Rear brake doesn't

would the cable having movement be anthing to do with it ? its only held on with 2 clamps on the toptube
see what i mean its frustrating now, why does the front work so well n the back so shit
ill have another quick piss about with it n report later

Do you have a full length outer? Does the whole outer move? Does the outer butt up to something on the frame, so that pulling the brake lever has something for the inner to act against? Hard to explain