3

When I try to shift up to the largest gear, the derailleur moves up, and the chain moves on to the gear, but then comes back down. Upon closer inspection I found that when I hold the shifter, it shifts up and seems fine, but after I let go of the shifting lever, the derailleur moves back to the second largest gear.

Earlier I thought someone was wrong with the l-screw, but I ended up loosing it too much, with the chain almost failing of the cassette.I also tried the barrel adjuster but no effect. The shifting for everything else is perfect. My only other thought is that the hanger is bent, but it doesn’t appear so (as far as I can tell with my eyes)

I have a road bike with SRAM rival for shifting, and it’s only been a few months after I bought it. The issue came about after I was realigning my derailleur for a different issue (it was skipping gears, but I fixed it)

Here a video of the issue if it helps: https://youtube.com/shorts/4dOJZHFjnSY

2 Answers 2

5

Since you already know about limit screws and derailleur hangers, you probably checked this first, but are you sure it's not just a case of needing a bit more cable tension on that derailleur? I.e. backing out one of the inline barrel adjusters on that derailleur's cable a half turn or so.

Keeping pressure on the shift lever like you mentioned simulates a little extra cable tension, and the fact that it will actually get to that gear suggests that the limit screw is not grossly out of range. You also mention it's a new-ish bike, and cable stretch in the first few weeks or months with a new bike, leading to exactly this type of degradation in shifting in that time frame, is a common scenario and usually fixed by simply adding a little cable tension.

Tiny adjustments are key. One approach I find works well is put the bike in a workstand, or hang it with some rope, or even just have another person hold the rear wheel off the ground. Then, without pedaling, shift into the gear you're having trouble with. Then start turning the pedals slowly. You'll then probably observe the chain do one of a few things:

  • Shifts to the target gear but then makes clicky noises and occasionally drops back to the smaller cog and/or moves back and forth spontaneously. The cable needs a tiny bit more tension in this case. You may find 1/8 to 1/2 turn sufficient to fix this.
  • Doesn't fully shift to target gear but gets part way there, e.g. rides up onto the larger cog for part of a cassette revolution before dropping back down. Will need more tension than the above case.
  • Doesn't shift or ride up but start making clicky sounds. Needs even more tension than previous case.
  • Doesn't shift or make any clicking sounds. Needs a lot of cable tension added.

If you find you have to back a barrel adjuster way out, you may instead want to wind it all the way in, and then unclamp the cable at the derailleur and pull in a larger amount of slack there before continuing with fine adjustment at the barrels. Ideally you don't want those spooled all the way out to the point where there's no room left for a mid-ride tension increase. And obviously you don't want them popping right out of their threads.

After the above, when you find the cable tension setting that makes the gear shift cleanly in a workstand setting, sometimes you'll need to then spool it back in a tiny amount (remove a bit of tension) to factor in that when you're shifting during a ride, you usually provide a little tension boost during the shift before releasing the shifter.

Finally, as mentioned in the comments below, you may find after working cable tension back and forth that you can't get a single tension setting that makes your derailleur work well across the entire cassette. E.g. maybe you can get it indexed really well for the 4 largest cogs, but then the 4 smallest cogs don't shift well. Then you fiddle it the other way and now the 4 smallest cogs shift great and the 4 largest are bad. And there's no way to get all of them shifting well. That's a hint that there's something else wrong besides cable tension. Could be a bent hanger as mentioned. I've also had the same thing happen when I had a very worn chain + casette (probably not the case here given the age of your bike). I've also had similar happen when I had a defective cable where the steel cable wrap had loosened bit over about an inch of cable that happened to sit right under the bottom bracket. So that caused extra friction and crummy shifting in a couple of gears as that portion of cable passed under the BB.

6
  • 1
    I had the same problem, it always makes sense to go with cable tension first because that is more likely to go off during riding then L or B-screws. The cable needs a minimum of tension so that it is even able to reach the largest cog, so I'd also bet on the cable, just give it a bang until the chain stays on. If that then compromises other shifts (or you never get all gears to shift cleanly), you might still have a bent derailleur (you might not have noticed it or sb else is to blame).
    – DoNuT
    Jun 22, 2023 at 7:08
  • Thanks, your solution worked! I’ve gotten it to shift up, but now it’s messed up the shifting on a few other gears ( skipping or rubbing against a another gear) Should I just keep on trying to adjust the cable?
    – Alex L.
    Jun 22, 2023 at 7:52
  • Derailleur adjustment is a bit fiddly and you might need to get back and forth until every gear works fine. Important is to make small adjustments and remember in which direction you went so that you can go back. If you increased tension and that made your last gear shift, back it off a twist and see if this improves shifts in the middle of the cassette while still staying on the large cog reliably, might need a few iterations. If you can't get an acceptable result, perhaps there is a tiny bend on the hanger. Maybe LBS can help/diagnose on the spot, then ...
    – DoNuT
    Jun 22, 2023 at 8:44
  • 1
    Agreed, tiny adjustments are key. I've added more detail to my answer to expand on this as well as notes on if you can't get the whole cassette shifting well.
    – SSilk
    Jun 22, 2023 at 9:17
  • @Alex L. If you feel the limit screws are set correctly, work on the appropriate cable tension. A good technique after the cable slack is removed from the system with shifter in beginning position and chain on smallest cog, is to shift up to the second to smallest cog. There should be adequate cable tension to complete this shift already from the slack removal. If not, back and dial up some tension with the barrel adjuster turned ccw. With shifter at the first detent and chain on second from smallest cog, turn the cranks while moving the shift lever about a 1/2 throw...
    – Jeff
    Jun 23, 2023 at 0:25
2

My guess is that the L-limit screw needs to be turned out (counterclockwise) an 1/8 of a turn. This will allow a little more free travel of the upper jockey wheel to the inside where it can better align with large cog and consequently keep the chain running there.

As you seem to have experienced, loosening the L-limit screw too much can cause the derailleur to over shift the chain to where it'll derail between the cassette and spokes. It can be a much worse situation when the derailleur cage gets snagged by a spoke resulting in a very messy situation. Thus, incremental adjustments of the L-screw is advised. Also, put pressure on the shift lever after the shift is made, much like when you describe holding the shifter which allowed the chain to stay running on the large cog. In this case you're checking that the limit screw is stopping the cage movement to the inside well before derailling the chain or causing the cage to contact a spoke.

The proper setting of the L-limit screw is done with the chain on the small front chainwheel (2x or 3x systems) and on the largest rear cog. Manipulate the L-limit screw so that the upper, jockey wheel of the derailleur runs directly under the large cog. The points of the teeth of each should share the same vertical plane. In addition to the 1/8 of a turn of the limit screw, you may have to dial in a bit more cable tension with the barrel adjuster.

Finally, while the chain is running in this position of small chainwheel/large cog, check that the B-screw adjustment has allowed the appropriate gap between the tips of the jockey wheel's teeth and teeth of the large cassette. Typically this gap should be 5-6mm but can be more when using a large range cassette having a large cog of 42 or more teeth.

4
  • Sounds unlikely: The question states that the derailleur moves to the largest cog without problems. It just moves back when pressure on the lever is released. It would not be able to move there if the limit scew prevented it, would it?
    – Burki
    Jun 22, 2023 at 9:10
  • @Burki moving just enough for the shift ramps on the big cog to pick up the chain, but not enough for it to stably sit on the cog, is certainly possible with a limit screw that's not quite right. I'm more used to seeing it try to engage but drop off within half a turn, in that case, then try to pick up again, and so on, but I've seen other similar versions of this failure mode
    – Chris H
    Jun 22, 2023 at 10:39
  • @Chris H is exactly correct. A mm makes a huge difference. Consider the fine threads of a barrel adjuster--a full turn either way moves the inner cable less than a mm and that can make all the difference in the quality of a shift. Now consider the advice to turn out the L-limit screw an 1/8th of a turn. Close observation will detect the resulting incremental movement of the jockey wheel that can make all the difference here.
    – Jeff
    Jun 22, 2023 at 23:57
  • Similarly, the additional force on the lever against the last detent will increase tension on the cable forcing a hard stop against the limit screw. There's enough flex in the system to cause a very incremental movement of the derailleur cage with it's jockey wheel that the chain can run sustained on the large cog. This quality is also why a forced over shift is a good check that the limit screw is not too far out that it will allow the chain to drop off the cog into the spokes: accounts for this wee bit of movement caused by increased cable tension when stopped at the limit screw
    – Jeff
    Jun 23, 2023 at 0:10

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.