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I have an old Trek mountain bike with a "Traditional" handlebar stem (Quill stem?) and I've suddenly become unable to adequately tighten the stem to a) remain in line with the wheel and b) stop the handlebars from being pulled clean out of the steering tube.

I've tried taking the stem out of the tube and there was a thin coating of rust over all the surfaces. I cleaned it all off with a wire brush and went inside the steering tube as best I could. This never had any significant effect.

It is not possible to tighten the nut any more yet the "wedge" no longer seems to generate enough friction to grip the forks. What can be causing this and what can I do to fix it?

EDIT In response to the question by ChrisH, here is a photo showing the wedge properly displaced from the stem as I understand it is supposed to work.enter image description here

  • Does the wedge actually work properly outside the steerer tube? Could the tube be deformed by over-tightening in the past? – Chris H Aug 12 '17 at 18:14
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    @ChrisH Yes, it does work properly, I made a point of making sure it would slide freely and it certainly appears to. I don't think it's been overtightened in the past, I've had it for about 15 years and I don't recall ever even loosening it or dismantling it for any reason so it's never really been tampered-with at all as far as I remember. – Lefty Aug 12 '17 at 19:21
  • I would guess that the steerer tube has split open. – Daniel R Hicks Aug 12 '17 at 22:14
  • @DanielRHicks That would be a good explanation for what I'm experiencing, I've already looked inside with a torch and saw nothing obvious, will check again though. – Lefty Aug 13 '17 at 9:02
  • Have any of the threads stripped? – David Richerby Aug 13 '17 at 14:10
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I'd guess that there are two possible causes.

  1. Old age. Your wedge as pictured shows some clear flat spots on the ridges that are supposed to bite into the inside of the steerer tube (the receiver that forms the top of the forks) So its very likely the steerer has equivalent wear on the inside, and you're simply seeing a lack of grip.

    First fix would be to file the wedge so its got more obvious ridges in it. Use a triangular file, or the edge of a quarter-round file for metal. Do be conscious of metal shavings and avoid getting them near bearings.

Another repair plan would be to buy a new wedge - this probably means a new/replacement quill stem. If there's a bike coop near you they might be able to help.

  1. The other cause is damage or wear inside the steerer tube. This is impossible to fix, you'd have to replace the front fork completely. To check, you need to undo the threadded headset and drop the fork out the bottom of the bike.

    You're looking for bends or swellings or even holes in the outside of the steerer tube, or significant wear marks inside.

Dropping out the fork also allows you to service/replace headset bearings too and clean out the bearing races, which may be due given its age.

  • +1 and will mark this as the answer. I genuinely never knew the ridges were supposed to be "sharp" and, as you point out, there are flat spots of 2-3 mm in width. I just cannibalised another old bike (not quite so old) and saw that the wedge has much better ridges. I swapped it into the Trek and all is perfect. Thank you! – Lefty Aug 13 '17 at 10:48
  • Filing the ridges so they are sharper is not a productive suggestion. – Daniel R Hicks Aug 13 '17 at 12:00
  • @DanielRHicks Why do you say that? I think I personally wouldn't bother just because it would normally be easier to replace the wedge, like I've done. But if that were not possible, I don't see why a bit of filing wouldn't be acceptable...? – Lefty Aug 13 '17 at 14:26
  • @Lefty filing takes a long time - I remember spending over an hour filing a skewer nut, but that was on the side of the road using a leatherman file. Also, its easy to slip while filing. and there's a chance that all the work won't make a difference, if the steerer tube is worn on the inside as well. – Criggie Aug 14 '17 at 4:16
  • @DanielRHicks Point taken - you're saying it's normally pointless rather than dangerous or damaging. – Lefty Aug 14 '17 at 15:38

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