GM Prizm/Nova 1985-1993 Repair Guide

Brake Rotor



  1. Raise and safely support the rear of the vehicle on jackstands. Block the front wheels.
  3. Siphon a sufficient quantity of brake fluid from the master cylinder reservoir to prevent the brake fluid from overflowing when removing or installing the brake pads. This is necessary as the piston must be forced into the cylinder bore to provide sufficient clearance to install the pads.
  5. Remove the wheel.

Disassemble brakes one wheel at a time. This will prevent parts confusion and also prevent the opposite caliper piston from popping out during pad installation.

  1. Remove the mounting (lower) bolt from the mounting bracket.
  3. Lift the caliper from the bottom so that it hinges upward on the upper pin and slide the caliper off the pin. Use a piece of wire to hold the caliper out of the way. Do not disconnect the brake hose and do not allow the brake hose to become twisted or kinked during this operation.
  5. Remove the brake pads with their shims, springs and support plates.
  7. If the rotor is to be measured, install all the lug nuts to hold the rotor in place. If the nuts are open at both ends, it is helpful to install them backwards (tapered end out) to secure the disc. Tighten the nuts a bit tighter than finger tight, but make sure all are at approximately the same tightness. Follow the measurement and inspection procedures listed under INSPECTION.
  9. Remove the mounting bolts holding the mounting bracket to the rear axle carrier.
  11. Remove the lug nuts and remove the rotor.


  1. Mount a dial indicator with a magnetic or universal base on the strut so that the tip of the indicator contacts the rotor about 1 / 2 in. from the outer edge.
  3. Zero the dial indicator. Turn the rotor 1 complete revolution and observe the total indicated run-out.
  5. If the run-out exceeds 0.15mm, clean the wheel hub and rotor mating surfaces and remeasure. If the run-out still exceeds maximum, remove the rotor and remount it so that the wheel studs now run through different holes. If this re-indexing does not provide correct run-out measurements, the rotor should be considered warped beyond use and either resurfaced or replaced.


The thickness of the rotor partially determines its ability to withstand heat and provide adequate stopping force. Every rotor has a minimum thickness established by the manufacturer. This minimum measurement must not be exceeded. A rotor which is too thin may crack under braking; if this occurs the wheel can lock instantly, resulting in sudden loss of control.

If any part of the rotor measures below minimum thickness, the disc must be replaced. Additionally, a rotor which needs to be resurfaced may not allow sufficient cutting before reaching minimum. Since the allowable wear from new to minimum is about 1mm, it is wise to replace the rotor rather than resurface it.

Thickness and thickness variation can be measured with a micrometer capable of reading to one ten-thousandth inch. All measurements must be made at the same distance in from the edge of the rotor. Measure at 4 equally spaced points around the disc and record the measurements. Compare each measurement to the minimum thickness specifications in the chart at the end of this Section.

Compare the 4 measurements to each other and find the difference between each pair. A rotor varying by more than 0.013mm can cause pedal vibration and/or front end vibration during stops. A rotor which does not meet these specifications should be resurfaced or replaced.


A new rotor will have a smooth, even surface which rapidly changes during use. It is not uncommon for a rotor to develop very fine concentric scoring (like the grooves on a record) due to dust and grit being trapped by the brake pad.This slight irregularity is normal, but as the grooves deepen, wear and noise increase and stopping may be affected. As a general rule, any groove deep enough to snag a fingernail during inspection is cause for action or replacement.

Any sign of blue spots, discoloration, heavy rusting or outright gouges require replacement of the rotor. If you are checking the disc on the car (such as during pad replacement or tire rotation) remember to turn the disc and check both the inner and outer faces completely. If anything looks questionable or requires consideration, choose the safer option and replace the rotor. The brakes are a critical system and must be maintained at 100% reliability.

Any time a rotor is replaced, the pads should also be replaced so that the surfaces mate properly. Since brake pads should be replaced in axle sets (both front or rear wheels), consider replacing both rotors instead of just one. The restored feel and accurate stopping make the extra investment worthwhile.


  1. Place the rotor in position over the studs and install 2 lug nuts finger tight to hold it in place.
  3. Install the mounting plate to the rear axle carrier and tighten the mounting bolts to 34 ft. lbs.
  5. Install the brake pads, springs and clips.
  7. Carefully mount the caliper onto the upper slide pin.
  9. Use GM Tool J-37149 or its equivalent to slowly turn the caliper piston clockwise while pressing it into the bore until it locks.
  11. Lower the caliper so that the pad protrusion fits into the piston stopper groove.
  13. Install the mounting bolt and tighten it to 14 ft. lbs.
  15. Remove the lug nuts holding the disc, install the rear wheel and install all the lug nuts.
  17. Depress the brake pedal once or twice to take up the excess piston play.
  19. Lower the car to the ground and fill the master cylinder reservoir to the correct level. Final tighten the lug nuts.