See Figure 1
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. You will need an assistant for this procedure.
Old brake fluid is often the cause of spongy brakes returning a week or so after bleeding the system. If all parts are OK, change the fluid by repeated bleeding.
- Raise and support the vehicle securely. Your assistant should remain in the vehicle to apply the brake pedal when needed.
- The sequence for bleeding is right rear, left front, left rear and right front. If the car has power brakes, bleed the vacuum by applying the brakes several times. Do not run the engine while bleeding the brakes.
- Clean all the bleeder screws. You may want to give each one a shot of penetrating solvent to loosen it up. Seizure is a common problem with bleeder screws. They can break off, usually requiring replacement of the part to which they are attached.
- Fill the master cylinder with DOT 3 brake fluid.
Brake fluid absorbs moisture from the air. Don't leave the master cylinder or the fluid container uncovered any longer than necessary. Be careful handling the fluid, it eats paint.
Check the level of the fluid often when bleeding, and refill the reservoirs as necessary. Don't let them run dry, or you will have to repeat the process.
- Attach a length of clear vinyl tubing to the bleeder screw on the wheel cylinder. Insert the other end of the tube into a clear, clean jar half filled with brake fluid.
- Have your assistant slowly depress the brake pedal. As this is done, open the bleeder screw 1 / 3 - 1 / 2 of a turn and allow the fluid to run through the tube. Close the bleeder screw before the pedal reaches the end of its travel. Have your assistant slowly release the pedal. Repeat this process until no air bubbles appear in the expelled fluid.
- Repeat the procedure on the other brakes, checking the level of fluid in the master cylinder reservoir often.
After you're done, there should be no sponginess in the brake pedal. If there is, either there is still air in the line, (in which case the process should be repeated) or there is a leak somewhere, (which of course must be corrected before the car is moved).
- Lower the vehicle.