Okay, I've tried everything to get my rear derailleur to shift properly, and nothing is helping. It's a DA 10 speed short cage, running a 12-27 cassette on a Mavic wheel. I have an identical setup on another bike, and it shifts like butter. I've asked a lot of people about it, and before I take it back to my LBS tomorrow, I wanted to put the problem out there.
The behavior is not consistent. Sometimes it wants to shift up more than one gear, and then it won't want to shift down until you've tapped the mech 2 or 3 times. So it seems tight, right? Then you loosen it, and it still shifts goofy! It'll grab gears erratically, it won't shift down cleanly, everything ends in a "clunk." Maybe you'll get 10 clean shifts, then 5 crappy ones. It's driving me nuts!
So, here's what I've done.
Replaced both housings, front and rear - there was little to no binding before or after the replacement whatsoever.
Checked the rear spring - it's not sticking, it returns fine.
Rethreaded the cable and retensioned it about 5 times to no avail.
Swapped wheels/cassettes - still did it.
Chain is fine.
Took it to LBS - he found the rear derailleur cage to be out of whack - straightened it and it's as bad or worse.
Note: before the LBS straightened the cage (and I trust this guy, he knows his stuff) the shifting problem seemed to occur later in my ride - that seems to be when I would shift into the big ring. Using the big ring seemed to bring the problem on.
Now it just shifts poorly in both rings.
Any suggestions? I've been chasing this for weeks. Thanks in advance!