I have an entry-level Trek mountain bike bought several years ago, with a Shimano derailleur. It's been hanging in my garage for the last few years, taken down only a few times for rides. I just did a ride with some hills, when I noticed it wouldn't shift into lower gears. It feels like there's so much tension in the cable that I can't physically move the shifter below gear 5.
After spending hours this afternoon looking at bike repair videos and questions here trying to isolate the issue, I've found or done the following:
- the derailleur hanger is straight
- I can manually move the derailleur to the lowest position and it shifts down to the lowest gear fine
- I've cleaned out the shifter with WD40, and when I relieved the tension in the cable by taking it out of the little cable holders between the derailleur and shifter (sorry don't know correct terms); with the tension gone, the shifter moved easily between gears 1-8
- when I had the cable unclipped as above so it was loose, I was able to move the cable housing up and down the cable easily; it didn't seem dirty or much friction, although I noticed the rear gears and derailleur were pretty dirty
It hasn't had a tune up or any self-service in years. It just seems like there's so much tension in the cable that's preventing it from shifting down below gear 5. Also I noticed even when I can shift down from 8 thru 5 that the derailleur looks like it's barely moving. This is just when it's sitting still, although while moving I didn't have much trouble shifting between 5-7.