What Causes Brake Vibration?

Few things can be as frustrating as taking your vehicle to your mechanic and being given a generic diagnosis along with an alarming repair estimate. Issues with a vehicle's braking system often fall into this category. While understanding exactly what is causing the problem won't make the repair bill any cheaper, it will help your peace of mind if you know the money was well spent.

Warped Rotors

There are no such things as "warped rotors." This is a generic term usually used by mechanics because detailed explanation of the cause would be lengthy and involved. While the term gives a general idea of why the brakes are performing strangely, it does not accurately describe the cause. Rotors do not truly warp, but are instead displaying an uneven surfacing condition, that is more easily described as "warped" to the layman customer. This can cause confusion because the true causes differ in how they are corrected, resulting in what may seem unusual repair costs for a simple problem.

Lateral Runout

Lateral runout is the measurement determining whether two axes' are parallel with each other. With automotive brakes, this is the measurement between the brake rotor axis and the spindle axis. When factory tolerances become too great, the rotor and spindle are not parallel, resulting in high points on the rotor contacting the brake pads during rotation when the brakes are not applied. This contact is slight, but has the effect of unevenly wearing away material from the rotor, resulting in an uneven rotor surface. This results in pulsation at the brake pedal when pressure is applied, vibration and shaking at the wheel because the rotor surface is no longer flat.

Corrosion

When a vehicle sits for prolonged periods or is driven in areas where salt is used on road surfaces, rust and corrosion can form on the brake rotors where the brake pads do not cover their surface. When the vehicle is driven, this causes uneven wearing of the rotor surface resulting in the rotor having variations in its thickness. This causes the higher points on the rotor to push back on the brake cylinder during braking, leading to vibration and shimmying.