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Just replaced the bearings in my DT Swiss 240 rear hub because they had become notchy. I used genuine DT Swiss bearings of the correct size and seated them correctly with a good quality bearing press. Yet they feel exactly the same as the old bearings, a strange notchyness and resistance when spun on the axle (freehub not fitted).
Any ideas?
Bent axle?
Funnily enough, Hambini did a recent review involving a DT hub, and reckoned the bearing fit tolerances were a bit tight. May or may not be your problem.
The seals of DT bearings are designed to run under compression (I.e. from a tight axle) without it they can feel rough from new.
There's also the chance you've been a bit enthusiastic pressing/hammering them in, take the free hub out and (ideally using the DT tools) give the drive side end of the axle a tap, if the bearings are crunched onto the axle this will free them up and make them feel smoother.
If that doesn't work then they could have been pressed in wonky or you could have a slightly bent axle.
Thanks everyone. None of the above. Removed one bearing ata time and found left side bearing was the culprit. Replaced with yet another bearing using exactly the same method and whole hub now runs like new.
Badly made bearing?
cheapo no name bearings?
I picked up a well used 350 hub with notchy original bearings, tapped them or, tapped the same ones back in, perfect.
It's a mystery sometimes.
My DT240 bearings on a front hub were notchy from new. Tapped them out and they were smooth.New ones in and they were notchy.Came to the conclusion that the hub shell was undersized and was crushing the bearings.
Father in law machined a tiny amount off the outer shell of the hub and the new bearings are still turning smoothly two years on.
+1 tight bearings = notchiness
Sometimes sanding/dremeling the hub shell can release the pressure on the bearing, so it runs smooth.
Tapping bearings in can damage them, best use a press which contacts against the inner or outer race depending on which carries the tightest fit.
All mentioned above...
Pressure needs to be applied to the edge of the outer race when fitting new bearings, overloading the inner race on installation will often give you notchy\damaged bearings. Using a proper bearing press with the correct size adapters is preferred, or use the old bearings as the adapter (or a socket if its a perfect fit).
Another common cause is an undersize shell which will constrict bearings. Sometimes in this case the notchy bearings will feel fine once removed.
I also do wonder if some straight pull hubs are prone to slightly distorted shells, enough to distort bearings if already a tight fit. They typically have higher spoke tensions (which is fine if they are all even) combined with the lack of extra material a hub with a J-Bend flange will have.