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When pedalling in higher gears, the crank or cassette seem to completely lose grip for a second, then grip then lose it again. I could probably pedal all day in 1st and any front ring but when start to go in 6/7/8th it will do it.

This is not a gear change problem, all gears change perfectly and when the bike is on the stand everything works perfectly.

In order to try to cure the problem, the front and rear derailleurs have been renewed including cables, the chain renewed, the derailleur hanger also, but the problem remains. I tried swapping the back wheel with known good one off another bike to eliminate the cassette, but the problem stayed the same.

The front crank has a tiny bit of play but the teeth look ok - none obviously more worn or broken than others - the biggest ring on the crank has been bent and straightened, not perfect but it has been working fine previously like that, plus the problem exists on the two smaller rings too.

Any help appreciated

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  • 2
    So, did you try with new chain and two used cassettes? Sounds like it's time for new cassette.
    – ojs
    Commented Mar 25, 2020 at 9:18
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    Sounds to me like a worn chain hanging up on the chainring.
    – Daniel R Hicks
    Commented Mar 25, 2020 at 12:22
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    Have you checked the frame for cracks?
    – renesis
    Commented Mar 25, 2020 at 13:16

3 Answers 3

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The comments above are probably correct; if your chain is new, then the issue is likely a worn cassette. Because they wear out as a pair, chains and cassettes are often replaced simultaneously. A new chain on an old cassette can lead to skipping, just like an old chain on a new cassette can lead to skipping.

Another possible cause of "losing grip" could be a damaged or missing pawl inside the freehub body's ratcheting mechanism. If, for example, one out of your three pawls is chipped or has broken off, the freehub will engage fine under light load, but heavier force (like pedaling hard in higher gears) can cause the hub to "freewheel" briefly in the wrong (pedaling) direction.

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  • Ok, thanks for all comments and assistance. Yes it is a new chain, but still the old cassette, The thing is, it had the issue before any parts were replaced.. Which lead me to suspect the cassette internals, but I thought I had illuminated that by swapping rear wheel/cassette but identical problem remained.. As the general consensus seem to be cassette then I guess that should be my next purchase and I will also check the frame thoroughly for cracks.. Any thoughts on chain length? As when chain was replaced I just took it out box and fitted it, regardless it had the issue with old chain.
    – Bodaeshus
    Commented Mar 28, 2020 at 6:44
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    While the cassette itself does not have any moving parts, the freehub body on which the cassette sits does (e.g., pawls). Regarding the chain, if you took the chain out of the box and put it on the bike without shortening it (removing links) to match the length of your old chain, then it is almost certainly too long. A chain that's too long can cause a handful of problems, including skipping/slipping off gears. If you already threw away the old chain, you can find loads of resources for sizing a chain to your bike on this site, Sheldon Brown's website, or ParkTool's videos, to name a few.
    – Poquontchn
    Commented Mar 29, 2020 at 9:48
  • Look at the teeth on the old cassette gears and they are probably really really worn, compared to new one. I just fixed this on a mtn bike that would "clunk" and skip the high gears recently.
    – NoBugs
    Commented Oct 7, 2020 at 3:36
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    Regarding chain length: The rear derailleur should be almost fully extended on the big-big gear combination and there should still be tension on the small-small gear combination. Usually one makes the chain as short as possible. Just long enough so that shifting to the big-big combination still works.
    – Michael
    Commented Oct 7, 2020 at 8:05
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I had the same issue after changing to a new cassette with a smaller highest gear (12 tooth instead of 14). I had to shorten the new chain so it was a link or two shorter than the old one. Even then, I still have occasional slipping when using small/small gear combinations. As a result, I don't put a large amount of torque on any combo smaller than smallest chainring w/ 3rd rear gear.

This point boils down to technique. If I have to put serious power on my drivetrain, I try to anticipate it and stay out of combos that will put a lot of slack in the chain.

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  • The risk here is binding the chain when changing to a large-large combo. You must still have enough links in the chain to make it into this gear, even if you never plan on using it. Otherwise the damage is immense - the frame will probably survive but I've seen hangers and rear derailleurs and rear wheels seriously damaged by a too-short chain.
    – Criggie ♦
    Commented Aug 7, 2022 at 5:00
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Get IG51 chain, it is 0.2mm narrower.

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    Welcome to the site - could you please expand on why you think this will help OP's problem ? IG51 is 6/7/8 speed rated, and OP appears to have an 8 speed cassette. Use edit to enlarge your answer with "why". You can also read the tour to learn how the site works, and look at other questions with highly upvoted answers for the level of detail that make a good answer. bicycles.stackexchange.com/help/how-to-answer can also be useful.
    – Criggie ♦
    Commented Aug 7, 2022 at 5:02

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