Car Clinic: Wheel Balance Woes

Car Clinic: Wheel Balance Woes
 

Question:

I recently took my car for a major service, followed by wheel alignment. Five hundred kilometres later a vibration appeared on the steering wheel at about 120km/h. What could the problem be? At the workshop and wheel alignment centre they said the car was in perfect condition.

George

Answer:

George, assuming the wheels were balanced during the alignment check (the two things are often done together), it would be unusual for them to go out of balance so soon. I suggest you first determine whether it is really a wheel balance problem, by taking the speed up to a point where the vibration is well established, and then quickly depressing the clutch pedal. If the vibration goes away when you do this, you are probably looking at a driveshaft problem rather than wheel imbalance. If the test exonerates the drivetrain, the following come to mind as possible causes:

-A tyre may have lost a balance weight — these things can work loose or be knocked loose by a jolt from a pothole

-Tread separation or some other structural defect could have appeared on a tyre — a bulge in the tread will cause vibration, although not normally speed-related

-One or more shock absorbers may have given up the ghost, allowing excessive wheel bounce — but again, it should be noticeable at lower speeds as well. I recommend that you have the wheels rebalanced, taking the opportunity to give them a close visual and tactile examination while they are on the balancing machine.

Gerrit Burger