Bleed Brake Lines
You are slowing down to stop at a traffic light only to find that your brakes are soft and the pedal is low. This could be a sign that air has crept into the brake lines. To fix this, it may be necessary to bleed your brakes. This is a two-man job that requires a coordinated effort. The result is a stiffer brake pedal and a more reactive braking system.
Contents
Steps
Getting Ready
- Confirm you need to bleed the brake lines. The sinking brake pedal often does mean the brake lines need to be bled. However, it is very important to confirm that the sinking pedal is not caused by something else.
- Try this simple test when you are stopped and waiting at a red light. With your foot, keep an even pressure on the brake pedal. Does the pedal sink lower, even a little bit? If so, then you should have your car's brake system inspected by an ASE Certified Master Auto Technician to confirm the root cause is not something else. If the pedal holds constant pressure, then there is no air in the system.
- A sinking brake pedal could also be caused by other things that could be very dangerous. For example, brake pedals can also sink if there is a hydraulic problem, like a failing master cylinder, a leaking rear wheel cylinder, a bad caliper or bad ABS. So it is important to rule out these dangerous possibilities via professional inspection before proceeding.
- Position your car on a flat surface. Cars with automatic transmissions should be in park and those with standard transmissions should be in first gear. The emergency (or parking) brake should be on at all times.
- Take off any hubcaps and raise the car and secure it on jack stands. Remove all four wheels.
- Release the hood and locate the Master Cylinder brake fluid reservoir. It's a fist size (or larger) transparent container that is bolted to the firewall on the driver’s side of the car. It will be connected to an aluminum object the has metal tubes coming out of its sides. These metal lines are the brake lines that direct the hydraulic brake fluid to your individual wheels. There the brake fluid activates either the disc or drum brake components that stop your car.
- Eliminate the old, dirty brake fluid that is present in the Master Cylinder Reservoir. Fill the Master Cylinder with fresh, clean brake fluid, making sure that it's the proper type for your car. If you have questions, ask the parts person to look up your car's brake fluid when you purchase it.
Bleeding the Brakes
- Go to the right rear wheel, wipe off any dirt from the brake bleeder screw area and remove its rubber dust cap. Using a box-end wrench, loosen the bleeder screw. Take a piece of rubber vacuum hose and put it on to the end of the bleeder screw and put the other end into an empty clear plastic bottle.
- Hold onto the box wrench while holding the plastic bottle. Have your partner pump the brakes slowly until the dirty fluid comes out of the brakes lines and into the bottle. Allow enough fluid to exit so that the end of rubber hose is submerged in brake fluid. (Check the Master Cylinder frequently to make sure there is plenty of brake fluid.)
- When the brake fluid becomes clear, direct your partner to hold the pedal to the floor. Close the bleeder screw with the wrench and have your partner pump the pedal 3 times and hold it. Open up the bleeder screw briefly to allow the brake fluid to exit the rubber hose. Have your partner tell you when the brake pedal is on the floor, and, have him/her keep it there while you close the bleeder screw. Repeat this process two more times. (Remember periodically check the Master Cylinder fluid level, so it does not go dry!) After the third time, tighten the bleeder screw and repeat this process on the other three wheels and, in this order; Left Rear, Right Front and Left Front.
- Depending on the vehicle, the bleeding procedure will vary in which wheel is bled first, second and so on. The above sequence will work for a large portion of vehicles, however you should check with a website like Alldata or similar to verify bleeding sequence.
- In order to make sure your brakes are not spongy and there aren't any leaks in the system, perform this test when your are finished bleeding the brakes. With the engine off, have your partner push down on the brake pedal and go around to all four wheels and check for leaks. Then, push the brake pedal with your foot. It should travel about {{safesubst:#invoke:convert|convert}} and stop. The brake pedal should feel very hard at this stopping point.
- Get rid of any surplus brake fluid in a proper and safe manner. Remember that brake fluid is considered hazardous waste and therefore should never be poured down the sink or toilet, onto the ground in your yard, in the garbage, or down the sewer drain or septic tank. Talk with your local auto shop or look for a household hazardous waste (HHW) recycling collection site.
Testing the Brakes
- Replace all four wheels and hand-tighten all the lug nuts. Lower the vehicle to the ground and properly torque the lug nuts. Replace the hub caps if necessary.
- Go for a test drive to verify that the brakes are functioning correctly. If there are still problems, have your car inspected by an ASE Certified Master Auto Tech.
Tips
- Always keep the brake fluid reservoir full.
- Follow proper safety procedures when jacking up a vehicle.
- Avoid brake fluid coming in contact with rubber or plastic materials.
- Bleed your vehicle’s brake lines every two years.
Warnings
- Do not release the brake pedal until the bleeder screw is closed.
- Dirt particles can contaminate brake fluid and cause brakes to fail.
- Brake fluid will melt your car’s paint.
- Only use the brake fluid that is recommended for your make and model vehicle.
Things You'll Need
- Jack stands
- Suction tool, such as a turkey baster
- Wrench (box)
- Brake fluid
- Clear plastic tubing
- Disposable waste container
- Soft cloth
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