GM Blazer/Jimmy/Typhoon/Bravada 1983-1993 Repair Guide

Power Brake Booster

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The power brake booster is a tandem vacuum suspended unit. Some early models may be equipped with a single or dual function vacuum switch which activates a brake warning light should low booster vacuum be present. Under normal operation, vacuum is present on both sides of the diaphragms. When the brakes are applied, atmospheric air is admitted to one side of the diaphragms to provide power assistance.

REMOVAL & INSTALLATION



See Figures 1, 2, 3 and 4

  1. Apply the parking brake and block the drive wheels.
  2.  
  3. Remove the master cylinder-to-power brake booster nuts, then reposition the master cylinder and combination valve out of the way; if necessary, support the master cylinder on a wire to prevent damaging the brake lines.
  4.  

When removing the master cylinder from the power brake booster, it is not necessary to disconnect the hydraulic lines, therefore the brake system should not have to be bled.

  1. Disconnect the vacuum hose from the power brake booster.
  2.  



Click image to see an enlarged view

Fig. Fig. 1: Common power brake booster attachment



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Fig. Fig. 2: Early model booster vacuum lines - 4-cylinder engine

  1. From under the dash, disconnect the pushrod from the brake pedal. On most vehicles this involves removing the retainer and washer.
  2.  
  3. From under the dash, remove the power brake booster-to-cowl retaining nuts.
  4.  
  5. Back under the hood, remove the power brake booster and the gasket from the cowl.
  6.  

To install:
  1. Position the booster to the cowl using a new gasket.
  2.  
  3. Install the booster retaining nuts and tighten to 1 ft. lbs. (20 Nm) for vehicles through 1988, to 2 ft. lbs. (22 Nm) for 1989-93 vehicles.
  4.  
  5. Connect the pedal pushrod and install the washer or switch and the retainer.
  6.  
  7. Connect the vacuum hose.
  8.  



Click image to see an enlarged view

Fig. Fig. 3: Common booster vacuum lines - 6-cylinder engine



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Fig. Fig. 4: Checking the piston booster rod using the gauge tool

  1. For 1992-93 vehicles, gauge the booster rod:
    1. Apply 25 in. Hg (85 kPa) of vacuum using a hand held vacuum pump or apply maximum engine vacuum.
    2.  
    3. Check the maximum and minimum rod lengths using J-37839 or an equivalent pushrod height gauge.
    4.  
    5. If the piston is not within limits, install a service adjustable piston rod and adjust it to the correct length.
    6.  

  2.  
  3. Reposition the master cylinder and combination valve bracket to the booster studs, then secure using the retaining nuts. For details, please refer to the master cylinder procedure located earlier in this section.
  4.  
  5. Start and run the engine, then check for proper booster operation.
  6.  

 
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