Be careful. If either the cable or caliper are seized, then the brake may also seize up and case you some real problems. What exactly are you trying to do? If the cable doesn't seem to have enough slack ,it may be finished or adjusted too tight. Also make sure BOTH caliper handbrake mechanisms are free. The arms MUST return to their resting positions without the cables attached. If one side has a problem, then it will affect the other; the cables attach at the handbrake lever on a common bracket that floats, so if one side is seized or too tight it will pull the other side. If the cable is stuck from where it slides into the caliper, just use some pliers to rotate it and it should come loose once the clip is removed.