My DT Swiss M1900 rear wheel was misbehaving where the friction in the freewheel was so high that when coasting the chain would completely detension and come off the chainset. After some headscratching I tried a different freewheel hub (MS instead of the original HG one) and that worked perfectly, so the freewheel hub was the problem. Basically the bearings where worn, but you could only tell that when the axle was under compression.
Not wanting to spend £60 on a new hub when only the bearings were gone I ordered two new 6902 bearings. I've just installed them this evening and the problem is still there, so I'm at a loss as to what the problem is? The new bearings seemed high quality and have two dust seals like the originals. The only thing I can think of is that some 6902 bearings don't work under lateral compression - is that right? How would I tell if I buy another set or bearings that they are going to work?
Any other thoughts as to what the problem might be?
Hub is out of tolerance and either the bearings are in too far or not far enough. Or crooked. I’d replace the freehub or at the very least send it off to DT Swiss UK.
Sometimes the spacers can mushroom a little that causes drag. Since the MS freehub was fine that suggests the ratchet ring spacer is ok. Is the dragging freehub hard to push on/pull off? How do the new bearings feel when the freehub is off?
The dragging freehub is possibly a little easier to pull off because it is older than the MS one. The bearings feel perfect to me. I did measure the spacer as well and it was on spec at 15.4mm. What I can say is that there is a lot of drag with the wheel off and therefore no compression, and that just gets worse under compression. Another theory I had was too much grease, so I didn't put any in.
Another thought I had was that the seals were making contact with something as there is a spacer that does butt up against the sit of the inner spacer. Might try and take that out as a next step.
Check to see if bearing seats are misaligned or not fully pressed. If one bearing isn’t fully seated in the freehub body even by fractions of a millimetre, that could be a problem.
Just to report back, I tried removing the space, reseating the bearings all with no luck. Bought a new freehub, which fitted and worked straightaway. I can only think that the DT Swiss bearing are designed to work under compression, whereas standard 6902s aren't.
Further update. I just put the wheel back on the bike for a ride and the problem returns with a brand new freehub. There is clearly something that isn't the freehub, that isn't right, but I'm at a loss to think what???
Have you assembled the rear hub in the correct order with no missing parts?
If you forget the shim washer (number 6 in the diagram) this can cause a binding issue, are the bearing seated properly?
Take a look here
https://www.rotorburn.com/forums/index.php?attachments/1607423893170-png.370245/
#9 will be the issue
OK, finally solved. When I took off the MS freewheel hub, the freewheel seal remained in the hub body. When I then put in the HG freewheel hub, then was then two seals. When I replace the MS freewheel with no seal on it all worked, because a seal was embedded in the hub. Every time I replaced with the HG version (including the new one), there was two seals! You really need to have good eyesight to notice.
Thanks all for the suggestions!