Galled Bearing Cones Puzzle - Shimano FH-M510 Hub ???

[FuzzyBunny666]

In all of the bearings that I have repacked over my many years of cycling I have never seen this. I posted a previous question about bearing "roar" when the wheel was spun up on the work stand. A few folks mentioned that this was probably the freehub and not to worry.

I finally got a chance to pull everything apart today. Both sides had plenty of grease on the wheel bearings. The non-drive side actually looked pretty clean.

Once I started to clean up all the parts I noticed that both bearing cones looked like they had galled in rather big chunks. The races in the hub and the freehub looked fine. The ball bearings also looked fine.

This hub is only about 2 years old and has been ridden about 5-6K miles in good weather. When I first got these wheels some folks in this group suggested re-greasing them as Shimano didn't use enough grease at the factory. Taking that advice I tore the hubs apart and regreased them using a good quality synthetic grease.

Can anyone explain why this bearing failure happened and what to do to prevent it from recurring? Is this a known problem with these hubs? It almost seems that the bearing cones were too brittle and rather than wear they just fractured.

As far as repair should I also replace the balls as well as the cones?

[FuzzyBunny666]

I don't think you have a proper picture of what is happening in this situation. The object is to be able to adjust the outboard bearing cone while the axle is under compression. To do this you are adding a washer to the end of the QR shaft so that you are actually compressing the end of the axle and not the outboard cone and lock nut.

[FuzzyBunny666]

Why do you need access to the side clamped in the dropout? You only need to adjust the bearings from one side and the frame does a good job of clamping everything in place so that makes adjusting the other side easier.

[FuzzyBunny666]

Thanks everyone for the response. Based on you comments I am going to chock this one up to too much preload. Parts are on order.

I just reassembled my rear MTB hub (different bike) and used the adjusting method on the Park Tool site where you basically clamp the wheel into one side of the frame with the QR skewer and a spacer/washer. This compresses the axle against one of the cones but does not compress cone-cone as in real life. Is this a good method to use and should I somehow compensate for the fact that the other bearing cone is not in compression?

I guess another way to put this is which parts do most of the deforming when compressed by a QR skewer? Is it the axle mostly or does compressing the other cone and lock nut add significantly more bearing compression?

Checking wheel rotation is a good idea, however, this should be done with the axle seals removed to avoid masking the result. On some wheels this is more problematic than others.

[FuzzyBunny666]

You mean the inner races? These are absolutely clean. I fact, I can't even tell the contact patch from surrounding raw material. I.e. there is no telltale bearing "wear line" at all.