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Hi! my bike is Trek Marlin 4. I don't know why my axle broke so easy and this happened second time.

its almost winter in my nation we don't have good bicycle shops. They will be close so soon. I can't order a new one what should I do and I want to know why this happened ? Please help me

Is it possible to weld?

I bought my bike about 4 months ago.

  • 2
    I would say that either the hub is warped or the bearings are going bad and causing the cones to self-tighten. – Daniel R Hicks Nov 10 '18 at 12:59
  • What were you doing on the bike when the axle broke in each case? Axles shouldn't break unless they're defective or abused and the fact that you've broken two in four months suggests that you're riding very roughly. I must've ridden at least 20,000km in my life and never once broken an axle. I doubt welding will make a good repair: axles are probably hardend steel and probably get their strength from being a one-piece part. – David Richerby Nov 10 '18 at 13:33
  • Is this a new bike? Or did you buy a used bike? – Andrew Henle Nov 10 '18 at 14:35
  • Welding would not align the two pieces sufficiently accurately and would affect the heat treatment of the material, probably weakening it. – Argenti Apparatus Nov 10 '18 at 22:27
  • 1
    That axle is scrap now - you require a new one. If you're that hard on gear, consider getting a nutted axle and not a QR axle. This will have roughly 1/3 more metal in it compared to the hollow QR tube axle. – Criggie Nov 11 '18 at 1:33

Simple answer is that the axle broke because it was overloaded.

Notice how the drive side bearing is a few centimeters inboard from the end of the axle. That creates a weakness on that side. This was a well known problem with freewheel (as opposed to freehub/cassette) hub designs with more than 6 or 7 sprockets.

Are you a heavy person? Are you carrying a heavy load on the bike? Are you hitting sharp bumps and edges hard? The bike may just not be robust enough for how you are using it.

Better riding technique - standing up and absorbing bumps through you legs, or avoiding them completely - may help you avoid damage to the bike in the future.

  • A plain axle might be better in this case, instead of a hollow one with a quick release. – Carel Nov 10 '18 at 12:39
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    I'm not sure about that. The crack in axle starts when bending pulls it apart, and quick release adds compression which works against that force. – ojs Nov 10 '18 at 22:10
  • 1
    @ojs axial compression works to re-enforce materials with high compression strength against lateral forces (concrete, carbon fiber composite). Metal can deform under compression, so tension does not add strength. – Argenti Apparatus Nov 10 '18 at 22:23
  • I can understand that axle could bend by compressing the inside of the bend, but not how how it could snap by compression. – ojs Nov 11 '18 at 1:30
  • QR vs Solid discussed here - bicycles.stackexchange.com/questions/29557/… – mattnz Nov 13 '18 at 3:30

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