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Chain slipping/jumping Trek 7.2FX

Scotsman64Scotsman64 Posts: 7
edited June 2018 in MTB workshop & tech
Hi everyone, new to the forum, so appreciate any help given.
I have a Trek 7.2FX it has SRam Suntour front drive chain, with Shimano Alivio derailleurs, it is an 8 speed bike, I replaced the chain as it was causing a problem, I think it might have had a bad link as it was jumping from the middle front cog to the smallest one without any tension, done about 5000 miles on it in 2 years, i replaced it with a Shimano IG51 chain, when i put them side by side, the old one was about an inch longer.
When I replaced it, it now has a different problem, the chain is slipping and not engaging properly, when I pedal the bike without stress, then it is fine, the moment there is tension it slips, all the chain links seem to be in the right place.
What could be the problem? could it be that the rear cassette needs replacing or the rear dérailleur? want to try and get it right first time without wasting too much money, and if it is suggested that it is the rear cassette, is there anyway to check it first.
Any advice please?

Posts

  • cooldadcooldad Posts: 32,601
    99% certain you need a new cassette.
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  • The RookieThe Rookie Posts: 27,748
    The worn chain almost certainly wore the teeth on the cassette which now cant mesh with an unworn chain, as CD says you almost certainly need a new cassette.
  • billycoolbillycool Posts: 833
    If you've done 5000 miles on it then both front chainring and rear cassette should need changing.

    If your chain is that worn out, it can cause additional/premature wear on your chainrings and cassette.

    You can buy chean measuring tools to make sure you replace your chain before it is too worn out. It works out cheaper in the long run.
    "Ride, crash, replace"
  • Scotsman64Scotsman64 Posts: 7
    Thanks everyone for your advice, I will look at the cassette to make sure I order the correct one.
    Thanks again!
  • Scotsman64Scotsman64 Posts: 7
    Actually after recalculating the distance, it is about 4000 miles on the last replacement of the chain and I have done 8000 miles on the cassette and front chainring! so definite in need of a change!
  • billycoolbillycool Posts: 833
    Scotsman64 wrote:
    Actually after recalculating the distance, it is about 4000 miles on the last replacement of the chain and I have done 8000 miles on the cassette and front chainring! so definite in need of a change!

    LOL - I think you're right! :lol:

    This is a useful article to help understand it a bit more:

    https://www.bikeradar.com/road/gear/art ... ned-46015/
    "Ride, crash, replace"
  • Scotsman64Scotsman64 Posts: 7
    billycool wrote:
    Scotsman64 wrote:
    Actually after recalculating the distance, it is about 4000 miles on the last replacement of the chain and I have done 8000 miles on the cassette and front chainring! so definite in need of a change!

    LOL - I think you're right! :lol:

    This is a useful article to help understand it a bit more:

    https://www.bikeradar.com/road/gear/art ... ned-46015/
    Thanks for that! excellent article, wish I had read it a year ago!
  • Just an update on results.
    Changed the rear cassette, what a difference! still I can feel not 100 percent perfect, so ordered the front crank drive and will replace, measured the old chain and couldn't believe it was over an inch longer! not surprised then with performance, will have a proper maintenance schedule from now on.
    Thanks everyone for your help
  • billycoolbillycool Posts: 833
    Glad you've got it sorted.

    Changing front chainring should help as well.

    Remember - look after it!
    "Ride, crash, replace"
  • 02GF7402GF74 Posts: 1,294
    Scotsman64 wrote:
    it was over an inch longer!


    Wow, that seems huge but doing a quick calculation is just 0.2mm per link.

    You can invest in a chain gauge, if replace at 0.75% you can run 3 or 4 chains on the same cassette. They cost around a fiver.
  • 02GF74 wrote:
    Scotsman64 wrote:
    it was over an inch longer!


    Wow, that seems huge but doing a quick calculation is just 0.2mm per link.

    You can invest in a chain gauge, if replace at 0.75% you can run 3 or 4 chains on the same cassette. They cost around a fiver.
    I know! Couldn't believe the difference over two years, I have a vernier guage and I will plan to keep it maintained, the cassette was only £13 so not bad, although the Crank was about £22, so all adds up.
  • 02GF7402GF74 Posts: 1,294
    I used to use a vernier gauge but trust me, the expense of the wear tool is well worth it, much quicker to use and avoids the guessing of where the centre of the pin is.
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