I have installed a new master cylinder on my 1939 plymouth Deluxe and the brake still comes on and the brake lock. I adjusted the piston rod adjusted when I had the old master on and brake light and brakes locked up. I adjusted the piston rod back to the previous mark when I installed the new master cylinder. Any suggestions what I should do to correct this problem. Frustrated.
I have not had this problem soI am just guessing. If u leave it a while do the brakes loosen up? There is a little one way valve on the MC piston-is it in the right orientation? Are the return springs on the shoes catching? With a new or rebuilt MC one would assume the little holes in the bottom of the resevoir are open.
any other things u might have noticed?
I had a similar problem a year or so ago with one of my 41's. I just received back from White Posts Restorations, my master and all four wheel cylinders.
After a few miles down the road, my pedal would keep creaping up on me, and within a few moments, I was locking up.
After many adjustments like the ones you discribed, I talk to Billy at White Posts.
Seeing that now they test their rebuilds with air, and not fluid, I told them I was going to return my master to them for inspection because I was simply at wits end, and had over 12 hours trying to fix.
Turns out that there was a small burr in the master. Once this was removed it worked as it should and no problems have yet to happen. Hope that this helps. I feel your pain!
What kind of brake fluid are you using? Had a new master cylinder installed on my 54 NY wagon a few years ago, using silicone brake fluid - after driving around on a hot day for an hour or so, my brake pedal did as yours did - took it to a local shop specializing in brakes - the guy told me that the silicone fluid I had used caused pressure to build up in the system - he flushed it out, replaced it with non-silicone fluid - I never had any more problems long as I owned the car - I'm sure there are legions of people who have never had a problem with silicone fluid who are going to say I don't know what I'm talking about - maybe they are right - I'm just relating my experience
Check out the relief port (1.) or compensating hole in this illustration and it's relationship to the piston, I've seen them sleeved and the hole not drilled and also assembled incorrectly or with the wrong parts so the piston is blocking the hole in the relaxed position causing this condition.
(https://www.plymouthowners.club/talk/proxy.php?request=http%3A%2F%2Fhomepages.slingshot.co.nz%2F%7Eanwylie%2Fute%2FMCylinder.jpg&hash=c38afcae064b1f3da34a8858d22338b2cd60f549)
Bleeding or priming it on the bench will usually pick up these sort of problems.
if all else fails, definitly pop off your drums and have a look at your return springs. I was having trouble getting the car moving, so I jacked up each corner and tried to manually turn each wheel. My drivers side front tire wouldn't budge rolling forward (but I could rotate it backwards..), so I popped off the drum to discover that both springs had snapped in half.
Another possibility is a collapsed rubber brake hose. Sometimes they look OK on the outside, but they collapse when you take your foot off the brake, and do not allow the shoes to retract.