Automotive brake systems operate using hydraulic pressure. The lines circulate brake fluid, which operates pistons in the brake assemblies. If air enters this closed system, the brakes will not function correctly. If you perform repairs on brake components that require you to disconnect the brake lines, or if you allow the fluid in the brake master cylinder to fall too low, you will need to bleed the brakes to remove air. Though the location of components will vary depending on the make and model of the vehicle, the basic procedure remains the same.
Instructions
- 1
Open the hood and clean the master cylinder and master cylinder cap. Most master cylinders are marked "Brake Fluid Only" and are a metal or plastic container. They are usually located on the driver's side of the engine compartment, near the firewall. Open the cap (you'll probably want to do this with a rag in your hand) and check the fluid level in the master cylinder. If it is below the "Full" mark, add brake fluid as specified by your vehicle's owner's manual. Close the cap.
2Loosen the lug nuts on all the wheels using your vehicle's lug nut wrench. Raise the car and support all four wheels with a jack stand. Place the jack stands below the lower control arms on the front wheels, and the axle on the rear wheels. Raise the stands until they contact the vehicle, and slowly lower the jack until the weight rests on the jack stands. Finish removing the lug nuts, and take off all the wheels. If you have only a single jack stand, you can bleed one brake assembly at a time, although it will take considerable longer.
3Locate the bleeder valve on the brake caliper, revealed when you remove the wheel. It is a small valve with a nut, usually covered by a rubber dust cap. Once you locate the bleeder valve, attach the tubing by sliding it over the valve and place the other end in a container to catch draining fluid. The tubing makes it easier to direct the flow of the leaking brake fluid.
4Direct an assistant to enter the vehicle and pump the brake pedal until the pedal is hard, and to then keep the pedal depressed. Open the bleeder valve using a wrench and allow the air to escape. Close the valve and direct the assistant to repeat the pumping procedure. Open the valve again, and close it when the air has escaped. Repeat this step until only brake fluid escapes from the valve when you open it. Remove the tubing and replace the dust cap.
5Recheck the master cylinder and add brake fluid if necessary.
6Repeat the procedure on the three other brake assemblies, checking the fluid level in the master cylinder each time.
7Replace the wheels and lug nuts. Raise the car with the jack until you can remove the jack stands, and lower the car. Fully tighten the lug nuts with the lug wrench.
