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I have a new bike with exactly the same problem and same drivetrain (SRAM GX) as shown in this video:

(not my video).

When pedalling with the chain on the 5th smallest cog, there is an irritating clicking sound. It is not loud enough to be heard on a busy road, but it is clearly audible when out in the quiet of nature. The cause is clearly visible in the video: one tooth on the 4th cog will pick up the chain and drop it back.

I live in a country where I do not speak the local language fluently, and I cannot get anywhere with the local shop. I gave up on trying to make the problem clear to them. I'm basically on my own.

What would you do?

Is it a good idea to just ignore the problem, and hope that it will go away once that tooth wears down? Will ignoring the problem cause damage (e.g. premature wear)? Should I try to push a warranty claim (I expect it not to be easy)?

It appears to be a rather common problem. There are many references to it online. The only suggested solutions I could find were to bend or grind that one tooth, neither of which am I ready to try.

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    Make sure all the teeth are straight and that you haven’t bent a cog. That’s usually the cause of single cog clicking.
    – MaplePanda
    Commented Aug 27, 2020 at 18:40
  • Ah, interesting. My GX Eagle has that exact same problem too, never knew it was such a common thing.
    – leftaroundabout
    Commented Aug 27, 2020 at 21:26
  • @MaplePanda I don't see how a cog could have been bent. It is basically new and it has not been abused. It is telling that the majority of complaints on forums are about the 5th cog, which suggests a manufacturing defect.
    – Magd
    Commented Aug 28, 2020 at 9:09
  • At this point, my main question is: can this be safely ignored or should I keep pushing the issue (e.g. try to get it fixed under warranty, which is difficult)?
    – Magd
    Commented Aug 28, 2020 at 9:10
  • @Magd I would definitely keep pushing for a warranty. If the cassette catastrophically fails, use that to your advantage “the cassette just exploded!” I’m thinking it’s due to GX’s pinned construction: there might not enough meat to hold all the cogs together, especially if the press fit tolerances are off. The higher end cassettes are machined from one solid chunk of steel.
    – MaplePanda
    Commented Aug 28, 2020 at 23:02

4 Answers 4

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The chain on a twelve gear cassette is very thin and the tolerances are close. Move the chain onto another ring and look directly at the cog as somebody turns the pedals. Look to see if the tooth is very slightly bent towards the larger ring by comparing to those next to it. Failing that, see if it is a machining fault, is the tooth chamfered in the same way as those around it. Note: some teeth are deliberately different to help the chain move across the cassette, but all should be slightly chamfered at the tip.

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I have had the same issue with multiple SRAM XG-1275 cassettes, regardless whether new or worn, always using GX Eagle chains (haven't tried other chains, but I doubt this would make a difference), and I can safely say that, although it is insanely annoying, from a functional point of view you can ignore it. I use the particular bike on which this occurs for everything from long climbs to enduro rides, and apart from the irritation I have never had any problems with the function of the drivetrain because of this.

What you could try as a solution is reindexing the gears. To be more specific, you could tighten the shift cable (by rotating the barrel adjustor on the shifter counterclokwise) so that the guide pulley, and consequently the chain, is a little closer to the wheel, i.e. further from the fourth smallest cog with which it collides and clicks. However, if your indexing is already fine, this could make the shifting worse, so only do this to an extent where it does not yet affect the overall shifting quality. For me, this marginally improved the situation, but never solved the problem completely.

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Looking around on pinkbike and MTBR it looks like a consistent issue with pinned eagle cassettes (like GX) and maybe the chains. I've seen folks take a light file or sand paper to an individual cog tooth. Have you already checked derailleur hanger alignment and chain line spacing (spacers at the crank?).

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"Make sure all the teeth are straight and that you haven’t bent a cog. That’s usually the cause of single cog clicking. – MaplePanda Aug 27, 2020 at 18:40"

After careful inspection, this is what I found as well. Thank you MaplePanda. I had significant clicking/skipping in the #6 (6th smallest) cog. After looking carefully, I found a bent tooth on the #7 cog, and this was engaging the chain upon each revolution. I straightened it with some needlenose pliers. I only hope by straightening it I didn't weaken it. Fingers crossed it won't break off!!

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