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  1. #1
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    Rear Derailleur acts like it needs adjustment - tuned an hour ago?!

    Latley the rear derailleur on my rockhopper shifts really slow and pops down a few rings when i hit a rock or bump. I thought it neded to be adjusted like usual and used the barrel adjuster a bit and it didnt help. I rode it a bit more and noticed its not having trouble shifting just up or down its both, so I took it into the bike shop and they looked at it and said that it just needed to be adjusted and lubricated. I took it outside and rode around and found it to be fixed, went back inside and bought some other stuff and left. I got home and rode around up and down my street and it started to do it again just after a few minutes of riding, its now much worse. I plan on taking it back up to the bike shop tomorrow but thought I'd see if anyone here has any ideas?

  2. #2
    Meh.
    Reputation: XSL_WiLL's Avatar
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    If they replaced the cables and housing, it may have stretched/settled into place.

  3. #3
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    Usually when RDs act this way I look at the cables or levers for the problem.
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  4. #4
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    The part about the chain hopping down is fairly common if your flying rock sections aggressively. I have hopped chains right on to bottom bracket during nasty sections while coasting.

    However I have Never hopped a chain while in it.. Meaning during pedaling and keeping tension on the chain. Are your hopping the chain while coasting or pedaling? are there any teeth bent on your cassette?? What type of components? Shimano, Sram?

  5. #5
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    Make sure that your derailleur hangar is straight. You need a special tool to check it. Any good bike shop should have the tool. Whenever I can't get a derailleur to shift correctly by making adjustments in cable tension and I "know" that the limit screws are set dead on, the derailleur hangar alignment is "usually" the culprit. Occasionally I'll find that a worn out shifter/chain/cassette is to blame but 99% of the time it is the hangar. I wrench at a local shop a couple of days a week and when I build up brand new bikes I find that 8 out of 10 of them come with the hangar a little tweaked.

  6. #6
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    The cables are about 3 weeks old, and they readjusted them yesterday.
    Not sure about the housing, or levers.
    Its hopping to the bottom bracket on the FD now even when I'm pedalling over any little root or tiny drop, the rear hops down 2-3 teeth constantly.
    I'll have them check out the hanger.
    thanks

  7. #7
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    Quote Originally Posted by Flat Ark
    Make sure that your derailleur hangar is straight. You need a special tool to check it.
    I'm actually very interested in what you say here. I've been looking at the Park tool for checking hanger-alignment, but that tool costs north of $50. Would it not work to simply lay the hanger on a flat surface and look for gaps? Is there a less-expensive approach that is still reliable, even though it might take longer than using the store-bought gauge?

  8. #8
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    Quote Originally Posted by JonathanGennick
    I've been looking at the Park tool for checking hanger-alignment, but that tool costs north of $50. Would it not work to simply lay the hanger on a flat surface and look for gaps? Is there a less-expensive approach that is still reliable, even though it might take longer than using the store-bought gauge?
    Sorry, it isn't a matter of checking for gaps. What you're trying ro determine is whether the derailleur mtg bolt axis is perpendicular to the plane of the rear wheel. If you good mechanically, you might improvise something, otherwise the best bet is paying the LBS for a quick check. though it isn't precise, you can eyeball this to an extent, and if it looks OK, I'd look for other possibe culprits..

    BTW- Usually it's best to approach a mechanical problem by checking out the most likely cause first, but it often makes sense to start by checking the simplest/cheapest possibilities first, and progressing to the complex, timeconsuming, or expensive.

    In this case check the possible causes that you can deal yourself with before shelling out dough only to find that the RD hanger isn't mis-alligned after all.
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  9. #9
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    Quote Originally Posted by FBinNY
    Sorry, it isn't a matter of checking for gaps. What you're trying ro determine is whether the derailleur mtg bolt axis is perpendicular to the plane of the rear wheel..
    Interesting. You're really checking more than just the hanger at that point, aren't you? Wouldn't bent dropouts also throw that alignment off? What about having the wheel seated unevenly in the dropouts?

    If the gauge tells you that alignment is off, you still don't know for certain whether the hanger is the problem or whether the dropouts are bent, do you?

    Maybe I'm wrong. Just trying to understand here.

    I'll probably buy the tool someday.

  10. #10
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    Now you're starting to ask the right questions.

    Since you're looking for an RD function problem, bent dropouts won't matter. They'll stress the rear axle, but the wheel will still be relatively in plane. Likewise with a mis-positioned rear wheel. If it's close enough to turn within the frame, then it's only a degree or two, well within the working tolerance for the RD.

    It's a matter of degree. (or degrees - nopun) A bent hanger can really misallign the RD, but the wheel can't be far off without being obvious.

    Unless you've crashed fairly recently the hanger is probably reasonably OK, so look elsewhere before spending $50.00.
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  11. #11
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    Quote Originally Posted by FBinNY
    Now you're starting to ask the right questions.

    Since you're looking for an RD function problem, bent dropouts won't matter. They'll stress the rear axle, but the wheel will still be relatively in plane. Likewise with a mis-positioned rear wheel. If it's close enough to turn within the frame, then it's only a degree or two, well within the working tolerance for the RD.

    It's a matter of degree. (or degrees - nopun) A bent hanger can really misallign the RD, but the wheel can't be far off without being obvious.

    Unless you've crashed fairly recently the hanger is probably reasonably OK, so look elsewhere before spending $50.00.

    Check out page 27 http://sram.com/_media/techdocs/MY08...%20English.pdf I have found that these trouble shooting techniques will work on sram or shimano rear derailleurs. Also make sure you have the right chain length. If your chain is not taught enough there will not be enough tension to keep it on the gears. To check your chain length try taking your chain through the big/big combo w/ oug going through the rear derailleur and then add 2 links.

  12. #12
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    Quote Originally Posted by buildthis
    ..... Also make sure you have the right chain length. If your chain is not taught enough there will not be enough tension to keep it on the gears. .....
    Not a likely cause. All derailleur systems have slack in the lower chord which is taken up by the lower chord. Obviously we couldn't depend on the spring tension of the RD to keep the chain from skipping.
    ---------
    I re-read your OP and would bet a bottle of chain lube that it's a cable/housing problem.

    Try this experiment: shift as usual and note the trim. Then pluck the bare cable away from the downtube (like a guitar string) and let it snap back. If the trim changes your cable is hanging up in the housings. Pull and relube the cables using a very thin lube such as Triflow or Prolink. Also reverse the sections of housings end to end. This puts the curved sections where wear occurs in different places bringing fresh sections into the areas with greatest wear (a poor man's new housing).
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  13. #13
    Meh.
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    I would also check to make sure there are no kinks in the housing/cable. And make sure that there are no really tight runs of housing. Check the ends to make sure it isn't pulling through.

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