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Shimano Dynamo Hub faliure

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Shimano Dynamo Hub faliure

Old 03-16-22, 05:33 AM
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Shimano Dynamo Hub faliure

I just wanted to share some information on the failure of one of the newer Shimano Dynamo hubs, a DH-UR705-3D. It seized up on me and when I opened I found the magnets inside completely corroded and some had shattered.
Has anyone else had similar experiences? This is after only one winter riding with the hub (in Switzerland, temperatures can be below zero Celsius, the bike is stored indoors). Severe case of condensation inside the hub?
Shimano won't warranty it as I've opened it myself (which I kind of understand, but not that I think it makes much difference with a failure of this type).
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Old 03-16-22, 05:51 AM
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In my hometown, they throw so much salt on the roads, this kills everything metal, even aluminum.

So people have winter beater bikes and winter beater cars.

Not sure what they do over there where you are, but corrosion causes are always the same: water infiltration.

You can try your best with preventive measures like loads of grease/lube/inhibitors, wash the bike after each ride, and despite all that it still happens.

You got it easy. Should see what this does to some new ebikes are 1 winter as well.

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Old 03-16-22, 06:01 AM
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I'd try to have it warranteed. Doesn't look normal.
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Old 03-16-22, 07:30 AM
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I've had good luck even with used (old) Shimano dynamo hubs, mostly with a solid axle, or with a quick release.
Recently, for my own bike, I risked buying a brand new one - with a quick release. What I did notice was cones being too tight from the factory, so I loosened them (yes, I understand magnets make it behave not like a normal hub, but it was still way too tight).

This problem however doesn't seem to have anything to do with bearing preload as far as I could tell. And I consider it unusual (someone please correct me if I'm wrong).
Those things are decently sealed to make any water or dirt intrusion more difficult.

Stupid questions, but just in case:
- Did you use any pressure washers on that hub?
- Do you store the bike indoors (condensation might play a part in that case - my bikes are stored outside, under a roof, but outside)?
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Old 03-16-22, 07:52 AM
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My older Shimano dyno hub is still going strong after some 9 years' year-round commuting. However, it's stored in an unheated garage. That might make a difference; there's a theory that thermal cycling between cold and dry air, and warm and humid air, will suck moisture into the hub where it will condense and potentially corrode the innards (to use a technical term).

After reading about that, and being quite happy with dyno lighting for winter commutes, I got another dyno hub for the spare bike a year later. The SON hub supposedly has a pressure equalization tube (or something like that) which catches the warm moist air and keeps the moisture from getting inside the hub.

Both mine are still working fine. But given the difference between my ambient storage and your inside storage, you might want to think about upgrading your hub to a SON.
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Old 03-16-22, 12:35 PM
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I have used Shimano dynamo hubs for a few years on two or three different bikes, no problems so far. But I think your situation in Switzerland with the cold temps in the winter and indoor storage has created condensation inside the hub, and that's caused the failure due to rust and corrosion . As already mentioned, SON hubs have in their current design a feature that prevents this. My understanding is that earlier SON hubs were prone to this also, and so they improved the design to prevent it. SON dynamo hubs are pricey, but they are the gold standard for dynamo hubs. I think this rust-related failure inside your Shimano hub shows why a new SON hub might be worth the expense.
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Old 03-16-22, 07:11 PM
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An early "Joule" hub, originally sold by Dahon, is similar in some ways to the Shimano dynohub. I had one of these hubs fail after a couple thousand miles. I was told it was not serviceable. Since I had a spare, I figured I had nothing to lose by trying to repair it. The process was documented HERE, and might be interesting.
On the subject of hubs "inhaling" moisture... the explanation makes sense, but I wonder how common this is. My Joule hub surely failed because of water incursion, but after its repair the problem has not recurred. I also have a SP dynohub on my folding commuter bike; the hub has over 10,000 miles on it. I'm riding in Chicago year-around; the bike is stored in an unheated garage at home, and indoors at work.
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Old 03-17-22, 04:59 AM
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Thanks for all the feedback. The bearings were fine in the hub, as was the wiring. My initial thought was that the easiest entry path for water would be along the wiring into the stator; the wiring didn't seem particularly well shielded. The link to the Joule hub is interesting. One thing I noticed is that the magnets in the Shimano hub are much thinner, and metallic in colour, perhaps a different composition? I think one of the reasons they shattered is because they are so thin. If they'd just rusted it would have been no problem to clean up the hub and get it running again.

What are people's thoughts on greasing / oiling the innards of the replacement hub with a thin layer to try and prevent the same problem reoccurring? (I have no qualms opening the new hub and voiding warranty as I believe in the right to repair / improve). Normally I service regular Shimano hubs before putting into to service because of lack of grease / over tightening of bearings from the factory.
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Old 03-17-22, 06:27 AM
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It does look like you got some significant water in there, which I find somewhat surprising.
I've only had issues with one Shimmano dynohub, when one of the magnets came loose. It dragged and made a lot of noise, but didn't really damage anything. I disassembled and glued the magnet back on, and all was well.
Can't see anything wrong with a thin coat of grease.
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