GM S-Series Pick-ups and SUV's 1994-1999 Repair Guide

Master Cylinder

Print

REMOVAL & INSTALLATION



See Figures 1 through 6

A scan tool is absolutely necessary to bleed the brake hydraulic system on models equipped with an Anti-lock Brake System (ABS). If your vehicle is equipped with ABS, be sure to refer to the ABS bleeding procedures in this section before performing any work on your vehicle's brake hydraulic system.


WARNING
Clean, high quality brake fluid is essential to the safe and proper operation of the brake system. You should always buy the highest quality brake fluid that is available. If the brake fluid becomes contaminated, drain and flush the system, then refill the master cylinder with new fluid. Never reuse any brake fluid. Any brake fluid that is removed from the system should be discarded.



Click image to see an enlarged view

Fig. Fig. 1: Place a rag under the line wrench to help minimize spillage when disconnecting the brake lines



Click image to see an enlarged view

Fig. Fig. 2: Once the line nut is loosened, carefully pull the fitting away from the master cylinder



Click image to see an enlarged view

Fig. Fig. 3: Once the lines are disconnected and plugged, loosen and remove the master cylinder retaining nuts



Click image to see an enlarged view

Fig. Fig. 4: Carefully pull the master cylinder from the mounting studs



Click image to see an enlarged view

Fig. Fig. 5: Common master cylinder mounting with/without a vacuum booster system



Click image to see an enlarged view

Fig. Fig. 6: Exploded view of common master cylinder assembly mountings

  1. Apply the parking brakes and block the drive wheels.
  2.  
  3. Use a line wrench to loosen and disconnect the hydraulic lines from the master cylinder. Immediately plug the lines to prevent system contamination or excessive fluid loss.
  4.  
  5. If equipped with non-power brakes, disconnect the pushrod from the brake pedal.
  6.  
  7. Remove the master cylinder attachment nuts, then separate the combination valve/bracket from the master cylinder.
  8.  
  9. Remove the master cylinder and, as equipped, the gasket and/or rubber boot from the vehicle.
  10.  

To install:
  1. In order to ease installation, bench bleed the master cylinder before installation:
    1. Plug the master cylinder outlet ports. This can be done using rubber or plastic plugs or, more effectively, using a single length of brake line with appropriately sized flares/flare nuts on each end.
    2.  
    3. Mount the cylinder in a soft-jawed vise with the front end tilted slightly downward.
    4.  
    5. Fill the reservoir with clean brake fluid, then use a tool with a smooth rounded end (such as a wooden dowel or pencil eraser) to stroke the primary piston about 1 in. (25mm) several times. As air is bled from the cylinder, the primary piston will no longer travel the full distance.
    6.  
    7. Reposition the master cylinder in the vise with the front end tilted slightly up, then continue stroking the primary piston to further bleed air.
    8.  
    9. Reposition the master cylinder so it is level, then loosen the plugs one at a time and push the piston into the bore forcing air from the cylinder. DO NOT allow the piston to return with the plugs loosened or air will be drawn back into the master cylinder.
    10.  
    11. Make sure the plugs are tightly sealed, then check and refill the reservoir.
    12.  

  2.  
  3. Position the master cylinder to the cowl or brake booster (as applicable), then reposition the combination valve bracket over the studs.
  4.  
  5. Install the master cylinder/combination valve bracket retaining nuts and tighten to 20 ft. lbs. (27 Nm) on 1994 models and 27 ft. lbs. (36 Nm) on 1995-99 models.
  6.  
  7. Working on one line at a time, remove the plugs and quickly connect the brake lines to the master cylinder. Tighten each of the line nuts to 20-22 ft. lbs. (27-30 Nm).
  8.  

If equipped with manual brakes, be sure to reconnect the pushrod to the brake pedal.

  1. Refill the master cylinder with clean brake fluid, then properly bleed the hydraulic brake system and check the brake pedal travel.
  2.  
  3. When all service is finished, remove the blocks from the drive wheels.
  4.  

 
label.common.footer.alt.autozoneLogo