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Disc Brake Lining Inspection And Repair (760) 741-7861
Inspect the brake linings every 6,000 miles and any time the wheels are removed. Check both ends of the outer lining by looking in at each end of the caliper. These are the points where the highest rate of wear normally occurs. At the same time, check the thickness of the inner lining to make sure it has not worn prematurely. Some inboard shoe and linings have a thermal layer against the shoe, integrally molded with the lining. This extra layer should not be confused with uneven inboard-outboard lining wear. Look down through the inspection hole in the top of the caliper to view the inner lining. Replace shoe and lining assemblies whenever the thickness of any lining is worn to within .030" (.76 mm) of the shoe. Replace riveted shoe and lining assemblies when the lining is worn to within .030" (.76 mm) of any rivet head. Always replace disc brake shoe and lining assemblies as a complete axle set. Check the flatness of the linings. Place the inboard and outboard lining surfaces together and check for a gap between the surfaces. This gap should be no larger than .005" (.13 mm) at the center of the lining surfaces. This applies to new or used shoe and lining assemblies. The shoe and lining assemblies have a wear indicator that makes noise when the linings are worn and need replacement.
ROTOR INSPECTION & REPAIR (DISC BRAKES)
Rotor Tolerance & Surface Finish
Tolerances of the braking surfaces for flatness, parallelism and lateral run out are closely held. The maintenance of close tolerances on the shape of the breaking surfaces is necessary to prevent brake roughness or pulsation. The surface finish must be held to a specific range of 60 Ra roughnesses or less. The control of the surface can improve lining life. Light scoring of the rotor surfaces not exceeding 1.5 mm (0.06 in.) in depth is normal and not detrimental to brake operation.
Thickness Variation Check
Check thickness variation by measuring the rotor thickness at four or more points around the circumference of the rotor. Use a micrometer calibrated in ten thousands of an inch. Make all measurements at the same distance in from the edge of the rotor. A rotor measuring thicker than .0005" (.013 mm) can cause pedal pulsation and/or front end vibration during brake applications. A rotor like this should be refinished or replaced.
Lateral Run out Check
The best way to check lateral run out is with the wheels still installed on the vehicle. This gives a much more accurate reading of the total indicated run out under real braking conditions. If equipment is not available to perform the check with the wheels installed, the next best reading can be made with the wheels removed but the caliper still installed.
1. Clean rotor surface. If the wheel must be removed, reinstall the wheel nuts to retain the rotor. Tighten the wheel nuts to the correct torque specification following the wheel nut tightening sequence.
2. Fasten a dial indicator to the steering knuckle so the indicator button contacts the rotor surface about .5 " (13 mm) from the outer edge.
3. Set the dial indicator to zero.
4. Turn the wheel one complete revolution and observe the run out indicated on the dial.
5. The total indicated run out must not exceed .0003" (.08 mm).
6. If lateral run out is not within specifications, refinish or replace the rotor as necessary.
In some cases, excessive lateral run out can be improved by indexing the rotor on the hub one or two bolt positions from the original position. If lateral run out cannot be corrected by indexing the rotor, check the hub and bearing assembly for excessive lateral run out or looseness. If the hub and bearing assembly lateral run out exceeds .0015" (.040 mm), repair or replace the hub and bearing assembly.