Lesson 1/Learning Event 1
Other common arrangements add an idler arm and drag link. In these
arrangements the idler arm is mounted on the right frame rail by a bracket
parallel to the pitman arm. The drag link connects the pitman arm and idler
arm so that moving the steering wheel causes both arms to swing in the same
arc. Each steering arm is linked to the drag link by a separate tie rod.
In this arrangement, the drag link may be called a relay rod, pitman armto
idler arm rod, and so forth.
Usually, the length of both tie rods can be adjusted independently when
aligning the front wheels. The ends on the drag links and tie rods of
vehicles with independent wheel suspension are usually not adjustable. On
some latemodel cars, tie rod ends are lubricated for life when manufactured
and do not contain lubricating fittings.
Either threaded or rubber bushings are used at the idler armtoidler arm
bracket pivot. Threadedtype bushings contain both internal and external
threads. The external threads are generally righthand threads and are
screwed into, and tightened in, a threaded hole in either the idler arm or
its bracket. The internal threads are generally lefthand threads and are
screwed onto the threaded end of the arm or bracket until it bottoms and
then backed up onehalf to one turn. This leaves the idler arm free to
pivot on the inner threads of the bushing.
With the steering wheel coupled directly to the pitman arm by a shaft, it
would be very hard for the driver to steer the vehicle. Something must be
used between the steering wheel and pitman arm so the driver can gain a
mechanical advantage to make steering easier. This is the function of the
The principles of steering gears can be demonstrated with a bolt and a nut
in the following manner. Screw the nut to the midpoint of the threads on
the bolt. Place the end of the bolt against a flat surface so it cannot
move back and forth but can be rotated. Hold the nut so it cannot rotate;
then, turn the bolt. When the bolt is turned clockwise, the nut is pulled
toward the bolt's head. When the bolt is turned counterclockwise, the nut
will be moved away from the bolt's head.
Now, if we cut out a section of the nut, attach a shaft to it, and place it
against the bolt, we can see how this principle is used in the steering
gear. With this arrangement, turning the bolt back and forth will cause the
nut section to swing back and forth, turning the shaft with it.