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  1. #1
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    Why doesn't my rear derailleur shift up (return to a smaller cog)??

    I'm running an XT 750 rear derailleur (top normal... the regular kind where it wants to return to the smallest cog) and SRAM X9 trigger shifters. Everything has been running great for 2 years until last week when I starting suffering from shifting issues. Here's the problem:

    I can adjust the rear derailleur such that it is able to down shift (i.e. go to a larger cog) cleanly with each click of the shifter. However, when I up shift (i.e. go to a smaller cog), nothing happens. In other words, I see the cable/derailleur give a little bit, but not enough to trigger a shift. It isn't until I shift twice before the chain moves to the next smaller cog, and it only moves one gear. It's almost like the derailleur spring isn't strong enough to "return" it to the next cog. I've tightened the cable, adjusted limit screws, b-tension, played with the cable barrel adjuster, etc., all according to Shimano's manual and based on my 15+ years of maintaining drivetrains on alll of my bikes. What am I missing here?

    TIA

  2. #2
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    did you try and unhook the cable, if it wont go down without the cable
    bent hanger? or bad deraillier
    if it does , bad cables or shifter

  3. #3
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    Quote Originally Posted by dan0
    bent hanger? or bad deraillier
    The hanger is not noticably bent, and I certainly don't recall having damaged the rear derailleur recently.. If anything, this problem occured after I replaced my rear wheel after getting it rebuilt. Hmm.

  4. #4
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    Quote Originally Posted by burndtjamb
    The hanger is not noticably bent, and I certainly don't recall having damaged the rear derailleur recently.. If anything, this problem occured after I replaced my rear wheel after getting it rebuilt. Hmm.
    you sure the wheel is in in the dropouts all the way?

  5. #5
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    Quote Originally Posted by dan0
    you sure the wheel is in in the dropouts all the way?
    Yep, I've had to replace the rear wheel at least once (got a flat) so I've checked that its seated properly in the drop out. Also I'm guessing if the wheel wasn't in properly, I would have noticed an issue with the disc brake rotor vs. caliper alignment.

  6. #6
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    Quote Originally Posted by burndtjamb
    Yep, I've had to replace the rear wheel at least once (got a flat) so I've checked that its seated properly in the drop out. Also I'm guessing if the wheel wasn't in properly, I would have noticed an issue with the disc brake rotor vs. caliper alignment.
    did you try unhooking the cable?

  7. #7
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    Quote Originally Posted by burndtjamb
    The hanger is not noticably bent, and I certainly don't recall having damaged the rear derailleur recently.. If anything, this problem occured after I replaced my rear wheel after getting it rebuilt. Hmm.
    Rebuilt? Might have something to do with it. More info, please. What's been done with this rebuild?
    I ..... need ..... DIRT!!!!!

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  8. #8
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    Quote Originally Posted by dan0
    did you try unhooking the cable?
    Hmm, which part of the cable? I unclamped the cable, cleaned the cable that resides within the housing "loop", dismantled the barrel adjuster assembly and cleaned that out, then I reassembled everything before using needle nose pliers to pull the cable tight and reclamped it.

  9. #9
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    Quote Originally Posted by burndtjamb
    Hmm, which part of the cable? I unclamped the cable, cleaned the cable that resides within the housing "loop", dismantled the barrel adjuster assembly and cleaned that out, then I reassembled everything before using needle nose pliers to pull the cable tight and reclamped it.
    just unhook the clamp on the deraillier, then try adjusting the stop screw. if you can get there, then its the shifter/cable thats the problem
    with no cable tension the deraillier should go to the high gear, when you pulled the cable tight you may have pulled it too tight

  10. #10
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    Quote Originally Posted by AndrewTO
    Rebuilt? Might have something to do with it. More info, please. What's been done with this rebuild?
    Ack, sorry for not being specific. Only my wheel was rebuilt (replaced alloy nipples with brass ones, and kept all other components). This probably doesn't make a difference though..

  11. #11
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    Quote Originally Posted by dan0
    just unhook the clamp on the deraillier, then try adjusting the stop screw. if you can get there, then its the shifter/cable thats the problem
    with no cable tension the deraillier should go to the high gear, when you pulled the cable tight you may have pulled it too tight
    Where exactly is the stop screw you're referring to?

  12. #12
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    Quote Originally Posted by burndtjamb
    Where exactly is the stop screw you're referring to?
    the limit screws

  13. #13
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    Quote Originally Posted by burndtjamb
    Ack, sorry for not being specific. Only my wheel was rebuilt (replaced alloy nipples with brass ones, and kept all other components). This probably doesn't make a difference though..
    it could if the dish was changed it would move the hub & cassette

  14. #14
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    Quote Originally Posted by dan0
    it could if the dish was changed it would move the hub & cassette
    The hub/cassette position is controlled by the frame dropouts and the quick release. The dish of the build will move the rim around in relation to the frame/hub/cassette..

  15. #15
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    "I'm running an XT 750 rear derailleur (top normal... the regular kind where it wants to return to the smallest cog) and SRAM X9 trigger shifters."

    Minor thread hijack, but I'll be brief; I thought the SRAM X9 shifter was a 1:1 ratio and would only work with SRAM derailleurs? Shimano derailleur are a 2:1 actuation.

    As far as your shifting problem goes, assuming the frame/hanger are correctly aligned then I'd be looking at either the spring in the derailleur or a shifter issue. The fact that you're needing to click the shifter twice to get the derailleur up-shifting gives me the hunch that it's your shifter that's at the root of the problem. Next guess would be that your derailleur has just had enough.
    .
    .


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  16. #16
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    I'm assuming you aren't running X9 shifters, but one of SRAM's shimano-compatible sets of shifters, otherwise you would shift 2 cogs at a time with each click.
    I've had a similar problem to you, and it is almost always attributed to a dirty cable. with the bike on a stand, pedal and shift all the way up to the largest cog (32 or 34), stop the cranks, and then trigger shift all the way without spinning the wheel, to let out all the the cable slack. You should now be able to slip the cable housing from the cable stop on the frame, and slide the housing along the cable. Make sure the exposed part of the cable is clean before you slide the housing over it. Once the cable is exposed, clean it with some WD-40 or other gunk remover, let it dry and put some Tri-flow on it, slide the housing back in place, rehook the cable housing and pedal the bike to see if the chain shifts into the 11 tooth cog. If that doesn't work, it might be time to replace all of the cables and housings. Also try cleaning and lubing the derailluer pivots.

  17. #17
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    Quote Originally Posted by BlownCivic
    The hub/cassette position is controlled by the frame dropouts and the quick release. The dish of the build will move the rim around in relation to the frame/hub/cassette..

    youre right , late night for me

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