Caliper rebuild: brake piston removal Qs

[deathpunk dan]

Hello
Last night I managed to rebuild the driver's side front (M) caliper with little drama except for the whole 20 degree angle thing (had to make a triangle out of cardboard).

On the passenger side front caliper, one of the pistons just will not come out. I am using a small air compressor and the piston won't budge. Should I assume it's seized and look for another caliper?

I would put it back on the car and try to use hydraulics to force it out, but I'm doing the work at my folks' house some 35 miles away from the car. (Dad has a real workbench/shop/good lighting).

Advice is greatly appreciated.

Dan

[mcaterino]

Hi Dan,

Not as cooperative as we hoped, huh. Sorry to hear it. Most of my calipers were reluctant to release their pistons, and one absolutely refused. The reluctant ones were best encouraged by alternating pushing the piston in (with c-clamp, vice, or whatever) to break it free, then pressurizing to push it out. You might only get a mm or so of movement inward, but with a few iterations it may come loose. Heating the caliper body also helped, some. But in the end you might just shop for a replacement. It's nice to conquer these challenges, but some of the headaches aren't worth it.

Mike

[Jaskas]

+1 Mike...

Been there done that! In the end the piston plobbed out.

[ajwans]

I used a grease gun. It should screw right up. Just plug the other
outlets with the right size bolts and pump it in. You should use a
block of wood in the middle to stop the pistons from blowing right
out.

andy

[John Brandt]

I've had a couple that needed a BIG air compressor.

PB Blast it and try to compress with a good C clamp and then let it sit overnight. Then take it somewhere with a 175+ psi choo choo and it will be out immediately.

[rusnak]

BE CAREFUL WHEN FORCING BRAKE PISTONS OUT.

They can shoot out with incredible force. Use wood, or a folded up newspaper between the pistons to prevent damage. Do not put your hand in there. Sometimes a small c-clamp can hold the free piston in while the frozen piston is worked free.

[mjw]

I just went through this exercise last week using the 125 psi shop air method. Seven pistons popped right out (used C clamps to control how far each piston can move and took it slow); the eighth piston wouldn't budge ... isn't that the way it usually goes?

I filled the bore/piston seam with PB Blaster and let it sit over night. Next day, using a C clamp, I was able to get the piston to break loose, pushing it further into the bore and then using air pressure to push it back out (~ 0.10 inches). It took a few cycles before the thing wanted to come all the way out. Make sure that both pistons are moving and close to the end of their stroke before letting them come out all the way (this is where a C clamp on each piston helps, just keep backing them off and putting air on the supply port).

In the end, it was just a little rust around the top edge of the piston and caliper bore that was causing the sticking and it cleaned right up.

Good Luck ,

Marty

[deathpunk dan]

I sprayed the stuck piston liberally with pb blaster, let it sit for a day and it came out on the 1st attempt.

The rest of the rebuild went smooth but I gave in to temptation and painted them silver.

Thanks for the pb blaster tip!

Dan