Shimano DH-T780?

[GideonReade]

I've got a SP PV8 dynohub on my tourer, it's done about 25,000km, and is making nasty bearing noises. Everyone seems to agree with SP that the bearings aren't serviceable except at their factory. Its identical predecessor lasted only about 5000km before succumbing to different bearing noises and worse. I'm not heavy, nor much off road, but the bike has maybe 12kg front baggage, and a shimmy habit possibly caused by a slightly off-street fork. Maybe those accelerate front hub wear. The supplier of the original has suggested that 25,000km is a typical life for these. Also suggested SON were good for a lot more, leaving aside a burst of premature failures a few years ago.
Anyway, I need to replace it.
I recall some tests in Germany years ago, where SON were efficient, low drag, and light, SP nearly as good but lighter, and Shimano heavy and draggy, low budget only. But since then Shimano introduced XT grade dynamos, as title, claiming much less drag. And I've been advised the bearings are field serviceable.
Is anyone aware of updated evaluation of these newer Shimano hubs, are they good?
And please, somebody tell me they didn't make the axle of aluminium....

[Gattonero]

SP hubs do use #6000 type bearings (10x26) which is a common size on lower-end hubs, while the SON does use a #629 type that's a bit odd (9x26) which I suppose is both using bigger/more balls inside and better quality of the bearing.
To my understanding, the only way to replace the bearings is to remove the hub and open the hub shell (it's two halves), so the answer is "don't!"
And TBH, an alluminium axle is probably the last problem.

Back to the SP hubs, what you can do to prevent the bearings to rust -as they will rust well before they would actually "wear"- is to remove the end caps of the hub axle (they are push-fit) and clean regularly plus you may lift the seals and squirt some good grease inside. That would do good, especially if using the bike in all weathers.

[andrew_s]

It's only the earlier and low-end Shimano hubs that are draggy. The original NX10 famously gave higher drag with the lights off than with them on, and I'd regard the current 3N20 and 3N30 hubs as being commuter/ town bike grade with regard to drag. 3N72 and upwards are all good, and mostly use the same electrical generator core.

The bearings are the same cup and cone as any other Shimano hub of the same grade. You can service the left side as normal, but the right side has the electrical connections threaded through in axle slots etc, and is difficult. It is possible to take them apart, but hamfistedness or too much bending can break the thin wires, so it's best not to unless necessary, and certainly not until out of warranty.
The bearings are frequently set too tight in the factory, and the amount of grease can be inadequate, so it's good practice to service before first use ( like all Shimano hubs). Whilst the left-side cone is off, push the axle across as far to the right as it will go, and inject extra grease in through the gap under the shield that should be exposed. Leave the right side alone, otherwise. The bearings should be set so there's a little play with the wheel off the bike, which just disappears when the QR is tightened.

SON hubs do last better. My oldest was on 45,000 km when its current rim went on, and the rim is now worn out. I've switched to disc now, so I've not got round to sending it back for service.

[Brucey]

I've got a SP PV8 dynohub on my tourer, it's done about 25,000km, and is making nasty bearing noises. Everyone seems to agree with SP that the bearings aren't serviceable except at their factory. Its identical predecessor lasted only about 5000km before succumbing to different bearing noises and worse.

Isons will service your hub and replace the bearings for about £25

...But since then Shimano introduced XT grade dynamos, as title, claiming much less drag. And I've been advised the bearings are field serviceable.
Is anyone aware of updated evaluation of these newer Shimano hubs, are they good?
And please, somebody tell me they didn't make the axle of aluminium....

They make both the windings and the axle from aluminium in DH-3N80. The various XT models are based on that design.

LH bearing is 'normal' and the RH bearing varies in accessibility. I serviced a DH3D37 model recently, and once the LH cone was backed out, there was good access through a gap into the RH bearing. They are not all like that.

cheers

[Brucey]

BTW I'd take test figures for drag with a pinch of salt; the shimano hubs always have their bearings set too tight and not enough grease inside/on the seals too. This can make the hubs surprisingly draggy unless they are attended to.

I built a DH3N72 hubbed wheel a while back and once I'd serviced and set the bearings properly, the wheel span for about twice as long, off load, as it did before. I thought this was a difference of about 1W . Unless the tests are carried out on similarly adjusted and lubricated hubs, they could be subject to errors of about that size.

cheers

[GideonReade]

Thanks guys (I guess!) for the good info. I'm not actually in the UK at present, I'm on the Arizona - New Mexico border on a RTW. So UK value service will have to wait.

How do the Shimano designations work? This hub is marketed as DH-T780, but Bruce writes as if it also has a designation 3Nxxxx as well. I can't see an explanation online.

Oh, and in my original post, non-street fork should have been non-straight! As in, the wheel runs slightly tilted to one side.

[andrew_s]

3N is 3W dynohub.
There are also 2N=2.4W and 1N=1.5W hubs that aren't sold much outside the Germany/Netherlands area.

The ones with just numbers are not part of any official series of parts, like the R650 and R451 57 mm drop dual pivots, with higher numbers being "better". The Sports level hubs (3N72, 3N80) were originally stated as being "Ultegra level", iirc.
Since then dynohubs have been added to some of the various groupsets with series numbers, like the DH-T780. Like Brucey says the electrical internals on all of the sports hubs are the same, with the hubs differing in bearing quality, seals, finish etc

[Brucey]

I said the DH-T780 design was based on the DH-3N80. The parts are mostly interchangeable; basically the former is the same as the latter, but in a slightly different frock.

http://si.shimano.com/pdfs/ev/EV-DH-T780-3192.pdf

Some generators have a DH-Txxxx designation, which offers you few clues, until you look up the specifications. But if it has a number like DH-3N80 (or is based on one that has, check the EV techdoc) then you immediately know plenty about it.

DH-3N80 where

DH- means hub generator (not strictly a dynamo, since the output isn't DC)
3 - is the nominal power, in watts (could be 1 for 1.5W, 2 for 2.4W instead)
N - 'normal' for rim brake ( could be D for disc, or R for roller brake)
80 - is the model number (higher means later/better)

The DH-3N80 model has been around for nearly ten years or so, and is well proven.

cheers

[interestedcp]

I recall some tests in Germany years ago, where SON were efficient, low drag, and light, SP nearly as good but lighter, and Shimano heavy and draggy, low budget only. But since then Shimano introduced XT grade dynamos, as title, claiming much less drag. And I've been advised the bearings are field serviceable.
Is anyone aware of updated evaluation of these newer Shimano hubs, are they good?
And please, somebody tell me they didn't make the axle of aluminium....

Regarding electrical performance all the top end dynamos are now remarkable similar. The SON's tend to show the lowest drag, but even the best tests I have seen of hub dynamos are all performed in a static setup IIRC even without any proper weight load.

Real world cycling also stress the bearings laterally something that cup-and-cone bearings theoretically are better suited for than standard cartridge bearings. I don't think it makes a big difference, but I think it is prudent not think that a 0.5 Watt advantage measured in a static setup, automatically translates into a similar amount in the real world.

IMHO, the choice of top end dynamo is much better taken by functionality and looks than the often tiny measured differences in drag and power output.

All the low-weight dynamo hubs from SON and SP requires factory servicing of the bearings, and also requires the wheel to be disassembled and reassembled. For some this is an acceptable compromise for the low weight. (around 100g saved compared to a Shimano hub)

SON has the best warranty period (5 years), and use SKS cartridge bearings, a brand that is generally highly regarded. SON hubs also have a "pressure compensation" design that reduces the chance of moisture destroying the bearings. SP hubs have a shorter warranty, use no-name cartridges, but are also somewhat cheaper.

Shimano hubs are heavier but can be DIY serviced in various ways and without taking the wheel apart.
One way to service the Shimano hubs is simply to replace the internal assembly, a job that is both easy and fast to do, meaning practically no down time for the wheel (as opposed to eg. taking the wheel apart and mailing the hub to Taiwan for service).

Shimano's borazon polished bearing races are IMHO superb, and while their lightest dynohubs like the 3N80 use a aluminium axle, I wouldn't worry about it; they are oversize and seemingly very strong. That model is around 10 years old and I have never seen either a picture or read and account that somebody have broken their axle.

(edit: changed weight savings to 100g)

[GideonReade]

Thanks again. I hope in a couple of days to rendezvous with a pair of new factory built wheels (my rims are well worn, one's cracked) with an LX rear hub and dynohub described as LX/3N80. Velocity Dyna rims, which I've not heard of before. Sounds fine on paper, and the LBS involved promises to pre-service the bearings.

Fingers crossed!

Sounds like it's worth me stripping the old hubs out, and posting back to UK for post trip service!

[Brucey]

...as opposed to eg. taking the wheel apart and mailing the hub to Taiwan for service....

in the UK an SP hub can be serviced by the importers and the bearings replaced, for about £25. The wheel still needs to come apart though.

cheers

[GideonReade]

Well, a very helpful change over at Gila Hike N Bike, Silver City, NM. The factory built wheels maybe not quite as pretty and light as Spa's originals, but nearly so. The new Dyna hub is labelled Deore LX and DH-T670 3N. According to the sequence of dynamos shown on Rose Bikes sites it is sort of upper/midrange Shimano. Should get me home. And Gila pre-serviced both front and rear hubs in the new wheels, which indeed were skimpily greased.

Rose, for good website list of dynamo hubs: https://www.rosebikes.com/article/shima ... aid:591989

Have to say Arizona and New Mexico an unexpected pleasure, winter touring wise, although we did get snowed in a couple of days. Absolutely frigid mornings and dark before 6pm, yet big distances - the dynamo lights frequently used.

[GideonReade]

For completeness - the new wheel set $420 US, and $100 for quite a bit of labour (not just the hubs).