Brake Pads and Brake Shoes

Brake pads and brake shoes are composed of metal backing plates and a friction lining material. Brake lining is a material having a suitable coefficient of friction, which is attached to the brake shoe and contacts the brake drum to retard the speed of the vehicle. The lining material is designed to wear down faster than the rotors and drums they rub against, so that they are the only part that usually has to be replaced. Because of intense friction produced in braking, brake linings were first composed of heat-resistant asbestos compound. Then it was discovered that breathing dust containing asbestos fibers can cause serious bodily harm. There are now three basic types of materials used in brake linings: (1) non-asbestos organic, which is usually made from filler materials and high temperature resins; (2) metallic; and (3) semi-metallic, which are composed of finely powdered iron or copper, graphite, and small amounts of inorganic filler and friction modifiers. The first and third types of brake lining are used for conventional brake service. Under extreme braking conditions (sports cars, ambulances, police cars), the metallic type of lining is used, because it provides more constant frictional characteristics than the other two. Organic pads and shoes wear down the rotors and drums less than semi-metallic or metallic pads, but also wear down quicker themselves, requiring more frequent replacement.