Rear mech conveniently snapping off....

airbusboy
airbusboy Posts: 231
edited October 2010 in MTB workshop & tech
Good evening,

I have owned and ridden my trek fuel ex 8 for about 20months (2009 version). The original chain finally gave in about a month ago so was replaced with a shiny new scram 991 :-). Since then I've snapped two rear mech hangers and can't work out why?!

Day 2 of a 4 day tour on a rather tame descent in the the lake district i managed to snap my rear mech hanger.. the rear mech was found stuck in the middle of my rear wheel.. bending my new chain :-(

Day 4 cannock chase.. launched a drop-off landed smoothly (ish) and BANG same result as day 2.

In both situations i wasn't pedaling nor was i changing gear. To my knowledge the indexing on the gears were all fine, and tbh running fairly smoothly.

Has anyone experienced this before? Could the mech be catching the wheel possibly under rear-sus compression?

Any help is appreciated.


Kind Regards

AB
'Ride hard for those who can't.....'

Comments

  • nicklouse
    nicklouse Posts: 50,673
    chain too short.

    have you checked for chain grow.

    changed anything else?

    how did you size the chain?

    what gears were you in?
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • allthegearnoidea
    allthegearnoidea Posts: 4,077
    i had the same issue on myold mech, one such hanger breakage was such that the mech had been forced over its stop, not instantly noticeable until snapped second hanger a couple of miles later!
    double check your mech's okay and not been forced over the stop!

    also had a hanger go when in the woods after an Mx'ers event, gulleys a bit deeper than normal and just pinged the hanger clean off 20 mins into the ride! glad i always carried atleast one spare with me!!!
    Timmo.
    After all, I am Cornish!
    http://cornwallmtb.kk5.org/
    Cotic Soul, The bike of Legends!:wink: Yes, I Am a bike tart!
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  • airbusboy
    airbusboy Posts: 231
    I believe I was in a fairly high gear ( but not the largest sprocket)...

    Chain length was determined by BIG-BIG ( outside of
    Mech) plus two sections and the other case SMALL-SMALL making sure chain ran parallel. Two different techniques but seemed to look alright.

    I'm sure the mech is ok...... It's a long cage( inthink) xt shadow mech.... Is worth considering a change???

    Cheers.

    AB
    'Ride hard for those who can't.....'
  • airbusboy
    airbusboy Posts: 231
    Ps. When I got a new chain I needed a new cassette...? Could the mech jockey wheels cause this??
    'Ride hard for those who can't.....'
  • The Rookie
    The Rookie Posts: 27,812
    As Nick said, have you allowed for chain length growth when the (rear) suspension is at full bump, most systems mean the chain needs to be a little longer to allow for this.

    Simon
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • airbusboy
    airbusboy Posts: 231
    How would you make sure the length is correct??

    Regards

    AB
    'Ride hard for those who can't.....'
  • flet©h
    flet©h Posts: 88
    Let all the air out of the shock so the bike is at full travel, then measure the chain as normal.
  • airbusboy
    airbusboy Posts: 231
    oh excellent, never thought of that......

    Cheers
    'Ride hard for those who can't.....'

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