I just gave my bike a going over with new bearing cages in the BB and a new chain. After putting everything back on I indexed the gears - finally getting the hang of the front but first time indexing the rear derailleur. It all felt fine on the stand, but when I go uphill with the rear gears on the lowest cog (6), when the pressure is on the pedals I get a weird jumping, clunking thing keep happening.

Now I was told this could be because my rear cassette is worn, but I've had a close look and done the brake-on-pedals-pushed test, no play on the chain on any cog, looks fine to me, how does this look to you :Rear cassette The mech doesn't look bent, either. Is it just that I need to get my indexing in better form, and need to perfect the cable tension, or are there other causes for this (like maybe wear on the drive cogs - do they look like they need replacing below?)?

drive train

  • Can you post another picture of your middle chain-ring without the chain on it? It sounds like your old chain was quite worn and "shark toothed" your chain-ring. Looking at your biggest ring, it is showing some pretty good wear. Commented Jun 18, 2016 at 16:35
  • 1
    The chain was pretty knackered, I'll be changing it more frequently from here on in! I've swapped out the drive train pic for one with a bit less chain, there's no doubt of the wear on it, I'm mainly wondering how bad the wear is on the cassette. Can wear on the chain rings cause this jumping as well?
    – James
    Commented Jun 18, 2016 at 16:53
  • Yes, a worn chain ring is actually worse, in my opinion. The chain will jump and about throw you off the bike if you are standing up. Commented Jun 18, 2016 at 18:43
  • Righto, if I'm going to change the cranks and drive train I'll bite the bullet and get one of these closed unit BBs, what measurements do I need to take to make sure the new spindle and chain rings will fit my front mech the same as the current ones? And are B-twin components okay?
    – James
    Commented Jun 18, 2016 at 19:10
  • The cassette doesn't look over-worn but the chain rings have the typical shark tooth look of severe wear.
    – Carel
    Commented Jun 19, 2016 at 8:31

1 Answer 1


Those teeth are severely worn, just by visual inspection. Try a new cassette, chain rings, and chain. (Don't try changing just one.)

It could have been the grime that was holding the worn system together, and when you cleaned it all the play now shows up. In the future, if you replace your chain more often you can make the chain rings last longer.

  • Is it really that bad? The drive train (bottom pic) I figured was pretty worn, but I didn't think the cassette (top pic) was worn, I thought the teeth start taking on a more shark-tooth profile as they wear?
    – James
    Commented Jun 18, 2016 at 16:30
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    If you've only just changed the chain, you can change the cassette without another chain. I've done this a couple of times. I recently fitted a new set of chain rings with about 70 miles on the chain and 50 on the cassette. That was also completely successful.
    – Chris H
    Commented Jun 18, 2016 at 16:48
  • I've only gone about 5-8 miles or so on the new chain. I think I'll look into a new drive train, would you say from that pic that the cassette needs replacing as well? Are B-Twin components okay (live near decathlon)?
    – James
    Commented Jun 18, 2016 at 17:26
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    You absolutely need to change the cassette, and probably the chain rings too. If you don't, your new chain will wear out very quickly.
    – BSO rider
    Commented Jun 18, 2016 at 19:45

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