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When I disassembled my Mountain bike's front hub (Shimano HB-MT400-B) so that I could clean and re-grease the bearings, I found that the cone on one side was developing pits. There are about 4 small spots (not all in the picture) and it did feel slightly rough before I disassembled it. It's a year old and I've put about 1000 miles on it in that time, mostly offroad in dry/dusty conditions. The grease was dirty.

I know the correct answer is to replace the cone/axle ("hub axle unit" per Shimano) but I am unable to find this part. One LBS I talked to said that it appeared Shimano does not sell this part separately. I also couldn't find any hubs of this model that I to swap parts with.

Given that, I am going to be riding this for a while longer, likely until the hub dies and I rebuild/replace the wheel. I would like to prolong its life as much as possible. Is replacing the ball bearings worthwhile? They did not appear to have any damage or marks. Should I increase the overhaul frequency? How much more life can I get from this hub?

Pitting on hub cone

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  • It's too late now but if you pack the bearings with good grease from new they will last better. The factory is a bit stingy with grease, often.
    – Noise
    Jun 10, 2021 at 19:42
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    If you're proactive at cleaning and relubing the bearings, you should be able to get significant mileage out of the unit. And catastrophic failure is unlikely, if well-lubed.
    – Daniel R Hicks
    Jun 10, 2021 at 20:13
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    Should I replace the bearings now and more frequently in the future?
    – JMayer
    Jun 10, 2021 at 20:38
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    Just slap some new grease in and call it a day. It’s like a $50 hub, max. No point babying it with new bearings and axles and cones and cups.
    – MaplePanda
    Jun 10, 2021 at 21:02
  • @MaplePanda - while its a $50 hub, its another $100 rebuild the wheel (or more likely buy a complete new wheel) when the hub is done, so its not just $50 you are saving. For some the cost a new bearings, grease and a bit of time is worth it.
    – mattnz
    Jun 10, 2021 at 23:15

2 Answers 2

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As a stuffed hub means a wheel rebuild or a new wheel (often cheaper), especially for a hub at this price point, a full repair is prudent if it can be done for a few dollars. I have been able to find a couple of online retailers selling the axle alone, but it costs more than you can buy the complete hub. If it were me, at around $US20 for a new hub I would be ordering a hub to get the parts needed for a repair.

If you decide not to replace the axle, as the comments have indicated, the axle has does have usable life left in it. Bearings are cheap, at least put new bearing in. I would shorten future maintenance intervals (with regular checks of how it feels between), and probably put new bearing in each time.

How long the hub has left to go is hard to guess. Its likely the damage was from not enough grease or over tightened bearings ex factory, so the wear is no indication of what will happen with correctly packed and set bearings.

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  • Curious sales politics though. Cup and cone make sense if spares are available. Else cartridge bearings (standardized parts) are the better solution.
    – Carel
    Jun 11, 2021 at 7:00
  • I think it's more agenda from the answerer's part. The spare part is available if you are able to order stuff from Internet. It costs almost 10€ though, so a new hub is cheaper than both cones.
    – ojs
    Jun 11, 2021 at 9:12
  • No agenda. I did a quick search, and saw parts prices listed higher than hub prices and reported what I found.
    – mattnz
    Jun 11, 2021 at 9:27
  • @ojs Curious as to where you've seen this part? Both of the LBSs I called couldn't order it from Shimano, and the only hits I've found when searching by the part number (Y2CR98050) are in Japan. I'm in the US, so I'd expect to be able to find it somewhere...
    – JMayer
    Jun 11, 2021 at 18:09
  • bicikli.de/shop/… was pretty close to top for me. The <10€ price was for the loose cone, the axle unit is actually more expensive than the whole hub.
    – ojs
    Jun 11, 2021 at 19:18
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This Bicycle Stack Exchange Q/A about pitted cups has some relevant info on pitting in cup & cone bearing systems. As you've noted, the best approach is to replace at least the cone nuts and bearing balls. Despite being a Shimano hub, instead of loose ball bearings it uses retainer rings with 5/32" bearings. See the schematic/exploded view of the hub here.

As noted in the other answer, a thorough cleaning of the hub and parts and repacking with new grease will do wonders for the feel. A little sanding and steel wool treatment of the cone to smooth the pitted areas will help the rough feel. See the linked SE question for some detailed tips on that.

Here's a link to a US website that appears to have this hub in stock.

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  • I will try polishing the cone a bit. Hopefully that (and new bearings and grease) will keep it going a while longer.
    – JMayer
    Jun 14, 2021 at 20:40
  • I'm sure it will. I've repaired quite a few cones like that and the continued to run pretty smooth. Definitely gets rid of the grinding. I'll bet it makes it through to next spring.
    – Jeff
    Jun 14, 2021 at 23:16

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