Rear Brakes Binding or not releasing

[DeiterPhotography]

I have a 81 fearing bike, and my problem is that the rear brakes are binding after being applied, I originally thought that the pistons were binding but after removing the caliper the pistons are easily pushed back, than I thought that there was a hydrostatic lock in the line or master cylinder was keeping pressure in the line, But if that was true I should brake open the bleeder screw and release the presure and the wheel would get freed up, but it dont......Has any one had this problem and does any know what the fix is? Thanks for your help!! ......Mike

[EMS]

Puzzling. Usually this occurs when the return bleed hole in the master cylinder is plugged. But if the calipers don't free up when you open the bleed screw....

[steve murdoch icoa #5322]

Any chance the binding is being caused by the caliper positioning?
Caliper sliding pins need grease?
Have you had the rear wheel off recently and maybe not placed the spacers in the right order?

[NobleHops]

I'd investigate that master cylinder. Put a hose on the bleed screw and do a complete fluid flush, see how well the master pumps. Has the master cylinder ever been apart as far as you know?

N.

[Goss]

Mike,

I have the same problem with an '81 prolink front and rear brakes, I assumed that because the pistons push back easily that they were ok but found that the seals no longer had the ability to make the pistons spring back, age I guess. The seals are cheap and easy to replace however, I would check what Steve said regarding the positioning, lubrication and assembly first. Let us know your progress.



Regards

Goss

[Larry Zimmer]

Mike,
From everything you said, I have to go with Goss. Pull the caliper down; and, decontaminate it. Replace the seals. Even though the pistons seem to push back easily, the seals don't exert very much force. Any bit of corrosion and/or contaminate along with old seals will be enough to bind.

[EMS]

There is one other -albeit remote- possibility. I hate to bring this up and I promise, I will not engage in any kind of discussion that may ensue!
Binding brakes can be a result of using DOT 5 brake fluid in a system that is not really designed for that. Among other parts,the piston seals in the caliper swell and keep the pistons from returning.

[Jeff Bennetts]

Mike,
From everything you said, I have to go with Goss. Pull the caliper down; and, decontaminate it. Replace the seals. Even though the pistons seem to push back easily, the seals don't exert very much force. Any bit of corrosion and/or contaminate along with old seals will be enough to bind.

I second Larry's stab at it.

The seals in the caliper are square shouldered, the reason for this is to allow the caliper piston to roll back away from the rotor after the pressure is released from the M/C, the seal rolls toward the rotor while under pressure and away from the rotor when the pressure is released. If the seals are worn or deposits have built up in the groove that the seals set in it can affect the roll back of the piston and cause drag.

[NobleHops]

When I was doing my brakes, I had disassembled it all and had the parts powdercoated, and thought they were all nice and clean. Just for fun I put a brass brush on my dremel and went after those seal recesses and POOF a puff of dried crusty brake spooge. This is AFTER I went in there with my dental pick.

N.

[daves79x]

That Dremmel and brass brush is the cat's meow for cleaning the crud from calipers and masters. Take the whole rear brake system apart and rebuild. You may not need any new parts - just clean up all the old stuff and carefully reinstall. Very easy to do on the rear - the front, not so much.

Dave

[George R. Garrison #0857]

The Cats Meow,,, I like that,,, good info.