Trouble tuning rear derailleur- Mtbr.com
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  1. #1
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    Trouble tuning rear derailleur

    Hey all, long time lurker but this is my first post.

    Just replaced my 20 year old 7 speed drivetrain with an 8 speed and I'm having some difficulty indexing the rear derailleur.

    I'm running a Deore derailleur, with Alivio cassette, SRAM MX Comp [Grip] Shifter and KCM 8x.99 chain.

    I can get it to shift smoothly up, or down, but not both, without jumping a gear in the middle... Usually between 4-6, depending on the direction I'm going.

    As advised by other sites, I've set the top wheel of the derailleur directly below the center of the 5th gear, but that doesn't help. I've also made sure the top derailleur wheel is also as close as possible to the bottom of the largest gear.

    FWIW - My old chain was SO stretched that I went with one less link on the new chain when comparing them side by side... But it's now occurred to me that I've gone from a 11-28 7 spd to an 11-30 8 spd and should probably have added a link, not removed one. But would this have an affect on the middle gears?

    I've done a bit of searching online but haven't found an answer and would greatly appreciate any suggestions.

    Thanks.

    Doc_V

  2. #2
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    Did you install new cable / housing?

  3. #3
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    Set your chain length by wrapping the chain around the biggest cog and biggest chainring WITHOUT routing it through the RD. Take that length and add 2 links. If in doubt, go long.

    I'm not sure what you mean by, "I've set the top wheel of the derailleur directly below the center of the 5th gear".

    This is what I do, more or less, to adjust or setup a RD:
    1. Shift it into the smallest cog.
    2. Loosen the cable.
    3. Slacken the adjuster barrel on the shifter all the way.
    4. Set the high limit screw so the derailleur is aligned to the small cog.
    5. Pull the cable (at the derailleur) just snug while tightening the clamp.
    6. Use your adjuster barrel to fine tune the indexing.
    7. While shifted into the largest cog, adjust the low limit screw.
    8. Fine tune the B screw.

    If it won't index across the cassette in both directions, check hanger alignment.

  4. #4
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    Thanks for the replies...

    keen: New cable came with the shifter, I replaced the short piece of housing that leads to the derailleur because I had a hard time feeding the new cable through. Only other housing section is from shifter to top tube, and that seemed to be fine, so I left it alone.

    dledinger: I pretty much did everything you said. As for hanger, my bike doesn't have one. Derailleur bolts directly to the frame.

    As far as aligning the top derailleur wheel under the 5th gear for indexing, this vid shows the technique:

    https://youtu.be/wQncKmddahk?t=112

  5. #5
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    I see now...I was thinking in my head from a different axis. Makes perfect sense.

    You might consider replacing the rest of that cable housing. Most bike shops sell it by the foot. Make sure the ends are cut nice, tidy and square.

  6. #6
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    Quote Originally Posted by Doc_V View Post
    New cable came with the shifter, I replaced the short piece of housing that leads to the derailleur because I had a hard time feeding the new cable through. Only other housing section is from shifter to top tube, and that seemed to be fine, so I left it alone.

    dledinger: I pretty much did everything you said. As for hanger, my bike doesn't have one. Derailleur bolts directly to the frame.
    I would for sure change all the housing, lots of times it will "feel" fine but just won't work. Also your bike does have a derailleur hanger and can be easily aligned with a tool, but I think the cable/housing is much more likely the culprit.

  7. #7
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    Quote Originally Posted by J.B. Weld View Post
    ...Also your bike does have a derailleur hanger and can be easily aligned with a tool...
    OK.. Just so I understand you, are you talking about bending / aligning the rear "dropouts"? And if so, any idea how much something like that typically costs to fix?

  8. #8
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    Quote Originally Posted by Doc_V View Post
    OK.. Just so I understand you, are you talking about bending / aligning the rear dropouts? And if so, any idea how much something like that typically costs?
    There are tools for that too but to align a one piece derailleur hanger/dropout you leave the wheel on and thread the alignment tool directly onto the hanger.

  9. #9
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    That's good to know. Sounds like if I get a long enough bolt, and maybe even a piece of pipe for leverage, this might be something I can just do myself. I'll check it out, hopefully it'll fix the problem.

    Thanks!

  10. #10
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    A 10mmm axle will fit the threads but I wouldn't recommend trying to straighten it unless you can see that it's obviously bent, and if it is bent you're much better off having a shop straighten it with a tool. Based on the information you've given I think the housing you didn't replace is much more likely the problem though.

  11. #11
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    IMO....it's always worth checking the hanger. Often people think everything is fine when it is not.

    That said....JB is right here. Problems with indexing related to the hanger will show up on one end of the cassette or the other, not in the middle.

  12. #12
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    Well I replaced the rest of the cable housing today and I'm still having issues...

    Guess the hanger is next.

  13. #13
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    Saw a new bike in the shop the other day, wouldn't shift right. Mech was giving it a thorough look-over before attempting to adjust anything, and noticed a twist to the rear triangle. It's no wonder it wouldn't shift right.

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