Re: Locking brakes.

Posted by HH56 On 2009/1/25 17:59:08

A flush certainly wouldn't hurt but unless you found chunks of sediment on your rebuild, probably wouldn't help either.

The residual valve is designed to keep 5-10psi in cylinders so rubber cups stay flat to pistons and lips against cylinder wall. Only thing I could see failing is if the rubber has been contaminated with petroleum product and is swelling with heat or the retainer has been smashed down and totally blocking the outlet. Would think there would be some indication when applying brakes that something was wrong if that the cause. Easy enough to remove the fitting and pull it out to check condition--unfortunately not something to be done on the fly and means bleeding brakes again.

Brian mentioned the vacuum portion. There are any number of things that could go wrong there. Another easy thing to do when fails is to pull off the vacuum line to brake. With no vacuum, that would eliminate that part and the pedal would be free to move if the vacuum were partially applying. Of course, something could also be jamming the power piston such as fluid which has leaked in, corrosion or mechanical damage. As I recall, there is not much clearance between the power piston and the plate covering the cylinder end under the toe board. Any chance something has gotten into the opening and preventing full travel. At any rate, sure sounds like something needs to be professionally gone thru.