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Thread: chain skips

  1. #1
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    chain skips

    I am trying to figure out why sometimes when I am riding my bike my chain will "skip" almost as if it were shifting when I have not told it to do so....of course this can be very dangerous while one is pedaling hard because it can almost make you lose your balance and make the bike crash...I thought perhaps my chain was bad but it is new...all I have done is add a sram link to it. I remember this happening to me as a child and it caused a horrific accident where I crashed and chipped my tooth...sooo...I'm a bit nervous when I felt it do it again the other night. It only happens when I am pedaling hard (the one time I really don't want it to happen)....it makes the noise like it's shifting...but doesn't shift. I am riding 2007 Gary Fisher Tassajara....I am also a clydesdale...350 and 6'1"....would this affect my chain. Maybe because of my weight, the stress on the chain is tremendous. I appreciate all of your thoughts!

  2. #2
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    Make sure there are no stiff links - check the SRAM link for sure

    You mention the chain is new. If the cassette is old a new chain can skip on it.

    Bent derailleur hanger

    Lose cable

  3. #3
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    I'll check the chain when I get home...It's possible because I have completely forgot to lube the chain since last season (DOH!)...I have only ridden it a short while on one day, so hopefully no harm done....cassette and everything is new...even though bike is 2007...I have maybe only put 200 miles on the bike...if that.

    Loose cable going to one of the derailleurs? How does one know how tight it should be ?

    The only other problem I have been having is my front derailleur will not shift up on to the upper chain ring. When I try and shift it, it just makes the noise like its trying and goes on and on but nothing happens. I was reading I should adjust one of the screws (cannot remember which one) 1/4 or 1/2 turn in one direction and hopefully that would help....could these two problems be related?

    Thank you again in advance

  4. #4
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    Could also be a broken rear axle. My commuter was doing that to me not to long ago with very few miles on it. Brought it in to my LBS after tweaking the shifting in an attempt to fix it. They dropped the wheel and found the axel in two pieces! Threw a new one in and I'm back up and running.

  5. #5
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    I'll take a look tonight...make sure it isn't broken. Thank you

  6. #6
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    Hi- lets define a few terms and address the possibilities.

    Chain Skips, meaning disengages from the cog, allowing the pedals to advance suddenly.

    Cause might be a stiff link or links. The problem will recur with a regular pattern, usually about once every 3 pedal revolutions. If you have multiple stiff sections the pattern may be more frequent, but it will still be regular.

    Verify the diagnosis by back pedalling and watching as links emerge from the bottom of the RD. Stiff links will show themselves with a sudden movement of the RD cage, or by still being bent in the lower chain loop.

    Hint-- you need better chain lube to cure or prevent stiff links.

    An other possiblity is a poor engagement between the chain and cassette, either from a severely worn cassette or from a large age difference between the chain and the cassette. The chain will skip randomly and unpredictably, but usually under load (what fun), and most often on the same one or two of the smaller (most worn) cogs. Check the chain for stretch, and eyeball the tooth profile on the cassette. If the teeth on the smaller or skipping cogs look very different from those on the larger (less used) cogs, you've found the problem but there is no fix. Give the cassette a decent burial and move on.
    -------------------------.

    The other Chain Skipping might more accurately be described as auto-shifting or ghost- shifting. The RD shifts up or down a gear on it's own unexpedtedly. Possible causes not related to the chain or cassette but are more related to the RD and control. RD may be out of trim between gears, and seeking back and forth between 2 gears, or possibly there's movement in the cable and housing, for example near the cable stops so that steering or suspension flex is changing the effective cable length. There are many other possiblities, such as a bent RD hanger, worn RD pivots, excess play, worn controls, and so on.

    Once you identify the nature of the problem, you can focus better on the possible causes.
    Last edited by FBinNY; 03-18-2009 at 12:40 PM.
    fb
    www.chain-L.com

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

  7. #7
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    The question is, is the shifty chain happening in the front or the rear. If in front, then yes the FDR may be the problem. You may be feeling the chain slip off the middle ring and then back on. So when you look down, hey look everything is ok. So adjust that first. Also check the middle chainring. That bike is a couple years old, and if you ride the middle ring a lot (like most of us do) it will get wornout. So the teeth should have nice square tops, not pointy.

    If it's the rear, then do all that other stuff listed above. Check to make sure the hanger isn't bent. Then the alignment of the RDR. Then replace the cassette. I'd leave that for last because they aren' t cheap.

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