gradually, I think. It happened once last year on a metric century, then again this past weekend. Can't shift up to the big ring when it happens. Bike is an '89 waterford paramount w/ 8 spd. dura ace, sti shifters. There is a cable tension ferrule thing at the front d. braze on boss, turning it solves the mystery slack, and shifting works fine. But what is causing it? Bottom attachment point at the front d. is tight.