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  1. #1
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    Chainline with XT M760 Crankset

    I'm having problems with a slipping chain on the middle chainring with a brand new XT outboard bearing crankset.

    The drivetrain is totally new - sram pc991 chain, XT cassette and XT crankset.

    I originally installed the cranks on my 2004 etsx-50 as instructed for a 73mm BB...with one 2.5mm spacer on the drive side...the result on the first ride was a constantly slipping chain on the middle ring only, second cog on the cassette.

    I then switched the spacer for the second ride to the non-drive side to try and improve the chain line (from advice from another mtbr thread)....it has improved, but still slips occasionally on the middle chainring and now 4th cog at the back...and catastrophically, losing skin from the shin!

    Has anyone had this problem, and managed to fix it? Is it likely to disappear as the drivetrain wears?

    Any other advice for a slipping new chain on just the middle ring?

    Thanks!
    Chris.

  2. #2
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    Reputation: Bikinfoolferlife's Avatar
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    You sure you've got the right chain length? Have you checked rear derailleur alignment? What exactly happens when it "slips"? BTW I have no idea what you mean by second or fourth cog as I don't know where you started counting from.. Since both your problems are relatively in the middle of the range (both front and rear) I wouldn't think it's chainline at all as I'd think it'd only show up at more extreme chain angles.
    "...the people get the government they deserve..."
    suum quique

  3. #3
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    Quote Originally Posted by Bikinfoolferlife
    You sure you've got the right chain length? Have you checked rear derailleur alignment? What exactly happens when it "slips"? BTW I have no idea what you mean by second or fourth cog as I don't know where you started counting from.. Since both your problems are relatively in the middle of the range (both front and rear) I wouldn't think it's chainline at all as I'd think it'd only show up at more extreme chain angles.
    I used the Shimano/Sram instructions to fit the chain...ie ran it through the largest cog and big chainring and added two links (powerlink+1).

    Second cog = second largest at the back
    4th cog = 4th largest

    It is a brand new XTR rear derailleur, and a brand new derailleur hanger (other one had been straightened and used an XT derailleur and ISIS Evolve XC cranks which ran fine).

    The "slipping" is very similar to when the front chainring is worn...it happens occasionally only when I pedal hard to jump up a drop off, or crank up a short climb. There is a loud crack and the chain falls off. It is strange that I get this worn chainring symptom from a totally new drivechain?!

    Do you think shortening the chain might make a difference?

    Thanks for replying!

    Chris.

  4. #4
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    XT M760 Crankset Problem Solved!

    My lbs solved my problem of the intermittent skipping chain on the front middle chainring - the chainring was faulty!

    Here is what they did:

    1) Replaced my middle XT chainring (2 rides old!) with a brand new one. I then rode around the carpark and replicated the problem again hopping off a gutter.

    2) They left the new chainring on and replaced my sram chain with a new wippermann chain - again the problem remained!

    3) They left the new chain on, and replaced my rear wheel and cassette with a brand new one (theory was that the ratcheting in the hub might be gone - but the problem remained.

    4) With no clues to the problem, they tried installing a non-shimano chainring - an Evolve XC chainring. This solved the problem!!

    This leads me to think that if 2 new XT chainrings were causing the problem, there must be a batch of faulty chainrings going around...has anyone else had a similar problem?

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