Shimano DH-3D37 QR hub generator

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Brucey
Posts: 44522
Joined: 4 Jan 2012, 6:25pm

Shimano DH-3D37 QR hub generator

Post by Brucey »

I recently bought one of these, in part encouraged by the fact that a friend of mine has had one for the last five years or so (which has just worked) and in part because I got a cracking deal on it.

Image

http://si.shimano.com/pdfs/ev/EV-DH-3D37-QR-3544.pdf

The hub came with

- the 'lego' connector block
- a steel QR skewer (~90g weight)
- a dust cover for the disc mount, should no disc be fitted.

The hub is marked with a ~~K912 StVZO approval mark and is recommended as suitable for wheels between 400 and 716mm overall diameter.

This hub is one of shimano's least expensive hub generators which includes a disc fitting, in this case a centrelock mount. It shares parts with the -31 and -35 models which preceded it. It isn't anywhere near as lightweight as the 'sport series' generators (I think it is about 100g heavier than a DH-3N72 for example), but the off-load drag seems comparable; if there is much more than 0.5W in it I would be surprised . [BTW It is 'quite a lot' lighter than the equivalent hub which accepts a roller brake; this would be because the roller brake mounting includes a slip clutch mechanism which is built in steel and appears to add about 200g to the hub weight.]

In terms of a weight penalty, the centrelock mount doesn't add much vs a rim brake hub, because the mount is aluminium and relatively compact. My idea was that even if I don't use the centrelock mount, e.g. on a bike with rim brakes, there wouldn't be any significant penalty. However this turned out to be only half-right; at 48mm apart, the flanges on this hub are more closely spaced than in the rim brake version of the hub, and are offset by ~4mm from the centre. This means that the flange offsets are 28mm one side and 20mm the other; the resulting wheel is about half as dished as many rear wheels. The rim brake versions of this hub have the LH flange ~8mm further out and the RH flange in the same place; such hubs build almost symmetrically, i.e. with almost no dish.

Internally the hub uses an M11 threaded axle and there are 12off 3/16" balls each side. It turns out that the dimensions of the LH cone are almost identical to the LH cone in a DH-3N72 hub, but the latter has a polished bearing surface and may also be in a different material (it ought to be, it is twice the price as a spare part.... :shock: ). The hub has lip seals, plus dust guards which prevent most crud from getting anywhere near the seal lips. If the LH cone and locknut are backed off, the centre can be drawn rightwards by up to ~5mm which means that the RH bearing can be regreased easily (and indeed the ball bearings could be replaced too), all without dismantling the connector assembly. [The connector assembly is the 'old' type, in which one of the terminals (the RH one) is grounded. Later versions of many shimano hub generators use a slightly different system in which there are two wires in the axle slot, and neither is grounded].

The whole centre is secured in the hubshell on a large RH screw thread. The correct tool to remove the centre is a 36mm octagonal spanner. From bitter experience I can tell you that whilst a headset spanner will fit, it is unlikely that you will be able to remove the internal with one, unless it is perhaps loose to start with. It is much more likely that you will simply round off the octagonal fitting in the attempt. If you do need to remove the centre, a full octagon spanner is the correct tool for the job.

The centre uses copper windings and radially oriented soft iron laminations, in an arrangement that is similar to many other shimano hub generators. The laminations may be somewhat smaller and lighter than in previous similar generators (e.g. -20, -30, models etc, judging from the amount of movement possible once the cones are slack). However the laminations are not usually very well protected against corrosion; in similar shimano hubs if water gets inside, I have found that the laminations tend to corrode which can even stop the hub dead in its tracks. [If this does happen, it usually take several years, and the hub can usually be revived, but the centre will have to be removed and cleaned.] For all-weather use/storage, I recommend regreasing the bearings at least annually (using a waterproof grease, sufficiently fluid to keep the seal lips wetted), and (ideally) pre-emptively treating the whole centre with a corrosion proofing compound, eg waxoyl.

The bearings are the usual shimano quality, i.e. they could be very smooth, but the hub comes badly adjusted from the factory, and there isn't very much grease in there, (and the grease itself isn't loaded with corrosion inhibitors like it ought to be). In common with other (brand new) shimano hub generators I have recently examined, it was possible to back the LH cone off by a whole 1/4 turn and the hub bearings still didn't have any free play in them. Whilst the correct bearing adjustment will vary slightly once the wheel is built, it is certain that the factory adjustment is about 250 microns out, and that the hub would be very likely to wear prematurely if the adjustment is not attended to. Needless to say the hub is obviously a lot smoother once it is correctly adjusted.

The hub has a ~2.5mm width spacer on the LH side of the axle, between the cone and locknut. I think it may be possible to respace the hub by moving this to the other side, which would then give a less dished (and stronger) wheel. However this would mean tampering with the connector assembly and RH cone, (which is not entirely risk free) but having done this on other hubs I might give it a go here too. This would yield flange spacings of ~22.5mm and 25.5mm, and almost zero dish. Obviously this will be OK with a rim brake in use but if there is clearance at the fork for the disc, and the caliper can be moved 2.5mm leftwards too, it ought to be possible to run this setup using a disc brake too.

In theory this hub retails at ~£50, or a bit less if you shop around. I'd normally reckon that it isn't super value, not at that price; I'd suggest that you spend a bit more and get a 'sport series' generator instead. However just now you can buy this generator for less than twenty quid, which makes it a much more attractive option, ideal for a commuting or training machine.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
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meic
Posts: 19355
Joined: 1 Feb 2007, 9:37pm
Location: Caerfyrddin (Carmarthen)

Re: Shimano DH-3D37 QR hub generator

Post by meic »

However just now you can buy this generator for less than twenty quid, which makes it a much more attractive option

Go on, give us a link, the best I can find is £30 plus p&p.

Didnt it come with the usual overvoltage protection part?

At that price it is worth building up a winter wheel for the shopping bike.
Yma o Hyd
Bonefishblues
Posts: 11010
Joined: 7 Jul 2014, 9:45pm
Location: Near Bicester Oxon

Re: Shimano DH-3D37 QR hub generator

Post by Bonefishblues »

Brucey
Posts: 44522
Joined: 4 Jan 2012, 6:25pm

Re: Shimano DH-3D37 QR hub generator

Post by Brucey »

meic wrote: Didn't it come with the usual overvoltage protection part?


No, it didn't; but I won't miss it; the lights I use don't need it.

At that price it is worth building up a winter wheel for the shopping bike.


exactly!

[BTW yes it came from SJS]

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
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Si
Moderator
Posts: 15191
Joined: 5 Jan 2007, 7:37pm

Re: Shimano DH-3D37 QR hub generator

Post by Si »

Ive not used this particular hub but we have low end shimano generator hubs on the bikes that weve been giving away and i have to say that ive been very impressed. Of around 3000 ive not heard of any failing. And ive noticed no discernable drag. Very tempted by the sjsc deal so i can get batteriless light on my onedown with disc braking.
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