Howdy,

Im really hoping someone can help me out.

I have a 56 sunliner with a 292, 4 bbl, slightly bigger cam. Several years ago I added the "factory" power brake kit to it. This is the hydro vac booster that mounts to the inner fender and is plumbed in-line with the stock master cylinder.

It has worked ok; my cam doesn't pull enough vacuum to really make it great, but it helps and it looks cool.

However, about a year or so ago I disassembled parts of it to paint it to keep it looking great (too much time on my hands, I know). Shortly thereafter it developed a weird problem that has me stumped.

If I stand on the brakes, they wont release. They stay applied. However, if I shut the engine off, they will release. I tried replacing the one way vacuum check valve, and that didn't fix it. It happens fairly consistently.

The short term answer is to disconnect the vacuum line; I have done that and the brakes now work fine, and release properly. If I hook the vacuum line back up, same problem.

I really don't want to have to rip this thing out, ship it off, flush the brake lines, etc. if I don't have to. Anybody have any ideas where to start/what to look at? The shop manual was of little help

Thanks!

Ron Grove

Wauconda, IL

Could the one way valve be installed backwards?

Lou, thanks for the reply. No, the valve cant be installed backwards; its threaded on one end and has a hose barb on the other.

Ron Grove

Wauconda, IL

It may be related to what was disassembled. Reading from the ford service guide "brakes won't release with engine running", these are the possible causes:Residual pressure too high in master cylinder, Diaphragm housing dented or leaking, Control piston sticking, Hydraulic check valve sticking and the last cause, Control valve spring broken or weak.

Having the basic understanding of the power assist function will enable you to remedy the problem.

Pat