Caliper piston stuck

[nek]

I am battling a sticking caliper issue. I replaced the caliper with another used one and the caliper is still stuck.
I removed the caliper (which was seized on the rotor) and I pumped the brakes to see what the calipers were actually doing.
The attached photo shows only one piston coming out but its hard to push back in.

Which piston is siezed, the one that wont come out or the one thats coming all the way out? I always thought when you pumped your brakes, the piston was supposed to extend and retract by itself, not stick out as it is doing.
I thought about buying a rebuild kit or just replacing it all together. Anything else I can do to fix this?

 

[Bud92gsx]

You mize well take the seal out, and rebuild the caliper.I had one stuck out once..Took the piston out, cleaned it up, put in a new seal, and never had a problem since.

Cost like 20 bux, cause I replaced all the break fluid.The seal was only a couple bux.

 

[rlacasse1]

Just rebuild it.

As for your question about the about the piston retracting, it does not retract. When you let off the brake pedal all that happens is the piston quits applying pressure to the brake pads. Imagine putting your thumb on the table and pressing down, that would be like you on the pedal applying pressure. As soon as you quit pushing down you are not applying pressure, but your thumb is still on the table.

Does that make sense?

The pistons only retract far enough to quit applying pressure, so the distance they move when you let off the brakes is retardedly small.

 

[pauleyman]

If you use the brake to remove the pistons without a stop it will only push out the piston with the least resistance. If you've already popped that piston on the right out then you'll either have to put it back in or grab the other piston with pliers or something. If you put something in the caliper first you can push both pistons out most of the way then remove them by hand. Do not put your hand or fingers etc in the way. They can pop out and will do so violently depending on if you used fluid or air etc. I'd play on just replacing the seals and boot. Cheap and easy.

 

[nek]

Thanks for clearing things up. Im a mechanical engineer so it all makes sense. Ive never dug into the caliper in much detail. Due to time restraints, I am going to advanced auto to buy a rebuilt caliper. The caliper is 55 bucks after I give them my core. They look very easy to rebuild but I would rather buy one with a warranty so I dont have to deal with it.
Realistically, to get the other piston to pop out, I should have put a wooden board or the rotor to block the piston from popping all the way out. Once it gets to far out, the fluid just releases from the rubber boot.

 

[pauleyman]

Sort of, It isn't the rubber boot holding it in it's the oring seal inside the caliper. Rotor would've been too thick. A board or one of the brake pads would've been good. But you have the idea put something in where the piston comes out quite a bit but not far enough to break the seal. Unless the 2nd piston is really screwed the brake hydraulics will push it out, you just popped the seal on the first one before you had enough push on the 2nd one.