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Chain skipping/jumping issue.

andyrrandyrr Posts: 1,498
8 Speed Shimano.
Chain was worn to 0.75 on my Park chain tool, the 1.0 wouldn't go in so by my reckoning it wasn't too bad - I'd not noticed any jumping or poor running issues but a new KMC chain at £11 was sourced and fitted last night. Today out on a ride initially it gave a few skips in the big ring even around the middle of the cassette but that pretty much stopped other than occasionally on the 3rd largest sprocket. I stopped and checked that the chain itself was ok, quick link was ok etc. Generally I can ride 90% of my rides on the big ring even without cross chaining to the biggest rear sprocket but I swapped to the inner ring and it skipped like hell. As far as I can see excessive slack in the chain is being permitted causing this.
I think this is purely a rear mech issue and I've given it a good pushing and pulling since, as far as I can tell it it is a bit 'sticky' in moving back to take up the slack, I've unbolted it from the hanger and soaked in WD40 to help it's movement. I'm not sure what else I can do to help the mech move more freely - I think the pivot can be dissembled but it's a bit tricky - not done this previously.

The cassette has been on the bike for a few years whilst I've renewed chains and the chainrings are old athough aren't badly worn, certainly not shark tooth profiled yet but could it just be a mismatch of new chain/worn rest of transmission?


  • arlowoodarlowood Posts: 2,449
    One rule of thumb is 3 chains per cassette so if you've changed chains 3 or more times then I'm guessing the problem could be that your cassette is worn to the point where it is causing issues with the new chain.

    Then again if the derailleur arm is not taking up the slack in the chain when your on the small chain ring then that may also be compounding the problem.

    New cassettes are pretty cheap so I would try that after you've refitted the derailleur following it's WD40 bath
  • andyrrandyrr Posts: 1,498
    Yup, Swapped the Sora mech (even this was a swap out a few months back) for an old but nicely running Ultegra one I had - no change.
    Swapped the original chain back on (thank you KMC quick links) - back to running properly now. So it is either the cassette or rings - I'd have gone for the cassette as I agree, it's survived multiple chain renewals but the strange thing is it is pretty good on all barring the 3rd largest rear sprocket / big ring but on the small ring it is really skipping on numerous sprockets, certainly the smallest 4 or 5.
    Cassette next then chainset/rings seems sensible but I can use it as is for a bit whilst I look around for deals.
  • veronese68veronese68 Posts: 22,800 Lives Here
    Probably the cassette as above if you've been through a few chains with it. Especially if you rarely use the small ring up front yet it skips more in that. I suspect the fact that there is more slack in the chain makes it more likely to skip.
    I take it the chain is the right length as you've obviously done this before.
  • andyrrandyrr Posts: 1,498
    Thanks - yes, chain is the same length as the replacement one. I've probably pushed my chances with just a chain swap whilst it needs both that and cassette renewed.
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