Auto Fundamentals, 11th Edition Page 502 (520 of 656)

502 Auto Fundamentals
Pitman Arm
The pitman arm (also called the steering gear
arm) is attached to the output shaft of the steering
gear. See Figure 25-9. The pitman arm is usually
splined to the output shaft and is held in place by
a large nut. Movement of the steering gear causes
the pitman arm to swing from side to side. The pit-
man arm may be equipped with a ball joint con-
nection where it is attached to the center link, or it
may have a hole to accept a ball stud.
Center Link
The center link (also called a relay rod, or
drag link) is a long bar that transfers movement
from the pitman arm to the other parts of the
steering linkage. The pitman arm is attached to
one end of the center link by means of a ball joint
connection, Figure 25-9.
Idler Arm
The end of the center link opposite the pit-
man arm is attached to an idler arm with a ball
joint connection. The idler arm pivots on metal
bushings or bearings that are placed on a solid
shaft that is bolted to the frame. Some idler
arms pivot on rubber bushings. The idler arm is
arranged so it is parallel to the pitman arm. The
B
C
Dust cover
Socket
Nylon
bearing
Socket
shell
Spring
A
Figure 25-6.
Different types of ball socket tie rod ends. B uses a nylon
bearing, while A and C have metal-to-metal bearing
surfaces.
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Inner
tie rod
Outer
tie rod
Locknut Locknut Rack Outer
tie rod
Boot Inner
tie rod
Boot
Figure 25-7.
Steering linkage for a rack-and-pinion steering system. Note the difference in design of the inner and outer tie rods.
Toyota
A Front of vehicle
Frame
support
Gear
Pitman
arm
Relay rod
Idler arm
Steering
arm
Tie rods
Axle
centerline
B
Axle
centerline
Steering
arm
Wheel
pivot
Steering
arm
Tie rods
Relay rod
Idler arm
Gear
Pitman
arm
Frame
support
Frame
support
Frame
support
Figure 25-8.
A—A parallelogram steering linkage located in front of
the axle centerline. B—This parallelogram linkage is
placed behind the axle centerline. These different linkage
setups will help to maintain the suspension geometry as
the steering and suspension move, keeping all parts in
proper relationship to one another.
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502 Auto Fundamentals
Pitman Arm
The pitman arm (also called the steering gear
arm) is attached to the output shaft of the steering
gear. See Figure 25-9. The pitman arm is usually
splined to the output shaft and is held in place by
a large nut. Movement of the steering gear causes
the pitman arm to swing from side to side. The pit-
man arm may be equipped with a ball joint con-
nection where it is attached to the center link, or it
may have a hole to accept a ball stud.
Center Link
The center link (also called a relay rod, or
drag link) is a long bar that transfers movement
from the pitman arm to the other parts of the
steering linkage. The pitman arm is attached to
one end of the center link by means of a ball joint
connection, Figure 25-9.
Idler Arm
The end of the center link opposite the pit-
man arm is attached to an idler arm with a ball
joint connection. The idler arm pivots on metal
bushings or bearings that are placed on a solid
shaft that is bolted to the frame. Some idler
arms pivot on rubber bushings. The idler arm is
arranged so it is parallel to the pitman arm. The
B
C
Dust cover
Socket
Nylon
bearing
Socket
shell
Spring
A
Figure 25-6.
Different types of ball socket tie rod ends. B uses a nylon
bearing, while A and C have metal-to-metal bearing
surfaces.
Goodheart-Willcox Publisher
Inner
tie rod
Outer
tie rod
Locknut Locknut Rack Outer
tie rod
Boot Inner
tie rod
Boot
Figure 25-7.
Steering linkage for a rack-and-pinion steering system. Note the difference in design of the inner and outer tie rods.
Toyota
A Front of vehicle
Frame
support
Gear
Pitman
arm
Relay rod
Idler arm
Steering
arm
Tie rods
Axle
centerline
B
Axle
centerline
Steering
arm
Wheel
pivot
Steering
arm
Tie rods
Relay rod
Idler arm
Gear
Pitman
arm
Frame
support
Frame
support
Frame
support
Figure 25-8.
A—A parallelogram steering linkage located in front of
the axle centerline. B—This parallelogram linkage is
placed behind the axle centerline. These different linkage
setups will help to maintain the suspension geometry as
the steering and suspension move, keeping all parts in
proper relationship to one another.
Goodheart-Willcox Publisher

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Chapter 25 Steering Systems 503
purpose of the idler arm is to keep the center
link in alignment as it is moved by the pitman
arm. Figure 25-10 shows a common idler arm
design.
Tie Rods
Tie rods, which were discussed previously,
are used to connect the steering arms to the cen-
ter link, Figure 25-11. The parallelogram steer-
ing system has two inner tie rods and two outer
tie rods.
A threaded tie rod sleeve is installed
between the tie rods to form a tie rod assembly.
The threads on one side of the assembly are left-
hand threads, while the threads on the other
side are right-hand threads. Therefore, turning
the sleeve will change the length of the assem-
bly. Tie rod assembly length can be changed to
adjust toe. This is discussed in more detail in
Chapter 27, Wheel Alignment. One type of adjust-
able tie rod end is shown in Figure 25-12. A
typical tie rod adjustment procedure is shown
in Figure 25-13.
The tie rod assemblies on parallelogram link-
age are usually equal length and about the same
length as the lower control arms. As the frame (to
which the center link is fastened via the pitman
arm and idler arm) moves up and down in rela-
tion to the spindle, there will be minimum distur-
bance in toe-in and toe-out, since the control arm
Center link Pitman arm Steering gear
Figure 25-9.
A pitman arm on a steering gear. The pitman arm is
connected to the center link with a ball joint.
Ford
Bracket
Idler arm
Figure 25-10.
Idler arm and bracket. The main job of the idler arm is to
support the linkage on the side opposite the pitman arm.
AleksandrN/Shutterstock.com
Pitman arm Idler arm
Outer tie rod Outer tie rod
Tie rod sleeve Tie rod sleeve
Inner tie rod Inner tie rod
Center link
Figure 25-11.
Tie rods connecting steering arms (knuckles) to the center link (relay rod).
Geo
Ball
socket
Clamp
Tie rod
adjusting sleeve
Threads
Figure 25-12.
Adjustable tie rod end. The ball socket can be screwed in
or out of tie rod. When proper adjustment is achieved, it is
retained by tightening the clamp on the tie rod. This will bind
the tie rod threads against those on the ball socket end.
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Chapter 25 Steering Systems 501
locknut. The inner tie rod sockets are covered
with a bellows or boot to keep out water and
dirt. The outer tie rods attach the inner tie rod
bar to the steering arms. The outer tie rods are
commonly called the tie rod ends, Figure 25-7.
Tie rod assembly length can be changed
to adjust relative tire position, or toe. To adjust
length, the locknut is loosened and the bar is
turned in the outer tie rod. This is discussed in
more detail in Chapter 27, Wheel Alignment. On
some older rack-and-pinion designs, the toe is
adjusted by turning a sleeve between the inner
and outer tie rod ends. Toe adjustment is dis-
cussed in more detail in the following section.
Parallelogram Linkage
When viewed from the top, the paral-
lelogram linkage is arranged in the shape of a
parallelogram, Figure 25-8. The parts of the par-
allelogram linkage include the pitman arm, the
center link, the idler arm, and the tie rods.
Dust boot
Snap ring
Ball joint
Outer
tie rod
Locknut
O-ring
Boot
Rack
Lock
washer
Inner
tie rod
Oil seal
Snap ring
Ball bearing
Snap ring
Pinion
Locknut
Adjusting screw
O-ring
Spring
Sleeve
Lock washer
Inner tie rod
Locknut
Outer
tie rod
Ball joint
Snap
ring
Dust
boot
Boot
O-ring
Clip
Rack mounting
boss
Rack housing
Rubber insulator
Figure 25-5.
An exploded view of a manual rack-and-pinion steering assembly. Study the overall construction and part layout carefully.
Subaru

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