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mi7rennie
I recently build up a new pair of commuter / tourer wheels for my Straggler. I used Deore XT M785 centre lock hubs for both. I've normally had good experiences with XT level hubs, however the rear one I bought for my personal wheels felt a bit too lumpy, so I disassembled it.
The drive side has 13no 3/16" (4.76mm) loose bearings, the non drive side has 11no in a plastic retainer. All looked in good order, as you'd expect from a new hub. I measured them and was a bit surprised by the results. They ranged in diameter from 4.698mm to 4.766mm. This is measuring each one multiple times in multiple places.
So I got two packets of genuine Y00091210 bearings and measured those also. There was similar variation between the 20 in each packet. I could however pick a set of similar size ones from the 60 odd I now had. I ended up with a full set of 4.763mm size ones, and reassembled with Dura Ace grease. I also ditched the ball retainer in the NDS so I could fit 13 in that side too. (The ball retainer is used to speed up factory assembly, it provides no performance benefit as I understand it). The hub now feels sublime, as good as DA I reckon. Time will tell how it lasts, however hopefully this will have extended its life. Mismatched bearings can't do anything other than cause premature wear.
Only writing this as I get the feeling the quality of upper tier Shimano kit is slowly being eroded.