Lesson 1/Learning Event 1
Rotary motion of the steering wheel causes the pitman arm shaft to move back
and forth in an arc, so that the drag link moves back and forth in a
straight line. The drag link transmits the movement to the left steering
arm to pivot the left wheel spindle and wheel back and forth on the steering
knuckle pivots. Pivot movements of the left wheel are transmitted to the
right wheel by the tie rod.
The drag link and tie rod are fastened to the pitman and steering arms by
adjustable, ballsocket joints that permit swiveling action. Balltype
studs are secured to the pitman arm and the left steering arm. A housing at
each end of the drag link receives the balls. Ballsockets, coil springs,
spring seats, and a screw plug in the housings hold the balls. The screw
plug can be screwed in or out to tighten or loosen the joint. Lubrication
fittings are provided for each joint. Shields hold the lubrication in and
keep dirt out.
The tie rod also uses ballsocket joints, but generally they are not
adjustable. A spring holds the ball in its seat to prevent slack. The ball
of a tie rod end has a tapered shank or stud that fits into a matching
tapered hole in the steering arm. The end of the ball stud is threaded and
drilled so it can be secured to the steering knuckle arms with a nut and
cotter key.
Each tie rod is threaded and screwed onto the tie rod end. A clamp bolt
prevents the tie rod from turning once the ends have been installed.
One tie rod end and one end of the tie rod have lefthand threads, and the
other tie rod end and the opposite end of the tie rod have righthand
threads. This is so the overall length of the tie rod assembly can be
adjusted when aligning the front wheels without disconnecting either tie rod
end.
If the vehicle has independent frontwheel suspension instead of an axle,
the steering linkage arrangement is different. Two tie rods are required so
each wheel can be raised and lowered without affecting the steering of the
other. Many different linkage arrangements are used with independent
suspension. Some are quite simple, with the linkage consisting of the
pitman arm, two tie rods, and the steering arms.
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