182 Auto Suspension and Steering
called the worm-and-peg, worm-and-cam, or worm-and-
pin steering gear. Note that the worm gear works directly
on the follower, causing the sector shaft to turn as the
follower moves on the turning worm gear.
Pitman Arms
The pitman arm is attached to the sector gear at the
steering gear. It converts the turning movement of the sec-
tor gear to linear (back-and-forth) motion and transfers this
motion to the steering linkage.
Note: The sector gear shaft is sometimes
called the pitman shaft.
The pitman arm has internal splines, Figure 9-30.
These splines match the external splines on the bottom of
the sector gear shaft. The splines are slightly tapered to
create a tight fit. The pitman arm is held to the sector shaft
by a large nut and a lock washer. The linkage end of the
pitman arm may contain the ball socket. Other pitman
arms have a hole to accept the ball socket shaft.
Relay Rods
The relay rod, or drag link, is used to transmit the
steering motion from the pitman arm to the inner tie rods
on each side of the vehicle. Figure 9-31 shows the
arrangement of a typical relay rod. The relay rod may have
ball sockets permanently installed, or may have holes for
installation of the ball socket studs attached to other
linkage parts.
Some vehicles have an additional piece of linkage
called a connecting rod. The connecting rod attaches the
relay rod to the pitman arm, Figure 9-32.
Another system uses two long pieces of linkage
instead of a center relay rod and tie rods. This design is
shown in Figure 9-33.
Idler Arms
If the linkage were not supported on the side of the
vehicle opposite the pitman arm, the linkage would flex
instead of moving the wheel on that side. To prevent
unwanted flexing, an idler arm is installed on the frame
across from the pitman arm. One end of the idler arm is
attached to the frame through a metal bushing, which
allows the arm to turn. The other end of the idler arm is
attached to the relay rod through a ball socket. Figure 9-34
shows an idler arm as it is installed on most vehicles. Some
large vans and pickup trucks have two idler arms. The idler
arm will usually have grease fittings on both the ball socket
and the bushing ends. Some vehicles have two idler arms,
Figure 9-35.
Ball
socket
Pitman arm
Internal splines
Figure 9-30. A pitman arm with internal splines. These splines
mate with those on the sector gear shaft, locking the two
together. (Moog)
Nut
Steering
knuckle
Ball joint
Nut
Inner tie rod
Relay rod
Inner tie rod
Adjuster sleeve
Nut
Steering knuckle
Ball joint
Clamp
Nut
Figure 9-31. Steering linkage illustrating the relay rod in relation to the other linkage parts. (General Motors)