Only one piston moving

fourier transform

Hi all, I took my bike out the other day after about 2 years in a shed, and have been working on it to get it back to good condition. My rear brake is a Magura Louise, and on inspection only one piston moves when I squeeze the brake. I've applied pressure to the working piston to force the non-moving one out, but it still doesn't move when I don't put pressure on the working one (I.e. Use it normally) . So my question is, does the brake need bleeding/calliper need rebuilding?

Any help at all is appreciated hugely, cheers

cooldad

Try lubing the stuck seal with some brake fluid - mineral oil not DOT. Obviously take the pads out first.

The Rookie

Use a wide cable tie to hold the moving one still, clean the other and then try and get it moving while the other one is held in place.

Even an only slightly stuck piston requires a lot of force holding the moving one to get it going.