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.
There are gadgets on the market to make it possible for one man to do this job. Usually they are a bleeder hose with a one-way check valve.
Start with the wheel closest to the master cylinder and work out. With disc brakes, the metering valve pin on the end of the combination valve must be held in slightly to allow fluid flow to the front brakes.
- Clean the bleeder screw at each wheel.
- Attach a length of hose to the bleeder screw and submerge the end in a container of clean brake fluid.
- Fill the master cylinder with brake fluid.
Brake fluid picks up moisture from the air. Don't leave the master cylinder or the fluid container uncovered any longer than necessary. Never reuse brake fluid which has been taken from the brake lines. Always use new fluid. Also, be very careful not to spill any brake fluid on any painted surface. It eats paint.
Check the level often during bleeding.
- Pump up the pedal and hold it.
- Open the bleeder screw about 3 / 4 turn. Have your helper press down on the pedal. Close the bleeder screw before the pedal reaches the end of its travel. Have your helper slowly release the pedal. Continue until no more air bubbles are forced out on application of the pedal.
- Repeat the procedure on the remaining three brakes.
It sometimes helps to tap the disc brake caliper with a soft hammer while fluid is flowing when bleeding the front disc brakes.