I had this really irritating squeal coming from the back passenger wheel that went as soon as I touched the brake and took the caliper off to investigate. Greased the back of the pads and its helped. However when I tried to wind the piston back it wouldn't budge. I've a feeling the squeal and the sticking piston are related..
I did have the reservoir open but maybe I should have had the bleed nipple open too? Never done this before - I take it the piston should glide back fairly easily? Fortunately I managed to get the caliper back over the brake pads, and the brakes certainly seem to work fine on that wheel (in fact they might be sticking a little judging by the heat.
Any ideas? How do I go about servicing the caliper / piston?