Shimmy

Lesson 1/Learning Event 3

Shimmy

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

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.

Erratic steering

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.

Rough steering

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

gear.