Lesson 1/Learning Event 3
Shimmy means the front wheels move in and out or vibrate at certain speeds.
Shimmy is definitely noticeable in the steering wheel. If the shimmy is bad
enough, it can be very dangerous because its force can break some of the
steering parts. Shimmy can be caused by wheels and tires that are out of
balance or bent wheels, as well as other causes. Shimmy will be worse if
the steering parts are worn or out of adjustment.
Wheel tramp means the wheels are bouncing up and down. This also is
noticeable in the steering wheel, but as a vibration, whereas shimmy tries
to turn the steering wheel back and forth. Wheel tramp, like shimmy, is
also caused by wheels and tires that are out of balance. However, the out
ofbalance portion is equal across the wheel or tire. This causes the wheel
to move straight up and down rather than sideways as in shimmy. Wheel
tramp, like shimmy, will be worse on a vehicle if some of the parts are
loose, worn, or improperly adjusted.
Vehicle pulls to one side
This can have many causes; however, the mechanical steering gear does not
cause this malfunction. The causes range from low tire pressure on one side
of the vehicle to a bent frame.
This means the steering does not act the same all the time. For example,
the vehicle could pull to the right for a while and then start pulling to
the left. If the vehicle pulls to one side when the brakes are applied, the
vehicle is also considered to have erratic steering. One cause of erratic
steering is a load that moves about or too much load on one portion of the
body, especially the rear.
The steering wheel does not turn smoothly. This could be caused by damaged
components in the steering gear or steering linkage. Damaged steering gear
components could be a pitted worm (helical cam, 2 1/2ton) or roller or
lever pins. Loose or pitted knuckle support bearings could also cause the
problem. A quick way to isolate the trouble is to first disconnect the
steering gear from the rest of the steering mechanism and turn the steering
wheel. If the roughness is still there, the trouble is in the steering