How to Bleed Air from Brake Lines: A Comprehensive Guide
Air in your brake lines can be a serious safety hazard. It can cause a spongy brake pedal, reduced braking power, and even complete brake failure. Bleeding your brakes is the process of removing air from the brake lines. This is a relatively simple process that can be done at home with a few basic tools.
Why Do Brake Lines Need Bleeding?
Brake systems are hydraulic, meaning they use fluid pressure to transmit force. When you press the brake pedal, it pushes a piston in the master cylinder, which in turn forces brake fluid through the brake lines to the calipers at each wheel. The calipers then clamp down on the brake rotors, slowing or stopping the vehicle.
Air, unlike brake fluid, is compressible. If air enters the brake lines, it will compress when you press the brake pedal, reducing the amount of pressure that is transmitted to the calipers. This can lead to a spongy brake pedal, reduced braking power, and in extreme cases, complete brake failure.
Air can enter the brake lines in a number of ways, including:
- Low Brake Fluid: If the brake fluid level in the master cylinder gets too low, air can be drawn into the system.
- Leaking Brake Lines or Calipers: Leaks in the brake lines or calipers can allow air to enter the system.
- Brake System Work: Whenever you open the brake system, such as when replacing brake pads or calipers, air can enter the lines.
- Old Brake Fluid: Over time, brake fluid can absorb moisture from the air. This moisture can boil when the brakes get hot, creating air bubbles in the system.
When to Bleed Your Brakes
You should bleed your brakes whenever you suspect that air has entered the brake lines. Some common symptoms of air in the brake lines include:
- Spongy Brake Pedal: The brake pedal feels soft or spongy when you press it.
- Reduced Braking Power: It takes longer to stop the vehicle than usual.
- Brake Pedal Goes to the Floor: The brake pedal goes all the way to the floor when you press it.
- ABS Light On: The ABS (anti-lock braking system) light may come on if there is air in the brake lines.
- After Brake Work: Always bleed your brakes after any brake work, such as replacing brake pads, calipers, or brake lines.
Tools and Materials You’ll Need
Before you start bleeding your brakes, you’ll need to gather the following tools and materials:
- New Brake Fluid: Use the type of brake fluid recommended in your owner’s manual. Do not mix different types of brake fluid.
- Wrench: A wrench that fits the bleeder screws on your brake calipers.
- Clear Plastic Tubing: A length of clear plastic tubing that will fit snugly over the bleeder screws.
- Catch Container: A container to collect the old brake fluid.
- Jack and Jack Stands: To safely lift and support the vehicle.
- Wheel Chocks: To prevent the vehicle from rolling.
- Gloves and Eye Protection: To protect your hands and eyes from brake fluid.
- Brake Bleeder Kit (Optional): A brake bleeder kit can make the job easier, especially if you are working alone.
Safety Precautions
Brake fluid is corrosive and can damage paint and other surfaces. Wear gloves and eye protection when working with brake fluid. If brake fluid gets on your skin, wash it off immediately with soap and water.
Bleeding Procedure
There are several methods for bleeding brakes, but the most common is the two-person method. This method requires one person to pump the brake pedal and the other to open and close the bleeder screws.
Here’s how to bleed your brakes using the two-person method:
- Prepare the Vehicle: Park the vehicle on a level surface and engage the parking brake. Use wheel chocks to prevent the vehicle from rolling.
- Lift the Vehicle: Use a jack to lift the vehicle and support it with jack stands. Make sure the vehicle is stable before proceeding.
- Locate the Bleeder Screws: Locate the bleeder screws on the brake calipers. These are small screws that are usually located on the back of the caliper.
- Prepare the Bleeder Screw: Attach the clear plastic tubing to the bleeder screw. Place the other end of the tubing in the catch container.
- Check the Master Cylinder: Make sure the brake fluid reservoir in the master cylinder is full. Add brake fluid as needed.
- Start Bleeding: Have someone sit in the driver’s seat and pump the brake pedal several times, then hold it down.
- Open the Bleeder Screw: While the brake pedal is held down, open the bleeder screw slightly. You should see brake fluid and air bubbles flowing through the tubing.
- Close the Bleeder Screw: Close the bleeder screw before the brake pedal reaches the floor.
- Release the Brake Pedal: Have the person in the driver’s seat release the brake pedal.
- Repeat: Repeat steps 6-9 until no more air bubbles come out of the bleeder screw.
- Tighten the Bleeder Screw: Once you are finished bleeding the brake, tighten the bleeder screw to the manufacturer’s specifications.
- Repeat for Other Brakes: Repeat the process for the other brakes, starting with the brake farthest from the master cylinder. The typical bleeding order is:
- Right Rear
- Left Rear
- Right Front
- Left Front
- Check the Brake Fluid Level: Check the brake fluid level in the master cylinder and add fluid as needed.
- Test the Brakes: Once you have finished bleeding all of the brakes, test the brakes by pumping the brake pedal several times. The brake pedal should feel firm and solid.
- Take a Test Drive: Take the vehicle for a test drive to make sure the brakes are working properly.
Using a Brake Bleeder Kit (One-Person Method)
If you are working alone, you can use a brake bleeder kit. There are several types of brake bleeder kits available, but they all work on the same basic principle: they create a vacuum or pressure that draws the brake fluid through the brake lines.
Here’s how to bleed your brakes using a brake bleeder kit:
- Prepare the Vehicle: Park the vehicle on a level surface and engage the parking brake. Use wheel chocks to prevent the vehicle from rolling.
- Lift the Vehicle: Use a jack to lift the vehicle and support it with jack stands. Make sure the vehicle is stable before proceeding.
- Locate the Bleeder Screws: Locate the bleeder screws on the brake calipers. These are small screws that are usually located on the back of the caliper.
- Prepare the Bleeder Screw: Attach the clear plastic tubing to the bleeder screw. Place the other end of the tubing in the catch container.
- Check the Master Cylinder: Make sure the brake fluid reservoir in the master cylinder is full. Add brake fluid as needed.
- Connect the Brake Bleeder Kit: Connect the brake bleeder kit to the bleeder screw according to the manufacturer’s instructions.
- Create a Vacuum or Pressure: Create a vacuum or pressure using the brake bleeder kit.
- Open the Bleeder Screw: Open the bleeder screw slightly. You should see brake fluid and air bubbles flowing through the tubing.
- Close the Bleeder Screw: Close the bleeder screw when no more air bubbles come out of the bleeder screw.
- Disconnect the Brake Bleeder Kit: Disconnect the brake bleeder kit from the bleeder screw.
- Tighten the Bleeder Screw: Tighten the bleeder screw to the manufacturer’s specifications.
- Repeat for Other Brakes: Repeat the process for the other brakes, starting with the brake farthest from the master cylinder.
- Check the Brake Fluid Level: Check the brake fluid level in the master cylinder and add fluid as needed.
- Test the Brakes: Once you have finished bleeding all of the brakes, test the brakes by pumping the brake pedal several times. The brake pedal should feel firm and solid.
- Take a Test Drive: Take the vehicle for a test drive to make sure the brakes are working properly.
Tips for Bleeding Brakes
- Use the Right Brake Fluid: Use the type of brake fluid recommended in your owner’s manual.
- Don’t Let the Master Cylinder Run Dry: Keep an eye on the brake fluid level in the master cylinder and add fluid as needed. If the master cylinder runs dry, you will have to bleed the entire brake system again.
- Use a Clear Plastic Tubing: Use a clear plastic tubing so you can see the air bubbles flowing through the tubing.
- Tighten the Bleeder Screws: Tighten the bleeder screws to the manufacturer’s specifications.
- Dispose of Old Brake Fluid Properly: Brake fluid is hazardous waste and should be disposed of properly. Check with your local waste management agency for disposal instructions.
Conclusion
Bleeding your brakes is a relatively simple process that can be done at home with a few basic tools. By following these steps, you can remove air from your brake lines and restore your brakes to their proper working condition. Remember to prioritize safety and take your time to ensure the job is done correctly. If you are not comfortable bleeding your brakes yourself, you should take your vehicle to a qualified mechanic.
