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System Bleeding

Q:   How do I bleed the system when installing brake calipers, lines and hoses?

A:  Always bench bleed the master cylinder first (see above), then the system. Make sure all calipers have bleed screws facing upwards to fully evacuate air from the system. Wilwood calipers with internal fluid passages and four bleed screws (two on each end) require only the upward facing bleed screws to be bled. Start bleeding the bleed screw farthest from master cylinder (typically the right rear caliper outboard half), and work towards the one nearest the master cylinder.

The most common method to bleed a system is to manually pump the pedal. This process is as follows: Pedal bleeding requires two people; one person pumps the pedal, and the other operates the bleed valves. First, connect a plastic hose to the valve on the outboard body bleed screw farthest away from the master cylinder. Submerge the other end of the hose in a container of brake fluid to ensure that no air is siphoned back into the system. Have the person in the vehicle depress the pedal and hold it at the floor. With the pedal on the floor, the person at the caliper should open the bleed screw 1/4 of a turn to allow the accumulated air and fluid to evacuate. Once the air and fluid have stopped flowing out of the bleeder valve, close it. Now, the person in the vehicle should slowly pump the pedal to refill the calipers with fluid. Once a firm pedal has been achieved, the pedal operator should depress the pedal and hold it, repeating the above sequence. Make sure that the reservoir of the master cylinder does not run out of fluid, as this will introduce air into the system. Continue in this manner until all calipers are bled on both the inboard and outboard bleed screw. You may have to repeat the process for optimal results. Three other methods to bleed a system are gravity, pressure and vacuum.

Wilwood Engineering, Inc
4700 Calle Bolero
Camarillo, CA 93012
Phone: (805) 388-1188
Fax: (805) 388-4938

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