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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.

  • Oddly, I suspect that the cable is too loose. – Daniel R Hicks Jun 6 at 22:37
  • I only have limited understanding of gears adjustment, but could it be a matter of the L screw being totally wrong? – pateksan Jun 6 at 22:54
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    can you move the mech/derailleur over by hand or is that stiff? Sounds like corrosion to me, in the mech or cables, Also do note you need the rear wheel turning to change gears - can't change far while standing still. Is very unlikely to be the limit screws unless you've already fiddled them. – Criggie Jun 6 at 23:25
  • Like Nathan I think it's the cable and housing. Materials are cheap if you can DIY. Even if it isn't the cause it's a wear item you should replace periodically. I had to replace mine on a new bike the first season (too many creek crossings I guess). – shox Jun 6 at 23:52
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    @pateksan you are absolutely right. However, I would normally worry about the cables first, unless the OP indicated that they tried adjusting their bike themselves. The reason is that cables can stretch in normal operation. In contrast, you have to actively find the limit screws and fiddle with them. – Weiwen Ng Jun 8 at 17:43
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It's a little unclear whether the shifter is refusing to get into the lower gears based on what the indicator is showing or if it's indicating lower gears than 5 but nothing is happening in back. Also I'm assuming by "lower" you mean larger cogs and that you don't have a Rapid Rise rear derailleur.

If the shifter is clicking from gear to gear but not moving the rear derailleur into the large cogs, it's likely you need a bunch more cable tension. This is one of the more common break-in type adjustments bikes need. There are plenty of questions here about this, but the basic process is loosen the RD cable, screw the barrel adjuster(s) on the shifter and/or RD in, and fasten the cable back so that you have all the slack taken out, barely taut, then use the barrel adjusters to fine tune from there.

If you mean that it's having a hard time getting into the small cog (the high gears), then check to make sure there's not a cable housing end hung up on either a housing stop on the frame or the where it enters the shifter or RD.

If you did happen to have Rapid Rise, either of the above problems can still occur, but the symptom that goes with each solution would be switched in terms of which end of the cassette you can't shift into.

Friction in the housings could cause this problem too but it sounds like you've eliminated that. Make sure you've checked all the RD housings - bikes can have 1, 2 or 3 of them depending on the design.

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  • Check the cable routing and possible excess friction at the bottom bracket cable guide, at the bottom of the bike where often the inner cables are routed on their way back to the derailleurs. Also check that the inner cable is routed and connected properly at the derailleur. Even a small error like securing the cable on the wrong side of the pinch bolt or out of the designated groove for it can cause poor shifting. – Jeff Jun 7 at 21:22
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    thanks for the reply; I ended up fixing it by taking the cables off whatever those things are called where the housing attaches to the frame, sliding the housings around, and then re-attaching them. – user26270 Jun 8 at 20:53
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It sounds like you need a tune up. If the cable is too loose or too tight, it wont shift properly. My suggestion is that if your not great at working on bikes (like me), you should take it to your LBS and have them check it out. Theyre most likely going to do a tune up though.

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  • I definitely need a tune up, but I don't want to lose my bike for a month in the middle of prime season. Last I checked, that was the wait time at the LBS. Although I ended up fixing it by taking the cables off whatever those things are called where they attached to the frame, sliding the housings around, and then re-attaching them. – user26270 Jun 8 at 20:51
  • oh ok nice. well its good that its fixed. All the bike shops are packed now because were told to stay inside, then everyone like "How about we have no idea how to ride a bike but buy one then try to fix and then take it to the LBS and then struggle to ride a bike!" – DripKracken Jun 8 at 20:53
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It ended up having something to do with the cable tension. I ended up fixing it by taking the cables off whatever those things are called where they attach to the frame, sliding the housings around, and then re-attaching them. Worked fine after that! No idea why. It seemed like you could adjust the tension between the 2-3 places where the cable housing attaches to the frame.

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