Chapter 12 Disc Brake System Components and Operation 185 Copyright by Goodheart-Willcox Co., Inc. are usually much smaller since the rear brakes perform less of the braking work than the front brakes. Virtually all rear brake calipers are single piston fl oating designs. Rear disc brakes must have a provision for a parking brake. Th is brake can be an internal device in the caliper that applies the pads, Figure 12-19, or an external mecha- nism that applies a separate set of small shoes, Figure 12-20. Parking Brake Designs Th ere are four mechanical parking brake designs used on rear brakes. Th ey are the screw type, which uses a screw inside the caliper to actuate the parking brake. Th e second is the ball-and-ramp, which uses three steel balls between a shaft and screw mechanism in the caliper to actuate the parking brake. Th e third is the cam-type, which uses a lever-operated cam to apply the brake pads. Th e fourth design is a lever-operated drum brake assembly inside the One-piece fixed caliper A Hub Ventilated rotor Splash shield Transfer tube Transfer tube Rotor Square cut O-ring seal Piston Boot Pad and plate B Adapter plate Caliper Kelsey-Hayes Figure 12-17. A four-piston, fixed caliper brake assembly. A—Overall view of the one-piece caliper. B—Cross-sectional view showing the internal parts. Piston Cylinder bore Piston seal—brake pressure off Caliper housing Dust boot B A Piston seal—brake pressure on Chrysler Figure 12-18. A—This shows the seal being bent outward as hydraulic pressure forces the piston out of its bore. B—Here the square-cut seal is in a normal resting position and shape after the piston has returned. Balls Operating shaft Lever Caliper Piston Adjuster is part of piston assembly Thrust screw Goodheart-Willcox Publisher Figure 12-19. A cutaway view of a ball-and-ramp parking brake assembly and clamp unit.