I just put on a new rear derailleur (Ultegra) on my bike. I made all the adjustments according to the Shimano specs. However, it hesitates when upshifting (going from large cogs to small cogs). Anyone have any hints before I go to the LBS?
In order to shift to a smaller cog, you release tension in the cable. If it is not shifting to the smaller cog correctly, the first guess is that the cable is a bit too tight. You loosen the cable by screwing in the cable tension adjuster where the cable housing ends by your derailleur. Just do small increments, maybe a quarter turn at a time.
It may be that you can’t screw the adjustment screw further in. If so, you have to take the cable off the derailleur and loosen it slightly so you will no longer be at the end of your adjustment range. Start over on adjusting cable tension.
This should fix the problem. If not, post again. Possibly your high and low gear limit screws are not adjusted correctly. Don’t stop until you get the shifters shifting reliably every time. If you get it right, it will stay right for a long time.
Go to the Park Tools website . Look up the ‘Rear derailleur adjustment’ piece. It will walk you through, step by step, on how to dial in your rear der.
Good luck!
p.s. You do NOT need to take your bike to the LBS. It’s an easy job and you’ll learn a lot doing it yourself. 