The Stovebolt Site Forums The Shop Area Driveline 1949 - 3800 - Brakes build pressure, wont release

Hello. New here. I tried searching but couldn't find an answer to this particular problem.

As I drive this truck, especially around town with frequent stops, the brakes will eventually lock up and make the truck unmovable. After a couple hours they release enough that I can load it load it on a trailer although they're still dragging a bit. Then after a day or so, they are fully released and free again.

Master cylinder was replaced in 2013 then the truck sat for a few years. Had some restoration work done on the body/interior that took a couple years and the truck wasn't driven. Finally got to driving it last summer when this started happening. Midas replaced all 4 wheel cylinders...had the same problem. A different shop just replaced the two front rubber hoses....still have the same problem. Hand brake works and seems to release. Seems to have proper free play in the pedal. With the truck on jack stands all 4 wheels are free spinning....Pump the brakes a few times and I can feel just a bit of pressure build in the pedal, and all 4 wheels then have a definite drag to them.

Leaning towards replacing the master cylinder again, or is this a situation of the drums not being set too tight to start with. They spin free, but do they need a couple extra clicks out?

I've got this scheduled to go into a different shop in a few weeks. This shop is much more familiar with older cars/trucks/hot rods so I'm hoping they can pinpoint the problem. Any help resolving this before then would be appreciated.

Sounds like it could be a hose not allowing fluid to return. You indicated two front hoses have been replaced there is one more on the rear axle.

When the master cyl was replaced back in 2013, was the truck driven to test the brakes before it was taken off the road?

Hy Justin726, welcome, it sounds to me like the master cylinder piston is not being allowed to return to its fully at rest position. Check the linkage under the truck to make sure there is some clearance in the linkage that must be taken up before the master cylinder piston actually moves. As others have suggested the flexible line from the frame to the rear axle brakes should also be replaced for age if no other reason. Hope that helps.

When adjusting the plunger on my dual-reservoir MC, 1/4 turn with those fine threads can make the difference or mine would do the same thing.

Thanks for the help/suggestions guys. Going to start with the master cylinder and correct adjustments on it since the problem seems to be affecting all 4 wheels.

I just got done removing and disassembling a master cylinder in my '49 3100. My truck was suffering the same symptoms as yours.
Decent feeling pedal.
Nearly no braking action.
Brakes lock up and won't release right away.
Here is what I found inside of the master cylinder.
Varnish plugging the tiny compensating port hole which goes between the fluid reservoir and the main cylinder. I can shine a light from inside of the main cylinder and see it shining through the varnish. I sprayed some Gun scrubber solvent in the in the reservoir and it refuses to go through that hole.
As soon as I can find my welding tip cleaner tool I will open up that blockage and reassemble and see how it goes.
This is a very low mileage master cylinder. Seems like you get a 50-50 chance to get a new one which works.