GM Lumina/Silhouette/Transport APVs 1990-1999 Repair Guide

Power Brake Booster

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The power brake booster used on these vehicles is a tandem vacuum unit. In a normal operating mode, with the service brakes in the released position, the tandem vacuum suspended booster operates with vacuum on both sides of its diaphragms. When the brakes are applied, air at atmospheric pressure is admitted to one side of each diaphragm to provide the power assist. When the service brake is released, the atmospheric air is shut off from one side of each diaphragm. The air is then drawn from the booster through the vacuum check valve to the vacuum source.

REMOVAL AND INSTALLATION



It may be necessary to remove other components to gain access to the booster assembly.

  1. From inside the vehicle, remove the vacuum booster pushrod from the brake pedal.
  2.  

When disconnecting the pushrod from the brake pedal, The brake pedal must be held stationary or damage to the brake switch may result.

  1. Support the brake pedal out of the way.
  2.  
  3. Remove the mounting nuts, which secure the vacuum booster to the firewall.
  4.  
  5. From under the hood, disconnect the negative battery cable.
  6.  
  7. Disconnect the vacuum hose from the booster assembly.
  8.  
  9. Do not disconnect the master cylinder fluid lines, unless there is a clearance problem. Unbolt the master cylinder from the booster unit and position it to the side, to gain clearance to remove the booster.
  10.  
  11. Pull the booster away from the cowl, to clear the mounting studs, and remove it from the vehicle.
  12.  

See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: Exploded view of the power brake booster mounting

To install:
  1. Position the booster and secure with the retainers. Tighten the attaching nuts to 15 ft. lbs. (21 Nm).
  2.  
  3. Install the booster pushrod to the brake pedal and adjust the brake switch as necessary.
  4.  
  5. Install the master cylinder to the booster and tighten the attaching nuts to 20 ft. lbs. (27 Nm).
  6.  
  7. If necessary, add fluid to the master cylinder and bleed the system. This should only be necessary if you had to disconnect the fluid lines for access.
  8.  
  9. Connect the negative battery cable.
  10.  

 
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