Brake hydraulic system – bleeding
Warning: The following procedure is a manual bleeding procedure. This is the only bleeding procedure which can be performed at home without special tools. However, if air has found its way into the hydraulic control unit, the entire system must be bled manually, then with a scan tool, then manually a second time. If the brake pedal feels spongy even after bleeding the brakes, or the ABS light on the instrument panel does not go off, or if you have any doubts whatsoever about the effectiveness of the brake system, have the vehicle towed to a dealer service department or other repair shop equipped with the necessary tools for bleeding the system.
Warning: Wear eye protection when bleeding the brake system. If the fluid comes in contact with your eyes, immediately rinse them with water and seek medical attention.
Note: Bleeding the hydraulic system is necessary to remove any air that manages to find its way into the system when it’s been opened during removal and installation of a hydraulic component
1. It will be necessary to bleed the complete system if air has entered the system due to low fluid level, or if the brake lines have been disconnected at the master cylinder.
2. If a brake line was disconnected only at a wheel, then only that caliper must be bled.
3. If a brake line is disconnected at a fitting located between the master cylinder and any of the brakes, that part of the system served by the disconnected line must be bled. The following procedure describes bleeding the entire system, however.
4. Remove any residual vacuum (or hydraulic pressure) from the brake power booster by applying the brake several times with the engine off.
5. Remove the cap from the master cylinder reservoir and fill the reservoir with brake fluid. Reinstall the cap. Note: Check the fluid level often during the bleeding operation and add fluid as necessary to prevent the fluid level from falling low enough to allow air bubbles into the master cylinder.
6. Have an assistant on hand, as well as a supply of new brake fluid, a clear container partially filled with clean brake fluid, a length of clear tubing to fit over the bleeder valve and a wrench to open and close the bleeder valve.
7. Beginning at the right rear wheel, loosen the bleeder screw slightly, then tighten it to a point where it’s snug but can still be loosened quickly and easily.
8. Place one end of the tubing over the bleeder screw fitting and submerge the other end in brake fluid in the container (see illustration).
9.8 When bleeding the brakes, a hose is connected to the bleed screw at the caliper and submerged in brake fluid – air will be seen as bubbles in the tube and container (all air must be expelled before moving to the next wheel)
9. Have the assistant slowly depress the brake pedal and hold it in the depressed position.
10. While the pedal is held depressed, open the bleeder screw just enough to allow a flow of fluid to leave the valve. Watch for air bubbles to exit the submerged end of the tube. When the fluid flow slows after a couple of seconds, tighten the screw and have your assistant release the pedal.
11. Repeat Steps 9 and 10 until no more air is seen leaving the tube, then tighten the bleeder screw and proceed to the left rear wheel, the right front wheel and the front left wheel, in that order, and perform the same procedure. Be sure to check the fluid in the master cylinder reservoir frequently.
12. Never use old brake fluid. It contains moisture which can boil, rendering the brake system inoperative.
13. Refill the master cylinder with fluid at the end of the operation.
14. Check the operation of the brakes. The pedal should feel solid when depressed, with no sponginess. If necessary, repeat the entire process. Warning: Do not operate the vehicle if you are in doubt about the effectiveness of the brake system. It is possible for air to become trapped in the anti-lock brake system hydraulic control unit, so, if the pedal continues to feel spongy after repeated bleedings or the BRAKE or ANTI-LOCK light stays on, have the vehicle towed to a dealer service department or other qualified shop to be bled with the aid of a scan tool.