GM Full Size Vans 1987-1997 Repair Guide

Bleeding The ABS System

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The brake system must be bled when any brake line is disconnected or there is air in the system.

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.
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  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.
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  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) will hold the metering pin in.
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  11. Depress and release the brake pedal three or four times to exhaust any residual vacuum.
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  13. 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.
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  5. If the BPMV has been replaced, perform 4 function tests with the TECH 1 scan tool. The brake pedal must be firmly applied.
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  7. On models with rear wheel ABS:
    1. Refill the jar with clean brake fluid and attach the bleed hose to the bleed valve on the Isolation/Dump valve.
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    3. Have your assistant slowly depress the brake pedal and hold it. Loosen the bleed valve and expel the air. Tighten the valve and slowly release the pedal.
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    5. Wait 15 seconds and repeat this procedure. Repeat bleeding the Isolation/Dump valve until all the air is expelled.
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  9. On models with 4 wheel ABS, repeat Steps 1-9.
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