Stuck brake piston in calliper - how to remove

[hampshirehog]

3-1 penetrating oil in a spray can works well. Or make your own from ATF and cellulose thinners (if you've got them in the garage).

[ukjules]

Calipers pistons unstuck and thanks for info all !

I had to use the grease method in the end.
This sounded mad to start with but it works ! I have a cheap ?13 lever grease gun (off ebay) and the nozzle fits
over the bleed nipple fine. I blocked off other air ways with bolts and stuffing a bit of inner tube in holes before hand.
I squirted grease in (blead nipple) and out came one side (prevented from coming all the way out with a piece of wood)
To get the other side out (they are twin piston calipers) i cut a bit of inner tube and covered the central hole
when the calipers are split , did them back up and pumped again. The other side then came out.

I did the same to the other caliper and I now have them in bits ready for renovation.
both pistons need renewing obviously.

I went through using wd40 - but ended up buying proper penetrating fluid !
A foot pump and bicycle pump, could not do it either they were well seized.
I didnt try a air line as dont have access to one.

i didnt realise that a grease gun goes up to 4-6000 psi !

thanks for help.