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I bought a Scott Aspect 980 recently and it was working fine for the first 10km but after that, I had this one problem, where if I pedal really hard (up a mountain or just fast in general, when standing up) from time to time my pedals just kind of snap into place and make a loud noise, it feels like something to do with the chain but I know that bike sounds sometimes behave weirdly. I've been searching all around everywhere for this issue, no luck.

Big point: We went to a service-type cleaning/ fixing place and they did a lot. After that, it seemed all fixed and I was happy, but this problem restarted surprisingly after the bike got really, really dirty (I drove through mud, sand, rain, dirt, everything for around 40mins) my bike had dirt EVERYWHERE, and then the problem came back.

Any ideas? Help would be appreciated!

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    Sounds like the chain is briefly hanging up, then snapping into place. There are about a dozen possible reasons for this.
    – Daniel R Hicks
    Jun 27, 2021 at 12:19
  • Does shifting generally work smoothly and crisp? Is there a lot of noise from the chain?
    – Michael
    Jun 27, 2021 at 12:31
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    Do you feel like the pedals jump forwards when that happens? Or is it just a noise with no physical feedback.
    – MaplePanda
    Jun 27, 2021 at 17:30
  • Sorry for not replying, but yes the pedals jump forwards and there is a lot of noise.
    – martispyc
    Jul 21, 2021 at 16:02

2 Answers 2

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Everything about the story is consistent with freehub problems, like for example low lubricity or wear is causing partial engagement in the mechanism that then slips at a certain point.

It is also possible that the chain is skipping on the cassette or rings. If you can make it do it at will, then have someone help get the visual on that. The recent service followed by things seeming better suggests otherwise though. If all the worn drivetrain parts were replaced, it's probably not that, although if one of the chainrings was left and in borderline condition that could also be an explanation.

The story you present makes one of the likelier explanations become the shop heard your issue, serviced the freehub in a basic way (i.e. flowing oil into an enclosed type) and it behaved for a while but wasn't enough to keep the issue from returning. Depending on the design and the resourcefulness of the mechanic, it may or may not be possible to do it better, which in a lot of cases like this would mean flush with solvent and air and then relubricate with something more tenacious and difficult to inject. It could also just be worn out though; 10k on the stock wheel and that may be what you get.

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  • For some hubs it’s possible to replace the pawls and springs of the freehub mechanism.
    – Michael
    Jun 27, 2021 at 18:38
  • Thank you for the answer! I know this is late but can I still ride the bike even if the chain is skipping? Or do I need to immediately fix the problem?
    – martispyc
    Jul 20, 2021 at 13:26
  • @martispyc If it is the freehub slipping due to partial engagement, in most freehub designs that will mean the pawl teeth are subject to more premature wear every time it slips. In this case, continuing to ride it could possibly take it from fixable to not. It sounds a little like the practical solutions at this point for you are either a new freehub body or a new wheel though, and if that's what you're going to do than no, it won't make anything else worse by riding it. This is all if it actually is the freehub body.
    – Nathan Knutson
    Jul 20, 2021 at 15:00
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If the "snaps into place" means the pedal suddenly falls a very small distance and then stops falling, this sounds like the bicycle chain is skipping on the rear cassette (or freewheel if your bike has old-style freewheel).

The most typical cause for this is that the bicycle had an old chain that was too worn and was used for too long. The old chain wore the old cassette to the point that some of the sprockets had their teeth shapes changed in such a way that they now only work with a worn chain. Then the chain was replaced to a new one. The new chain no longer works under hard pedaling with the old worn cassette on some of the sprockets. Usually the most-used and smallest sprockets are affected.

The solution is to replace the cassette (or freewheel). See https://www.sheldonbrown.com/free-k7.html for identifying which one you have.

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