While preparing a repaint of the rear brake callipers, I noticed one of the piston-rubbers is damaged. I happen to have a refurbishment kit.
Does someone know how to remove the piston? For my front Brembo callipers I just used air pressure via a brake nipple and the pistons popped out, but this does not work for the rear brakes.
Second question: there is also a rubber near the lever for the handbrake: between the lever and the housing. This is not included in my kit. Does anyone have experience with replacement and where to buy?
I think that, because of the handbrake lever, the rear pistons are screwed to a lever in the caliper. That's why you need to unscrew the piston (turning it anti-clokwise?) so it will get free from the lever. That's why there are 4 grooves on the piston surface.
I bought a full kit, including the pistons from Bigg Red here http://www.biggred.co.uk/brake-caliper-piston-repair-kit-brkp69 This kit includes the rubber seal for the handbrake lever cable. It also includes some O rings used inside the self adjusting mechanism inside the pistons. This mechanism is very fiddly to remove as there is a difficult to reach internal circlip holding it all in. I used a tiny flat balde jewlers screwdriver to reach down and release the circlip, but it's very frustrating work, and don't break the circlip as they are very, very, very difficult to find!!