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I just purchased a bike, with 7 gears. When I cycle in 5th and 6th gear it's making a clonking noise when pedalling. It doesn't do this noise in any other gear just the 5th and 6th.

My partner said it sound like it's coming from the crank shaft but it's not that. It is from the back somewhere. He has checked it and it's not misaligned and he has tightened up the screws if it was the derailleur why would it only happen in 5th and 6th gear. I'm confused by it.

I would anyone know what the cause of this is and is it a fault with the bike?

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  • Where is the clonking sound coming from, do you know? I assume it's somewhere near the drivetrain/towards the back? It might just be misaligned (usually when you're in the smallest/biggest gear in the back some sound might occur). Though I would not specify this as clonking. Perhaps the derailleur/derailleur wire is hitting the spokes?
    – Bono
    Commented Apr 22, 2021 at 8:38
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    Try hanging the bike so the rear wheel is off the ground. Then gently hand-pedal the cranks with left hand while watching at the back, and changing gears with your right hand. That may help show what's going on. Do be careful of spinning parts and your fingers.
    – Criggie
    Commented Apr 22, 2021 at 9:04
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    Does the noise appear while coasting in those gears ? (suspect not) Does the noise happen if you backpedal while riding ? (likely) Is the noise frequency lower in the harder gear? A clear, well-lit photo of the rear of the bike, from the right hand side could be useful too - try using edit to add that to your question.
    – Criggie
    Commented Apr 22, 2021 at 9:07
  • My partner says it sounds like the crank shaft but it's not that .its from the back somewhere he has checked it and it's not misaligned and he has tightened up the screws. If it was the derailleur why would it only happen in the 5th and 6th gear. I'm confused by it all
    – Sue
    Commented Apr 22, 2021 at 9:07
  • When he gets in I will ask him some more questions about what it's doing then I will post
    – Sue
    Commented Apr 22, 2021 at 9:12

1 Answer 1

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If it's only making sounds in certain gears then it's most likely related to the cassette and derailleur. Top or bottom of the range (first or last gear) would indicate an issue with the limit screws.

Middle of the cassette issues tend to be caused by a bent derailleur hanger. Fixing this is best done by a shop or someone with a derailleur alignment tool (a Park tools DAG is probably the best known example). Another alternative is to get a new derailleur hanger which should be straight when new. Depending on the bike they can be inexpensive. Most are specific to the bike (or a range of models) though there is a new universal derailleur hanger specification (UDH) that many new bikes are supporting (some 2022+ bikes with rear through axle). If the bike does not have a replaceable hanger, then the derailleur mount point must be bent straight (again using a tool to verify alignment).

Another possible cause of noise in some gears or poor shifting is the b-tension screw (assuming the derailleur has one). I'd expect this to cause noise across the entire range of gears though.

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    how would you go about confirming that the issue is, in fact, a bent derailleur hanger?
    – njzk2
    Commented Apr 14, 2023 at 18:34
  • A visual inspection can be sufficient if it's quite bent. Fresh damage (i.e. scuffs/scratches) to the derailleur would be a good indicator that it's likely bent. Having owned a Sram Eagle driveline I would just assume it was bent (very picky to alignment) and get out the DAG. Mind you I ride a mtb in janky terrain and it's safe to assume I hit something. I guess a sticky cable could also cause mid cassette issues. Everyone should have an extra derailleur hanger on hand (many/most bikes come with one), swapping it out would verify the hanger is the issue if you don't have a tool.
    – shox
    Commented Apr 14, 2023 at 20:43

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