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  1. #1
    Masher
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    Broken teeth on rear cassette woes

    Ok,

    I have a Cannondale F4 with a Shimano front deraileur SRAM rear and Shimano X-7 Shifters. In the past few days I have been going crazy dealing with my chain skipping severely under pressure in my largest and second largest gear. i.e. 3 -> 9 and 3 -> 8. I had broken three chain links before this and I noticed a similar problem when a link was about to break so my first instinct was to replace the chain. I also gave the drivetrain a thorough cleaning and the problem persisted. Finally I gave my cassette a close inspection and I noticed that one of the teeth at 3 -> 8 has broken off.

    I understand the severity in 3 -> 8 but for some reason it is affecting 3 -> 9 as well. Regardless I assume it needs to be replaced. I have only had this bike for about two months and I just want to know if this is a common problem and how often can I look forward to replacing my cassette. If there is anything besides doing a better job keeping my drivetrain clean that I can do to prevent this I would love to know.

    I ride my local trails pretty hard and I understand things break but 2 months seems like a pretty short lifespan for almost any component but I do ride everyday. God, I can't wait for my singlespeed.

    On a related note, I am looking forward to my SS arriving, first a Capo and then the 1FG 29er whenever it is available. Anyways, I have been riding my big gears around town and have been making my trail riding as hard on myself as possible which means I spend a lot of time in these broken gears and it also means that these gears see a lot of high pressure pedaling. Is this bad for my drivetrain in a way that I should avoid it becasue it is breaking things?

    Any advice is helpful as I am still pretty noobish.

  2. #2
    mtbr member
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    first i have ever heard of cassettes snapping teeth,and the riding your doing should not be a problem either.

    not sure but it could be a duff cassette if its still under warranty take it back to the shop.

    also i think your shifters are sram x-7.

    also when changing up,the cogset try and soft pedal without any power,this way your gears might not crunch up either.

  3. #3
    ballbuster
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    You sure....

    ... you aren't just looking at the ramped teeth? Some of the teeth are shorter to allow the chain to flex up and over the next cog when you shift. All modern cassettes (even the cheap ones) do this, and it makes shifting under load much smoother and quicker than the olden days without the ramps.

    If your chain is skipping, you most likely let the chain wear too far before you replaced it. When you did replace it, the pitch of the chain (distance between the pins) is now shorter than the pitch of your worn teeth.

    If your chain is brand new (under 30-50 miles or so) just replace your cassette. If you have more miles than that, you might want to replace both the cassette and the chain. If your chainrings are worn, you might have to replace those too, or you'll get chainsuck. ($$$)

    What happens is that when your chain wears, it stretches. Not really stretching like a rubber band, but the pins in the chain wear from round to oval, letting the pins and plates get farther from each other ... as in, the chain's pitch changes. This makes the teeth on the chainrings and cassette wear in the same pattern. Since everything wears on everything else, it will work fine until you replace one component in the mix.

    If you still have your old chain, measure it next to a ruler. The pins should be close to centered on the 1/2" marks for a whole foot. More than 1/16" off at the end, it was worn past its limits which probably means that everything else is worn past its limits.

  4. #4
    Masher
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    Well it looks like the bike shop is going to fix it without a fuss. They said a rep needs to look at it or whatever. Nothing is ever easy. I understand things break but why do MY things have to break.

  5. #5
    Masher
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    I'm pretty sure. The tooth is broken clean off, like, there is no tooth to be seen. The proof, really, is that the same pattern is not present on any other gear. Broken or not, its an anomally. And keep in mind this bike is only a couple of months old and didn't see many miles the first month or so bcause the weather was still on the chilly side. But maybe the extra exertion I am putting on the drivetrain is causing accelerated wear. This is likely all moot because I think my shop will be fixing it post haste. But I do love to know things.

    I appreciate the information. It's certainly something to keep in mind. That's the kind of advice you don't usually hear until it's too late.

  6. #6
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    How is your shifting style? Changing gears while standing and pedaling hard put a lot of stress on the drivetrain, without any benefit since the chain is in between cogs and unable to put power to the ground.

  7. #7
    Masher
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    I agree whole heartedly which is why I am always yelling at my friend for doing just that. Funny how I tell him he is going to break something, more likely his chain, shifting under power and here I am with broken teeth.

    But I digress, no I do not. I try very hard to anticipate my gearing needs and long, oh so long, for single speed bliss. This isn't to say that I have never changed gears under pressure in a desperate effort to get up some ridiculous climb but what horrible luck that I break my cassette on the handful of occasions where I sinned as such.

    I already noted that I actually shift gears very little but I spend most of my time in 7, 8 and 9 when I ride in town that can be quite hilly at times. I'll let you guys know what the shop says when I bring it in on Monday. This will be my first ever warrantee work and I hope it doesn't take an eternity.

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