daoswald

I have a Shimano 105 3x10sp group set (I think it's 5700) with a Shimano 105 11-28 rear cassette, and in front 50/39/36.

The shifting has become awful lately, and I can't quite put my finger on the issue.

Symptoms: Toward the smaller-end of the cassette upshifts are becoming unreliable. Toward the middle of the cassette, downshifts are becoming unreliable.

The rear cassette has about 1200 miles on it. The Shimano 105 chain has about 1600 miles on it. The RD shift cable has 200 miles on it. The shifter and RD are original, so about 6000 miles.

I cleaned the shifter pretty thoroughly at the beginning of the season. It still feels crisp.

I keep the RD clean all the time. The RD doesn't appear misaligned but I don't have appropriate tools to verify that. I've never fallen on the derailleur side though.

Here's the fly in the ointment: 1200 miles ago I swapped the rear cassette from 12-25 to 11-28 because I have relocated to significantly more hilly terrain. I didn't add links to the chain. I did adjust the B-screw, tightening it quite a bit to prevent the RD guide wheel from pressing the chain against the cassette when I'm in 30t(front)/28t(back). It's as tight as it has to be, but not even an eight of a turn tighter than it must be to prevent contact.

My inclination is to swap out the rear chain since it has 1600 miles on it anyway, and at that time go a couple links longer, and re-set the B-screw with less tension to promote better shifting.

I could take it into the shop, and probably will end up doing that anyway, but I'm not convinced they'll take the time to get it "just right". If I can manage to improve the situation myself I'd prefer doing it that way. Until recently, it's been working out fine to do my own work. This time I'm stumped though.