GM Full-Size Trucks 1988-1998 Repair Information

Bleeding the Brakes

Print

EXCEPT HYDRO-BOOST OR ABS



See Figures 1, 2, 3 and 4

To bleed the brakes on a vehicle equipped with ABS, please refer to the ABS bleeding procedure in this section.

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.
  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.
  6.  



Click image to see an enlarged view

Fig. Fig. 1: Connect one end of a clear plastic tube to the bleeder screw and submerge the other end in clean brake fluid



Click image to see an enlarged view

Fig. Fig. 2: Have an assistant pump, then hold in the brake pedal, while you bleed each wheel



Click image to see an enlarged view

Fig. Fig. 3: Using the combination valve depressor-R/V Series



Click image to see an enlarged view

Fig. Fig. 4: Using the combination valve depressor-C/K Series

  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, 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.
  2.  
  3. 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.
  4.  
  5. Depress and release the brake pedal three or four times to exhaust any residual vacuum.
  6.  
  7. 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.
  8.  

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.
  2.  
  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.  

HYDRO-BOOST



The system should be bled whenever the booster is removed and installed.

  1. Fill the power steering pump until the fluid level is at the base of the pump reservoir neck. Disconnect the battery lead from the distributor.
  2.  

Remove the electrical lead to the fuel solenoid terminal on the injection pump before cranking the engine.

  1. Jack up the front of the car, turn the wheels all the way to the left, and crank the engine for a few seconds.
  2.  
  3. Check steering pump fluid level. If necessary, add fluid to the "ADD" mark on the dipstick.
  4.  
  5. Lower the car, connect the battery lead, and start the engine. Check fluid level and add fluid to the "ADD" mark, as necessary. With the engine running, turn the wheels from side to side to bleed air from the system. Make sure that the fluid level stays above the internal pump casting.
  6.  
  7. The Hydro-Boost system should now be fully bled. If the fluid is foaming after bleeding, stop the engine, let the system set for one hour, then repeat the second part of Step 4.
  8.  

The preceding procedures should be effective in removing the excess air from the system, however sometimes air may still remain trapped. When this happens the booster may make a gulping noise when the brake is applied. Lightly pumping the brake pedal with the engine running should cause this noise to disappear. After the noise stops, check the pump fluid level and add as necessary.

 
label.common.footer.alt.autozoneLogo