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OBJECTIVES: After studying Chapter 76, the reader should be able to: Prepare for ASE Brakes (A5) certification test content area “C” (Disc Brake Diagnosis and Repair). Describe how disc brakes function. Name the parts of a typical disc brake system. Describe the construction of disc brake pads. Describe the difference between fixed caliper and floating or sliding caliper. Continued

KEY TERMS: brake shoe • rotor/disc • brake line bonded linings • proportioning valve • brake pad fixed brake caliper • floating caliper • gas fade drum • wheel cylinder • kinetic energy • heat energy lining fade • pad wear indicators • sliding pin Continued

Brakes are energy converters They convert kinetic energy into heat via FRICTION.

The master cylinder controls the entire brake system. Fluid reservoir Feed the system It stores the brake fluid It pressurizes brake fluid Located in front of driver on the fire wall

Brake fluid comes in 3 flavors DOT 3 – Glycol based, hygroscopic, recommended by most manufacturers DOT 4 – Same as DOT 3 with additives to reach a higher boiling point. Can be mixed with DOT 3, but the boiling point is reduced. DOT 5 – Silicone based. Not hygroscopic. Not mixable.

Now we have fluid and pressure! Where do we go next?

Drum Brakes They do not get rid of heat well They don’t work well when wet They do not give a linear feel They are more complicated to service They are cheap It is very easy to make them work with a cable for emergency/ parking brake application Only 20% of braking is done in the rear, so they work fine back there Star Adjuster

Wheel Cylinder The wheel cylinder is filled with pressurized brake fluid. The piston then expands outwards forcing the shoes into the drum eventually slowing down the vehicle.

Brake Shoes Check for contamination Minimum thickness is 1/16” or a bit more than the metal they are attached to. Check for cracks and missing chunks

DISC BRAKES Disc brakes use a piston(s) to squeeze friction material (pads) on both sides of a rotating disc (rotor). The rotor is attached to and stops the wheel. Disc brakes are well suited for use as front brakes, which must provide 60% to 80% of the vehicle’s total stopping power. Brake Caliper Brake Hose Brake Pads Brake Rotor Caliper (fixed or floating/sliding)

Kinetic Energy BRAKE ROTORS The brake rotor provides the friction surfaces for the brake pads to rub against. Figure 76–19 Disc brake rotors can be either solid or vented. Slotted / Cross Drilled / Vented rotors have cooling passages between friction surfaces Solid rotors are used on the rear of vehicles equipped with four-wheel disc brakes. Kinetic Energy

DISC BRAKE CALIPERS While the hydraulic operation of all brake calipers is similar, calipers differ in two important areas: how they attach to the vehicle, and how they apply pressure to the brake pads. There are 2 types of calipers: Floating / Sliding Fixed Continued

Figure 76–21 (c) Notice the cross-over hydraulic passage that connects both sides of the caliper. (Courtesy of Allied Signal Automotive Aftermarket). (c) Continued

Figure 76–20 Four-piston fixed caliper assembly on a race vehicle. Continued

Figure 76–5 The square-cut O-ring not only seals hydraulic brake fluid, but also retracts the caliper piston when the brake pedal is released. Continued

DISC BRAKE PADS Riveting Bonding Figure 76–10 A typical disc brake pad. Many brake pads have slots that help prevent gas fade Slots allow gasses and dust particles to escape Riveting Bonding Continued

Figure 76–15 Typical pad wear sensor operation Figure 76–15 Typical pad wear sensor operation. It is very important that the disc brake pads are installed on the correct side of the vehicle to be assured that the wear sensor will make a noise when the pads are worn. If the pads with a sensor are installed on the opposite side of the vehicle, the sensor tab is turned so that the rotor touches it going the opposite direction. Usually the correct direction is where the rotor contacts the sensor before contacting the pads when the wheels are being rotated in the forward direction. Continued

Electrical wear indicators use a coated electrode imbedded in the lining material to generate the warning signal. The electrode is wired to a warning light in the instrument panel and when the lining wears sufficiently, the electrode grounds against the rotor to complete the circuit and turn on the warning light. Figure 76–16 Electrical wear indicators ground a warning light circuit when the pads need replacement. Continued

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