Shimano dynamo hub bearing life
 

I have been using a Shimano DH-3N80 dynamo hub for about 3 years now, probably over 15K miles. While it's still working as well as the first day, I keep wondering if and when I should overhaul the bearings.

On one hand, I am worried that I won't be able to feel when the bearings begin to go. The hub feels notchy due to the magnets. I don't mind having to replace the cones, but I am concerned that the cups may be damaged by the time I detect a problem. Then there is the worry that the hub will seize in the middle of a brevet.

On the other hand, overhauling the bearings is not so easy on this model. The dynamo wire is fragile, and adjusting the bearings just right is quite difficult because of the magnets.

So, what is the collective wisdom? How long have you gone without service with a Shimano dynohub?

About 16,000 miles so far.

Unofficial instructions for servicing Shimano dynohubs can be found if you google around. It's far from rocket science but relative to other bike mechanicing jobs it's what I would describe as a difficult procedure. There are more bits than a regular hub to put back together again, and more things you could break (the wire, the stepped threading). And like you said, it's tricky to get preload right because the magnets make it hard to feel. That said, with lots of kms piled up on your dynohub it's nice to know that you have new bb's, clean grease and no pitting in there. When I opened mine at 15 000 kms the grease had gotten pretty gross looking.

It's almost impossible to find cones afaik. The dynohub axle is extra fat to make space for that wire and so they made special cones to fit on it. If you do manage to source some please let us know!

I have a hub I bought used that I think probably should be overhauled. I have the instructions, they look a little tricky, but not too bad. The wire actually looks like it could be repaired without too much difficulty if you did manage to break it. One of the issues is that it is normally bent, and you have to straighten it to get the hub apart.

I was thinking about modifying my spare to work with the Schmidt dropouts so I don't have to get one of the schmidt hubs right away

Cones seem to be available from UK mail order shops, but not cheap at $32. I had not realized (but should have expected) that different Shimano models (70, 72, 80) use different size cones.

I have been using a lower end model on my commuter the past 10 13 years. And while the rear IGH has worn out at 30,000-40,000km (18,000-25,000 miles) the front is still going strong.
No maintenance whatsoever on the front and limited maintenance on the rear hub though.

The DH-3N80 is a higher end model with better quality bearings IIRC so I wouldn't worry about it too much.

I finally had the 3n72(?) die on me. I'm not sure if I can resurrect it. I suppose I should have overhauled the bearings back in 2011 when this thread was current. It was used when I bought it and I used it for most of 8 years, so I guess it doesn't owe me anything. I'm not sure what's going on with my 3n80 hub. I thought it was making noise when I took it to France, but I'm pretty sure it has stopped. I finally have one of the SON hubs with the contacts built into the axle, waiting for the frame to be painted to install the wiring

What are the symptoms of a dying Shimano dynohub? Was it a catastrophic failure that stops you somewhere or did the electrics die while you could continue rolling?

I bought a used wheel with a 3N71, I would assume that is similar to your hub.

***

Slightly off topic, but when this thread started SP was not making dynohubs. I have only heard of two SP that failed, those two are described in the links below:
1
https://www.bikeforums.net/20040873-post1.html
2
https://www.bikeforums.net/19730971-post1.html

Back about the time this thread started, I put a 3N72 (I think) on. Some 30,000 miles later it's still going str - CLUNK! Karunch! grind grind grind THUD

Maybe that'll be enough to ward off Murphy's Law and keep it going strong another 30,000 miles.

About ten years ago I bought a couple Shimano dynamo hubs that were for sale pretty cheap. Both were the same model, I think 3N72 but I am not sure.

I put one on a folding bike with 16" wheels that I commuted on every day for several years, all kinds of weather. After the bike wore out (I actually wore out two frames before I moved on to a folding bike with 20" wheels. Unless I'm confusing it with another one (that's a possibility), it hub had 10k-20k on it when I retired it. I later built that same hub into a wheel for my touring bike. On a tour through central NY state five years ago that hub started making loud grinding clucking poppin crunching sounds. It continued to generate electricity and it seemed to roll fine, but the noise was embarrassing and worrisome. I retired it. Using that hub in a 16" wheel probably caused more wear and tear than a normal wheel would have.

The other went on my son's bike that he rode to school every day. That bike had normal sized wheels. But the hub didn't last long; only a few months later the thing stopped producing electricity, and on closer inspection the axle was impossible to turn by hand. It would turn when the wheel was securely installed in the fork, but with a lot of mechanical resistance and no power generation. I don't know what went wrong with it.

I can add a third to that list. It makes power just fine and the bike is still rideable, but the bearings rumble and cause pinging noises in the spokes. Guess you don't get low hub resistance for nothing.

Planning on starting a thread in a week or two.

I'm a bit embarrassed to admit the first thing I noticed was that the wheel would rub on the brake shoes under certain conditions. The axle doesn't turn all that well, but is really loose. I'm afraid to take it apart and see the damage. I had to put a new rim on it some time ago, but I think it might be a total loss. I have contemplated attempting to convert it to a connectorless design.

Once I start using the SON, I'll have to overhaul the remaining Shimano hub before it suffers a similar fate.

Talk about a zombie thread! Let me give my update. I ended up opening up the hub to overhaul, and broke the wire that I knew to be fragile. I put it aside to solder later, then discovered that I had misplaced a small part (one of the terminals in the connector). So I kept the hub to use as spares if needed (cones, axle, etc), and built a wheel with a new 3N-80 which is still going strong. I don't plan to open this one up until something goes wrong, and now I have spares!

This is the first time I have seen an update on a post from the OP after eight years. That might be a new record.