GM Storm/Spectrum 1985-1993 Repair Guide

Master Cylinder

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REMOVAL & INSTALLATION



See Figures 1 and 2

Before the master cylinder is reinstalled, the brake booster pushrod must be adjusted. This adjustment requires the use of special tool J-34873-A booster pushrod gauge.

  1. Disconnect the negative battery cable.
  2.  
  3. The master cylinder is equipped with a brake fluid level warning sensor. Disconnect the sensor harness connector at this time.
  4.  



Click image to see an enlarged view

Fig. Fig. 1: Power booster assembly



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Fig. Fig. 2: Correct procedure for adjusting brake booster pushrod length

  1. Clean area around the reservoir and brake lines at master cylinder. Remove the cap from the master cylinder. Drain the fluid out with the use a turkey baster or similar syringe. Deposit the fluid into a container.
  2.  

Take the proper precautions to prevent brake fluid from contacting painted surfaces. If brake fluid does come in contact with painted surfaces, the finish will be damaged.

  1. Remove the top of the air cleaner and air duct if necessary.
  2.  
  3. Disconnect the brake lines from the master cylinder. Drain the fluid from the lines into the container. Plug the lines to prevent fluid from leaking onto and damaging painted surfaces or the entry of moisture into the brake system.
  4.  
  5. Remove the 2 nuts that attach the master cylinder to the brake booster assembly. Remove the master cylinder.
  6.  

To install:
  1. Clean the brake booster and the master cylinder flange surfaces. Install a new gasket onto the brake booster if so equipped.
  2.  
  3. Adjust the length of the brake booster pushrod as follows:
    1. Set the special tool on the master cylinder with the gasket and lower the pin of the tool until it lightly contacts the piston.
    2.  
    3. Turn the special tool upside-down and position it onto the booster.
    4.  
    5. Measure the clearance between the booster pushrod and the pin head of the tool. There must be zero clearance. To obtain ZERO clearance, adjust the pushrod length until the pushrod just contacts the head of the pin.
    6.  

  4.  
  5. If a new master cylinder is to be installed, bench bleed as follows:
    1. Mount the master cylinder into a vise or suitable holding fixture. Take care not to damage the cylinder.
    2.  
    3. Fill the cylinder to the correct level with the specified fluid.
    4.  
    5. Block off all the outer brake line holes but one, then using a long tool such as rod, position it in the cylinder to actuate the brake master cylinder.
    6.  
    7. Slowly depress the piston inside the master cylinder, which will force brake fluid from the cylinder. While holding the piston in the depressed position, cover the open hole and allow the piston to return to a resting position.
    8.  
    9. Repeat this procedure until the fluid exiting the master cylinder is free of air bubbles.
    10.  
    11. Repeat this procedure on the remaining ports.
    12.  

  6.  
  7. Install the master cylinder over the mounting studs and tighten the 2 mounting nuts to 9 ft. lbs. (13 Nm).
  8.  
  9. Reconnect the lines to the master cylinder. Use the proper tool (flare wrench or line wrench) to tighten the fittings at the master cylinder.
  10.  
  11. Connect the level warning switch connector.
  12.  
  13. Fill the brake fluid reservoir to the proper level with clean brake fluid. If air is present in the system, bleed the brake system as described in this Section.
  14.  
  15. Check for a firm brake pedal and for fluid leaks. Check and/or adjust the brake pedal as required.
  16.  
  17. Road test the vehicle for proper operation.
  18.  

OVERHAUL



See Figure 3

Use this service procedure and exploded view diagram. If in doubt about overhaul condition or service procedure REPLACE the assembly with a new master cylinder.

  1. Pour brake fluid out of the reservoir.
  2.  
  3. Separate the brake fluid reservoir.
  4.  



Click image to see an enlarged view

Fig. Fig. 3: Master cylinder assembly - Storm

  1. Place the master cylinder in a soft jawed vice. Push IN on the primary piston with an appropriate tool and remove the secondary piston stop bolt and gasket. Maintain pressure and remove snapring. Remove the dust seal.
  2.  
  3. Remove the proportioning valves.
  4.  
  5. Remove the primary and secondary piston assembly from the master cylinder.
  6.  
  7. Clean all parts with DOT-3 brake fluid and dry with compressed air.
  8.  
  9. Check the master cylinder inner wall for wear, rust or damage. Check the pistons for wear or damage. Replace pistons if any wear is evident.
  10.  
  11. Check bore for obstructions. Blow away foreign matter with compressed air if possible.
  12.  
  13. Inspect brake fluid reservoir for cracking or damage. Inspect gaskets and snaprings for fatigue or damage. Replace as necessary.
  14.  

To assemble:
  1. Inspect parts carefully for foreign matter and lubricate with clean brake fluid.
  2.  
  3. Clamp the cylinder into a soft jawed vice. Install the primary and secondary piston assemblies. Push the piston in with an appropriate tool and install the snapring. Install the dust seal--the dust seal notch must be facing downward.
  4.  

Be careful not to scratch the piston cups when installing the piston assemblies.

  1. Maintain pressure on the piston an install the stopper bolt and gasket hand tight. Torque stopper bolt to 6 ft. lbs.
  2.  
  3. Press the piston all the way into the cylinder and release several times. Check for smooth piston return and brake fluid being forced from the front and rear outlets.
  4.  
  5. Install the proportioning valves. Torque valves to 33 ft. lbs.
  6.  
  7. Install the brake fluid reservoir.
  8.  
  9. Fill the reservoir with fluid and bleed the master cylinder. After installation, bleed brake system.
  10.  

 
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