Brake hydraulic system — bleeding
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 hose, line, caliper or master cylinder.
When to bleed the brake system
1. If air has entered it due to low fluid level.
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.
Bleeding procedure
4. Remove any residual vacuum (vacuum booster) or pressure (hydraulic booster) from the power brake booster by applying the brake several times with the engine off.
5. Remove the master cylinder reservoir cap 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 screws.
7. Beginning at the right rear wheel, (farthest brake from the master cylinder) loosen the bleeder valve 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 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 depress the brake pedal slowly and hold it in the depressed position.
Note: Good communication between you and your helper is essential during this process. Make sure both of you can hear each other before attempting this procedure.
10. While the pedal is held down, open the bleeder valve just enough to allow a flow of fluid to leave the screw. Watch for air bubbles to exit the submerged end of the tube. When the fluid flow slows after a couple of seconds, close the valve and then have your assistant release the pedal.
11. Repeat above steps until no more air is seen leaving the tube, then tighten the bleeder screw securely and proceed to the left rear wheel, the right front wheel and the left front wheel, in that order, and perform the same procedures again. Be sure to check the fluid in the master cylinder reservoir frequently.
Warning: Never use old brake fluid or a bottle of brake fluid that has been left open for a long time. Brake fluid is hydroscopic, meaning it will attract moisture. Moisture in the brake fluid will cause the fluid to boil under heavy braking conditions and render the brake system inoperative.
12. Refill the master cylinder with fluid at the end of the operation.
13. Check the operation of the brakes. The pedal should feel solid when depressed, with no sponginess. If necessary, repeat the entire process.
14. Before driving the vehicle, sit in the driver’s seat and perform the following test:
a) Take your foot off the brake pedal
b) Start the engine and let it run for a minimum of 10 seconds. Watch the amber ABS light on the dash.
c) If the light comes on and does not turn off after 10 seconds, have the vehicle towed to a dealer service department or other qualified repair shop. A scan tool will have to be used to bleed and/or diagnose the ABS system.
d) If the ABS light goes off after three seconds or so, turn off the ignition.
e) Repeat the above steps one more time. If the ABS light turns off, test drive the vehicle in an isolated area before returning the vehicle to normal service.
Warning: Do not operate the vehicle if you’re in doubt about the effectiveness of the brake system.