Chain rub

TheSloog
TheSloog Posts: 50
edited March 2011 in Workshop
Hi...
My chain seems to rub and catch ever so slightly on the the next-biggest sprocket on the rear cassette - mostly when it's on the highest gear and biggest front chainring - and makes an annoying clicking/grinding/whirring noise.
Not bad enough to stop me, but enough for me to hear it.
Is this normal? Do I imagine it? Am I OCD?
Already replaced cassette and chainring to no avail...
It's a trek 1.5 compact.
Any ideas what it could be?

Comments

  • ds690
    ds690 Posts: 17
    Its probably the H limit screw or too much cable tension preventing the derailleur from moving far enough outboard to prevent the chain from rubbing on the next cog.

    Look at the top jockey wheel from the back of the bike and see how it lines up with the smallest cog. If it needs to move outward, loosen the H limit screw slightly and you should see the derailleur move. If it does not move, loosen the cable tension and try again.
  • John.T
    John.T Posts: 3,698
    TheSloog wrote:
    Hi...
    My chain seems to rub and catch ever so slightly on the the next-biggest sprocket on the rear cassette - mostly when it's on the highest gear and biggest front chainring - and makes an annoying clicking/grinding/whirring noise.
    Not bad enough to stop me, but enough for me to hear it.
    Is this normal? Do I imagine it? Am I OCD?
    Already replaced cassette and chainring to no avail...
    It's a trek 1.5 compact.
    Any ideas what it could be?
    I am a bit confused. I assume you mean when the chain is on the big ring and the second largest sprocket. The big sprockets do not give high gears. They are the low ones while the big chainring gives higher ones.
    To answer your problem (I think). Firstly you should not be using the 2 biggest sprockets with the big ring or the 2 smallest with the small ring. This is because the chain is running a long way out of line on these gears which could well be what is causing the noise. From the sound it could also be that the indexing or low limit stop are a little out of adjustment.
    My Fleet.
  • TheSloog
    TheSloog Posts: 50
    No, it's actually when on the big chain ring and the smallest sprocket (the highest gear). The chain sort of rubs and catches on the next-biggest sprocket - it almost seems like the cassette and the chainring are at slightly different angles.
    Doesn't seem to happen on bigger sprockets, really, or with the smaller chainring.
    In fact, it seems to run most smoothly when on the big ring and middle-to-big sprockets.
    It's shifting fine up and down, front and rear too - just to add more confusion!
    Thanks for taking an interest - hopefully this may help you help me!
  • John.T
    John.T Posts: 3,698
    In that case follow ds690's post.
    Sorry if I was confused but high and low gears get mixed up a lot on here. :(
    My Fleet.
  • TheSloog
    TheSloog Posts: 50
    I know - it'd be so much simpler for all of us if those blasted bike companies would just make the small sprockets lower gears!
    But I don't think it's the limiters either - doesn't make any difference to the clicking when I move if down!
  • sungod
    sungod Posts: 16,551
    have you tried going through the complete adjustment procedure for your rear mech?

    for shimano you'll find it at http://techdocs.shimano.com other makes' are also on their websites

    also...

    the cable tension is lowest on the smallest sprockets, if the cable housings are gunked up it might be causing enough drag to stop the rear mech moving out fully

    if the rear hanger is slightly bent it can cause shifting problems/noisy operation
    my bike - faster than god's and twice as shiny

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