How to Bleed the Master Cylinder Without Removing it From a Car

by Jeffrey Caldwell

Rich Ellgen/Demand Media

Bleeding the master cylinder and brake lines is the process of removing air from the hydraulic lines. Brake bleeding is one of the most important things you can do to ensure the proper operation of your brakes and the safe operation of your vehicle. Air bubbles in the brake lines will decrease the amount of force the brake pedal applies to the brake pad or shoe at each wheel. Air bubbles will also make the brake pedal feel “spongy,” meaning when you press the brake pedal down, little or no braking force will be felt by the driver.

Bleeding the Master Cylinder

Step 1

Remove the master cylinder cover and top off the reservoir with fresh brake fluid. Make sure the reservoir does not run dry at any point in the bleeding process.

Step 2

Attach a length of clear plastic tubing to the bleeder valve on the master cylinder.

Step 3

Immerse the other end of the clear plastic tube in a plastic or glass container half full with fresh brake fluid. Make sure the end of the tube stays covered with brake fluid at all times during the bleeding process.

Step 4

Have an assistant working inside the vehicle pump the brake pedal a few times, then hold it down.

Step 5

Open the bleeder valve. As brake fluid flows through the clear plastic tube, the assistant will notice the brake pedal falling towards the floor. Close the bleeder valve before the pedal reaches the floor.

Step 6

Repeat the process described above, and pay attention to the fluid flowing the clear plastic tube. Initially you will see small air bubbles in the line. Repeat the process until there are no bubbles in the line.

Bleeding the Brake System

Step 1

After you’ve finished bleeding the master cylinder, or if your master cylinder is not equipped with a bleeder valve, check and see if there is a bleeder valve on the proportioning valve just below the master cylinder. Bleed this valve using the process listed above for the master cylinder.

Step 2

If there is no bleeder valve on the proportioning valve, or your vehicle is not equipped with a proportioning valve, bleed the calipers or wheel cylinders at each wheel. Begin by raising the vehicle and support with jack stands placed underneath the frame.

Step 3

Remove the wheels and tires.

Step 4

Move to the wheel closest to the master cylinder. On most vehicles, this will be the left front. Bleed the bleeder valve on the back of the caliper using the technique listed above.

Step 5

Move to the wheel next closest to the master cylinder. On most vehicles this will be the right front. Bleed using the same process used on the master cylinder.