Common occurence.
1. Push working piston fully into caliper – a ring spanner works well as it will not damage centre pin. If its stiff use a lever through the back (small) opening of the caliper.
2. Hold this piston – an open ended spanned works for this but can't remeber what size – about 14mm i think – basically whatever only just slips over the caliper body to hold the rim of the piston.
3. Force stuck piston out by operating brake – do not allow the piston to come all the way out if/when you get it moving ! A couple of strokes on the lever is plenty.
4. Clean around the exposed piston with brake fluid and wipe dry.
5. Lubricate with a drop of clean brake fluid.
6. Push piston back in fully
7. Repeat lots. Each time you do it should free the piston marginally more but it can take a while !
8. Every now and then, check piston action by releasing the good pistion and operating brake lever. Pistons should move roughly equally. If not, go back to (1.) !!
Good luck.
Bleed kit only required if you pop a piston out by mistake. That said, if you have air in the caliper you'll never get the brakes working satisfactorily.
Mine were stiff from new and a piston in each caliper seized within a few rides. I ended up splitting the caliper so had to fork out for a bleed kit and was tearing my hair out with despair at brakes that never seemed to work right and rubbed all the time – now they're sorted and I have to say they have given no trouble since !
