Technical and Training Technical Articles Brake Squeal

Brake Squeal

It is no secret that a rushed brake job can leave some things undone that may contribute to noise and comebacks. Generally brake noise is caused by the vibration of brake pads.

Brake discs

Discs must be smooth, clean and flat to provide optimum braking. If the brake disc is rough, warped, scored or glazed the pads are going to vibrate or chatter every time you apply the brakes. If the brake discs are to thin the brake system will operate at a higher temperature resulting in glazed pads. For every 1mm taken of a disc it adds between 80-100 degrees to the operating temperature of the brake system.

Brake pad vibration

Another form of brake squeal is caused by the Brake Pad vibrating when brake pressure is applied. Heavy braking usually stops the squeal because the extra pressure dampens the vibration. If heavy braking does not stop the squealing it is a sign of a significant problem. Squealing that appears under light braking is not a safety concern; it is just very annoying.

When this type of squealing occurs it is usually the leading edge of the Brake Pad that is in contact with the rotor causing a twisting force on the pad making the trailing edge want to lift away from the disc.

Vibration dampers

One option to help reduce the Brake Pad squeal is to fit Brake Pad vibration damper pads. The vibration dampers are a self-stick fibre material shim that sticks to the back of the brake pad. Some Brake Pads have a spring at the back of the backing plate located in the middle of the pad. The spring fits tightly into the piston with the fibre shim sticking to the back of the brake pad. The theory is that the fibre shim will help cushioning the vibration of the brake pad.

Anti-squeal compounds

A second option is to coat the back of the Brake Pad with a quality anti-squeal compound. This is applied to the back of the brake pad. It is said that a combination of vibration dampers and a coating of anti-squeal compound usually reduces low speed squeal.

Article by Stephan Visser
Issued by Safeline: June 2002

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