There is some kind of buildup on the inside of that clamp. You need to make sure that clamp is good and clean and get right of that buildup. Could be rust or maybe the clamp is just ruff. If you take off too much of the inside of the clamp by sanding you will have problems with it gripping so be careful.
I would try putting a little toothpaste on the inside of my clamp and putting it on the bar down at the end. Adjust it so you can rotate it around he bar (not side to side.) Then rotate it back and forth for a while.
Toothpaste has a very fine grit in it and may clean it up for you. Then clean the bar and your clamp with alcohol and try it again. If that does not work try some lapping paste. You can get that at a auto supply store. It is a grit past used to seating valves.
A Picture may help it may be possible to see the problem.
Everyone has the right to be stupid... it's just that some people abuse the privilege
Last edited by Irvin; 08-04-2011 at 12:38 AM.