Originally Posted by
Andrew R Stewart
BTW it's time to check your shift cables as they enter the lever's cable spool, just beyond where it's easy to see them if the casing was pulled back/out of the lever's seat. A fraying (and Shimano shifters are very well known for this wear point) will inhibit the fine movements of the cables, as in the trim functions. Andy
That happened to me once and it took me way too long to figure out what the problem was. It's now one of the first things I check. Actually, the cabling is the first thing I look at. See if all the ferules are seated properly etc. Then I start working on the problem.