I'm having a problem with my right front brake randomly locking up on me. (Right side engages to a lock but left side does not. If I let off brake it all releases though) Creates quite a freaky moment when it decides to happen. Car yanks over to the right and the right tire is squeeling to a stop. It was happening last year before I put it away for the winter. I had swapped out both front calipers(bleed screws broke off so had to) and it seemed fine for the last few weeks I drove it before putting away. I just took out a couple of weeks ago and all was fine until yesterday. Sure enough it's back. On these recent times, it appears to happen right after the car has been sitting a bit(like 8 hours or more). If I pump the brakes down hard a few times it goes away and brakes fine until it sits again.
Lines are not kinked. Front lines were bled(back bleed screws are rusted on so have not bled whole system) and new calipers put on in fall with brake pads.

Any ideas??

Thanks
SP

check/ change proportioning valve (place where lines split). Im not sure if its built into your master cylinder or somewhere near it under the hood. my guess is that your right brake is getting too much pressure and your left isnt getting enough.

Does it lock up on light braking or only on hard stops? Did it do this before the brake job?

check the porportioning valve

Thanks that is one I haven't checked yet. What can you do to this though. Is there some good way to clean it? Noticed Autozone doesn't even carry one.

To the other question, it locks up with pretty light braking. Definately not a panic or hard stop. Just slowing down behind another vehicle will do it. It did this before the brake and caliper change too. Just went away for awhile after I did it. Thought of grease or oil on the pads but not it. Odd how it does it sometimes and not others though. But if I sit there and push hard on the brakes at a stop, it makes it go away for that trip sometimes. Sometimes it takes a few go rounds of this.

Quite crazy when your wheel locks up and your being yanked to the right with all that screeching. Scared the heck out of a few people in front of me.

Thanks
SP

Is your pedal high and firm when pressed? If not you still have air in the system which will prevent it from working properly. You may have a restriction in the left line. I found that the factory rubber lines have a bracket that holds it to the frame that is crimped too tight causing a restriction. Mine was enough to make it pull to one side but yours sounds much worse. My 74 Chevrolet service manual says the proportion valve is nonadjustable and non serviceable. I bought one from Year One or Classic Industries and it was expensive, $70 or so if I remember correctly. New rubber lines were less than $20 each and available locally so I would try that first. Let us know what you find.

TIME OUT! Is it the FRONT brake locking up or the REAR one?
If it is the front - check to see if the left side is applying. It can be the valve. Also do check the line to the left side. If pads are thin and not wearing the same thickness, the piston can be jammed in the caliper
If it is the rear - it can be the fact that the shoe surface can be contaminated or adjusted up too tight . . .