OK, but you really did not answer my question. I will assume you have the cable routed around the back. Take off the seat cushion. Is the cable clamped down on both sides to a piece of the seat frame? If not, that is your problem. If it is, I advise pulling up the frame and removing the cable, take it to home depot and make a nice new one, make sure it is the EXACT same size as the old one. Clean and lube all the rollers and reinstall the new cable. Be sure the cable crosses itself on its journey from one side to the other. That is very important. Also - are the 2 springs still in place?
