i am rebuilding the stock calipers on my 85,the problem is i cant get the pistons out with compressed air.any ideas?
Try your normal brake fluid action. Usualy works sooner or later after pumping.
Bleeders closed and applying the air thru the banjo bolt hole? I've seen grease from a grease gun used as a last resort, but it was a bitch to clean up....
Had something like this once. One comes out and the other was 'stuck'. I put the loose piston back in. Safety wired both pistons in and left a rag between them. You'll likely see that the jammed one is in ever so slightly crooked. Try to seat it back in squarely if you can. up the air in 5 psi increments until you hear the 'PING' noise. :D Watch where you hold on and keep fingers clear! My next step was going to be penetrating oil, but the air got it.
My solution to a similar problem was like FeralJuggernaut's with one (in my case) important addition. I pushed the sticky piston all the way into the caliper using a big C clamp and then used ultra-fine bronze wool to clean the grunge out of the caliper which was above the seal on the poston, but previously hidden by the rim of the piston. At that point the air was able to push it out.
Good Luck!