'70 911 calipers

I'm having trouble getting the pistons to come out of the caliper. Removed pads, brake
line, caliper,and seal. (ala haynes) attempting to push piston out w/air, 80psi by way of brake fluid port. moves a little but won't come out. What's the trick???

After buying my 70'911T, the very next day I got stuck with the left rear wheel totally stuck!!!
This was to be my first real Porsche experience, I meant expensive experience.
I tried to rebuilt the calipers but just like you, the pistons somehow with age, water = rust stayed rock solid stuck ( I got two out with 200PSI, very scary when they popped ).
I ended up buying new ones ! ( at the time, it was a real struggle to find someone to rebuild them fair and fast ).
Remember most of all to check ( replace is a good way to go ) your rubber brake lines. Mine were totally swollen shut. The pressured brake fluid would go toward the wheels but not the other way, explaining how I would get locked up wheels.
Thierry

Hmmm. 80 PSI and no luck? I got pistons out of '70 "S" calipers that had sat outside with mostly H2O for fluid for 11 years, with 80 PSI. You might need to shoot some penetrant in there and let 'em cook for awhile. Are these "S" brakes or standard? If they are the standard calipers, the chances are the bores are corroded out anyway. Toss 'em and buy a rebuilt pair. Lower headache levels at a fair price.

Griffith,
Are you sure the piston is straight in the bore, i.e. not crooked? It can happen sometimes, and all it takes then is a hit on the piston to straighten it.
Of course if the caliper is corroded it's not the problem, but it can't hurt to check.
My $0.02, GeorgeK