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rear mech just obliverated itself?!

jon 0.1jon 0.1 Posts: 48
edited June 2008 in MTB workshop & tech
hey guys, just been out on my bike just to get to the shops and on the way my rear mech (an sram x 9 i think) just snapped off with no given reason then destoyed itelf in the wheel taking out 7 spokes :? it then mangled itslef in the bash guard adn destroyed the cable- this mech is new, could this be a manafacture fault and if so would i be right to try to send it back? im just trying to see what other people think seeing as it is like a month old :(
thanks
Jon

Posts

  • supersonicsupersonic Posts: 82,708 Lives Here
    Did it not overshift into the spokes due to an ill set L stop?
  • Hi Jon,

    amazing! I had the exact same problem a few weeks ago, with a reasonably new (few months old) SRAM x.9 rear derailleur. Snapped off like a cookie (at the stiffest/strongest point no less), and no, this had nothing to do with an ill set L stop. I think we have to contact SRAM about this issue.

    Can you post a pic of your destroyed mech?

    Michel
  • grantwaygrantway Posts: 1,430
    Did your lbs put this on? If so take it back and get a new one.

    I had a similar thing happen to me on my new bike but turned out to be a bent
    hanger and the rear mech just mashed up and had to replace chain too as it
    snapped.
    Just went back to shop and got it all replaced.
  • rob colerob cole Posts: 706
    there are 3 reasons a rear derailleur goes into your back wheel

    1. the low stop screw is not setup right
    2. the derailleur hanger is bent
    3. the derailleur is bent

    all of the above reasons allow the derailleur to drift into the spokes, often during a hard up shift into the largest cog (i.e. 32T)

    if you fitted the derailleur yourself you may have not setup the stop screws properly, and you are to blame for the damage

    if the shop fitted the derailleur and has not set it up properly they could be to blame

    however, your derailleur hanger or derailleur may have bent in a small crash or from something as simple as laying the bike down on the driveside, and this has caused the problem - which means the shop is not to blame...you are responsible for keeping your bike in good working order
    check out my riding - www.robcole.co.uk Banshee Factory Team rider, Da Kine UK Team rider, www.freeborn.co.uk www.eshershore.com
  • jon 0.1jon 0.1 Posts: 48
    hey guys thanks for the replies- i had the mech fitted by my local bike shop and yes it also snapped at the strongest point. your problem sounds exactly the same as mine too Michelletje, i dont really know what to do about it as im on very limeted funds and its like new :cry: I also think the top screw was set up right as ive never had any problems with it before now and its allways stopped at the top perfectly, i also question this because i was only half way through the gears and not even changing???

    Thanks for all the help and suggestions so far
    pict2664mj2.jpg
  • AnonymousAnonymous Posts: 28,799
    loose mech mounting bolt?
  • ian_worbyian_worby Posts: 331
    the only thing i notice from your pic is that the have one of those hanger banger thingy bobs. I'm sure I heard they're not recommended for sram mechs, I dont recall way.

    From the picture the mech has taken a hefty knock and where normally the hanger would fail, its not able to and hence the mech has sheared off. My only advise would be to look and see if it failed due to faulty manufacture, possible stress fracture which resulted in this.
  • rob colerob cole Posts: 706
    hanger bangers are actually a really bad idea because the whole point of the derailleur hanger is that it snaps before the dropout tip of your frame does

    I have seen numerous bikes (being the mechanic at Freeborn / Esher Shore bike park where derailleur damage is very common) where the hanger banger has twisted the dropout tip instead of the derailleur hanger snapping clean off....which can result in frame damage, have actually seen a few frames where the dropout tip has cracked or snapped through

    the derailleur hanger is sacrifical for a reason

    whenever we sell Specialized bikes like the SX Trail i always take the hanger banger off and advise the customer why
    check out my riding - www.robcole.co.uk Banshee Factory Team rider, Da Kine UK Team rider, www.freeborn.co.uk www.eshershore.com
  • nicklousenicklouse Posts: 81,520 Lives Here
    my thoughts are the mech stops were wrong and this caused the mech to be bounced into the wheel and then...... see above.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • jon 0.1jon 0.1 Posts: 48
    yeh the guy in my local bike shop said they wernt so great but i dnt exactly know how to take it off to be honest! :oops: the only thing i can see with the top screw not being set properly is that i was in like 3rd or 4th gear so it wasnt actually anywhere near the wheel right? or have i got the wrong idea?
  • nicklousenicklouse Posts: 81,520 Lives Here
    are you never mentioned what gear you were in.

    in that case i would say something was bent before it happened.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • jon 0.1jon 0.1 Posts: 48
    oops sorry thought i did, looking at it now it looks like it was
    previously stressed- ive spoken to my dad about it too and hes a mechanic and said it looks like its metal fatigue or something. i think i might get in contact with sram and see what they suggest
  • supersonicsupersonic Posts: 82,708 Lives Here
    Contact the shop, not SRAM - your warranty and receipt are with the shop.
  • jon 0.1jon 0.1 Posts: 48
    ahhh ok thanks- ill pop the bike in and speak to them then and see what they reckon.
    thanks for all the help guys- really appreciated
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