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  1. #1
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    Chain slap on BOTTOM of FR DER cage

    gave my new bike (2008 Trek Fuel EX9) a thorough work out today. while riding on my usual trails, i noticed an incredibly annoying amount of chain slap on the BOTTOM of the front derraileur cage (not the sides). while applying forward pressure on the cranks, the chain passes 1-2 mm above the bottom of the cage. looks to me like the front derraileur should be ~2 mm lower (currently ~4mm clearance above big ring teeth when over top), i'll fix that but it's not gonna be enough to eliminate the chain slap. really loud. definitely BOTTOM of front cage. wierd.

    The derrailleur is Shimano XT M771. i never noticed this on any of my older bikes (with older XT derraileurs). are there any front derraileurs that have longer cages than the M771?

    thanks, phil
    Last edited by Phil; 10-21-2007 at 08:21 PM.

  2. #2
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    maybe your chain is too loose. IDK it's kinda a weird issue.

  3. #3
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    Quote Originally Posted by mountainbikeloco
    maybe your chain is too loose. IDK it's kinda a weird issue.
    well, umm, in the interest of complete disclosure, i have to report back that you actually aren't too far off the mark. my chain length is correct, but after careful inspection, i have determined that the chain slap noise is not from the upper run of chain hitting the bottom of the front derraileur cage. it is coming from the lower run of chain hitting the chain stay a few inches behind the cranks. maybe the new Shadow XT rear derraileur has a slightly weaker spring than the older XTR models i'm used to? i dunno. i will replace the existing stock chain stay cover with a inner tube wrap making sure to cover that area, i'm sure that'll do the trick.

    thanks for taking the time to respond to my rather bizzare post!

  4. #4
    CAN YOU DIG IT??!!??!!!??
    Reputation: man w/ one hand's Avatar
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    Quote Originally Posted by Phil
    well, umm, in the interest of complete disclosure, i have to report back that you actually aren't too far off the mark. my chain length is correct, but after careful inspection, i have determined that the chain slap noise is not from the upper run of chain hitting the bottom of the front derraileur cage. it is coming from the lower run of chain hitting the chain stay a few inches behind the cranks. maybe the new Shadow XT rear derraileur has a slightly weaker spring than the older XTR models i'm used to? i dunno. i will replace the existing stock chain stay cover with a inner tube wrap making sure to cover that area, i'm sure that'll do the trick.
    thanks for taking the time to respond to my rather bizzare post!

    That should do it. You'll get chain slap on the chain stay no matter what derailluer you're running.

    No post asking for help is bizzare, now some of the answers you'll get can be.
    "Why are you willing to take so much & leave others in need...just because you can?"

  5. #5
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    I had the unbearably annoying (especially since I come from bmx and road riding where all you hear is tires and grunts when you fall) front deralleur slap. I ripped a piece of 3/8" wide, 12" long piece of racers tape for my car and rolled it around the bottom of the cage like 5 or 6 times. Now it clanks against 1/8" of soft duct tape-like surface and its quieted down and doesnt interfere with shifting

  6. #6
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    Quote Originally Posted by 743power
    I had the unbearably annoying (especially since I come from bmx and road riding where all you hear is tires and grunts when you fall) front deralleur slap. I ripped a piece of 3/8" wide, 12" long piece of racers tape for my car and rolled it around the bottom of the cage like 5 or 6 times. Now it clanks against 1/8" of soft duct tape-like surface and its quieted down and doesnt interfere with shifting
    what a great idea! i was thinking about wrapping a fat zip tie around the bottom of the cage, but i think tape would be much better (softer and no fear of the chain snagging on a rough end). i'll keep this in mind in case i still get noise from that area after wrapping the chain stay with an inner tube. thanks

  7. #7
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    Quote Originally Posted by man w/ one hand
    That should do it. You'll get chain slap on the chain stay no matter what derailluer you're running.

    No post asking for help is bizzare, now some of the answers you'll get can be.
    noise like that just kills me, i let it totally ruin my ride, just can't help it. i spent a long ride once trying to adjust all sorts of stuff on my road bike because i kept hearing a ticking sound - turned out to be the metal pull tag on my jersey zipper flapping against the metal zipper. now that really is bizzare, you've got to admit it.

  8. #8
    CAN YOU DIG IT??!!??!!!??
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    Quote Originally Posted by Phil
    noise like that just kills me, i let it totally ruin my ride, just can't help it. i spent a long ride once trying to adjust all sorts of stuff on my road bike because i kept hearing a ticking sound - turned out to be the metal pull tag on my jersey zipper flapping against the metal zipper. now that really is bizzare, you've got to admit it.
    That's one way to look at it, but these lil noises have away of making us better wrenchs. When you get that lil noise that annoys you till you figure it out, it really helps us to become familiar w/our bikes & the mechanics of its workings. It's amazing how the mechanical resonance of some small obscure part can reverberate up through the frame and sound like yer bike is gonna fly apart, or at least distract you just long enough to send you OTB or down through the woods off of the trail, in some gnarled up tech section of trail.
    "Why are you willing to take so much & leave others in need...just because you can?"

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