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I have a ten year old decathlon cheapo bike and I wanted to take out the axle out of the rear wheel to see if I could replace it with a quick release mechanism and also learn a bit about how it works (the bike is cheap and not important). I undid a few nuts until I could take out the large axle bolt but when I did, out fell a load of ball bearings from either side.

I don't think I'll be able to reassemble it and a lot of the parts are rusty and probably need replacing but I don't know what to replace them with and like I said, ideally it would be quick release.

As far as I can tell the assembly is a freewheel cassette. Then there was this large bolt going through the wheel with two nuts and another threaded item I cant identify either side. Inside there were the bearings each side with a washer like cover. But they seemed only to be held in place by the presence of the bolt.

Edit: The bike is a rockrider 5.0 from about 2010 or so.

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    The description sounds like you removed the axle ("this large bolt going through the wheel") and loose ball bearings got loose. Searching for hub rebuild instructions should find many, many illustrated instructions for rebuild.
    – ojs
    Aug 5, 2019 at 6:48
  • Note that if you replace any of the balls you should replace them all (not expensive to do) and note that the balls come in several sizes, so take a few of the old ones with you when you visit the bike shop.
    – Daniel R Hicks
    Aug 5, 2019 at 16:51
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    The cone still on the axle looks damaged
    – Argenti Apparatus
    Aug 6, 2019 at 21:52

3 Answers 3

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Yes, that bolt was the closing side of the ball bearings, your current axle is probably a "cup and cone" hub.

You opened the cup, so the ball bearings that where rolling on the cone just fell off.

You have to replace them (same diameters and possibly same hardenss ...), clean and grease all the parts (rusty and not rusty, it does not really matter).

Finally, you can replace the axle with a quick release skewers, but it must be of the same (internal) length as the one you are replacing (130mm, probably).

Giving the exact bike model or at minimum a picture of the wheel&hub may help us help you.

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You obviously have what's called a 'cup and cone' bearing hub. In this type the axle is threaded and the loose ball bearings sit between 'cups' machined into the hub body and 'cones' threaded onto the axle and held with locknuts. You removed the locknut and cone on one side and pulled out the threaded axle (the 'large bolt') so all the bearings fell out.

Reassembly is actually not too hard if you know how the hub goes together. If you lost ball bearings they can be replaced, you can replace the axle with a quick-release type also Here's a video from RJ the Bike Guy where he does exactly that.

External surface rust can be cleaned off. If the balls or cone bearing surfaces are corroded or pitted they can be replaced. If the cup surfaces machines into the hub itself are pitted you have a bigger problem.

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    Your last sentence seems to have been truncated. (It also had a couple of typos in it, which I fixed.)
    – David Richerby
    Aug 5, 2019 at 17:48
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Based on your expressed desire to, "learn a bit about how it works," I'd encourage you to go ahead and replace the axle and bearings. This is a fairly basic task and learning how to clean and repack (with new grease) the bearing system on a bike wheel will extend the life of your hub (the wheel's center) and produces a smoother, quieter ride.

Your wheel has what's termed a cup and cone bearing system. The "cup" is the depressed circular aspect of the hub and the bearings move thru this area. While generally pretty durable and long lasting, the cup can become pitted, the bearings can wear a groove in it, especially when sand and dirt contaminate the grease. If the cup is bad the hub needs replacing though one can perhaps get by for a time by sanding smooth the race area of the cup.

The cone is a threaded nut that moves toward the bearing-filled cup where at the sweet spot allows free movement of the bearing balls but no wobble or "play" of the axle, just smooth rotation. These pieces can become pitted and worn as well, and are typically the first item to show it.

Here's a great article by Sheldon Brown describing the detailed steps for hub overhaul

Cone adjustment is detailed in this article by Brown.

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