186 Auto Brakes Copyright by Goodheart-Willcox Co., Inc. brake rotor. Chapters 6 and 18 include additional informa- tion about parking brakes. Disc Brake Pads Th e disc brake pads are designed to create friction when forced into contact with the spinning rotor during brak- ing. Th e disc brake pad consists of a lining (the brake friction material) and a shoe (the metal lining support), Figure 12-21. Th e lining is designed to give the best coef- fi cient of friction with acceptable wear, smoothness, and quiet operation. Th e lining absorbs heat and transfers it to the shoe assembly. Th e shoe provides a rigid area for the piston(s) to push against. Disc brake pads are made in many shapes and sizes. Lining Construction Linings are made of heat resistant materials, as discussed in Chapter 11. Th e lining is constructed by mixing the vari- ous temperature-resistant and bonding materials. Th is mix- ture is carefully controlled to create the proper coeffi cient of friction. Th e mixture is then placed in a mold, compressed, and heated. Th e fi nished pad is machined to give it a smooth surface. Some pads are grooved to aid in self-cleaning, air transfer for cooling, and noise reduction. Th e groove also acts as a wear indicator. When the pad is worn until the groove is gone, the lining should be replaced. Shoe Construction Th e shoes to which the linings are attached are made of fl at, heavy gauge steel, punched and formed to match the Parking brake cable Backing plate Pin Drive axle Splash shield Shoe strut Disc (rotor) Plug Parking brake drum inside of hub Rear disc brake caliper assembly Shoe return spring Parking brake shoe lever Shim C-washer Spring Guide plate Front shoe Adjuster Tension spring Shoe hold-down cap Shoe hold-down spring Rear shoe Toyota Figure 12-20. An exploded view of a rear disc brake assembly that uses a set of drum brakes for parking. The parking brake cable acts through a lever to force the brake shoes into contact with the drum section inside the rotor hub. Goodheart-Willcox Publisher Figure 12-21. Brake pads come in all sizes, shapes, and materials. A—Lining side of a brake pad. B—Shoe side of a brake pad. A B