PLEASE DON'T USE 125 PSI ON THAT CALIPER!!!!!!!!!

The piston, if it does come out, will bounce off the other side and come flying out of the caliper, likely killing you if it hits you. In effect, a small canon!

re-assemble (you can use the old seal for the other piston), and attempt to force it out with hydraulic pressure. Air simply isn't safe here, it's going to take quite a bit of force to move it. You can also generate several hundred psi safely, as the hydraulic fluid won't explosively expand if the piston pops out.

An even better option is to replace the caliper. Very likely the piston or bore is corroded if it is that stuck, anyway.

You may also have some luck using a pair of small prybars -- the green handled ones at AutoZone about the size of a large screwdriver. Hook them under the dust boot lip and pry agains the housing on all sides, alternating directions and positions. This may force the piston back into alignment with the bore so you can get it out. At least it won't blast out of the caliper this way!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!