Empi rear calipers. Piston not winding back

[Leo the biker]

74 beetle based trike.
Hi all, I have an issue with my empi brake calipers. I removed them to sort an oil leak from the gearbox. I'm attempting to fit new brake pads due to contamination.
When I try to wind the piston back (clockwise) the piston turns but doesn't appear to move back. Neither the new pads, or the old ones have enough room to fit without the brake completely binding. Can anyone help?
I'm assuming that they piston needs to be wound back in and not just pushed.
As the old pads had only been in a month or so, it's possible that the piston is already back as far as it goes, but that wouldn't explain why the pads no longer fit

[slalombuggy]

You have to compress and turn the piston at the same time. There is a special tool for this. You can kind of do it with a big C-clamp and channel locks but its a pain in the ass and the tool is much easier.

[Leo the biker]

Already tried with the wind back tool. I'm used to working on motorcycles, where opening the master cylinder reduces the pressure in the caliper to push them back. I have discovered that with these calipers, you need to release the bleed screw for them to compress. All good now thank you.