GM Full Size Vans 1987-1997 Repair Guide

Bleeding the Brakes

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EXCEPT HYDRO-BOOST OR ABS



Manual Bleeding

See Figures 1 and 2



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Fig. Fig. 1: Attach a length of vinyl hose to the bleeder screw of the brake to be bled. Insert the other end of the hose into a clear jar half full of clean brake fluid



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Fig. Fig. 2: Have your assistant hold the brake pedal down, then open the bleeder fitting. Close the fitting before releasing the brake pedal:

Never bleed a wheel cylinder when a drum is removed.

  1. Clean the master cylinder of excess dirt and remove the cylinder cover and the diaphragm.
  2.  
  3. Fill the master cylinder to the proper level. Check the fluid level periodically during the bleeding process and replenish it as necessary. Do not allow the master cylinder to run dry, or you will have to start over.
  4.  
  5. Before opening any of the bleeder screws, you may want to give each one a shot of penetrating solvent. This reduces the possibility of breakage when they are unscrewed.
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  7. Attach a length of vinyl hose to the bleeder screw of the brake to be bled. Insert the other end of the hose into a clear jar half full of clean brake fluid, so that the end of the hose is beneath the level of fluid. The correct sequence for bleeding is to work from the brake farthest from the master cylinder to the one closest; right rear, left rear, right front, left front.
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  9. The combination valve must be held open during the bleeding process. A clip, tape, or other similar tool (or an assistant) can be used to hold in the metering pin.
  10.  

See Figure 3



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Fig. Fig. 3: Use a tool such as J 39177 to depress and hold the combination valve stem

  1. Depress and release the brake pedal three or four times to exhaust any residual vacuum.
  2.  
  3. Have an assistant push down on the brake pedal and hold it down. Open the bleeder valve slightly. As the pedal reaches the end of its travel, close the bleeder screw and release the brake pedal. Repeat this process until no air bubbles are visible in the expelled fluid.
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Make sure your assistant presses the brake pedal to the floor slowly. Pressing too fast will cause air bubbles to form in the fluid.

  1. Repeat this procedure at each of the brakes. Remember to check the master cylinder level occasionally. Use only fresh fluid to refill the master cylinder, not the stuff bled from the system.
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  3. When the bleeding process is complete, refill the master cylinder, install its cover and diaphragm, and discard the fluid bled from the brake system.
  4.  

Pressure Bleeding

See Figure 4



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Fig. Fig. 4: The GM Pressure Bleeder adapter, J-29567 or equivalent, is needed when using this bleeding technique

The following procedure requires the use of the GM Brake Bleeder Adapter tool No. J-29567 or equivalent, and the GM Combination Valve Depressor tool No. J-35856 or equivalent.

  1. Using the GM Brake Bleeder Adapter tool No. J-29567 or equivalent, fill the pressure tank to at least 1 / 3 full of brake fluid. Using compressed air, charge the pressure tank to 20-25 psi. (138-172 kPa), then install it onto the master cylinder.
  2.  
  3. Using the GM Combination Valve Depressor tool No. J-35856 or equivalent, install it onto the combination valve to hold the valve open during the bleeding operation.
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  5. Bleed each wheel cylinder or caliper in the following sequence: right rear, left rear, right front and left front.
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  7. Connect a hose from the bleeder tank to the adapter at the master cylinder, then open the tank valve.
  8.  
  9. Attach a clear vinyl hose to the brake bleeder screw, then immerse the opposite end into a container partially filled with clean brake fluid.
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  11. Open the bleeder screw 3 / 4 turn and allow the fluid to flow until no air bubbles are seen in the fluid, then close the bleeder screw.
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  13. Repeat the bleeding process to each wheel.
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  15. Inspect the brake pedal for sponginess and if necessary, repeat the entire bleeding procedure.
  16.  
  17. Remove the depressor tool from the combination valve and the bleeder adapter from the master cylinder.
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  19. Refill the master cylinder to the proper level with brake fluid.
  20.  

WITH ABS



Refer to the ABS system bleeding procedure outlined later in this section.

 
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