GM Buick/Oldsmobile/Pontiac/Full-Size 1975-1990 Repair Guide

Brake Bleeding

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The hydraulic brake system must be bled any time one of the lines is disconnected or any time air enters the system. If the brake pedal feels spongy upon application, and goes almost to the floor but regains height when pumped, air has entered the system. It must be bled out. Check for leaks that would have allowed the entry of air and repair them before bleeding the system. The correct bleeding sequence is: right rear wheel cylinder, left rear, right front, and left front. If the master cylinder is equipped with bleeder valves, bleed them first then go to the wheel cylinder nearest the master cylinder (left front) followed by the right front, left rear, and right rear.

MANUAL BLEEDING



See Figures 1 and 2

Standard Systems

This method of bleeding requires two people, one to depress the brake pedal and the other to open the bleeder screws.

  1. Clean the top of the master cylinder, remove the cover and fill the reservoirs with clean fluid. To prevent squirting fluid, replace the cover.
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CAUTION
On vehicles with front disc brakes, it will be necessary to hold in the metering valve pin during the bleeding procedure. The metering valve is located beneath the master cylinder and the pin is situated under the rubber boot on the end of the combination valve housing. This may be taped in or held by an assistant. Never reuse brake fluid which has been bled from the system.

  1. Fill the master cylinder with brake fluid.
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  3. Install a box-end wrench on the bleeder screw on the right rear wheel.
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  5. Attach a length of small diameter, clear vinyl tubing to the bleeder screw. Submerge the other end of the rubber tubing in a glass jar partially filled with clean brake fluid. Make sure the rubber tube fits on the bleeder screw snugly or you may be squirted with brake fluid when the bleeder screw is opened.
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  7. Have your friend slowly depress the brake pedal. As this is done, open the bleeder screw half a turn and allow the fluid to run through the tube. Close the bleeder screw, then return the brake pedal to its fully released position.
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  9. Repeat this procedure until no bubbles appear in the jar. Refill the master cylinder.
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  11. Repeat this procedure on the left rear, right front, and left front wheels, in that order. Periodically refill the master cylinder so it does not run dry.
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  13. If the brake warning light is on, depress the brake pedal firmly. If there is no air in the system, the light will go out.
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Fig. Fig. 1: Have an assistant pump the brake pedal while you bleed each wheel



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Fig. Fig. 2: Bleeder screw location on rear drum brakes

Powermaster® System
  1. Pump the brake pedal 10 times with the ignition switched off to remove all power boost effect from the system. Fill the reservoir to the indicated full mark with clean, fresh fluid meeting the specifications shown on the cover.
  2.  
  3. Disconnect the brake line connectors at the master cylinder outlet ports. Allow the fluid to bleed through the system by gravity until it flows out all four ports. Reconnect the brake lines to the ports. Refill the fluid reservoir, if necessary.
  4.  
  5. Tighten the connector closest to the cowl. Then, have an assistant slowly apply the brake pedal fully (50 lbs. pressure). As he holds this position, tighten the forward connector. Then, have the assistant release the pedal. Refill the fluid reservoir, if necessary.
  6.  
  7. Wait five seconds, and then have your assistant re-apply the brake pedal, and hold it down. Open the forward connector 1 / 2 turn to purge air. Before the pedal bottoms out, retighten the connector and have your assistant release the pedal again. Repeat the procedure in this step until all air is purged from this port. Refill the fluid reservoir, if necessary.
  8.  
  9. Repeat Steps 3 and 4 to bleed the remaining connectors (the connector closest to the cowl need not be bled). When the bleeding operation has been completed, operate the brakes with the ignition on and system pressure restored. Brake pedal travel should be normal and the brake warning indicator must not light when brakes are applied.
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