Got a Guy with a 36 Chevy Deluxe Coupe. Stock braking system. After driving for a while say maybe 5 miles both front and rear Brakes lock up. We figure fluid gets behind the piston in the master and prevents the piston from retracting? According to his manual there is a 'weep hole' and a adjustment of some .030 that is suppose to maintain. We don't quite understand. I don't believe there should be any fluid behind that piston if the 'O' Ring and bore are correct.
The .030 clearance is referring to the distance between the pushrod and the master cylinder piston when the brakes are released. If that clearance is lost due to a sticky pedal, mis-adjustment, or lack of a return spring and the return of the piston is restricted, the brakes will not release. Sometimes the bore of the master will become corroded at the open end and restrict the piston returning fully. It is also possible the compensating port inside the master is plugged. You can usually see this thru the cap unless the fluid is really murky. I would check the pedal is free and returning fully and that there is actual clearance that you can feel between the pushrod and piston first of all. If that is OK, then look at the master cylinder.
Surprised only one response so far. Where are all the Antique Chevy Experts? Bore size, Scuffed 'O' ring? Any Body have links to Master Cylinders for this coupe or Rebuilders
The one response covered the situation pretty well. Might want to do what he suggested, and look at the master cylinder. Yeah, it's a bitch to get to, but you might be able to figure out what's wrong and fix it.
Have Huck brakes on my 49. About 20 years ago I found a NOS master cylinder at NAPA. I was not having issues with the master but thought I should do a complete brake rebuild. I am approaching 75,000 miles without problems except the filler cap was pretty much frozen in place. I had to remove the transmission cover to access the cap horizontally to get a grip. I do doing I damaged the two tabs on the top. Another point I am sure you know about is converting the front Huck brakes to the bigger Bendix is a very simple job.
We did that, car up on a lift @ Kustoms Unlimited. Not really hard to get to. two bolts , brake line and cotter pin and it's out. Maybe found a bit of crap in the master blocking the weep hole. Anyway cleaned it all up rebled the system drove it for a while same thing. Don't know why there should be crap in the line? I'm tending to think 'O' ring or bore size, piston out of spec? No information on what those spec's should be.
How old are the rubber hoses in the system? and the wheel cylinders? how much pedal free play does it have?
I'm OK with nostalgia except for when it comes to brakes, the owner really should update his car to the safer and more effective Bendix system. Now to the problem; if everything is fine in the garage but after a few miles on the road the brakes lock up, without pictures to go on I'd say the exhaust is too close to a brake line or the master cylinder, in other words after a mile or so heat is causing the brake fluid to expand, applying the brakes.
If the system is working properly, the expanding fluid will be let back into the reservoir by that little hole. But if the hole is plugged or covered by the cup because there's no free play, then pressure will indeed build in the lines.
Squirrel you might have just jared a thought in my head. I will tell the owner and I will also check it with him that little bleed hole is not being covered when this whole thing is assembled. I'll keep ya posted
This Brake issue started with a leaking wheel cylinder. They have been replaced, bled and working properly for a while. then this issue with the wheels locking up started.
All I can tell you is the stock MC works great with later Bendix units front and rear. 1962 Corvette in front and 57 Pontiac in the rear.
Squirrel, FYI, the brakes locking up problem was on my '63 Chevy long bed that had been "late modeled", in the build the metering valve was mounted directly across from the downward dump on the exhaust manifold the problem being after a few blocks that metering valve would heat soak and the front brakes would lock up. If I "bled" the front calipers I could get the truck to move until I applied the brakes again, the solution was to move the metering valve to the front crossmember below the radiator where it got some cooling air. 1940 willys, from what you've said so far everything worked fine until you fixed it meaning it's time for you to take the entire brake system apart to check/rebuild/replace everything as needed. just keep going, you'll get it eventually.
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