Anybody have any experience with this problem?
For the first time this winter, earlier this week (outside temp was about 0F) I went out on my bike. After going less than half a mile, I was unable to shift down, only up on my rear derailleur (Trek FX 7.2, which appears to have a Shimano Alivio rear derailleur from my quick-n-dirty Google-fu). So I'm stuck in an annoying gear, but get myself back home after playing with it a little.
I bring it back inside, and look at it again a few hours later, and it's fine, shifts as it should. I write it off as a fluke.
This morning (~14F), I take it outside and the same thing happens. This time though, I need to get to the bus, so I deal with it for a mile and a half. And I'm aware of the problem, so I'm able to stay in a relatively sensible gear.
So tonight riding home I'll be dealing with it, but I'll probably check on it first to see if anything is obvious. I'm hoping this is something simple like something needing to be oiled. I'm not too mechanically familiar with my bike yet. It's only a few years old, and when I got it last April it seemed to be rarely used. So I don't think it's anything failing due to age or wear.
Thanks.