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My chain is a SRAM PC-971, worn less than .75", and my derailleur is 9-speed 105. I just installed a new Shimano HG-400 cassette, and it seems like the chain isn't 'meshing' correctly, causing a rhythmic crunching noise as it jumps from the jockey wheels to the cassette (video, worse when under load). This happens in all gears, big/small chainring, with the B-screw in all the way and with it removed completely. The bike shifts well and otherwise performs fine. Is this noise/misalignment anything to worry about? Will it go away over time?

Screencap from video of chain and cassette before a "jump": enter image description here

And immediately after: enter image description here

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    Typically, similar issues when replacing a cassette but not the chain are due to the chain being worn. The old cassette wore along with the chain, so changing only the cassette and not the chain maximizes the wear mismatch even if the chain seems to still have usable life left in it. I'd try a new chain and save the old one if you want for use when your cassette is more worn.
    – Armand
    Jul 29, 2022 at 3:49
  • Another possibility is that when you rejoined the chain as part of reinstalling it, the link there is stiff or misaligned. Perhaps undo and redo the quick link, and make sure it is fully seated after closing it by e.g. applying rear brake to secure wheel and using foot to rotate crank forward with quick link chain section taut between cassette and cranks.
    – Armand
    Jul 29, 2022 at 3:56
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    A previous similar question with some more ideas: bicycles.stackexchange.com/questions/65215/chain-cassette-noise
    – Armand
    Jul 29, 2022 at 4:00
  • My chain wear indicator says the chain is worn less than 0.75", and it seems to 'jump' every couple of links (precluding the possibility of a single stiff link). I also never removed the chain, just removed the wheel and swapped cassettes.
    – JoshuaF
    Jul 29, 2022 at 4:08
  • That question seems pretty relevant -- it seems like other people have had issues with 9-speed sram chain + shimano cassette compatibility
    – JoshuaF
    Jul 29, 2022 at 4:09

1 Answer 1

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The chain checker tools are only an indicator and in my experiences are relatively coarse.

Your results show that the chain is indeed skipping on a cog. Possible causes:

  • Chain is worn or damaged. Grab two adjacent links between forefingers and thumbs, and feel for play. "Barely perceptible" is okay, much more indicates wear.
  • Chain is too long and has insufficient tooth engagement. Ensure there's barely enough chain to be in big-big without binding.
  • Cassette is damaged or poorly made. Might have burrs on it.
  • Indexing is a bit off and the chain is not sitting clearly on one cog. Twiddle a barrel adjuster and see if this helps.
  • Chain is not consistent across its length - you many have a stiff link, or maybe a damaged master link.

I had the stiff link once, but only in one direction when going over the top jockey wheel. It was not easily visible even when standing beside the bike. Try and mark the chain with permanent marker and see if the skip happens at or near the same link, or some other commonality.

Good luck ! These problems can be challenging to isolate, but a new chain may be the quickest and easiest solution. If it doesn't fix the problem, then you have a spare chain for the future.

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    New chain mostly resolved it
    – JoshuaF
    Aug 4, 2022 at 22:31

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