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Here is my bike: https://www.trekbikes.com/gb/en_GB/bikes/hybrid-bikes/fitness-bikes/fx/fx-1-disc/p/27987/

What appears to have happened is that the axle through my hub has sheared off due to some reason. I don't really know how to describe what has broken but it's the part that's gone through the middle of my hub that's not the quick release. It broke when I took my wheel off to inflate it. When I put it back on the wheel fitted but was super wobbly. The axle kind of comes apart in two pieces now and you can see the ball bearings inside. It has sheared within a threaded part of the axle. Is this just a case of finding a replacement axle part or do I have to replace more than this. I have a decent bike tool set and can take apart different parts of the drive chain. The rear wheel and component parts have been changed since the bike was bought. The freehub is from nervar. broken part freewheel other side wheel

If anyone know what I have to do please give me the items I need to buy, the tools I need and some sort of method. The bike is screwed up in other ways but I want to learn how to fix this part. Is there a way I can replace the whole rear hub and just fit my old freewheel back on? I want to preserve as much of the wheel and drive chain as possible.

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Axles of this type are standardized and replaceable, but the problem in a situation like this (axle is discovered to be broken upon wheel removal) is that by the time of discovery, it's very likely that other, harder to replace parts are also damaged. These include the hub cones and cups. If the pitting etc on these parts is only light, you could keep the wheel going with a new axle and ball bearings and it might be okay for some time, but more commonly it's more than just light and you won't be able to get any kind of reasonable adjustment on the hub at all.

Almost all axles on QR 135mm disc freewheel hubs are M10x1x146 (10mm diameter, 1 millimeter per thread, 146mm long). You can measure to double check but that's likely what you're in need of if the axle is the only problem.

You need the correct freewheel tool and cone wrenches to do any of the work needed.

There's also the option of replacing the QR axle with solid (nutted). It will be less prone to breakage.

Generally speaking, anyone that's broken one disc freewheel hub should really just call it quits on them and go to a cassette hub. Disc freewheel hubs more or less shouldn't exist and veer hard to being hub-shaped objects. In the fairly likely case of needing to replace the wheel, look hard at getting a reasonable quality cassette wheel and a cassette, although that will tend to also mean a new chain too.

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    I didn’t even know that disc freewheel hubs existed!
    – Paul H
    Commented Jan 24 at 15:45
  • +1 " but the problem in a situation like this [...] is that by the time of discovery, it's very likely that other, harder to replace parts are also damaged" This is true of unfortunately numerous aspects of life. Not improving the answer but couldn't stop myself sharing. Be healthy!
    – Vorac
    Commented Jul 9 at 10:38
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It is hard to tell from the image, but is your axle actually broken?

Having rode bicycles of this type for years, I know that the axle often comes unscrewed on an axle like this if you loosen it too much, and all you need to do is reassemble it correctly.

Then again, maybe it is broken. I cannot actually tell as your image is blurry. Before doing as Nathan suggests, see if the axle can be reassembled, or just take it to a local shop and see if they can. You might be surprised. Worst case you find out you really do need a new axle and cassette. Many bike shops will do this inspection free of charge or cheaply on the spot even.

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