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Posted by john copeman ontario can. on Sunday, February 03, 2008 at 18:15:41 :
In Reply to: W500 brakes locked up posted by JerryinIdaho on Sunday, February 03, 2008 at 14:16:50 :
IF MEMORY severs me correct some of these trucks have a hydo- vac unit under the cab which is like another master cylinder thats were the vacum from the engine is (sent) from the storage canisters (it acts like the booster on the fire wall of a modern car)and this thing looks like another master cylinder with a booster sometimes mounted in the frame if you have one you cant miss it they will do two things give you a hard pedal and no assist or just lock on ,it could be frozen but they were a big issuse in brake probs way back when. IF YOU DO NOT HAVE a hydro vac a check valve in the master cylinder is at fault test with a presure guage static 4 to 6 psi and standing on the brake pedal at a wheel cylinder (engine running) booster working 1600 psi and when yo release the brakes pressure should drop tp 4 to 5 psi residual
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