Chapter 12 Disc Brake System Components and Operation 189 Copyright by Goodheart-Willcox Co., Inc. circuit exists through a dashboard light to this sensor. If the pads wear down far enough, the electrical lead contacts the rotor when the brakes are applied. Th is grounds the lead and completes the circuit, illuminating the dashboard light. Electric Calipers In the future, calipers may be operated by electric motors. Such a caliper will resemble a hydraulic caliper, Figure 12-26. Th e pads will be pressed against the rotor by the rotation of a small high-speed electric motor operating through a worm drive. No hydraulic system will be needed. Th e motor will be energized through a control module that responds to sensor inputs, typically brake pedal pressure and wheel speeds. Th e anti-lock brake system will be built into the control module. Calipers are constructed of cast iron or aluminum. Th ey are either fl oating or fi xed. Th e fl oating type can move in relation to the spindle. Fixed types are solidly bolted onto the spindle. Rubber dust boots protect the pistons from water and dirt. Floating calipers have one or two apply pistons. Fixed calipers on newer vehicles are usually aft ermarket units with two or four pistons. Th e pistons on all calipers are moved outward by hydraulic pressure. Th e piston seals are used to return the piston to its unapplied position when brake pres- sure is released. Some future calipers may be operated by electric motors. Brake pad linings are made from various heat resistant materials. Th ey are bonded or riveted to the steel shoe. Th e shoe is a backing plate for the lining and a rigid meeting place for the apply piston(s). To reduce brake noise, shoes are sometimes equipped with special insulators. Some brake shoes also incorpo- rate warning devices to alert the driver that brake work is necessary. Review Questions—Chapter 12 Answer the following questions using the information provided in this chapter. 1. A ventilated rotor has internal _____ to remove heat. 2. Solid rotors are cooled by air passing over the _____ surfaces of the rotor. 3. Rotors are attached to the wheel _____, which is attached to the spindle through _____. 4. On some vehicles, an extra _____ holds the caliper to the spindle. 5. Removing brake drag improves _____. 6. A caliper that moves in relation to the spindle mounting is called a(n) _____ caliper. 7. All modern fi xed calipers have _____ pistons, _____ on each side. 8. All rear disc brake calipers are equipped with a(n) _____ brake. 9. What two parts make up a disc brake pad? 10. Th e two disc brake pad parts in Question 9 are attached to each other by what two methods? Delphi Figure 12-26. In the future, calipers similar to the one shown here may be operated by electric motors. Summary Disc brakes use a rotor or disc that provides a braking sur- face for the pads. Th e rotor also aids in cooling. Rotors are round and come in many diff erent diameters and thickness. Th ey are constructed from cast iron and are either solid or ventilated with fi ns between braking surfaces. Th e rotor must be thick enough to absorb heat, and fl at enough to provide for smooth stops. Th e rotor is protected by a splash shield.