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  1. #1
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    Rear derailleur broke - whose fault?

    So I'm pretty new to road biking. I bought a bike from Bikesdirect a few weeks ago, had it built by my local bike shop, and prior to tonight, had gone on precisely 2 (short) rides.

    Tonight, I decided to bike to a soccer game (where I ended up spraining my ankle - what a night!), when my rear derailleur just sort of ... catastrophically failed.

    I was biking at very low speed, as I was just working my way through a bunch of traffic lights. The chain was in the middle of the cassette, and I was in the middle chainring on my triple. All of a sudden, I heard some "crunch" noises and the rear wheel starting locking up. When I stopped, here's what I found:



    Hi-res image: http://i.imgur.com/2QtNk.jpg

    So - what the hell? The hanger appears to be bent, but other pieces appear to have just basically snapped off.

    Who's likely at fault here? Is this a component problem that might be covered by warranty? Did my LBS screw something up? It seems like this sort of thing shouldn't happen on my third-ever ride, especially when I wasn't riding hard or anything...

    Input much appreciated.

    -------------------------------------------------

    UPDATE:

    I emailed bikesdirect and they got back to me in a matter of hours. After looking at my pictures and reading the description of what happened, they agreed that the chain was likely the culprit. They are sending me a new derailleur, hanger, and chain.

    Not bad!
    Last edited by rover19; 03-28-2012 at 11:47 AM.

  2. #2
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    Too many unknowns. Usually RDs break like this when shifting to low and overshifting into the wheel. However you say you were in a middle gear so that rules out that cause.

    Other possibilities include, a weak hanger. Dealers tell me that some of the breakaway hangers break much to easily, and are like a 10amp fuse in a 20 amp circuit. It could also have been a misadjusted "B" screw that had the RD riding too close to the sprocket, a stiff chainlink jamming in the idler cage, or some other gremlin. Trying to figure out what initiated the problem is about as easy as finding which of two young brothers started the fight.

    Unfortunately for you, it may be hard to make a warranty claim since the dealer will say it was the bike (or you) and the seller will say the bike was fine, and obviously not assembled or maintained correctly.

    Sorry, I wish I had better news.
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    Solving any problem requires understanding the underlying cause

  3. #3
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    Hmm... that's not good news.

    Just to reiterate, the hanger is still attached. It never broke. It bent a bit, but didn't break. It appears that it broke where the cage plate attaches to the... umm... other thingy.

  4. #4
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    I took a closer look, and it seems that the cage is broken away from the lower body of the derailleur. Looking at how twisted the cage is, I'd guess that it got tangled in the spokes of the moving wheel. Look for a bent or scratched spoke to confirm that.

    But, you're still left with a chicken and egg mystery as to what started the problem. As I said earlier this almost never happens except when shifting to the low gear sprocket, since on any other the RD is far away from the spokes.

    If this were built by the seller it'd be easier to press a "part defect or misadjustment, it's all the same since you provided both" claim, but you have two entities and it'll be nearly impossible to sort out who's at fault.
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    Solving any problem requires understanding the underlying cause

  5. #5
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    I think it's the derailleur.

    Just go on Ebay and get another one for cheap. Done.

  6. #6
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    I think the rear derailleur failed, therefore BD should replace the derailleur and the bent hanger under warranty. Have the bike shop confirm in writing that the derailleur failed due to manufacture defect and then contact BD.

    The pic is not real clear but it looks like the outer plate came apart maybe due to the pin shearing off that goes through the lower knuckle spring; take a look and see if that pin is sheared.

    Secondarily it could also be a malfunction of the chain, where a faulty link may have started to let loose and the derailleur caught it destroying it. So check to see if you see a damaged chain link.

    Make sure no spokes were damaged in the process because if so then it's possible that if the derailleur or the chain failed due to manufacture defect then you have to get the spokes replaced to. If it was a component failure I would try to get BD to replace the bike in it's entirety since it scratched the paint, gears both front and rear, chain, maybe the spokes, and bent stuff etc.

    Again take it to the LBS that worked on it and see if they can determine the cause which could help you get a new derailleur and hanger for free instead of buying one on E-bay. They, the LBS, can also check to see if there was any other damage like to the frame.

  7. #7
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    Quote Originally Posted by froze View Post
    ...Have the bike shop confirm in writing that the derailleur failed due to manufacture defect and then contact BD.

    ...
    it could also be a malfunction of the chain, where a faulty link may have started to let loose and the derailleur caught it destroying it. So check to see if you see a damaged chain link.
    My plan is definitely to take the bike to my LBS, but they're unfortunately closed today.

    The chain is completely screwed up. One of the links detached/broke on one side and is pretty much mangled on the other side. It's kind of hard to tell whether that happened before or after the derailleur incident though. Obviously I need someone with more knowledge to take a look...

  8. #8
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    Quote Originally Posted by rover19 View Post
    My plan is definitely to take the bike to my LBS, but they're unfortunately closed today.

    The chain is completely screwed up. One of the links detached/broke on one side and is pretty much mangled on the other side. It's kind of hard to tell whether that happened before or after the derailleur incident though. Obviously I need someone with more knowledge to take a look...
    Now I'm leaning toward a chain failure, though could be wrong of course. But I once saw a pin fail, as I mentioned in my earlier post, but the chain remained intact. I think a chain link either had a pin not fully inserted or a side plate came slightly detached due to a pin issue and caught a gear tooth and wham.

  9. #9
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    which is more likely? a broken RD causing the chain to break? or a broken chain causing the RD to break??

    I'm thinking a broken chain causing RD to break. Well if the LBS assembled the chain (they must have since a new bike doesn't ship with a chain intact), then heck maybe it's the LBS that didn't put the chain together correctly!

  10. #10
    tlg
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    Quote Originally Posted by aclinjury View Post
    which is more likely? a broken RD causing the chain to break? or a broken chain causing the RD to break??
    Neither. It's 50/50.

    Well if the LBS assembled the chain (they must have since a new bike doesn't ship with a chain intact), then heck maybe it's the LBS that didn't put the chain together correctly!
    Many things are possible. Proving it is not very likely.
    Last edited by tlg; 03-27-2012 at 01:14 PM.

  11. #11
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    And there you have it.

    It's either a chain that broke because it wasn't closed correctly, which would be the mechanic's fault
    OR
    it's a defective derailleur that broke which would be a product defect and the sellers responsibility.

    Of course, this is just speculation based on a photo of the end result, and it would take an expert looking at the bike in the flesh to have any hope of a better answer. Even then maybe it could be impossible to know for sure.

    Unfortunately you now have the scenario I alluded to earlier, where each will say it's the other guy's fault, leaving you stuck in the middle. I hope I'm wrong and you have a decent outcome, but if not, consider this an object lesson in the dangers of shared responsibility, or what happens when you buy from the net and have the service done locally.
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  12. #12
    tlg
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    If you could post more pics from different angles, it would greatly help in diagnosing it.

    There's too much going on to see what could have been the cuase from just that photo.

  13. #13
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    My brother has a Motobecane Vent Noir he bought off BD a year ago, which might be the same as your bike based on the wheel and frame color you have there. He also had a catastrophic rear derailleur failure while under light load, his mechanic told him it was something to do with the spring inside the der. parallelogram detaching or something like that. Ultimately, he had to buy a new RD, and has had no trouble since. He never thought to contact BD, but considering it might have been the same failure you had on the same bike, it might be something they should know about.
    Last edited by Dan333sp; 03-28-2012 at 06:28 AM.

  14. #14
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    Is it an ultegra chain? There was a batch of defective ultegra chains that had the plates split. That could definitely have caused this problem.
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  15. #15
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    First, I wouldn't waste a LOT of time getting this sorted out because the path of least resistance might be to simply buy a new derailleur, chain and hanger and have them all installed.

    I wonder about "installation"... don't the bikes come with the rear derailleur,chain and crank installed?

    If not, I would talk to the installer and see if they'll quickly and easily agree to replace the broken parts.

    I'd also contact BD immediately and tell them what happened. They may quickly and easily agree to provide the 3 broken parts and ship them to you.

    But I'd give each a quick stab, but if neither agree quickly and easily to get it done, just buy the parts yourself and have the same or different bike shop install them if you aren't set up to do it yourself... and get back on the road.

    Even assuming that the bike shop and BD are both acting in good faith, I can see that there's real uncertainty as to where the defect lies and who is responsible. We can all speculate and maybe one or the other will feel differently and you'll be good to go, but without some serious analysis of the parts and speculation I wouldn't be surprised if reasonable people could interpret and assign blame differently.

    Sometimes you just have to take care of business and forget about absolute fairness. Assuming this is a fairly low level component group, I'll bet $50 or $75 in parts and an hour labor will get you back in business. And maybe the shop will even install the parts for free as a gesture to your bad luck? Maybe one or the other will give you the parts at a discount or wholesale price as a gesture too. Either of those scenarios would be absolutely fine if it were me. But I wouldn't be broken hearted if neither could offer full restitution, and I'd just swallow and look at it as a cost of the risk you take when you buy deep discounted items over the net. No fraud, just a risk and sometimes it doesn't work out perfectly.
    Last edited by Camilo; 03-27-2012 at 04:59 PM.

  16. #16
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    Thanks to everyone for chiming in. Here's some more info and answers to your questions.

    Quote Originally Posted by FBinNY View Post
    ...It's either a chain that broke because it wasn't closed correctly, which would be the mechanic's fault
    OR
    it's a defective derailleur that broke which would be a product defect and the sellers responsibility.....
    Quote Originally Posted by Camilo View Post
    I wonder about "installation"... don't the bikes come with the rear derailleur,chain and crank installed?
    The chain came pre-installed on the bike.

    Quote Originally Posted by Dan333sp View Post
    My brother has a Motobecane Vent Noir he bought off BD a year ago, which might be the same as your bike based on the wheel and frame color you have there. He also had a catastrophic rear derailleur failure while under light load, his mechanic told him it was something to do with the spring inside the der. diamond detaching or something like that. Ultimately, he had to buy a new RD, and has had no trouble since. He never thought to contact BD, but considering it might have been the same failure you had on the same bike, it might be something they should know about.
    It's a Windsor Knight. the rear derailleur is an Ultegra 6700. I'm planning on contacting BD; just wanted to get some second opinions.

    Quote Originally Posted by DrSmile View Post
    Is it an ultegra chain? There was a batch of defective ultegra chains that had the plates split. That could definitely have caused this problem.
    It's a Shimano 5600 chain - so a 105, I believe.

    Quote Originally Posted by tlg View Post
    If you could post more pics from different angles, it would greatly help in diagnosing it.

    There's too much going on to see what could have been the cuase from just that photo.
    More pictures posted. You can see the gnarled chain, the destroyed cage, and where the derailleur broke in the new pics.



    Here's a gallery with several more angles:
    Bike+failure - Imgur

    Thanks again to everyone for the help.

  17. #17
    tlg
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    Quote Originally Posted by rover19 View Post
    Here's a gallery with several more angles:
    Bike+failure - Imgur

    Thanks again to everyone for the help.
    Ok, I think I have a pretty good theory. One that would be easy to verify. Is/was your chain in the large chain ring? And were you shifting in the middle/top of your cassette?

    If your chain is too short, and you shift into your big/big gear combinations, it will stretch out your derailluer. And that's kinda what it looks like in your pics.

    This is what it would've looked like prior to getting too tight and snapping your derailleur.


    As you can see, if this chain were shorter, it would tear the derailleur apart trying to get into this combination. This is why you should never use the big/big combination. Even if you think your chain is correct.

    Now the part about this being easy to verify. Any good mechanic could verify this in a few minutes. How well do you trust your LBS? If they don't want to take responsibility they'll just say it was fine. Perhaps have another bike shop check it out?

  18. #18
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    Quote Originally Posted by tlg View Post
    Ok, I think I have a pretty good theory. One that would be easy to verify. Is/was your chain in the large chain ring? And were you shifting in the middle/top of your cassette?

    If your chain is too short, and you shift into your big/big gear combinations, it will stretch out your derailluer. And that's kinda what it looks like in your pics.
    Derailleurs are designed to work with the chain as short as 1" longer than the shortest chain that can loop the big/big combination. The idler pulley can rise high enough clear the almost straight lower loop prevent RD damage riding big/big.

    Also when a chain is too short to loop a gear combination it's rarely the chain that loses. Generally it's the axle that bends, or the chainring that collapses.

    I would hope that both the OEM spec and the assembling mechanic would provide for a chain that isn't too short.

    BTW- the reason not to ride big/big, has little to do with then RD. It's because running the chain on mis-aligned sprockets is less efficient, and increases chain and sprocket wear. It isn't a black and white issue of not being able to ride big/big, but a matter of avoiding doing it too much.
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  19. #19
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    I would go back to the LBS tell them what happened and if they say it is BDs fault then just buy a RD have them put it on. The call BD tell them what happened. While this is going you can get back to riding.

  20. #20
    tlg
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    Quote Originally Posted by FBinNY View Post
    Derailleurs are designed to work with the chain as short as 1" longer than the shortest chain that can loop the big/big combination.
    As I said, a chain that is too short.. hence shorter than 1" longer.

    Also when a chain is too short to loop a gear combination it's rarely the chain that loses.
    The chain didn't lose. The derailleur did. It's broken. The chain is only bent, likely caused by the failed deraileur. The derailleur will lose before an axle or chainring failure.

    I would hope that both the OEM spec and the assembling mechanic would provide for a chain that isn't too short.
    There's lots of things we can hope would happen. But humans make mistakes.

    BTW- the reason not to ride big/big, has little to do with then RD. It's because running the chain on mis-aligned sprockets is less efficient, and increases chain and sprocket wear.
    That is the case with a properly sized chain. If you have a chain which is too short, it WILL cause damage.

    Tell Sheldon Brown he's wrong!
    If the chain is too short, it will be at risk for jamming and possibly ruining the rear derailer if you accidentally shift into the large-large combination. Never run with a chain that is too short, except in an emergency.
    http://sheldonbrown.com/


    Bicycle Chain is Too Short?
    On the flip side, if the chain is too short, and you shift into the large-large combination you take the risk of sucking the rear derailleur into the sprocket and damaging both chain and cog. If the rear derailleur straightens out fully when on the large gear and chainring, you have a clear indication that the chain is too short.
    Bicycle Chain Length:How to Get The Right Chain Length For Your Gear Setup
    Last edited by tlg; 03-27-2012 at 07:24 PM.

  21. #21
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    As I said, I'd expect that both the OEM, and the mechanic would be able to properly measure a chain, but if not, it still wouldn't have pulled off the RD. The idler cage has enough travel for the lower pulley to swing above the straight line between the bottom of the sprockets.

    If you go back to the bike whose picture you posted, you'll see that there's enough swing for the RD to not be damaged by a straight lower loop.

    So without a bent axle or other clear evidence of a too-short chain, it doesn't make sense to look in that direction. In any case the chain is still there for the OP or anyone else to see if it can loop big/big with an inch to spare.

    As for arguing with Mr. Brown, that isn't possible anymore, but he and I had plenty of good conversations when he was still alive.

    A few others have given the OP good advice. Go back to the shop, let them look at it, and see if they'll either warranty it, or at least offer a "bad break" price. Then see if BD steps up and offers any compensation.
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  22. #22
    tlg
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    Quote Originally Posted by FBinNY View Post
    As I said, I'd expect that both the OEM, and the mechanic would be able to properly measure a chain,
    OEM wouldn't have sized the chain. The LBS would have when they installed it. Just because you expect they'd do it properly doesn't mean people can't make a mistake.

    but if not, it still wouldn't have pulled off the RD.
    You're plain wrong. Reality and Sheldon Brown say so.

    The idler cage has enough travel for the lower pulley to swing above the straight line between the bottom of the sprockets.
    Not if the chain is too short.

    If you go back to the bike whose picture you posted, you'll see that there's enough swing for the RD to not be damaged by a straight lower loop.
    Because.... that chain is NOT too short. Key words... not too short. I'm talking about a chain that is TOO short. Take 2" off that chain and I guarantee you it would not look that way. I dare you to try it on your bike.

    So without a bent axle or other clear evidence of a too-short chain, it doesn't make sense to look in that direction.
    Hence why I said it would be VERY easy to verify if the chain is too short. Makes complete sense to check it out.

  23. #23
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    Quote Originally Posted by aclinjury View Post
    Well if the LBS assembled the chain (they must have since a new bike doesn't ship with a chain intact), then heck maybe it's the LBS that didn't put the chain together correctly!
    That's incorrect. Most complete bikes ship with the chains installed.

  24. #24
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    Quote Originally Posted by tlg View Post
    OEM wouldn't have sized the chain. The LBS would have when they installed it. Just because you expect they'd do it properly doesn't mean people can't make a mistake.
    The chain most likely was installed at the factory. Very few complete bikes ship without chains installed.

  25. #25
    tlg
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    Quote Originally Posted by JacksonDodge View Post
    That's incorrect. Most complete bikes ship with the chains installed.
    Quote Originally Posted by JacksonDodge View Post
    The chain most likely was installed at the factory. Very few complete bikes ship without chains installed.
    You didn't read the thread. It is the case here since as the OP said.....

    "I bought a bike from Bikesdirect a few weeks ago, had it built by my local bike shop"

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