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I have a new chain on a used bike that has been working perfectly for 500km and the chain has started jumping a cog on every different speed. It definitely feels like a cog and chain slipping, the pedal falls forward and catches on again.

Can it be inside the rear wheel bearings? The chain is the only thing that can be faulty? It's by a good company and fairly new, and I couldn't see a fault on the chain. What can it be?

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  • A video would help diagnosing Jan 14 at 6:48
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    95% likely its chain wear or sprocket wear, or both. A picture of the cassette would help, and check the chain for stretch by measuring 10 links exactly while under tension.
    – Criggie
    Jan 14 at 7:13
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    Likely new chain on old sprocket syndrome. How many km did the old chain have when it was replaced? How many km did the sprockets have?
    – Carel
    Jan 14 at 7:22
  • @Carel this is not a comment but a (correct) answer. Please also add that riding for say 100km will wear the chain enough to make it fit the cassette.
    – Vorac
    Jan 18 at 15:31
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    @Vorac running a new chain on a very worn cassette is likely to destroy the chain very fast rather than making it fit! :-O
    – Carel
    Jan 19 at 15:51

5 Answers 5

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When cogs are worn, new chain makes things worse. In my case, the old chain was skipping time to time but the bicycle was rideable. With the new chain the two fastest gears went completely unusable. The same new chain works now well after I replaced also the cassette.

Surprisingly, first problems with drivetrain also appeared as soon as after 400 km. This may be aggravated by my previous riding style, using the fastest gear mostly all the time.

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I had the same/similar problem straight after replacing a stretched chain.

In my case, the new chain was just a bit too long, which meant there wasn't enough tension in the rear derraileur - resulting in the chain slipping.

Solution for me was to remove a single pair of links from the chain.

Compare the length of your old chain and new chain first. If the new one is longer, this solution could work for you.

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    Count links, do not just measure the length
    – nightrider
    Jan 15 at 8:48
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It is likely to be the classical new chain on old sprocket syndrome.

How many km did the old chain have when it was replaced? How many km did the sprockets have or rather how many chains have been used-up on the existing sprockets?

If the chain was very badly worn, like having been used for 5000+ km it is most likely that the sprockets are so badly worn that they need replacing as well.

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Regular skips suggest that LifeInTheTrees may be on the correct path. Check every link on the chain and confirm that every pivot moves freely. A quick-link seems to me to be the least likely culprit, but you may have a regular link binding somewhere. If you have a chain tool, you may be able to free up the binding link by moving the chain's rivet a little.

It seems more likely to me that the problem is in mating a new chain with an old, worn freewheel/cassette. In normal operation, both the chain and the cogs experience wear, and after a couple of thousand miles, a new chain doesn't really fit the enlarged spacing of the cogs. I've gotten into the practice of replacing chain and freewheel together after an unexpected skip made me fall on a busy road.

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If you are using indexed shifting, and the chain is slipping on every cog in the same manner, it could just be a matter of adjusting the derailleur so that the chain is aligned with cogs when you are in-gear. All the answers above look reasonable as well, and if you're not able to figure it out on your own, your local bike shop (LBS) might be your next best stop. Best!

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