Ok, so having a nightmare with some Hayes Stroker Carbon hydraulic brakes.
The pistons were not moving well so I decided to try and sort them out by pumping them out of their bores to add Dot 4 fluid around them and then easing them back in. To cut a long story short I now have the caliper pulled apart and one piston stuck firmly in its bore. Normally Hayes suggests pumping the pistons out with compressed air by attaching the compressor hose to the banjo hole or bleed nipple and blocking off the connector hole through to the other half of the calliper with a finger. This is not working at all! I have tried for hours trying various sealing methods but firstly it is hard to get a perfect seal at the banjo hole with an air compressor hose or a track pump, and secondly the finger blocking the other hole is not good enough either.
Even when I do get some pressure going in, the piston doesn't move even a bit. It looks like it is stuck solid. I tried pulling it by its central pin but the pin just came away. I have tried a variety of pliers around the small bit of protruding edge but the ceramic coating just crumbles and its impossible to get much of a grip.
By the way, I tried before I took any of this apart, pumping the brake lever lots to try and push the piston out with the fluid but that didn't work either. I also tried putting the calliper in a boiling kettle and then pumping the air through - no luck either. I have not tried freezing it but I have little faith in those spray can penetrating fluid things.
One bit of hope was that the piston was protruding more when I had originally pumped it with the brake intact, but I then added Dot fluid around the bit that was out and pushed it back in to try and lubricate the bore - now it won't come out at all.
This is the clean bore from the other half of the calliper -
The only things I can think of at this stage is using some JB Weld to try and stick a bar onto the piston and pull it out, but I don't expect even JB Weld to stay attached to that flaky ceramic coating.
Any other ideas anyone?