1981 longbed with a 1987 rear axle, LC front rotors, S12W front calipers. Yesterday I replaced my rear wheel cylinders because they were leaking (Dorman garbage), and my master cylinder while I was at it. The original master was a 13/16" bore, and the brakes were strong but the pedal was too soft after the LC/V6 front upgrade. I don't know if it was leaking internally or not, but I got a NOS OEM 1" master. Bled the brakes, adjusted the rear shoes, and they felt great. Drove a few blocks home, no problem.

Today I go on a drive and after a while I notice the brakes are dragging pretty bad. Jack up the rear axle - yep, hard to turn. Jack up the front axle - impossible to turn by hand. Thinking that it was just the pushrod not being adjusted right, I disconnect the master from the booster, swing it well clear of the pushrod... and the front wheels, still off the ground, are still stuck. I look at the back side of the master, and see no leaks and the piston in its "home" position

Just in case, I shortened the pushrod a little, reinstalled the master, cracked the flare fittings loose to bleed off excess pressure, and continued on my drive... only to have the same thing happen a few miles later. I think it only happens after I actually use the brakes, not spontaneously.

This master sat on a shelf for a while (years? decades?) before I bought it. While it doesn't leak internally or externally, I suspect the bores are sticking. Thing is, while bench-bleeding it, the return spring felt quite strong and smooth.

Any ideas before I go cough up 90 bucks for another master?

 

I think you nailed the problem.

For what ever reason the Master Cylinder is not releasing pressure.

Could be because fluid is trapped behind the piston ??

The bore is just rusted from sitting all these years .
Hydraulics don`t take much dirt or rust to not move like they should

One brake hanging up I could blame on a mechanical issue on that brake all 4 master cylinder

 

I've been a professional mechanic for 5 years and this is the first time I've seen anything like it. Like you said - one brake dragging is a sticking caliper, but all four?

Guess it's time to hassle the seller of this cylinder, and go searching for another one. Or just put my old one back on.

 

Wait till you have 30 plus years The strange and interesting things you will see!!

 

How does a cylinder stick like this?