Tips From Wil­wood Bleed­ing Brakes

Street Rodder - - Shop Manual -

Al­ways bench bleed the mas­ter cylin­der first (see above), then the sys­tem. Make sure all calipers have bleed screws fac­ing up­ward 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 to­ward 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 a quar­ter 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.

♦ Elec­tronic brake fluid testers are avail­able at many parts houses and on­line. They run around $25 and up. There are a va­ri­ety of ways to de­ter­mine if brake fluid is con­tam­i­nated, the most in­ex­pen­sive method is test strips that in­di­cate the amount of...

♦ Bleed­ing brakes man­u­ally is nor­mally a two-per­son op­er­a­tion; bleed­ing with a vac­uum pump can be done by one.

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