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Bent Axle + Worn Cone
Hiya guys. Been cruising the internet for a while identifying problems and causes, but I could do with some expert input if at all possible, in figuring out which parts of what I'm seeing is causal, and which is just an effect of the issue.

A while ago I decided I'd had enough of being ripped off by the local bike shop, and decided to manage my own bike. It's fun aside from anything else, but I'm very new to this.

3 months ago my rear axle (hollow, 2 years old) broke, apparently without warning. Like a noob, I was more worried about getting back on the road than asking questions such as "Why?", so I bought a new axle online, replaced it, and things seemed to run better than ever.

Yesterday I suspected some problem with the rear wheel, and sure enough, I have two symptoms, but I need two questions answering before I can go ahead and fix this:

Q 1) Which symptom caused the other? I can see arguments for both
Q 2) What should I watch out for when replacing the axle this time to prevent this?

The symptoms mentioned are:

Symptom 1) Rear axle is bent very slightly at the bearings on the freewheel side.
Symptom 2) The corresponding cone in contact with the bearings is very badly worn. There is a bearing-shaped groove around its circumference at least 1mm deep.

Did something cause the bearings to wear the cone, bending the axle, or did something cause the axle to bend, which then wore out the cone? And what should I be watching out for to avoid this next time?

Will add some extra info here in case it proves useful:

1) I would love to simply blame shoddy parts rather than me own inexperience, but I don't tax it very hard beyond the odd pot-hole.
2) No parts have been replaced before except the axle. I have a new chain-set etc. ready to go on when I find the time to sort that.
3) When I took it apart the first time, bearings went everywhere, and I had to buy some new ones. I made sure these were very well greased, and the correct size.
The bearings were either not adjusted properly, or the lock was not adequately torqued against the bearing cone, and then it loosened.

You need: a new axle, new cones, and possibly a new hub.

The right (drive) side should be locked down very very tightly, do this with the axle outside of the hub. Make sure you locate the cone properly with respect to the end of the axle. There is typically ± 3 or 4 mm margin for this. Then grease bearing pocket on the drive side of the hub, install the new balls (must be new now with all the damage), grease the non drive side bearing pocket, install the new balls; then run the axle through. Install the non drive side cone. Tighten so that the wheel spins nicely, but does not wobble at all. This takes a bit of playing around. Next install the non-drive side lock nut; torque the lock nut against the cone. Double check the wheel spins nicely with no wobble - may have to re-do this step a couple of times.

Put the bike back together, go for a short (<1 mile) ride, check the wheel again. Check it every day for the next week - adjustment may be needed. Then check weekly.

As long as you got a bicycle wheel axle there is no issue with the materials. (some people try to use threaded rod which is fine as long as you use the hardened type, but then the bike axle is a lot cheaper).
The two problems might be unrelated. Cone wear usually comes from poor adjustment or lack of clean lubrication. Bent axles are usually caused by force/impact. However, riding with a bent axle can wear the bearings because it can create a tight spot/loose spot situation because the cone and cup on the hub are no longer parallel.

Unfortunately, bent axles are much more common on bikes with freewheels. This is one reason most newer bikes have switched over to the freehub/cassette system.

Try to find a cromoly axle instead of plain steel. They're stronger. Switching to a solid axle instead of hollow may be more durable as well as long as losing the quick release is not a problem for you.

Finally, check the bearing cup on the hub carefully. If it is pitted or badly worn, you need a new wheel.
Fantastic. I hardly ever end up posting on forums, but you guys have been a massive help. I'll order the axle tonight, and keep all of your advice in mind when I have a crack at it this weekend. Hoping the wheel is undamaged. Great idea to check for that too.

Thanks a ton for taking the time to post.

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