I'm having a problem with my right hand brake lever, when I pull the lever the first few mm of displacement cause no pull at all of the brake cable. I can manually pull the brake cable tight, causing the problem to go, but as soon as I then use my brakes it happens again causing the rear caliper to rub slightly. I've tried cleaning the inside of the shifter and can see nothing that would stop the brake cable being pulled back by the rear caliper. The cables are new and move freely as far as I can tell. When the rear caliper is disconnected from the cable it opens fully so it isn't the spring in that causing a lack of cable tension.
Anyone got any ideas?