The purpose of bleeding the brakes is to expel air trapped in the hydraulic system. The system must be bled whenever the pedal feels spongy, indicating that compressible air has entered the system. It must also be bled whenever the system has been opened or repaired. If you are not using a pressure bleeder, you will need a helper for this job.
When bleeding the brakes, air may be trapped in the brake lines or valves far upstream, as much as 10 feet from the bleeder screw. Therefore, it is very important to have a fast flow of a large volume of brake fluid when bleeding the brakes, to make sure all of the air is expelled from the system.
- Attach a clear plastic hose to the bleeder screw, then place the hose into a clean jar that has enough fresh brake fluid to submerge the end of the hose.
- Have an assistant pump the brake pedal 3-4 times, and hold it down before the bleeder screw is opened.
- Open the bleeder screw at least one full turn. When the bleeder screw opens, the brake pedal will drop.
- Close the bleeder screw. Release the brake pedal only AFTER the bleeder screw is closed.
- Repeat the procedure 4 or 5 times at each bleeder screw, then check the pedal for travel. If the pedal travel is not excessive, or has not been improved, enough fluid has not passed through the system to expel all of the trapped air. Make sure to watch the fluid level in the master cylinder reservoir. It must stay at the proper level so air will not re-enter the brake system.
Test drive the vehicle to be sure the brakes are operating correctly and that the pedal is solid.
NOTEConstantly check and refill the master cylinder. Do not allow the master cylinder to run dry.