Project: I want to restore my old GT6 brake calipers and the old chipped paint us very VERY tough so I plan to use paint stripper. To do this without harming the seals and soft alloys I need to split each caliper and remove pistons.
Problem: The pistons are stuck in, and will only come out under pressure.
Fix: I took an old piece of copper-nickel brake line and re-attached it to each caliper with the bleed nipple closed. The other end of the brake line has a flared end and tube-nut which just happens to perfectly fit into the Schrader adaptor on my bicycle Track Pump. Once attached I pumped the.. uh.. pump and watched the pistons move out of the calipers. They both popped out at around 20-30 PSI. Of course if you want to do this spectacularly and potentially damage the pistons, use a compressor 🙂
Important: When you pump the pistons out, you don’t want them to fire out and spray residual DOT 4 everywhere, you also don’t want the pistons to lock together, so it’s important to find a peice of wood slightly thinner than the brake discs and place it between the pistons.