod length
Turn upward
to increase
rod length
Left-hand
sleeve
Right-hand
sleeve
Figure 25-13
Tie rod adjustment. This type uses a double-end sleeve
with two clamps.
Mercury
Idler arm
Center link
Ball socket
Steering gear
A
Tie rod
Tie rod
end
C
D
B
Figure 25-14.
The center link and tie rods should be nearly parallel.
A—Setup with the tie rods and center link not parallel
(front view). Notice distance C between tie rod ends. B—
When the body of the vehicle dips downward, the center
link is carried down with the frame. The tie rod ends are
fastened to the steering arms and cannot move down.
As the center link travels down, the angle between the
link and the rods narrows. The tie rods must spread out
(distance D), forcing the steering arms out and toeing the
wheels in. When a vehicle is at normal curb height, the
link and rods should be almost parallel, as in B. In this
position, the link can move up and down with a minimal
effect on toe-in and toe-out.
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