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 leaking. You will need a helper for this job.
The customary procedure is to start with the wheel farthest away from the master cylinder and work in. In other words, right rear left rearright frontleft front.
- Clean the bleed screw at each wheel.
- Attach a small rubber hose to one of the bleed screws and place the end in a container of brake fluid.
- Fill the master cylinder with brake fluid. Check the level often during bleeding. Pump up the brake pedal and hold it.
- Open the bleed screw about one-quarter turn, press the brake pedal down and hold it, close the bleed screw, and slowly release the pedal. Continue until no more air bubbles are forced from the cylinder on application of the brake pedal.
- Repeat the procedure on the remaining wheel cylinders.
Disc brakes may be bled in the same manner as drum brakes, except that the disc should be rotated to make sure that the piston has returned to the unapplied position when bleeding is completed and the bleed screw closed.