OK, this oughta be a softball for all the experts out there. I'm having trouble with my '84 Cinelli SuperCorsa's friction shifter staying in position. It's set up with Campy Super Record, with shifters on the down tube. The problem I'm having is that the shifter for the RD won't stay in place; when I'm riding--and especially when accelerating or climbing--the shifter tends to move, usually resulting in the derailleur jumping cogs, and I'm constantly having to twist the little D-ring to keep it tightened down. I'm wondering if I have the shifter cable too tight, or if there are washers inside the shifter that need replacement. Advice is appreciated!