Hey guys, I have been working on the brakes of a 51 F5 truck. The front wheel cylinders looked fine so I left them. The rear axle seems to be out of a late 50's or 60's F600 and I replaced all 4 of the rear wheel cylinders. The master was fine but the Hydrovac booster was leaking and I replaced it with a new one out of a 58 F350 which is slightly larger but the same working unit as the original, it actually fit the original brackets. Now Im having an issue where the wheel cylinders will not release. I have checked the play in the master cylinder push rod and it is fine. What am I missing here?

 

I had a similar problem with my brakes. After trying everything else, I bypassed the booster and no more problem. Could your replacement booster be bad? If the booster is really good, you should check the relief valves. If you have a relief valve in the booster and also one in the MC, I have been told that that would cause the problem.

 

My F-5 did the same thing! had the booster re-built....same thing would not release.
Swapped the booster with another. worked great.

 

You can run into problems with the push rods being to long and holding the cylinders in an engaged position rather than allowing them to go back to rest .

 

I think I found the problem. The master and the booster had relief valves. Im installing a new master tomorrow for the hell of it and I swapped the original non-relief snout onto the new booster.