See Figure 1
Front disc brakes, offered as an option since 1965, have been of two types. Pre-1968 models were four-piston, fixed-caliper discs. Since 1968, single-piston, floating-caliper discs have been used.
Instead of the traditional, expanding brakes that press outward against a circular drum, disc brake systems utilize a cast iron disc (rotor) with brake pads on either side. Braking effect is achieved in a manner similar to the way that you would squeeze a spinning phonograph record between your fingers. The disc or rotor is a one-piece casting with cooling fins between the two braking surfaces. This design enables air to circulate between the braking surfaces thus making them less sensitive to heat buildup and fade. Dirt and water do not affect braking action since such contaminants are thrown off by the centrifugal action of the rotor, or are scraped off by the pads. Also, the equal clamping action of the brake pads tends to ensure uniform, straight-line stops. All disc brakes are inherently self-adjusting.
Kelsey-Hayes four-piston fixed-caliper brakes are used on 1964-1967 models. These brakes are called fixed-caliper because the complete caliper assembly is rigidly bolted to the wheel spindle. The caliper assembly consists of two caliper halves bolted together, each half housing a pair of pistons. Braking effect is achieved by hydraulically pushing both pads against the disc sides.
Kelsey-Hayes single-piston floating-caliper brakes are used on 1968-1973 models. These differ from the fixed caliper units in that the one-piece caliper is free to move inboard and outboard parallel to the axle spindle, as the brakes are applied and released. The caliper is located atop the rotor by a single stabilizer bar bolted to the anchor plate on the spindle. A single piston is located in the caliper assembly. Braking effect is achieved by hydraulically pushing the inboard shoe into contact with the rotor, while the reaction force thus generated is used to allow the caliper to move slightly along the axle centerline and pull the outboard shoe into frictional contact with the rotor.
- Raise the vehicle until the wheel and tire clear the floor. Place safety stands under the vehicle.
- Remove the wheel cover. Remove the wheel and tire from the hub and rotor.
- Visually inspect the shoe and lining assemblies. If the lining material has worn to a thickness of 0.030 inch or less, or if the lining is contaminated with brake fluid, replace all shoe and lining assemblies on both front wheels. Make all thickness measurements across the thinnest section of the shoe and lining assembly. A slightly tapered condition on a used lining should be considered normal.
- To check rotor run-out, tighten the wheel bearing adjusting nut to eliminate end-play. Check to see that the rotor can still be rotated.
- Hand-spin the rotor and visually check for run-out. If the rotor appears out of round or wobbles, it must be machined or replaced. When the run-out check is finished, loosen the wheel bearing adjusting nut and retighten it to specifications, in order to prevent bearing damage.
- Visually check the rotor for scoring. Minor scores can be removed with a fine emery cloth. If it is excessively scored, the rotor must be machined or replaced.
- The caliper should be visually checked. If excess leakage is evident, the caliper should be replaced.
- Install the wheel and hub assembly.