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  1. #1
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    drivetrain nightmare, kula primo build

    Ahoy-

    Looking for some help from some mechanics on this one...I just finished building my xc hardtail and for some reason when the chain is in the 3 smallest cogs on the rear cassette, the chain skips, bad. So hard that I have broken two chains. I dont have to pedal hard, just with a moderate amount of torque and about every half crank POP! In the 6 larger cogs everything is fine.

    On the stand everything is perfect. The new XT shifters and the XTR rear derailleur easily and crisply slide the new chain through all 9 gears. I have tuned the drive train to obsessive perfection and there are no visible problems. Quiet, fast, perfect. As soon as I pedal on the ground though it starts skipping and popping again.

    I must point out not all the parts are new. The cassette and original chain were slightly used, I only added a new chain when the older one burst on a climb. The BB is several years old as is the crankset and rings. Visually the cassett and crankset look good and clean. Teeth show moderate wear but no shark toothing or broken teeth yet. As trouble shooting goes I have- swapped rear derailleurs, replaced chain, cleaned and lubed all parts, broke down and re-assembled rear hub, swapped cassetts (even tried my buddies entire wheel and it still popped), adjusted cable tension, tried multiple cable housing combos....and used every curse word you could recommend.

    Next step is to dissassemble the BB and cranks but I am not sure if there is any reason to. The only thing I can think of is that the chainrings and cogs are not lined up properly causing the chain to want to climb when in the little cogs...maybe some sort of spacer for the BB that would push the rings out? I dont know....If all else fails i will have to take it to the LBS, but I realllllly dont want to...they are a pretentious group of roadies that will surely roll their eyes and ask why i didnt just buy a box bike!!!

  2. #2
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    It definitely isn't chain line since the RD feeds the chain to the cassette and would resolve any problems except when back-pedaling.

    Other than a cassette wear issue, which is always more pronounced on smaller cogs, I'd suspect a chain wrap issue. I haven't seen the bike so I'm just guessing but try adjusting the "B" screw to bring the RD further forward so the chain wraps the cassette 180 degrees on the smaller cogs. Also re-check the chain length, since longer chains cause the RD cage to rotate bringing the jockey wheel forward.

    Lastly check the trim and hangar allignment to make sure there's no ghost shifting.

    If all else fails, try a new cassette and chain of the same brand together. Cassette wear might be the problem even if the cassette looks OK to you. If you give up and want to visit a (an?) LBS, PM me & I'll give you the names of a few that I know to have skilled mechanics, and no attitude problems.
    fb
    www.chain-L.com

    The key to solving any problem is to understand and address the underlying cause.

  3. #3
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    OK, good to rule out chain-line....that saves some headache. I will try adjusting the RD position as soon as I get home. Hopefully the B screw is the issue and not a bad hangar allignment because both the frame and hangars (plural because I already swapped out the first one under suspicion that it could be the prob) are new which would mean the frame is damaged and I have a larger issue.

    I am pretty sure I measured the new chain correctly (wrap around the large rings etc....) and I tried my buddies wheel and it did the same thing so I would like to think I could rule out the cassett. given the same problem with two different rear wheels, it definatly sounds like it would be some kind of allignment issue.

    Will try suggestions and report asap! gotta ride this weekend!

  4. #4
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    All attempts failed. Took to lbs and first replaced cassette...better...still a problem under a lot of torque but much less often. Measured deraileur alignment found to be 1/8" off due to damaged RD...new XT rd and seems to be working perfectly.

    So it looks like it was a combined problem of a worn cassette and derailleur that wouldnt get along. I missed it because in my swapping parts out I never swapped deraileur and wheel out at same time!

    FBinNY thanks~!

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