One rear brake doing nothing?

[taki100]

As stated in the title my passenger side rear brake on my cup isnt moving at all. The handbrake works ok and the piston seems to move fine when we have screwed it in and out. Does anybody have any ideas on what the problem could be??? There isnt any brake fluid leaking either so i dont think its a seal.

 

[James105]

Tried bleeding it to make sure your getting brake fluid out and no air?
The fact the handbrake works would possibly suggest it's fluid related, as the piston isn't stuck.

 

[Dan519]

remove the hose from the caliper and see if fluid comes out when you press the pedal. If not it may be the bias valve above the axle is clogged up. Used to happen a lot on mk1s

 

[taki100]

Havent tried anything yet but try your suggestions when i get some free time. Its a good job a have to depend on public transport to get to work