How to Bleed the Brake Master Cylinder

Besides the brake lines, you need to bleed the brake master cylinder when you remove it for repairs to ensure proper operation. Most manufacturers include bleeding

instructions with their rebuilt or new units. But you can also use your hand-held vacuum pump.

Use the next steps as an alternative bench bleeding method to ready the brake master cylinder before you install it.

1.Get your vacuum pump ready by connecting the pump's reservoir jar with a piece of tubing. Then attach a length of tubing of the appropriate size to the reservoir jar; you'll need to connect the other end of the tubing to the master cylinder's ports, in turn, during the bleeding procedure. Use tubing and adapters of the appropriate diameter that come with your kit. (Usually, manufacturers include a couple of plastic tubes and plugs with their units for bleeding as well.)

2.Ask an assistant to hold the piece in place during the bleeding process with the push-rod end at a slightly higher angle than the opposite end. Or you can use a vise, but be careful not to damage the cylinder's body when securing it to the vise.

3.Fill the cylinder reservoir with new brake fluid. Use the fluid type recommended by your vehicle manufacturer. During the bleeding procedure, don't let the brake fluid reach bottom to prevent air from entering the cylinder; otherwise, you'll need to start the bleeding process all over again.

4.Unplug one of the cylinder ports and plug in the vacuum pump to it.

5.Pump the cylinder until you see brake fluid free of bubbles entering the pump's reservoir jar.

6.Disconnect the pump from the outlet port and tightly plug the port.

7.Repeat the bleeding procedure in the other port(s).

8.Now, with all the ports plugged, position the cylinder push-rod end at a slightly lower angle than the opposite end.

9.Then, use a Phillips screwdriver or a punch to slide the cylinder push rod in and out about 1/8 inches. Repeat until you see no bubbles in the master cylinder reservoir.

10.Raise the angle of the push-rod end again and bleed the cylinder again through the ports.

11.Now you can install your new brake master cylinder.