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I'm working on restoring a bike which I found at a council dump and I've a couple of questions about the rear axle.

I took the rear axle into a hardware shop today to buy a new locking nut (I mislaid the original when I took it out of the wheel - my bad). They said they didn't have one as the axle was imperial and they only stocked metric locking nuts. They recommended another shop which might stock imperial nuts, but I'm thinking it might make more sense to buy a metric rear axle given that they are easier to get hold of. So my specific question is would it be ok to replace my imperial axle with a metric axle of similar size i.e is there a risk that it might compromise the safety of the wheel. The axle is about 6.5 inches long and the locking but has a diameter of about 5/8 of an inch : so I think this would mean a new axle of length 165mm?

I guess this leads to a more general question. If you replace an axle does it have to be exactly the same length as the original.

Thanks in advance for your help.

Chris

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    Don't buy critical safety parts from a hardware store. Even if you found something that fits, it probably won't be the right hardness or tensile strength.
    – Criggie ♦
    Commented May 3, 2017 at 4:27
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    If you replace the axle, replace the entire wheel. But there is a muddle of different axle sizes and lengths for the era you're talking about (probably prior to 1970), so you'd have to double-check that everything fits. (Despite what the OCD types tell you, the axle length, nut to nut, can vary by about 3mm without causing problems. The axle diameter, of course, must not be significantly larger than the old one or it won't fit in the "dropouts".)
    – Daniel R Hicks
    Commented May 3, 2017 at 12:16
  • Thanks Daniel - can I check I've understood your first point properly. If I decide I need a new axle I should get a new wheel. Is this a general rule ie new axle means a new wheel. Or is it due to the specifics of my question eg the fact that I'm working with an imperial axle?
    – Chris
    Commented May 3, 2017 at 13:11

2 Answers 2

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A hardware store is exactly the wrong place to go.

Go to a local bike shop (the older/dirtier the better). They should have the right nuts for your bike in their junk drawer. If not, they can replace the axle in its entirety for you.

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  • Thanks Karen. The interesting thing is that there aren't any of these older/dirtier bike shops in the immediate vicinity of where I live/work. They're mainly the more modern shops which sell more expensive bikes and accessories rather than spare parts. However I will try and find somewhere along the lines of what you suggest. Thank you.
    – Chris
    Commented May 3, 2017 at 8:00
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Generally you cannot swap into an axle with a different thread under almost any circumstances, because the cones you've got won't work on it and there aren't going to be suitable ones of the new thread type available. If you really looked and got adept at making mismatched cones work, which is an arcane skill even in bike mechanic land, you could find some corner case exceptions, but that's about it. There are some products out there labelled as generic replacement axle kits, but the cones that come with them really only match certain relatively populous generic hubs, not all of them or even a tenth of them out there in the world.

If you have any kind of reasonable bike shop handy, and all you need is either a new locknut or axle nut (unclear from the post) just go there with either the axle or a measurement of its thread type and get a new one. If you don't, get a caliper and thread pitch gauge and measure the axle so you know what you're dealing with, and just order the part, or one of the aforementioned generic axle sets in the size you need if you can't find a single nut (they're super cheap, and there's nothing wrong with getting them to use the axle, locknuts, or axle nuts from.)

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  • Thank you Nathan (hit enter too early :)) - this is really helpful. You've raised another question which I hadn't really thought of. Let's say I replace my old axle/cones/nuts with a metric axle/cones/nuts, and let's say the new axle is as close in thread size and length to the old as it can be. Are you saying it won't be compatible with the hub? In other words unless I change the hub I will have to get either a replacement locking nut (sorry wasn't clear about that) or a replacement imperial axle? Thanks again.
    – Chris
    Commented May 3, 2017 at 7:57
  • Sorry Nathan - I think my follow-up needs clarifying. Am I stuck with an imperial axle even if the metric equivalent is very similar in thread and length?
    – Chris
    Commented May 3, 2017 at 8:02
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    Essentially yes, because in almost all cases, acceptable replacement cones can't be had across axle types. The other side of this is that the imperial sizes are all pretty common in the world at large, it's not an imperial vs metric country thing, so just getting replacements for what you had is probably the easiest path by a lot. (I'm sure there are places where this isn't true.)
    – Nathan Knutson
    Commented May 3, 2017 at 14:11
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    Cones have design aspects that are meant to work with their specific hub. The shape and position of the ball race, their role in the hub's sealing (sometimes just a matter of having the right OD, other times more complex like with labyrinth or rubber seals), and their overall length are the big ones. Randomly mismatching them can easily get you a hub that either overtly doesn't work, has the balls grinding against the axle (dangerous), balls not really on the cone race, no sealing, etc. A given hub shell needs either its intended cones or very carefully selected replacements.
    – Nathan Knutson
    Commented May 4, 2017 at 7:50
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    If you're curious for more reading about this you can find free copies of an old edition of Barnett's Manual on the internet, which has a whole chapter about cone matching.
    – Nathan Knutson
    Commented May 4, 2017 at 16:43

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