Originally Posted by
Old Hammer Boy
Are you shifting from large to small when you're in a small rear cog? If so, that could contribute to the problem. Is it a brand new bike?
I was shifting from a middle-ish cog. On the trainer now (warmed up from NYC cold) it does shift properly from the two largest cogs, not from any of the others. It's brand new, so there shouldn't be any dirt/grime clogging the cable guides.
Originally Posted by
Homebrew01
Also sounds like a cable issue to me .... binding or sticking somewhere. Next time it malfunctions, let go of the shifter & stop riding. Pull gently on the front derailleur's bare cable running down the downtube. When you pull, is it tight at first, but then you feel something give making it go slack (bad), or is it already slack ? If it's already slack, will the front derailleur move the rest of the way if you give it a little push with your finger on the cage ?
Tried this too. The cable is reasonably slack once it tries to switch to the smaller chainring and I can't feel anything give when I pull on it a bit. Once the problem happens, I can't move the front cage at all by pushing on it.
I really appreciate all of the ideas and input (ah, so much to learn). I'll try to get them to inspect & replace the cable too.