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So, I have this problem [problem].

This happened today while I was putting it in a car to store overnight, but clearly I have to fix this.

Could someone please tell me: what exactly qent wrong here, and how likely would this have been to kill me?

Just in case it is hard to see, this is my handlebars coming off of my stem.... problem

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    It's unusual for this to happen without considerable "warning", as the handlebar keeps twisting left and right relative to the fork. The only way I can see it happening without such warning would if the handlebar were adjusted extremely high, such that it was barely seated into the fork tube.
    – Daniel R Hicks
    Aug 10, 2017 at 22:31
  • And there was no warning? No weird-feeling steering? The front wheel never pointed subtly off-track when the bars were straight-ahead? I'd strongly recommend you give the whole bike a careful once-over looking for other warnings. This is totally fixable, but what else might you have missed? Consider asking a bike-knowledgable friend for assistance, or apply an M check bicycles.stackexchange.com/questions/2161/pre-ride-checks is relevant, read through all the answers.
    – Criggie ♦
    Aug 11, 2017 at 0:48

1 Answer 1

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This is a "quill stem" and uses a "wedge" or an "expander" to press against the inside of the steerer tube (the top part of the fork.)

When fitted correctly, the quill stem sits in the fork and is held in place because the grey part at the bottom is pulled up by a long thread and it is pressing against the inside of the fork. Here the thread that pulls up the bottom piece must have been come loose or broken.

If this happens quickly it is dangerous because you no longer can steer the bike with the handle bar and quite likely will crash. If it happens slowly you will find that front wheel and handle bar are no longer properly aligned and this would trigger you to inspect it.

I can't answer how likely a fatal accident would have been but count yourself lucky to have noticed the problem.

enter image description here

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  • This may be a stupid question, but a safe repair is not immediately obvious to me... Than you foe thr answer though... do I need a new clamp bolt?
    – user1833028
    Aug 10, 2017 at 22:13
  • You should be able to just reinstall it and make sure you tighten it down good and well, nothing looks broken, probably just became loose with use over time. Loosen the bolt on the top of the stem, insert then tighten the crap out of it, then check to make sure it is snug. You can hold the front wheel between your legs and give it a wiggle and pull up to make sure its tight.
    – Nate W
    Aug 10, 2017 at 22:20
  • There is a very slight chance that the headtube has cracked (a very unusual thing). You would notice this when you reinstalled, however, as the handlebar would feel wonky and likely the headset bearings would be binding.
    – Daniel R Hicks
    Aug 10, 2017 at 22:33
  • I've added some words to help the indexer find this question easier.
    – Criggie ♦
    Aug 11, 2017 at 0:51
  • Also, make sure when you re-install it that you have it inserted far enough into the steerer tube to cover the minimum insertion line.
    – Jamie A
    Aug 11, 2017 at 18:52

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