Shimano MTB hub with pitting cones

Question

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?

mattnz · Accepted Answer

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.

Jeff · Answer

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.

Shimano MTB hub with pitting cones

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