Stuck Piston in Brake Caliper won't come out

[diesel don]

I'm having a difficult time rebuilding a caliper because I can't get the stuck piston out. With significant PSI of compressed air and a worthy shield between me and the potential missile, it still won't budge. I've use PB Blaster and heat on it and still no luck.

Any ideas?

Thanks

Don

[tenknots]

The last rebuilt (MB) caliper I bought was $50 - might be time to just replace it.

[diesel don]

I have no problem buying rebuilds if that is the last resort but these things are very, very easy in theory. With five daily drivers, I wouldn't mind rebuilding them as it looks easier than most DIY jobs. The one piston popped out and the seals are so easy to replace. I took the rust off the opening of the one cavity and the piston slides in so nice now.

Thanks

Don

[mplafleur]

The ones I've removed that were stuck would not have come out with compressed air.

I clamped down the other piston so it won't come out and then used the hydraulic force of the brake system to force the remaining piston out. You may have to pump the pedal hard a few times, but if it's going to break loose, it will.

[Pete Burton]

try tapping IN on it a bit first with something like the end of a wooden hammer handle, as it may be slightly cocked in the bore. Rap the outside casing sharply with a hammer all around too. Push out, in, etc. on the piston several times

[william rogers]

If it won't come out with air and pb blaster then the bore will probly be too rusty and pitted for a rebuild. I have heard of using a grease gun on them but have never tried it..............

William Rogers...............

[MS Fowler]

I have a tool that I picked up somewhere that has enabled me to remove very stuck pistons. Its like an internal pipe wrench. The moveable jaw is operated by a hex key. I have also use the hyraulic brake system to pop pistons as posted above. I have been able to use the pistons by spending a lot of time on the buffing wheel. Its been my experience that if they are truly stuck, they are likely very rusted. I have been able to buff them smooth enough to work, but its been on my car; not for anyone else. I don't want that liability.

[mplafleur]

I've had very bad looking pistons and calipers before and brought them to almost new condition before by cleaning them up with steel wool or one of those small green scouring/sanding pads. the remaining small pits won't affect anything as they are much smaller than the width of the rubber seal with is fairly wide.

[BoostnBenz]

Maybe I've been more lucky or maybe this method actually works but I normally just popped the dust covers off then used a small set of channelocks to grab the lip the dust cover sets on. After getting enough force that I can twist the piston I twist it back and forth while pulling up on it at the same time, it has worked everytime for me so far but I haven't had any rusty pistons.

[kip Foss]

D-Don, A couple of suggestions;

One, Don't try to remove a caliper piston with compressed air. If it doesn't come at first people invariably stand in front of the piston, bend over and look straight in to it. A 2 in. dia. piston with 100psi air behind it has about 300 psi pushing it directly at your face. You probably don't have enough spare eyes and teeth to do this very often.

Two; You can, as suggested above, use a grease gun, esp. the ones with the long handle. They will generate about 10K psi. If that doesn't break it loose opt for a new calliper. Some where along the line your time and labor is worth something.

[psfred]

Likely the piston is cocked in the bore and rusty to boot from being run on too thin a rotor (why or why do people do this?????).

Try tapping the piston toward the bottom of the caliper while applying force INWARD -- if it's sidways, this may straighten it out enough to get it out.

Never use more than 15 psi of air pressure using a blower tip. Higher pressure won't likely move a stuck piston, but if it does come out, the high pressure air expands explosively, and the piston is heavy enough to crack your head (that is, kill you outright). Not funny. At LEAST put a board in there so the piston cannot come free, but it's best to use air only to push a moving one free.

Put the other piston back in if you havent yet, install the brake line but leave the caliper hanging, and use a C clamp to hold the good piston in place. Bleed the air out and STAND on the pedal -- likely you can get the piston to move a bit. If the pedal sinks, keep pumping until it pops out (no exposion here!). If you cant get it to move, get another caliper, that one is shot.

Do not use any piston that is not perfect below the seal, it won't retract properly and/or the pits will eat the seal and it will leak. The pistons are chrome plated, and should NEVER be cleaned with anything more abrasive than cloth and brake parts cleaner. Pits ABOVE the seal are OK, although they can cause trouble.

You can remove rust above the piston seal in the bore with crocus cloth, very fine sandpaper. or Scotchbrite, but you MUST NOT touch the area below the seal. Clearance is very tight, embedded abrasives (there will be some no matter what you do) will remove the clearance and the piston will seize, or you will remove too much material and the piston will go sideways and stick...

If in doubt, get a new one.

Peter

[diesel don]

Well, I've reworked 3 calipers now and am have fair success. The real question is 'how long will they last?' But the price is right and I'm learning some things along the way.

Thanks for all the advice. Much of it was helpful in getting the stuck pistons out. I used wet-800 sandpaper very lightly and it seemed to do the trick.

Don

[callenderevent]

Just replaced a RR caliper on my 87 TD wagon since I couldn't get one stuck piston out on the old caliper. I was using brake pressure with no luck. Well, when I put on the new caliper, I couldn't bleed the brakes and the new pistons weren't pushing out against the new pads. Read a post about bleeding the brakes and realized that while I thought the fluid reservoir was full, the back part of the reservoir which is for the rear brakes, was empty. I had to overfill the reservoir so that fluid would spill over the internal divider. After doing this, I was able to easily breed the rear brakes and activate the new pistons. Makes me wonder if I had tried this on the old caliper, maybe the piston would have popped out. Will probably try it and if it works I will rebuild it and sell it as a rebuilt caliper.
Don't know if you are working on rear calipers, but thanks to the shop forum, I was able to get my new brake parts working perfectly.

[whunter]

Originally Posted by callenderevent

I was able to easily bleed the rear brakes and activate the new pistons. Makes me wonder if I had tried this on the old caliper, maybe the piston would have popped out. Will probably try it and if it works I will rebuild it and sell it as a rebuilt caliper.

Do NOT rebuild and sell the caliper.
Liability would destroy you for the rest of your life, if anything happened.

[callenderevent]

Thanks....you're right it is not worth the risk!