My front derailleur wouldn't let me shift to the small chain ring, and after some investigation I located the issue to this plastic plug/fitting/thingy that seems to have popped out of the little hole in the frame. I think this prevents the gear cable from moving smoothly and rendering me unable to shift to the lower gear. Can someone give me some tips on re-fitting the plastic thing? I have a subtle hope that I can do it without having to remove the cable altogether :)
If what you're saying is that you think the liner piece got scooted up out of the frame and there is now an internal area where the cable is meeting higher friction because of it, typically to push them back into place you need to get all the tension off the cable, and even then it can be difficult.
The black knobbly piece is there to keep debris out of the liner, so it's where it should be if the liner is also where it should be.
Thanks for the input. You are correct: the small piece of plastic is indeed just a cover to prevent dirt form getting into the sleeve in which the metal gear cable is running. Instead a gave the cable a good amount of grease around the hole in the frame and movedit a bit back and forth. That seems to have made the shift go much more smoothly. Hope this was the fix. Fingers crossed.