178 Auto Brakes Copyright by Goodheart-Willcox Co., Inc. shield is usually fastened to the spindle assembly, and is far enough away from the rotor to allow air to circulate. Some splash shields are designed as air scoops, directing air over the rotor when the vehicle is moving. Figure 12-6 illustrates the use of a splash shield and wheel for protection. On some rear disc brake assemblies, the shield also acts as a backing plate to hold the emergency brake shoes. Th e shield may be held by the caliper assembly on some four- wheel-drive vehicles’ front brakes. Front Disc Brake Caliper Th e disc brake caliper provides a housing for the hydraulic components and the brake pads. Calipers are made of cast iron or aluminum. Th e caliper is usually attached by bolts to the front wheel spindle assemblies, Figure 12-7. Calipers have a dust boot over every piston to keep dust and water away from the inner seals, to retract the piston, and to reduce the possibility of sticking. i viewfinder/Shutterstock.com Figure 12-3. A disc brake rotor that incorporates internal fins and cross-drilled (side-to-side) air holes. These air holes aid in cooling the rotor. Braking rotor Bolt-on brake rotor Wheel stud holding rotor to hub Hub Inner bearing Outer bearing Spindle Shoe and lining Wheel Caliper Boot Seal Piston Mounting bolt Adapter Seal Mounting bolt Splash shield Steering knuckle Chrysler Figure 12-4. A brake rotor that is secured to the hub with wheel studs. Study the construction.