Jammed brake piston

[wolfie]

I'm out of ideas now and I'm praying for help as I've got a brake piston refusing to budge from the caliper. None of them would come out under brake pressure so put the caliper on the workbench and put my air line in and 3 blew out but the 4th refuses to move. Heat hasnt worked. neither has a good WD40 soaking so any miracle ideas out there? Pleeeeease as I'm not going to spend money on another caliper that might have the same problem

[Jvr19630]

Are you reusing the piston and is any of it sticking out proud of the caliper housing ?

[Stuart]

I take it you tried the air line with one piston clamped in place, and a block of wood stopping the other two free ones from moving too?

[wolfie]

caliper's being rebuilt with new pistons so not bothered about wrecking it and yes to the keeping the other pistons held in place. The 1 that's jammed has only got a few mill standing proud so not enough to get purchase with mole grips or plumbers jaw grips

[DavidL]

Sorry, I only noticed this thread today!
A couple of thoughts, which you might already have had...
I presume the piston surfaces would be flush with the caliper when fully retracted (if the stuck one is fully retracted then this won't work!).
Can you squeeze it further into the caliper? That might be enough to get it moving.
Otherwise, if you can grind (die grinder, Dremel, etc) a couple of 8mm (or thereabouts) holes in the face of the piston, and put a couple of M8 bolts through a length of bar matching the piston holes - then try to twist it. Depends on just how badly stuck it is, of course.

[streetsy]

If you have a grease gun you could put the wood in as if you are using the airline but attach the grease gun instead of the brake hose and pump it out hydraulically with grease instead of brake fluid.

[wolfie]

Tried and failed that method. The caliper is now residing in the 'give it to the tat man' pile

[Rich]

Put the caliper back together, retain the moving pistons with a block of wood and a G-clamp and hook the caliper back up to the cars hydraulic system and bleed the caliper as normal.

Then stand on the brake pedal, hard. It'll come out.

You can also lash up something similar with a hydrolastic pump and the connector from the rear of a Mk1/2 metro.