Why am I breaking chains?

Discussion in 'Mountain Bikes' started by Two Bikes, Oct 22, 2003.

  1. Two Bikes

    Two Bikes New Member

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    A few weeks ago, I broke the chain on my road bike while hammering a real steep hill. I figured no biggie, it's an older chain.

    Last night I took my mtn bike for it's maiden voyage since converting over to an XT 9-speed system. I actually upgraded quite a few other parts as well so I hit the trail kinda slow. The whole time, my chain (Ultegra/X7) was "catching" - kinda like it had a tight link. I stopped and checked it several times, folding each link over my fingers....nothing, they all felt fine.

    After I got home, I put the bike on the stand and checked it a little closer. It looked like the chain was maybe a link short so I added one back in. After making sure they were all moving freely I went out for a spin in the neighborhood.

    This brand new chain broke in two places (five links apart) about 500 yards from my house.

    Any guesses at to what's going on?
     
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  2. daveornee

    daveornee New Member

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    Is it breaking where you installled the Shimano pins?
    If so, you need to be more careful to follow Shimano's directions or go with a removable link like Craig Super Link
     
  3. Two Bikes

    Two Bikes New Member

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    Nope - that was first thing I checked and it's fine.

    The two that broke were just regular links. One popped towards the inside, the other to the outside.
     
  4. daveornee

    daveornee New Member

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    Well, I started by judging you by my past mistakes.
    Next take a careful look at the tooth profiles on the cassette cogs and chain rings. Something is acting to bust the chain apart under load. I you can't see it, you may be able to feel and/or hear it while it is in your shop area.
    I doubt that you are using IG cassette cogs, but they are thicker than HG cassette cogs, and should not use HG chains with IG cogs.
     
  5. Two Bikes

    Two Bikes New Member

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    Thanks, for your help -- now we're getting somewhere. How do I know the difference between an HG and a IG?

    I bought all of this set up as a complete upgrade kit, I would (like to) think that they matched like parts with like parts.
     
  6. Two Bikes

    Two Bikes New Member

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    I just remembered, a Hyperglide will have the little swirl-looking rises on the cassette facings.
     
  7. daveornee

    daveornee New Member

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    As long as it came out of a Shimano 9 speed cassette group, you know it has to be HG.
    If someone built it from cogs and spacers it might be possible to do. It is very unlikely, since all IG cogs I have seen were from 7 speed.
    I would be back to a careful examination of tooth profiles.
    If a tooth is twisted more than it should be, it will act as a cutting wedge. Pedal backwards, with bicycle in stand, through all the gears. Watch for anything that varies from smooth operation.
    Note the ring and/or cog if you can spot it. You can go back to your dealer or Shimano directly when you completed your trouble shooting. If you have a faulty part they will provide warranty replacement.
    If all that doesn't work, you can try a SRAM PC59, PC69, or PC99 chain. They all seem to work well on Shimano HG cassettes and come with the SRAM joining link instead of the Shimano joining pin.
     
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