What causes it?
If the brake rotors installed on the vehicle have more than .05mm of run out (where the brake rotor moves from side to side more than a minimal amount of .05mm), then brake vibration will occur through the steering. Usually, this is due to one of two different reasons. The face of the disc may have some rust or dirt on it, which is causing the run out figure to be incorrect. Such build up may occur during the lifetime of the rotor, and this can cause the run out to be up to five times the limit installed by the factory. If the problem is not due to this, it may be that a ‘thin spot’ has occurred on the rotor (where there has been intermittent pad contact instead of a constant motion). When the brake pedal is pressed this causes the brake vibration to occur. This is technically known as Disc Thickness Variation, or DTV for short.
As it is essential that your brakes run true, this must be sorted out as quickly as possible.
How to rectify the problem
The first thing to do is to determine whether it is the front or rear rotors that are causing the brake vibration. If the steering wheel itself is shaking, it is more likely to be the front, whereas if the whole car and bodywork shakes, it will probably be the rear. Additionally, it is not necessarily the pair of rotors that are the problem; it may only be one of them. Finding the location of the shaking is the first step to solving the problem, however.
Depending on whether you undertake your own mechanical work, there are two routes to take here. Firstly, you can rectify the brake vibration yourself, or secondly, you can take the vehicle to a garage to resolve the issue. Either way, if the problem is a dirty disc surface, having the rotors turned or skimmed to present a clean, smooth surface to the brake pads can solve this. If the rotors have a thin spot, they will need to be replaced with new ones. Regardless of which method you choose, they must be checked when fitted back to the car that the run out is the correct measurement.
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