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Recently, my rear axle was broken. I purchased a new axle online, which seemed to match the dimensions of my old one.

However, I don't think I've installed it correctly, as there seems to be a gap between the internal lock nut and frame which I don't think should be there (but I'm not sure). Unfortunately, I haven't been able to find any images online to check how this should look.

I'd appreciate advise on how to repair this correctly.

Current state

photo of axle installed with axle showing between outer lock nut and inner lock nut

diagram showing same as photo

Options

I think either:

  1. I need to insert extra spacers so that the inner lock nut is against the frame
  2. I need to add another internal lock ring so that the outer lock nut presses against something (in which case, maybe I can remove the spacers altogether?)
  3. I've installed it correctly
  4. I need to do something else

Option 1

diagram of bike axle with extra spacer so that the internal lock nut is against the frame

Option 2

diagram of bike axle with extra internal lock nut while there is axle showing between the internal lock nuts

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  • 1
    Somethings very wrong - what is happening on the other side? What spacers did the old axle have and how did it all fit together? The length of the axle from hub to frame is a recipe for another broken axle. Could you also provide the space between the dropouts, you possibly have an old wheel in a new frame or road wheel in MTB frame. (Option 2 is a guaranteed broken axle.)
    – mattnz
    Feb 26, 2023 at 1:01
  • On the other side it has a 7-speed cassette, and the spacers seem to be such that it looks like Option 1 inside I think. The space from the outside of the dropout to the other outside of the dropout is 135mm. The inner space is 132mm. The wheel hasn't changed, and I believe is the one that came with the bike. Unfortunately I'm not sure what the old axle had - it snapped completely when I was out and while I was trying to figure out what had happened I think I lost some parts.
    – domdomegg
    Feb 26, 2023 at 12:41
  • 3
    Those sketches are awesome and very helpful. +1 for the effort there !
    – Criggie
    Feb 26, 2023 at 18:11
  • Correction: Space from the outside is 150mm, not 135mm. (don't seem to have the option to edit my previous comment). Inner measurement correct.
    – domdomegg
    Feb 27, 2023 at 22:35

1 Answer 1

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The statement in the comment that you may have lost some parts is helpful in figuring out what happened here.

You need to determine two target dimensions: the distance between the drive-side flange and the drive-side locknut face (R), and the distance between the non-drive flange and the non-drive locknut face (L).

Lacking other information about what R was initially, choose a distance for it such that the chain clears the inside of the frame with the freewheel mounted by 3-4mm. Put it together and make sure you're happy with how that side looks. Then determine your OLD (same number as your frame spacing), and subtract from that number the distance between the drive-side locknut face and the non-drive cone outer face. Then subtract the thickness of the non-drive side locknut you're using. The remainder is the thickness of your ideal non-drive side spacer stack. Put that in and your L value is perfect. Center the axle protrusion with the hub in that configuration and dish the wheel.

The 3-4mm above is a fudge factor that most freewheel hubs more or less conform to. It also represents the smallest practical clearance gap. By using the smallest value practical there, the wheel is at its strongest. Using 3-4mm as a guideline will probably lead to a drive-side spacer stack dimension that is close to whatever it was originally, but not exact. If it's not exact, you need to redish the wheel. If you want to do this in a way that avoids the need to correct the dish, you'll have to put the hub together and check the dish until you've inferred what the drive side spacer stack dimension was initially.

The 135mm number you mention in the comments as the outer dropout dimension is not material to any part of this.

The 132mm number you mention in the comments is suspect. Either it and/or the 135 number are incorrect, since the dropouts of the bike in the picture are not 1.5mm each. Your frame likely was made with a target spacing (the internal dimension) of 126, 130, or 135. That part doesn't really matter; just get an accurate measurement of it and build up the hub OLD to match. On an aluminum frame, it is unacceptable to have significant difference between the hub OLD and the frame spacing. They're tolerant of 1-2mm, but with what you're doing there's no reason it shouldn't be zero.

The part you identify as an external lock nut is usually called an axle nut.

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  • Thanks, this was really helpful! To confirm my understanding: set my drive-side (cassette side) spacers such that when the chain is on the smallest rear cog, there should be about 3-4mm between the chain and the frame at its closest point. Then, measure and fill in my non-drive side spacers so it looks like my Option 1 diagram?
    – domdomegg
    Feb 27, 2023 at 22:38
  • 1
    Yep, you got it. Feb 27, 2023 at 23:59

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