I have a DT swiss 350 rear hub and the axle does not rotate freely. Rotation is smooth (not rough) but with noticeable amount of resistance. I have to pinch the axle hard with my fingers to even rotate it. In contrast the front hub (also DT 350) rotates both smooth and easy.
When the wheel is on the bike it is noticeable that rear wheel slows down and stops much faster if I spin it. I even tried with the wheel flipped in the frame to eliminate the freehub drag contribution.
The hub is only ~ 6000km old and had a relatively easy life.
I would like to take it apart and see what exactly contributes to axle not turning easily. My dillema is that all manuals that I see (including DT swiss one, recommend hammering the bearings out with an axle (which has shoulders). This will put pressure and shock on bearing inner race which is normally a no-no. That would not be an issue if I wanted to throw away the bearings and replace them with new ones, but I suspect that bearings are in fact fine and probably not preloaded correctly (to much?).
Hence the question: Is there a way to remove DT 350 bearings without hammering the inner race and risking damaging them?
The answer to original question is: No, for DT Swiss and and similar hubs removing bearings from the hub without damage and re-using them is not an option
Correct answer is from @Criggie with plenty of useful info and a bonus link for Hambini fans.
I was contemplating bearing service before a bikepacking trip in Morocco and decided against it as axle rotation felt smooth, not rought at all thought with a noticeable amount of resistance. The bike survived ~360km of road and gravel, loaded. Upon return, I decided to investigate further.
Removing rear axle bearings
The first thing I found out that the recommended and seemingly the only way to get the first axle bearing out of the hub is to hammer it out. One could argue that the benefit of DT swiss design is that you don't need an additional tool to extract the bearing. The axle is your tool and you use it to hammer the bearing out. Here is a diagram (shamelessly stolen from DT Swiss website). This is for the front hub but the principle is the same. Axle is shown in read. Note the shoulders that effectively leave axle trapped between bearings:
To my surprise both bearing felt smooth and very easy to rotate as soon as the axle was out. Which leads me to conclusion that it was wrong amount of preload after all. Preload is not adjustable on DT Swiss hubs, so my best guess is either
a. Bearings pressed too hard into the shell during assembly
b. Bearings not pressed enough during assembly
c. Hub build tolerance?
Drive side hub lock ring
This procedure is demonstrated in DT Swiss video around timestamp 2:39. I want to warn fellow cyclists about buying cheap ringnut removal tools. I sourced one for ~ £10 and it shattered when I applied torque to it. Not only did the tool break, it also damaged the axle which I now need to replace as it won't go back in. I bought a second tool (slightly burlier yet still very cheap) and this one worked...
Removing freehub body bearings
For completeness I share my notes on removing freehub bearings too. Situation with these is even worse. There is a nylon sleeve with no shoulders trapped between the freehub bearings. I could not find any material on how DT swiss recommend removing these. I assume DT swiss treats the entire freehub body as replaceable unit? The only way (that I could think of) to get the first bearing out is to shift the sleeve inside bearings and keep hammering it with a screwdriver alternating the sides until it comes out... The method is beautifuly demonstrated by a gentlement with a classy accent in this video.
Cost of the bearings
I would like to also respond to the comment by @Vladimir F about bearings being cheap. The hub in question is DT swiss 350 rear. It needs two 6902 bearings for the axle and two 6802 bearings for the freehub body. I would put aside the idea of buying bearings made of cheese (widely available on eBay) and costing ~£5. My LBS sells Enduro bearings ( which are lower quality than what is originally installed in DT swiss hubs) for £12 a piece. Actually decent quality bearings (SKF, FAG, NTN and or similar) can be sourced for a comparable price online £12 pounds a piece.
I can buy a brand new DT 350 for around £100. Quick math:
- Replacing only axle bearings would be ~25% of the new hub price
- Replacing all bearings would be ~50% of the new hub price
This is still cheaper than buying a new hub, but not cheap by my standards...