Why Does My Steering Wheel Shake When I Brake?
Main Cause of Shaking Steering Wheel
The main cause of shaking or shimmying of the steering wheel when braking is warped front brake rotors (also called brake discs). The vibration is caused by the brake pad making inconsistent contact with the rotor, sort of like a warped record spinning on a turntable.
Common Causes of Warped Brake Rotors
Brake rotors can warp when they are heated up and then one portion becomes cooled at an uneven rate. A classic example of how this can occur is coming down a long hill or mountain, where repeated long braking is required, causing heat buildup in the rotors. Following this with braking to a stop, like at a stoplight, is where the problem occurs. The portion of the rotor that is clamped under the brake pads retains heat, while the exposed portion can freely dissipate it to the air. There are other circumstances under which rotors can warp, but the aforementioned describes the basic process.
Conditions that Exacerbate Brake Rotor Warpage
This differential in the ability of the heated brake rotor to cool is the source of the warpage, it can be exacerbated with older, worn, thinner rotors, especially those that have not been changed during brake replacement. A proper brake replacement job, as specified by BMW, MINI and most performance and luxury vehicle manufacturers, entails changing pads, sensor and rotors (which is how we do it here at Pacific Motorsports). Some places may go cheap or cut corners and not replace the rotors thinking that there might be “plenty of life left”. This is faulty thinking and false economy.
Normal Brake Rotor Wear
The brake rotor in your car was specified to be a certain thickness when new. After X years and Y thousands of miles of use, they become thinner, as they are designed to be “consumed” along with the brake pads. The evidence of this can be seen in the brake dust deposited on the vehicle’s wheels. Once a certain minimum thickness has been reached, the rotors need to be discarded (we recycle them here at Pacific Motorsports, along with all worn metal parts) and replaced, as they no longer meet the minimum specification for doing their job properly.
Brake Rotor Recommended Maintenance
For the sake of proper brake operation and safety, not to mention of comfort and driver confidence, make sure that the brake rotors are replaced every time the pads are replaced. It’s how the system was designed and what the engineers intended, and it will keep the steering wheel safely in your hand, regardless of the speed at which you may be applying the brakes.