STI shifter performance is a lot more sensitive to excess friction in cable housings. This can be caused by wear from the cable, dirt, cable oxidation, and other impurities. I recommend replacing the housings and cables any time there are symptoms of excess friction.
Replacing the cables and housings often restores shifting performance.
I think it is just as important to replace the housings as the cables.
Last edited by Al1943; 03-10-11 at 08:41 PM.