I'm working on a vintage touring build and it is an alloy frame. The LEFT Front 600 SL-6400 shifter does not have a stop when the lever is rotated back toward the down tube. It just keeps on rotating down and finally stops at about 7 0'clock. I'm using the flat alloy washers. Aligning the flat washer notch at about 10 o'clock. The right is fine and performs as it should and stops in line with the down tube. I even took the shifter completely apart and reassembled and no difference. It has got me stumped?!?!?! Any info as to what is causing this would be much appreciated. I hate to think how many of these I've installed in the past and have never had or seen this over rotation without a stop. Thanks, js