The best thing you could have done with the rear caliper was to have left it connected to the line and used the master cylinder to pump the piston out as far as you can before you remove it. You'll have a job to get it out now its disconnected and air pressure alone may not be enough to push it out of the bore. I assume you're going to replace the seals and perhaps the piston? EDIT... you replaced the whole thing anyway.......! 😁
When I took the rear caliper to the mechanics for some advice he said the same thing! Ahahahha lesson learned!! Still, no harm done as I’m gonna totally rebuild it. I replaced the front 2 as I got 2 rebuilt ones for pennies! Rear though is getting new seals but the Piston can be saved.
