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What Causes a Control Arm to Vibrate?
The Control Arm
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A control arm is often a V-shaped component that attaches the front wheel and knuckle assemblies of a vehicle to the support frame. The top of the V is bolted to the frame on a lower control arm, and the bottom of the V is attached to the lower ball joint. At each connection of a control arm is a bushing that prevents the metal of the control arm from contacting the metal of the frame. Most trucks and SUVs have both upper and lower control arms. Most front-wheel drive vehicles that use struts instead of shocks only have a lower control arm.
The Control Arm Bushings
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After time, wear and tear--and being exposed to the environmental elements--the control arms bushings may deteriorate or become out of round. This creates movement in the suspension and steering while the vehicle is driving under duress. Once the bushings have worn or have become oblong shaped, they allow the control arm to move more than it is designed to do so. Prominent knocking or clunking sounds may emit when going over bumps, and high speed vibrations may be prevalent when driving with excessively worn control arm bushings in one or both sides of the vehicle.
The Ball Joint
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Excessive play in a lower ball joint connected to the control arm can also create a vibration when driving. The ball joint is bolted to the control arm. If there is excessive play, it could cause axial or radial play in the wheel of the vehicle during operation. This could be the case for upper control arms in trucks and SUVs that attach to upper ball joints as well.
eHow Article: What Causes a Control Arm to Vibrate?
