Servicing a Shimano Dynamo Hub

[Heltor Chasca]

Specifically a DH-T785-1D

I put my tourer up on the work stand today with the intention of re-seating the front tyre as it displays a kink when riding. Annoying but at least the rim is true.

However when spinning the wheel I can hear a smooth rumbling as I spin the wheel. I have never noticed this before. I did not make any adjustments to the hub when I first got it about 2000 miles ago.

I can't find any PDFs or YouTube videos specific to this hub. Any advice would be gratefully received.

[Brucey]

the noise may just be the magnets cogging round, i.e. it is normal; if the noise is a hum or a buzz, with a tone, rather than a rumble, then it is very likely this.

But having said that, I'd say the chances of the bearings having been correctly adjusted from new are about zero. I bet they were too tight from new.

The correct adjustment is a little free play that just disappears as the QR is tightened. Adjust on the left side.

You can see how the hub is put together by looking at the EV techdoc. This does not however reveal how the connector and RH bearing are assembled.

cheers

[Heltor Chasca]

Many thanks Brucey. You are right: No correct adjustment 'at birth'. It runs freely enough. Hopefully it lasts for at least another 10 years with any luck.

[Brucey]

I would strongly recommend that you adjust any shimano dynohub, including yours. I find that I have to back off the LH cone up to 1/2 turn in a new hub before it all comes good. The bearings will suffer vastly accelerated wear if the adjustment is that far out. You can't feel if the bearings are set too tight because the magnets interfere with your perception of bearing roughness.

EV techdoc here

http://bike.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/DH/EV-DH-T785-3193_v1_m56577569830753740.pdf

I recently built a DH-3N72 hub and the parasitic drag ( judged by time to run down with lights off) about halved once I had adjusted the bearings correctly.

cheers

[Heltor Chasca]

Thank you. The LH cone being No. 7 in the diagram? Will I have to remove the disc rotor and parts 8, 9 and 10 to get to it? I assume I will have to borrow a lock removal tool (TL-LR15) too. LBS perhaps?

Apologies for the inane questions. The rotor is as 'deep as I have dug' into this hub before.

[pete75]

Have You seen this document? https://www.docdroid.net/0CQRiqZ/overha ... h-3n72.pdf

[Heltor Chasca]

Have You seen this document? https://www.docdroid.net/0CQRiqZ/overha ... h-3n72.pdf

Thank you. Picture = 1000 words. I love a bit of guts and gore.

[MikeF]

My dynohubs wheels will rock to and fro between magnet cogging before coming to a complete rest after the wheel is spun. As Brucey says you need to adjust it so that there is just a teeny bit of play on an unclamped hub. I've found it a bit of a fiddle to get it "just" right.

[Brucey]

Have You seen this document? https://www.docdroid.net/0CQRiqZ/overha ... h-3n72.pdf

Thank you. Picture = 1000 words. I love a bit of guts and gore.

you don't need to worry about any of that as yet, you just need to adjust the bearings, and maybe add some fresh grease.


Also, what they don't tell you explicitly is that

a) this is an inherently risky procedure; if you have not done it before there is about a 1 in 4 chance that you will break something, probably the wire
b)you don't need to disassemble the RH bearing to get fresh grease into it
c) you don't need to disassemble the RH bearing to remove the internal
d) if you use an open-ended (headset) spanner on the internal of a well-used hub, it is very likely that the octagon will just round off. You need a full octagon wrench, ideally.
e) more modern shimano hub generators have two wires, not just one, and they are often aluminium not copper, which makes repair more difficult
f) the wires have a thin layer of insulation and are 'potted' into the axle groove in mastic (not 'Teflon'.... )
g) if you breach the insulation on the wires the generator can stop working

cheers

[Brucey]

Thank you. The LH cone being No. 7 in the diagram? Will I have to remove the disc rotor and parts 8, 9 and 10 to get to it? I assume I will have to borrow a lock removal tool (TL-LR15) too. LBS perhaps?

Apologies for the inane questions. The rotor is as 'deep as I have dug' into this hub before.

First remove the rotor using a suitable tool (one for a cassette lockring will usually work on a front hub), then for adjustment treat as per any other QR hub, working on the LH side.

It is easiest if you grip the RH locknut in a bench vice. Use a cone spanner and a second spanner on the LH side of the hub. Brace the cone spanner CW , and release the locknut ACW. Back the cone out about 1/4 turn and retighten the locknut. You should have a small amount of free play in the hub bearings. Trial fit the hub into the forks and retighten the QR. If the play just disappears then that is it, job done. If there is free play still, adjust the setting and try again.
[ it is by trial and error, this; if you want to speed the procedure, use (make) a hub vice instead as per Sheldon Brown]

If you have just regreased the hub or lost the cone setting, screw it in finger-tight, and back it out about 1/4 turn. That will be a good starting point for adjustment.

cheers

[pete75]

Have You seen this document? https://www.docdroid.net/0CQRiqZ/overha ... h-3n72.pdf

Thank you. Picture = 1000 words. I love a bit of guts and gore.

you don't need to worry about any of that as yet, you just need to adjust the bearings, and maybe add some fresh grease.


Also, what they don't tell you explicitly is that

a) this is an inherently risky procedure; if you have not done it before there is about a 1 in 4 chance that you will break something, probably the wire
b)you don't need to disassemble the RH bearing to get fresh grease into it
c) you don't need to disassemble the RH bearing to remove the internal
d) if you use an open-ended (headset) spanner on the internal of a well-used hub, it is very likely that the octagon will just round off. You need a full octagon wrench, ideally.
e) more modern shimano hub generators have two wires, not just one, and they are often aluminium not copper, which makes repair more difficult
f) the wires have a thin layer of insulation and are 'potted' into the axle groove in mastic (not 'Teflon'.... )
g) if you breach the insulation on the wires the generator can stop working

cheers

In spite of what you say Brucey I get the impression that whoever wrote those instructions knew exactly how to service that dynohub.

[Brucey]

In spite of what you say Brucey I get the impression that whoever wrote those instructions knew exactly how to service that dynohub.

possibly, but they certainly omitted to mention a few vital details.

BTW the bit about bracing your thumb against the connector housing is another red herring; the nut bears against parts that are located into the axle, that cannot turn.

cheers

[pete75]

In spite of what you say Brucey I get the impression that whoever wrote those instructions knew exactly how to service that dynohub.

possibly, but they certainly omitted to mention a few vital details.

BTW the bit about bracing your thumb against the connector housing is another red herring; the nut bears against parts that are located into the axle, that cannot turn.

cheers

Oh well obviously he won't be as good as you - perish the thought

[Cyckelgalen]

I service and adjust my cup and cone hubs but find dyno hubs almost imposible to adjust. One needs to feels how smoothly the bearings run, any tinny irregularity is transmitted to the fingers, but I cannot feel anything between the dyno hub's "magnetic notches", so it is mostly guesswork and hope for the best rather than precise adjustment.

I have a DH-T785 XT hub with 3k miles, the locknut had worked loose and a ball's surface has peeled off and the cone is badly pitted. I have not opened the connector side, the "unserviceable" side that Shimano sell as a unit with. The other cone you can get for under a tenner and the balls are standard 3/16.

My question is, can I happily replace the damaged cone and bearings that I can access without attempting to crack open the connector side bearing or should I have to assume that both sides are equally damaged? It seems logical to me that a loose locknut will produce equal damage in both sides. Replacing the whole internal assembly that shimano sell plus the other cone and bearings costs almost as much as a new hub. I would only save having to relace the wheel.

If anyone has replaced both cones, are they identical on both sides? As Shimano don't sell the connector side cone as a spare I can't find non data/measurements on that cone.

Thanks

[Brucey]

in most such shimano hub generators the RH cone is indeed the same part as the LH cone, and yes you can usually replace the LH one in an easy way. However if the bearing has failed in the left side it is almost certain that the bearing in the RHS is bad too; the only mitigation of this is that in a disc brake hub the LH bearing sees a lot more load than the RH bearing because of the disc brake loading, and this may occasionally cause the LH bearing to fail whilst the RH one is still serviceable.

Some tips;

1. If replacing the LH cone only, grip the RH locknut in a bench vice and don't try to lift the wheel clear of the RH cone; in many shimano hubs of this sort, if the RH cone comes out of position this is an invitation for the balls to become dislodged and this will smash the hub up PDQ, (in fact the same applies to most shimano front hubs, generator or not). If you must draw the RH cone away from the bearing (eg to introduce lube), do it with the RHS of the wheel uppermost; the balls ought to stay put more or less. However even then there is a fair chance of balls becoming dislodged.

2. When adjusting these hub bearings it is indeed pointless trying to feel for bearing drag. Also note that you will always benefit from adjusting the bearings because (IME) shimano hub generators are always shipped with the bearings set way too tightly. The last DH-3N72 I had in my hands needed the LH cone to be backed off a full 1/4 turn (i.e. 250 microns of bearing clearance) before it was correctly adjusted. The correct adjustment is to have a tiny amount of free play in the bearing which just disappears when the QR is used to tighten the wheel in the frame. [The axle squashes by about 80 microns under QR pressure and this mostly comes out of the bearing clearance. No free play with the QR loose (or even half tight ) means the cones are set wrongly in the hub. An absence of free play (with the QR tight) following a small adjustment means that the adjustment is correct. By small adjustment I mean about 1/50th of a turn on the cone; even this tiny adjustment is 20 microns in the bearings (quite a lot, in bearing terms).

3. If you want to feel how the RH bearing is without taking the connector assy apart you can remove the centre (keeping the wheel RHS uppermost throughout, once the LH cone is loose), and NB you should lift the centre assy out by the bearing plate not the axle. Then the stator and axle can be spun whilst holding the bearing plate and you will feel if the bearing is in really bad shape or not, without the drag of the magnets in the usual way.

hth

cheers