506 Auto Fundamentals
Steering Gear
The steering gear is designed to multiply the
driver’s turning torque so the front wheels can
be turned easily. When the parallelogram link-
age is used, the torque developed by the driver is
multiplied through gears and is then transmit-
ted to the wheel spindle assemblies through the
linkage. On rack-and-pinion steering systems,
the steering column shaft is connected directly
to the pinion shaft. Turning the pinion moves
the rack section, which moves the linkage. Late-
model vehicles use either manual steering gears
or power steering gears.
Manual Rack-and-Pinion Steering Gear
A manual rack-and-pinion steering gear is
shown in Figure 25-17. A steering shaft from the
steering wheel fastens to the pinion shaft, usu-
ally through a universal joint. The teeth on the
pinion are meshed with the teeth on the rack.
When the pinion is turned, it forces the rack to
move, either to the right or left. The ends of the
rack are connected to the steering arms by fl ex-
ible joints and short tie rods. All gear rack move-
ment is transferred directly to the steering arms.
Manual Parallelogram Linkage Steering Gear
The simplest form of the manual steering
gear used with parallelogram steering systems
is the conventional steering gear, Figure 25-18.
It consists of a steel shaft with a worm gear on
one end. The other end is attached to the steer-
ing shaft. A pitman arm shaft passes at right
angles to the worm gear. The inner end of the
pitman arm shaft (also called cross shaft, roller
shaft, sector shaft, or gear shaft) engages the
worm gear either through gear teeth, a round
steel peg, a roller gear, or a notched arm that
passes around a peg affi xed to a ball nut that
rides on the worm.
In Figure 25-18, a tapered follower peg,
(10), rides in the worm grooves. As the worm is
revolved, it causes the peg to follow along the
worm grooves, imparting a turning motion to
the pitman shaft assembly. Splines in the pitman
arm attach it securely to the pitman shaft.
The worm gear end of the steering shaft is
supported by ball or roller bearings located on
each side of the worm. These bearings remove
end play and side play in the worm. Bearing
adjustment is provided by shims. The pitman
arm shaft operates in bushings or needle bear-
ings. There is an adjustment screw to control
worm and pitman shaft clearance.
A cast housing surrounds and holds all
parts in alignment. The housing is partially
fi lled with gear oil for lubrication. Seals pre-
vent the escape of lubricant and keep out dust
and dirt. The housing is bolted to the frame or
some other rigid area of the vehicle. The steering
shaft passes up through a steering column to the
steering wheel.
Recirculating Ball Steering Gear
Figure 25-19 is a cross section of the
recirculating ball steering gear. Instead of a
tapered peg riding in the worm grooves, this steer-
ing gear uses a ball nut that rides from one end of
the worm shaft to the other. Ball bearings ride half
in the worm shaft and half in the nut. When the
Ball joint
Outer tie
rod (fixed)
Joint
Inner
tie rod
Boot
Rack
housing
Bearing
Flexible
coupling
Rack
Outer tie
rod (adjustable)
Inner tie
rod stub
Clamp
Steering
shaft
Pinion
Figure 25-17.
Cutaway view of a rack-and-pinion assembly. Note how the rack-and-pinion gears mesh.
Goodheart-Willcox Publisher