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  1. #1
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    Another snapped XTR rear derailleur??? wtf!

    I posted maybe 4 months ago because I was riding on a trail when suddenly my rear xtr snapped and was being sucked around in the chain. I've never seen such a thing. Some guys advised that most likely I grabbed a stick or something and didn't realize it.

    Well, I replaced it with another xtr, long cage. Today, I was riding Brown Mountain in SoCal. This is a very tame fire road. There was 100% no chance I picked up a stick. I've NEVER bashed this derailleur on anything. However, at 6 miles up, clunk, crunch.......the same thing happened. It snapped right at the wheel that's closest to the cassette. ?????? Turning it in to a single speed didn't work either as the chain jumped onto a bigger ring and put so much pressure on my Chris King hub, it wouldn't even turn. I had to just break the chain and throw it away. What a pita.

    Am I the only one who keeps having this problem?? Do I have my own little twilight zone thing going or is there an explanation?

  2. #2
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    I don't know what your experience was last time, and really not much about it this time except you were JRA when it happened. Not knowing your specific setup, your skill in setting it up, what you may have done otherwise to affect it let alone what you were exactly doing when it happened....OTOH I haven't heard of rampant XTR rear derailleur problems. Without knowing anything more sounds like a low limit screw setting or alignment problem for your derailleur to get into your spokes without any outside influence like a stick or something ...
    "...the people get the government they deserve..."
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  3. #3
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    No, setup was perfect. Perfectly straight and aligned, dead center over the appropriate rings. Limits perfect. When it went, it wasn't even in the granny gear, so spokes/limits are 100% eliminated. No sticks anywhere to be found. Just peddling at the end of a flat spot on a wide fire road, then snap.

    I just don't understand why such a delicate part, prone to slight bending, would ever be made of aluminum (worlds weakest metal). This must happen to others.

  4. #4
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    How did you size your chain? What gear combo were you in? Were you changing gears at the time? What is your drivetrain setup exactly (as in what crank/rings, cog range, chainline etc).

    BTW your rear derailleur does not sit over any of your chainrings, it sits over your cogs... XTR rear derailleurs are not exactly "delicate" either.
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  5. #5
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    Sizing chain- done by visual (to be honest, I don't even know the guideline here). Setup- Race Face Deuce 3-ring, XTR 9-spd cassette, Shimano Hallow Pin 9 spd chain. Derailleur- XTR, long cage, low normal. All limits and alignments were dead perfect.

    I wonder if this is a low-normall and long cage issue. I have other bikes and have never had a problem with the older high-normal derailleurs. The long-cage surely is MUCH more proned to torsion, due to length, but all my dereailleurs are long-cage and the only ones to break have been the low-normal versions.

    BTW- XTR aluminum derailleurs are THE most delicate atb derailleur. XTR is more expensive because they are for gram counters....the trade-off is strength. The arm is made of 100% cast aluminum. Check the fatigue strength of aluminum compared to all other metals. Aluminum is generally very stiff but incredibly weak in terms of being able to handle ANY type of repetitive torsion. This is why I won't even ride an aluminum bike (I weight 250 at times and an aluminum xc frame not be safe after 1000 miles). Bottom line is anything that can be easily destroyed with your pinky finger can't be considered "robust".

    The bottom line is I wonder how the cage/arm was proned to being twisted or bent repetitively? Since this is an xc bike, it was primarily used to climb 10 miles and then come back down, almost all fireroads. The climbing is 90% granny gear, although both derailleurs actually broke while NOT in the granny gear. I can only assume the damage was done while in the gg, since this is where I ride most of the time.

  6. #6
    Hmmmmm
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    Quote Originally Posted by maximilan
    Sizing chain- done by visual (to be honest, I don't even know the guideline here). Setup- Race Face Deuce 3-ring, XTR 9-spd cassette, Shimano Hallow Pin 9 spd chain. Derailleur- XTR, long cage, low normal. All limits and alignments were dead perfect.

    I wonder if this is a low-normall and long cage issue. I have other bikes and have never had a problem with the older high-normal derailleurs. The long-cage surely is MUCH more proned to torsion, due to length, but all my dereailleurs are long-cage and the only ones to break have been the low-normal versions.

    BTW- XTR aluminum derailleurs are THE most delicate atb derailleur. XTR is more expensive because they are for gram counters....the trade-off is strength. The arm is made of 100% cast aluminum. Check the fatigue strength of aluminum compared to all other metals. Aluminum is generally very stiff but incredibly weak in terms of being able to handle ANY type of repetitive torsion. This is why I won't even ride an aluminum bike (I weight 250 at times and an aluminum xc frame not be safe after 1000 miles). Bottom line is anything that can be easily destroyed with your pinky finger can't be considered "robust".

    The bottom line is I wonder how the cage/arm was proned to being twisted or bent repetitively? Since this is an xc bike, it was primarily used to climb 10 miles and then come back down, almost all fireroads. The climbing is 90% granny gear, although both derailleurs actually broke while NOT in the granny gear. I can only assume the damage was done while in the gg, since this is where I ride most of the time.
    Were you in the big ring at the time of these incidents?
    It could be your chain isn't long enough, although I can't see your setup.
    Shimano's guidelines for chain length are as follows.
    You wrap the chain around your biggest cog in back and biggest chainring up front, then add two links.
    This is especially important if you have a high forward single pivot like a Santa Cruz Heckler or Mountain Cycle Fury.

    Were you coasting when this happened?
    It could be your freehub is locking up intermittently.
    I had this happen to me once on an older bike and it will definitely start instantaneously pulling things around the cassette...
    It will also confuse you, by operating just fine again for weeks or even months.

    Then there is the possibility, that the XTR dérailleur can't take whatever abuse you're dishing out. They are by Shimano's own admission, a lightweight group, but not their most durable.
    Try a new Shadow XT RD M-772. I'm trying one around Bootleg and it's surviving our rocks and me.
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  7. #7
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    Sizing chain- done by visual (to be honest, I don't even know the guideline here

    Might be the problem, add two links after wrapping your chain around the big chainring and big cog.

    I wonder if this is a low-normall and long cage issue. I have other bikes and have never had a problem with the older high-normal derailleurs. The long-cage surely is MUCH more proned to torsion, due to length, but all my dereailleurs are long-cage and the only ones to break have been the low-normal versions.

    While I'm no fan of the low normal setup, there's no reason with proper setup (and shifting technique) that it shouldn't work fine for a long time.

    BTW- XTR aluminum derailleurs are THE most delicate atb derailleur. XTR is more expensive because they are for gram counters....the trade-off is strength. The arm is made of 100% cast aluminum. Check the fatigue strength of aluminum compared to all other metals. Aluminum is generally very stiff but incredibly weak in terms of being able to handle ANY type of repetitive torsion. This is why I won't even ride an aluminum bike (I weight 250 at times and an aluminum xc frame not be safe after 1000 miles). Bottom line is anything that can be easily destroyed with your pinky finger can't be considered "robust".

    If you can break an XTR derailleur off with your pinky finger, you may just be breaking all this stuff due to your inhuman level of strength. There's no reason after only 1000 miles an aluminum bike should be unsafe unless it has been abused. I've got XTR derailleurs that still function fine after many years of use. There's no reason your derailleur is getting any torsion it wasn't designed for unless perhaps you have poor shifting technique.

    The bottom line is I wonder how the cage/arm was proned to being twisted or bent repetitively? Since this is an xc bike, it was primarily used to climb 10 miles and then come back down, almost all fireroads. The climbing is 90% granny gear, although both derailleurs actually broke while NOT in the granny gear. I can only assume the damage was done while in the gg, since this is where I ride most of the time.

    Still sounds like you're guessing as to what gear you were in when it happened, yet you were there? The granny is your small ring up front. If you ride in your lowest possible gear much of the time (assume that's what you mean by gg), you're not even shifting so can't imagine how that would damage the derailleur.
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  8. #8
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    [QUOTE=maximilan]BTW- XTR aluminum derailleurs are THE most delicate atb derailleur. XTR is more expensive because they are for gram counters....the trade-off is strength. The arm is made of 100% cast aluminum. Check the fatigue strength of aluminum compared to all other metals. Aluminum is generally very stiff but incredibly weak in terms of being able to handle ANY type of repetitive torsion. This is why I won't even ride an aluminum bike (I weight 250 at times and an aluminum xc frame not be safe after 1000 miles). Bottom line is anything that can be easily destroyed with your pinky finger can't be considered "robust".

    The arm is actually made of cold-forged aluminum for XTR, which makes it the most durable out of any Shimano rear derailleur in terms of the material used. Most of the whole derailleur is actually made of the industry's finest cold-forged aluminum. From what I've read from Japanese bicycling magazines, not a lot of Shimano parts are made of plain jane cast aluminum, which would be weak. Most of it is at least heat-forged, making it far stronger than any CNC machined stuff you'd wreck with your pinky.

  9. #9
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    I'm running an XTR rear derailleur. The same one for 8 years or so, now. Never had a problem with them.They're great. You have either really bad luck or your hub is screwy, like Eric said. It makes sense. Deraileurs made of cheese should be able to hold up to "just riding along" conditions.
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  10. #10
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    How heavy are you and how strong are you? Are you dumping a lot of force into the chain?

  11. #11
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    you have a strange misconception about the strength of aluminum.

  12. #12
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    Quote Originally Posted by dnoyeb
    How heavy are you and how strong are you? Are you dumping a lot of force into the chain?

    dnoyeb is on to something there, but I think it is more to do with dumping gears (shifting across several sprockets for a single continuous push of the.thumb lever on trigger shifters or wave of the hand on dual controls).

    Assuming that the drivetrain is in good physical condition and properly setup (checking for straight hanger etc), then a rear derailleur with worn pulley wheels may be the culprit. If you dump gears often, then what typically happens is that the upper pulley wheel develops a lot play - to the extent that you can rock it left and right 3 or 4mm parallel to the pivot axle. The next time you dump gears, the chain slips off the pulley wheel into the space between pulley wheel and derailleur cage plate where it can snag.

    A derailleur with the upper pulley wheel that is set too closely or too far away from a sprocket (by use of the B-tension adjustment screw) may also exacerbate the problem.

    An overly long chain, or a badly joined chain link are potential culprits. For the latter, make sure that the joining pin doesn't portrude out too far above the link plate.

    Also check that there is a sufficient clearance between the smallest sprocket and the drive-side dropout.

  13. #13
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    Quote Originally Posted by dnoyeb
    How heavy are you and how strong are you? Are you dumping a lot of force into the chain?

    161 lbs, 6'3". I have strong(ish) legs. I have snapped only 2 chains in the 27 years I have been on 2 wheels. I snapped one chain with said XTR rear drlrs. I sometimes shift hard and my cassettes' teeth can verify that. They are quite chewed up and the XTR kit is still tight and smooth. I have even had 3 big wrecks with those drlrs, too. You must be really unlucky with bike parts...
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  14. #14
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    my rapidrise XTR got sucked into the rim twice
    Coincidence?
    I think not.

  15. #15
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    Quote Originally Posted by Garlock
    my rapidrise XTR got sucked into the rim twice
    Coincidence?
    I think not.
    Into the RIM? Spokes, maybe. Rim, never.
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  16. #16
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    I've also had this happen twice with the 970 stuff....rapid rise....though it was with the same derailleur both times. After the first time, we checked the hanger and tweeked the cage back into shape and it worked fine for several races until it got sucked over the cassette one day. Both times I was climbing and got light on the rear end to hop over a root/rock. When I went to pedal again...CRUNCH. This has never happened with another derailleur (been riding mtbs since 1990). I just got a 971 this time so we'll see...If it happens again, I'm going with XO.

  17. #17
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    Quote Originally Posted by shiggy
    Into the RIM? Spokes, maybe. Rim, never.
    you get the message

    Quote Originally Posted by yater
    I've also had this happen twice with the 970 stuff....rapid rise....though it was with the same derailleur both times. After the first time, we checked the hanger and tweeked the cage back into shape and it worked fine for several races until it got sucked over the cassette one day. Both times I was climbing and got light on the rear end to hop over a root/rock. When I went to pedal again...CRUNCH.
    same here

  18. #18
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    Happened to me last night

    Here's the link and pictures I posted on the ibex forum of what happened: Can you guess what's wrong in the picture?

    I believe my hanger may have been slightly out of line. The derailleur climbed around the cassette when I was pedaling going up a hill after going over some loose small old rotted logs . The shifting was funny from the beginning of the ride, but I didn't give it a second thought now I wish I would have at least looked to see if everything was lined up. We were riding very technical trails that were not maintained very well there were a lot of branches, small logs across the trail and the brush was so tight it was scratching our arms. I'm just counting my blessings that the wheelset wasn't trashed, it hit 2 spokes and only put small bumps in them and the rim is still true and the cassette doesn't appear to have any damage.

    I really love the rapid rise shifting and I do have a rapid rise XT derailleur at home that I'm stripping off another bike to put on my FS for now, but I'm really beginning to wonder if I should try the new shadow design which claims to limit bouncing and chain suck? Any idea if shimano is going to offer a shadow design with rapid rise or low normal operation?
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  19. #19
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    I was gonna say...

    Quote Originally Posted by tomsmoto
    you have a strange misconception about the strength of aluminum.
    if alu is so weak, why do they make freeride and downhill frames out of it?

    Heck, Audi makes a whole car out of it, the A8, and Porsche makes their suspension control arms out of it to save weight.... not to mention just about every airplane made up to the 787 and the Airbus A380.

  20. #20
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    ....and engine blocks, and heads.... building frames..... trusses.....
    Where am I? And how the hell did I get here?

  21. #21
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    Quote Originally Posted by yater
    I've also had this happen twice with the 970 stuff....rapid rise....though it was with the same derailleur both times. After the first time, we checked the hanger and tweeked the cage back into shape and it worked fine for several races until it got sucked over the cassette one day. Both times I was climbing and got light on the rear end to hop over a root/rock. When I went to pedal again...CRUNCH. This has never happened with another derailleur (been riding mtbs since 1990). I just got a 971 this time so we'll see...If it happens again, I'm going with XO.
    That's just about the same thing that happened to mine, I was climbing and went over some branches and crunch!
    If you're not falling, then you're not riding fast enough!
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  22. #22
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    The biggest problem I see with al is that it has no fatigue strength which means that it can't take flexing stresses very well so it has to be designed to be stiff to limit it's chances of failing due to fatigue, so this can lead the part to be more brittle and more likely to snap but this shouldn't happen under normal conditions. I really have to call into question how well your drive train was set up because if the b-limit screw was set bad and the chain was to short and you were in a lower gear the derailleur could bite into the cassette and get snapped off.
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