Originally Posted by sydney
It's a good bet your hi limit screw is set too tight.Then you add more cable tension,throw in some force to try and make it shift and the cable brakes. The cable clamp bolt could also be too tight and partially cutting the cable.
www.parktool.com has derailer adjustment n the repair section. A BB spindle a few mm longer shuld not create or add to the problem, if the derailer is adjusted correctly.
This sounds the most likely to me as well. I hadn't messed with the limit screws because everything seemed to be shifting fine. I just recently noticed the chain rubbing on the outer edge of the cage when in outer/outer combos.
I took the broken portion of the cable out of the clamp. It snapped cleanly, flush with the upper edge of the clamp. The clamp is just two pieces of metal and a screw. (wire sandwiches between them) I don't see anything that could be cutting it.