GX Eagle 12sp dropping gears when under heavy torque- Mtbr.com
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  1. #1
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    [SOLVED] GX Eagle 12sp dropping gears when under heavy torque

    Ok so last ride I was pedaling along and suddenly my rear derailleur started making a clicking sound and then when I hit the next climb and stood to pedal it very abruptly and loudly fell to the next gear causing me to stall out. Afterwards it was fine for a while but started happening again more and more.

    Now I can't ride my mtb because it has gotten so bad that it broke my chain. New chain installed now but I don't want to damage it or break it either.

    The situation - derailleur drops gears (seems to be toward the middle most gears) when I change the torque or pressure I pedal with. Speeding up quickly? Gear falls violently. Standing to pedal? Gear falls. Heading up an incline? Violent metallic crunch.

    What I've tried - checked upper and lower limits, tried barrel adjuster, checked the B-gap, cleaned and lubed everything, and visually checked the alignment of the derailleur which looks straight enough but I admit I don't have the most keen of eyes for that kind of thing since I don't stare at my derailleur every single day to know how it should always look.

    What can I try? Getting to a shop mechanic is difficult right now but I can order anything affordable that's needed from Amazon or something. I just want to ride if I can't work.

    Bike is a 2020 Trek Top Fuel 9.8 pretty much all stock.
    Last edited by drdocta; 1 Week Ago at 05:32 PM.

  2. #2
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    Sounds like derailleur hanger or b screw. The hanger alignment needs to be pretty precise (with alignment tool) and the b screw has to be checked at sag. I find that having the hanger alignment tool is a necessity. If anything, when issues pop up at least you're not left wondering if it's the hanger.

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    Quote Originally Posted by jeremy3220 View Post
    Sounds like derailleur hanger or b screw. The hanger alignment needs to be pretty precise (with alignment tool) and the b screw has to be checked at sag. I find that having the hanger alignment tool is a necessity. If anything, when issues pop up at least you're not left wondering if it's the hanger.
    Yeah did the B-gap at sag. Could you link the hanger alignment tool you'd recommend?

  4. #4
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    The derailleur can be bent in or out. It also can be twisted clockwise or counter. If you're not good at seeing those planes take it to a good service tech and watch him check and adjust it.

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    Quote Originally Posted by eb1888 View Post
    The derailleur can be bent in or out. It also can be twisted clockwise or counter. If you're not good at seeing those planes take it to a good service tech and watch him check and adjust it.
    Would love to if we weren't sheltered right now due to cv19!

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    Quote Originally Posted by drdocta View Post
    Would love to if we weren't sheltered right now due to cv19!
    I've had one bike with a very weak derailleur hanger design (GT Sensor). Shifting started getting wonky a few miles before it would snap off. It also threw me a curve ball when the shifting was off with a new hanger but then I found the cracked chain stay. So check your frame too especially if you've had any creeking issues.

    On a road bike the rear shifting will get the same way you describe right before the cable snaps. It starts to fray inside the goods because of the tight bend. I haven't had this happen with mtb shifters but it's worth checking your cable condition or just replace them anyway if it's been a while.

    If it isn't hanger alignment, hanger condition, loose axle, cable condition or a cracked frame than that leaves the derailleur itself.

  7. #7
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    Barrel adjuster at shifter
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  8. #8
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    Considering what you've already tried I'm guessing bent hanger or derailleur. Some hangers can bend just from laying the bike on that side. It's happened to me. now I always always lay my bike on the non drive side.

  9. #9
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    Sorry if this is too basic, but is your rear axle tight? Just this past weekend I was fighting shifting issues I didn't realize was just a loose axle until after ending up with a busted hub.

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    It's just the Park Tool derailleur hanger alignment tool.

  11. #11
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    Well if you're sheltering then it's the time to learn alignment. Trial and error.
    You can adjust the bend with you hand. Make an adjustment and look carefully at how you're changing the angle.
    Test ride. Repeat as necessary.
    To adjust for twist it's not going to be tool free. I use a big crescent wrench cranked down on the cage to get leverage.
    Watch what happens as you move it. Then test ride.
    You'll start to see a lot more as you let your eyes calibrate the change. Human eye is incredibly precise.

  12. #12
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    The hanger on my Ibis gets bent very easily and this is how I know it's tweaked.

    Sent from my Moto Z (2) using Tapatalk

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    dont try bending the bracket, mine bust before it bends, did 2 before i learned the lesson

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    Quote Originally Posted by drdocta View Post

    What can I try?. .
    Turn your bike upside down, and watch how it tracks on the cog on cassette, in the middle. Use your barrel adjuster to get teh chain centered, and take a picture and post it here. bent hangers are obvious. What you describe is a barrel adjustment, and there is a sweet spot you need to find and we can help

  15. #15
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    Many people keep a spare hanger on hand. I keep one in my bag because I've been that guy who has bent his hanger on a wipeout and then curses the whole time while trying to ride home. My point is if you had one you can either fix or rule out this as the problem instantly. Aside from that you can take it to the lbs and they can check it for you using a tool. I've even removed one and laid it on flat concrete then pounded it flat with a 4lb hammer, but in the end I still had to replace it for optimum shifting to come back.

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    my 11spd is doing the same thing. started last fall, then winter came. I recently cleaned everything, rebuilt hub bearings, one chain stay bearing and re-assembled. put a new chain on, deflated shock to set b gap at sag using an eagle alignment tool. used a hanger alignment tool to verify the hanger is perfect. still no luck. drops a gear on hard power from 16 tooth to the 14. I am going to replace the shifter cable and see if that helps, will let you know if it works.

    I do wonder why on hard power. the only thing that changes with hard power is torque into the cassette. so its possible we both have a weak or degraded cassette. one bent tooth is all it takes. I know my cassette is worn badly.

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    Quote Originally Posted by Fuse6F View Post
    I am going to replace the shifter cable and see if that helps, will let you know if it works.
    I'd also replace/upgrade the cable housing and the ferrules. Look closely at the point where the housing is cut for burrs. Look at the hole in the ferrule where the cable goes through. That spot can wear into a slot and catch the cable.

    One other thing to check is the lower jockey wheel on your derailleur. Had to replace mine.

  18. #18
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    Check for bent cog in cassette, inspect teeth in the gears that are affected

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    Quote Originally Posted by AluminumMonster View Post
    Sorry if this is too basic, but is your rear axle tight? Just this past weekend I was fighting shifting issues I didn't realize was just a loose axle until after ending up with a busted hub.
    Welp! Massive oof on my part, almost completely loosened rear axle. 10+ years of riding and I've never had one loosen up on its own but threaded and torqued it back in and so far it seems to have eliminated the issue after a brief test ride.

    So I guess new question is apparently I rode about 4-6 miles of intermediate mtb singletrack on a very loose rear axle. What all should I check over now before I head back out to the trail?

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    Quote Originally Posted by drdocta View Post
    Welp! Massive oof on my part, almost completely loosened rear axle. 10+ years of riding and I've never had one loosen up on its own but threaded and torqued it back in and so far it seems to have eliminated the issue after a brief test ride.

    So I guess new question is apparently I rode about 4-6 miles of intermediate mtb singletrack on a very loose rear axle. What all should I check over now before I head back out to the trail?
    Hope you caught it before damaging anything!

    Depending on your hub, it might be worth checking that you didn't lose a pawl, or that they didn't damage the hub body/teeth. While everything is apart, check where the cassette engages. I'm no expert, but those are things I can think that may have been affected.

    There are some other tips and things from more knowledgeable people than me in my thread: https://forums.mtbr.com/wheels-tires...e-1131905.html

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    Quote Originally Posted by AluminumMonster View Post
    Hope you caught it before damaging anything!

    Depending on your hub, it might be worth checking that you didn't lose a pawl, or that they didn't damage the hub body/teeth. While everything is apart, check where the cassette engages. I'm no expert, but those are things I can think that may have been affected.

    There are some other tips and things from more knowledgeable people than me in my thread: https://forums.mtbr.com/wheels-tires...e-1131905.html
    Awesome thanks! Don't have the tools or know-how to remove the hub internals but after checking all pivots for proper torque and cleaning / lubing everything it all seems peachy so hopefully I am just lucky to have avoided too much degradation. Going to ride soon and see how it plays out. The hubs are bonty 54t three pawl hubs that so far over the past 3 years I have been sufficiently impressed with, so hoping they remain bulletproof.

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    Quote Originally Posted by AluminumMonster View Post
    Sorry if this is too basic, but is your rear axle tight? Just this past weekend I was fighting shifting issues I didn't realize was just a loose axle until after ending up with a busted hub.
    Same thing happened to me and my buddy a a few weeks ago. My friend (18 Canyon Spectral AL w/ DT hub) and mine (19 SB130 w/ crap Novatec hub).
    Quote Originally Posted by drdocta View Post
    Welp! Massive oof on my part, almost completely loosened rear axle. 10+ years of riding and I've never had one loosen up on its own but threaded and torqued it back in and so far it seems to have eliminated the issue after a brief test ride.

    So I guess new question is apparently I rode about 4-6 miles of intermediate mtb singletrack on a very loose rear axle. What all should I check over now before I head back out to the trail?
    I would check the torque settings on all pivots just to make sure they are
    snug.

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    Quote Originally Posted by Staktup View Post
    Same thing happened to me and my buddy a a few weeks ago. My friend (18 Canyon Spectral AL w/ DT hub) and mine (19 SB130 w/ crap Novatec hub).


    I would check the torque settings on all pivots just to make sure they are
    snug.
    Yeah torqued everything to proper torques and took it out for a romp on my local trail and it is riding like brand new. Shifting beautifully and the creaking I was hearing is gone now too. Going to start checking the torques more frequently from now on.

  24. #24
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    Quote Originally Posted by Staktup View Post
    I would check the torque settings on all pivots just to make sure they are snug.
    Quote Originally Posted by drdocta View Post
    Yeah torqued everything to proper torques...
    Going to start checking the torques more frequently from now on.
    Most already know this, but many reference checking torques but fail to understand that in order to properly check the torque (torque specifications), the fastener must be loosened, then it can be re-torqued to specification. You will not get a proper torque by just setting your specified torque on your torque wrench and see if it clicks at that set torque.
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  25. #25
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    True, but it will tell you if something has loosened up significantly and it keeps heavy handed folks from breaking stuff.

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