Seat Bolts keep breaking

Discussion in 'Bicycle Mechanics and Repairs' started by Trig, 19 Apr 2010.

  1. Trig

    Trig Active Member

    Hi,

    I have a problem in that in the last 18 months the bolt holding on my seat has broken 3 times. I've bought new ones from various places but it seems that I must be either doing something wrong when fitting it or when riding because the bolts have sheared in what seems like the same place every time.

    The bike is a dawes mountain bike and you can see a sheared bolt here(thats a pic of the last time it broke, it happened again yesterday)

    http://www.blipfoto.com/view.php?id=312044&month=6&year=2009

    And the sort of seat mounting I have here

    http://www.blipfoto.com/view.php?id=312697&month=6&year=2009

    So does anyone have a suggestion as to what I'm doing wrong.

    Thanks.

    Trig
     
  2. swee'pea99

    swee'pea99 Legendary Member

    Too many pies? :smile:
     
  3. OP
    OP
    Trig

    Trig Active Member

    [quote name='swee'pea99']Too many pies? :smile:[/QUOTE]

    Hi,

    that had occurred to me. But I'm not that overweight.

    Trig
     
  4. Moodyman

    Moodyman Guru

    Are you (like me) overzealous when you tighten your bolts?

    I've got a tendency to overtighten bolts - just for peace of mind, but learnt to my detriment that this increases the chances of the Bolt snapping.

    Only tighten as much as you need.

    Can't think of anything else.
     
  5. OP
    OP
    Trig

    Trig Active Member

    Hi,

    it could be that, but then how do you know when it's tight enough - after all I don't want the seat sliding around with me sitting on it.

    Trig
     
  6. Moodyman

    Moodyman Guru

    You could get a torque measuring tool, but really, I think it's trial and error.

    Tighten, lean on the saddle with your elbow, if it doesn't go down stop tightening, if it does, tighen some more.
     
  7. monnet

    monnet Über Member

    It sounds most likely like overtightening. That said, I have enough bits of carbon on my bikes to worry about torque and so invested in a torque wrench. A very useful bit of kit. The first thing I noticed, in most cases, was that I was rarely close to the maximum torque - ie: mostly well under. THat said i am both very cautious with carbon and having a cyclists physique, hardly a candidate for world's strongest man.

    I should emphasise torque settings are generally quoted in a range (eg 3-5Nm) with the larger number being the max recommended, not the recommended.
     
  8. Globalti

    Globalti Legendary Member

  9. OP
    OP
    Trig

    Trig Active Member

    Hi,

    thanks for replies, I'll take more care when tightening the next one.

    Trig.
     
  10. 02GF74

    02GF74 Über Member

    that looks like M6 socket head bolt. What are you using to replace it? bolts come in different tensile strengths, usually 8.8 but most socket heads are 12.9 - the bigger the number, the stronger it is.

    IF you struggle getting replacement, I can get a bolt for you if you measure it.

    Is your saddle positioned centrally in the clamp? Seems unsulay to be breaking bolts, I've never bust one, M6 is a fair old size.
     
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