On my brembo brakes that is. In fact it's not jammed, it just moves so slow when compared to the other piston. If I clamp the good piston down, the problem piston pushes out lovely. Should try bleeding? I'm gonna put this off until my new pads come through. This all came about btw when my fork seal blew and oil went all over the calliper. By the the end of the ride it was caked in a mud and oil. When the fork was removed for servicing I set about cleaning the calliper. I presume the pads are ruined as they were saturated in oil. annoying as they were new! Just another annoyance I thought I would mention. When the fork seals were being sorted it was found the bottom pre load spacer was missing on one fork (the blown fork). To my knowledge the forks have never been looked at so must have left the factory incomplete!!