GM Prizm/Nova 1985-1993 Repair Guide

Adjustments

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DRUM BRAKES



See Figures 1 and 2

The rear drum brakes are equipped with automatic adjusters actuated by the brake mechanism. No periodic adjustment of the drum brakes is necessary if this mechanism is working properly. If the pedal travel is greater than normal, it may be due to a lack of adjustment at the rear. In a safe location, drive the car backwards at low speed. While backing, pump the brake pedal slowly several times. (Neither the speed of the car or the speed of pumping the pedal has any effect on the adjustment. The idea is to apply the brakes several times while backing.) Drive forward and check the pedal feel by braking from moderate speed. It may take 2 or 3 passes in reverse to bring the pedal to the correct travel; each brake application moves the adjuster very little. It will take several applications to take up excess clearance.

If brake shoe-to-drum clearance is incorrect and applying and releasing the brakes in reverse does not adjust it properly, the parts will have to be disassembled for repair.

An alternate method of adjustment can be used when the brakes have been disassembled or when the reversing method does not work.

  1. Elevate and safely support the vehicle. If only the rear wheels are elevated, block the front wheels with chocks. Once the vehicle is firmly on stands, release the parking brake.
  2.  
  3. Remove the rear wheels.
  4.  
  5. Remove the brake drum. It will not come off if the parking brake is applied.
  6.  


CAUTION
Brake pads and shoes contain asbestos, which has been determined to be a cancer causing agent. Never clean the brake surfaces with compressed air! Avoid inhaling any dust from brake surfaces! When cleaning brakes, use commercially available brake cleaning fluids.

  1. If the brake drum cannot be removed easily:
    1. Insert a screwdriver through the hole in the backing plate and hold the adjusting lever away from the star wheel.
    2.  
    3. Using another screw driver or a brake adjusting tool, turn the wheel to reduce the tension (increase the clearance) on the brake shoes.
    4.  

  2.  
  3. Use a brake drum measuring tool with both inside diameter and outside diameter capability (GM Tool J-22364-01 or equivalent). Measure the inside diameter of the brake drum and record the reading.
  4.  
  5. Measure the diameter of the brake shoe assemble at the friction surface. Use the adjusting wheel to adjust the brake shoes until the diameter of the shoes is either 0.60mm (Prizm) or 0.33mm (Nova) less than the diameter of the drum. This small clearance is important; over-adjusted brakes cause drag and premature wear on the shoes.
  6.  
  7. Install the brake drum(s) and install the rear wheel(s).
  8.  
  9. Apply the parking brake and lower the car to the ground.
  10.  



Click image to see an enlarged view

Fig. Fig. 1: Measuring the diameters of the drum and shoe assemblies. GM tool shown.



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Fig. Fig. 2: Backing off the adjuster

BRAKE PEDAL



The correct adjustment of the brake pedal height, free-play and reserve distance is critical to the correct operation of the brake system. These 3 measurements inter-relate and should be performed in sequence.

Pedal Height

See Figure 3

  1. Measure the pedal height from the top of the pedal pad to the floor. Correct distances are: Nova, 147-157mm, 1989-92 Prizm, 139-149mm and 1993 Prizm, 143.6-153.6mm.
  2.  



Click image to see an enlarged view

Fig. Fig. 3: Pedal height

  1. If it is necessary to adjust the pedal height, loosen the brake light switch and back it off so that some clearance exists between it and the pedal arm.
  2.  

On Novas, it may be necessary to remove the lower dash trim panel and air duct for access.

  1. Adjust the pedal height by loosening the locknut and turning the pedal pushrod.
  2.  
  3. Return the brake light switch to a position in which it lightly contacts the stopper on the pedal arm.
  4.  

Pedal Free-play

See Figure 4

  1. With the engine off, depress the brake pedal several times until there is no vacuum held in the booster.
  2.  
  3. The free-play distance is between the at rest pedal position and the position at which beginning of pedal resistance is felt. This represents the distance the pedal pushrod moves before actuating the booster air valve. If there is no free-play, the car goes down the road with a slight vacuum leak and the brakes slightly applied. Correct free-play is 3-6mm for 1985-92 Nova and Prizm, and 1-6mm for 1993 Prizm.
  4.  



Click image to see an enlarged view

Fig. Fig. 4: Pedal free-play

  1. If adjustment is necessary, adjust the pedal pushrod to give the correct clearance. After adjusting the pedal free-play, recheck the pedal height.
  2.  
  3. Double check the adjustment of the brake light switch; it should trigger the lights just at the end of the pedal free-play.
  4.  

Pedal Reserve Distance

See Figure 5

  1. With the transaxle in PARK or NEUTRAL and the parking brake fully released, start the engine and apply normal braking effort to the pedal. Depress the pedal fully, but don't try to put it through the floor.
  2.  



Click image to see an enlarged view

Fig. Fig. 5: Pedal reserve

  1. While the pedal is depressed, have a helper measure the distance from the top of the pedal pad to the floor, as illustrated. This distance is the extra travel available to the pushrod if it must work without vacuum assist or if the brakes are worn or severely out of adjustment. If the pedal height and pedal free-play are correctly adjusted, the pedal reserve distance must be at least 65mm for Nova or 55mm for 1989-92 Prizm and 70mm for 1993 Prizm. The reserve distance can be greater than specified but must not be less. If the reserve distance is less than specification, the brake system must be diagnosed for leaks or component failure.
  2.  

 
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