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  1. #1
    ProPedal
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    Mongoose Seat Post Shear off

    Hey,
    Today morning I did took out my bike for ride. All of a sudden I got the seat post stem got sheared. It's a Mongoose. What can I do now? It's a four year old bike. I am afraid I wasn't sure about the seat post height under the min level. This one is Mongoose XC Aluminium Frame 6061
    Last edited by jhbalaji; 07-25-15 at 09:37 PM.

  2. #2
    ProPedal
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    Last edited by jhbalaji; 07-25-15 at 09:30 PM.

  3. #3
    Senior Member
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    If you're talking about the part of he frame extending up from the top tube (crossbar) cracking, then the fame is toast.

    I can't comment about why without knowing much more, starting with your weight, and how far the post extended both above and below the break.

    But why barely matters, as you'll be shopping for a new bike anyway.

    EDIT - posted the above before you're photos were up. yes, the frame is toast.

    BTW- if you;re interested, there are emergency repair options, if the goal is to keep this going only until you can source a replacement. I'll offer a suggestion, but only on the condition that you accept it as a short term stop gap kind of thing.
    Last edited by FBinNY; 07-25-15 at 09:32 PM.
    FB
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    An ounce of diagnosis is worth a pound of cure.

    “Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

    “One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

    WARNING, I'm from New York. Thin skinned people should maintain safe distance.

  4. #4
    ProPedal
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    Quote Originally Posted by FBinNY View Post
    If you're talking about the part of he frame extending up from the top tube (crossbar) cracking, then the fame is toast.

    I can't comment about why without knowing much more, starting with your weight, and how far the post extended both above and below the break.

    But why barely matters, as you'll be shopping for a new bike anyway.

    EDIT - posted the above before you're photos were up. yes, the frame is toast.
    Cant I get a Al welding done for that? Is it so fatal?

  5. #5
    Senior Member
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    Quote Originally Posted by jhbalaji View Post
    Cant I get a Al welding done for that? Is it so fatal?
    No, if the original failed, there's no reason to expect a butt welded splice to do better. There are also technical considerations that make welding on a frame like this impractical. One of those is that you'd be welding tight at an existing weld.
    FB
    Chain-L site

    An ounce of diagnosis is worth a pound of cure.

    “Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

    “One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

    WARNING, I'm from New York. Thin skinned people should maintain safe distance.

  6. #6
    Senior Member TinyL's Avatar
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    Just judging buy the pictures I would bet you did not have enough seat post in the tube. "Give me a long enough lever and I can move the world". The fatigue and fracture started at the top edge of the weld joint facing forward. I can see the "pin" of the fracture which means the last point the metal was attached before it was completely separated at the rear of the tube. The edge of the weld is always the weakest point. With not enough seat post to offset the forces above the clamp you developed a fatigue crack. As far as welding it you might get away with it...but without the proper matched AL rod and a skilled welder you will probably develop another crack pretty rapidly...but this is just an educated guess...I see this type of metal failures everyday in my job.
    2015 Surly Disc Trucker
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  7. #7
    coprolite fietsbob's Avatar
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    I agree ^^ Buy a new frame *, and this time get a longer seatpost.

    Bodging it together? consider welding a long tube sleeved inside the frame , then at the top of that use a very long but smaller diameter seat post

    that also goes way down inside the frame ..

    those breaks typically are caused by pulling the seat post up too high and not having sufficient seat post length left inside the frame.

    the max line Marked on a seat post is irrelevant on a frame like that , as You found out Why.

    *If it's a Mountain bike used in the woods on single track a Lot its probably new bike time.
    Last edited by fietsbob; 07-26-15 at 10:24 AM.

  8. #8
    Andrew R Stewart Andrew R Stewart's Avatar
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    Make a trials bike out of it. Don't need no seat to hop. Andy.

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