ghosting on rear cassette

robertzee
robertzee Posts: 21
edited May 2013 in MTB workshop & tech
Hi all,
I hjave an ongoing problem with gears jumping on the rear. This started last year and so I fitted a new 9 speed chain which did not resolve the issue so a couple of months later fitted a new 9 speed slx cassette. The slx cranks are also new as are the xt front and rear mechs. The gears work fine on the workstand and also seem ok for periods of flat riding but as soon as any pressure is put on the pedals the chain starts jumping and also can just change gear on its own free will. Please note this only happens on the large front chainring. Could it be the shifters as these are the only item I have not renewed?
You may be too old to rock but never too old to roll.

Comments

  • bennett_346
    bennett_346 Posts: 5,029
    Can be due to flex in the frame/wheel/axle etc.
  • maringirl
    maringirl Posts: 195
    Is it a full sus bike? If the gear cable outer is routed under the bb too tight on one of these this can happen as the frame 'expands' then contracts. You need to leave a big loop underneath the BB to accommodate(doesn't look pretty).
  • robertzee
    robertzee Posts: 21
    no its a hardtail,upgraded Trek4500, Thanks.
    You may be too old to rock but never too old to roll.
  • robertzee
    robertzee Posts: 21
    bennett_346 wrote:
    Can be due to flex in the frame/wheel/axle etc.
    There is slight play in the cassette ( maybe 1mm max) but when I pointed this out at my lbs when having a spoke replaced I was told this is quite normal.
    You may be too old to rock but never too old to roll.
  • cooldad
    cooldad Posts: 32,599
    It is normal.
    And highly unlikely to be the shifters.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • swod1
    swod1 Posts: 1,639
    Have you tried re indexing the gears ?

    you mention it only happens on the large front ring, you mean the big one as could be chain length ?
  • dv69
    dv69 Posts: 19
    robertzee wrote:
    Hi all,
    I hjave an ongoing problem with gears jumping on the rear.

    When you say jumping I assume you mean the chain is shifting between gears. This happened to me when the derailleur hanger had a very slight twist; under increased chain tension the derailleur was twisted back into line and the chain started skipping onto the next gear.
  • robertzee
    robertzee Posts: 21
    swod1 wrote:
    Have you tried re indexing the gears ?

    you mention it only happens on the large front ring, you mean the big one as could be chain length ?
    How would I do that please?
    You may be too old to rock but never too old to roll.
  • njee20
    njee20 Posts: 9,613
    If it only happens on one chain ring I'd be looking at that ring - worn, damaged, bent etc.
  • swod1
    swod1 Posts: 1,639
    njee20 wrote:
    If it only happens on one chain ring I'd be looking at that ring - worn, damaged, bent etc.

    also the front mech setup as robertzee mentions was new also, could be something in this that is why the chain jumps ?
  • njee20
    njee20 Posts: 9,613
    Very unlikely, it has a very passive role in the drivetrain - only really does anything when you change gear.
  • robertzee
    robertzee Posts: 21
    Thanks for all your suggestions but think I am going to try new cassette and chain and go from there.I could do without the expense at present but am running out of ideas.
    You may be too old to rock but never too old to roll.
  • swod1
    swod1 Posts: 1,639
    Did you fit all these yourself, because i would get a bike shop to take a look ?
  • robertzee
    robertzee Posts: 21
    I did yes but had a total strip and rebuild last year by a very highly rated bike mechanic to hope resolve the problem, but to no avail.
    You may be too old to rock but never too old to roll.
  • njee20
    njee20 Posts: 9,613
    Why change your chain and cassette? If it only happens on the big ring take that out of the equation. Seems very straightforward to me!
  • cooldad
    cooldad Posts: 32,599
    What njee says. Also have a look at the mech hanger.
    If it still happened after you replaced the chain and cassette, replacing it all again seems a bit pointless.
    A remote possibility, but are the BB spacers right. Could be an extreme chainline in the big ring.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • robertzee
    robertzee Posts: 21
    Just to confirm. The chain jumps on the rear cassette but only when on the big front ring. It does not jump when on the big rear sprocket however which is where you will get the most cross chaining. There is no jumping when on the middle front ring all the way through the 9 rear rings.
    You may be too old to rock but never too old to roll.
  • cooldad
    cooldad Posts: 32,599
    We got that. So why a new cassette and chain if they work perfectly?
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • njee20
    njee20 Posts: 9,613
    As above, you've explained it, you've narrowed the problem down to the big ring, so why are you looking anywhere else?

    Check it carefully for damaged teeth, if it's bent etc. Don't waste money on parts that aren't causing the problem!
  • bazza333
    bazza333 Posts: 86
    I had exactly the same issue this week on a bike I hadn't ridden for ages.......half a turn on the cable adjuster at the shifter and it's fine. Just can't see this is anything to do with the cassette or big ring.
  • robertzee
    robertzee Posts: 21
    Ok, Thanks for that I will give it a try
    You may be too old to rock but never too old to roll.

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