Drum Brake Problems

[Wlee56]

I have a 1969 C-20 Longhorn with manual drum brakes and recently the pedal became very hard & had little to no travel. The brakes will not lock up and when you give the pedal all you can, fluid forces out the master cylinder cap.

I have replaced the proportioning valve and the short lines from the master, along with the front rubber lines and the rear rubber line. All 4 drums have been turned and new shoes have been installed. One wheel cylinder was leaking, so it was replaced. The system was bled and the problem still exists.

I'm thinking it must be the master cylinder as the lines flowed when we bled the system and didn't appear to be blocked.

Anyone have any thought on what this problem may be?

[custom10nut]

You're on the right track. I would say something corroded. Master Cylinders are not expensive, and since you replaced everything else, do that too.

[saxart]

I'd say you have some wheel cylinders that are rusting on the inside. Mine exhibited the same symptoms, then started to leak so I replaced what looked like new cylinders. I pulled them apart once the job was done to see what was going on inside, and they were coated in a crystal rust. Locked them up tight!

If it were my truck, I'd replace the 3 remaining wheel cylinders. They're not bad in cost, just not fun to replace.

[Ironangel]

I agree with replacing the master cylinder "and" the three remaining wheel cylinders...Be ready to replace some brake lines as well, "Kroil" is your friend on those rusted fittings... https://www.amazon.com/Kano-Aerokroi...SP94ZXQMJJ721K