The hydraulic system must be bled whenever the pedal feels spongy, indicating that compressible air has entered the system. The system must be bled whenever any component has been disconnected or there has been a leak.
Brake fluid sometimes becomes contaminated and loses its original qualities. Old brake fluid should be bled from the system and replaced if any part of the hydraulic system becomes corroded or if the fluid is dirty or discolored.
- Clean off the top of the master cylinder and remove the cover. Check that the fluid level in each reservoir is within 1 / 4 in. of the top.
- Attach a 7 / 32 " inside diameter hose to the bleeder valve at the first wheel to be bled. Start at the wheel farthest from the master cylinder and work closer. Pour a few inches of brake fluid into a clear container and stick the end of the tube below the surface.
- Open the bleed valve counterclockwise 1 / 3 turn. Have a helper slowly depress the pedal. Close the valve just before the pedal reaches the end of its travel. Have the helper let the pedal back up.
- Check the fluid level. If the reservoir runs dry, the procedure will have to be restarted from the beginning.
- Repeat Step 3 until no more bubbles come out of the hose.
- Repeat the bleeding operation, Steps 3 to 5, at the other three wheels.
- Check the master cylinder level again.
- If repeated bleeding has no effect, there is an air leak, probably internally in the master cylinder or in one of the wheel cylinders.