Cycling UK Forum

Can I swap in a longer generic 3/8x26 front axle in my GH6 Dynohub?


Okay, so I bought a new-in-box 12-78 GH6 Dynohub, 36 hole...and it has the GL621A 4 3/4" axle. I'd like to put the hub into revenue service on a bike with a 100mm OLD fork. An Internet search doesn't come up with an available genuine GL621 5" axle. (Imagine that - S-A quit making them 38 years ago and Dynohubs were always kind of a rare item here in the States).

Don't separate the armature and the magnet! Right! Got it!

Muchas gracias upfront & in advance, etc.

yes you can do exactly that. The main wrinkle is that most SA front hubs with 3/8" front axles have some kind of feature on the axle which is designed to prevent the possibility of the RH cone precessing into the hub and grinding the bearings to atoms. You might want to replicate that. Permanent threadlock under the RH cone ought to do it.

Another possible wrinkle is that the distance between the cones is rather less than in most other hubs so it is possible that the plain shank in some axles will be too long for a GH6.

I am told that BITD some folk drilled 3/8" axles in dynohubs and turned them into QR axles. I've never seen this done myself though.

[edit; BTW SA have made several front and rear brake hubs which used cup and cone bearings and a 3/8"x 26tpi threaded axle, most recently 'steelite' and SBF models. One of these hubs would provide a suitable axle, I expect, eg...

https://www.sjscycles.co.uk/hub-spares/sturmey-archer-axle-cone-538-hsb303/

perhaps?]

cheers

And all done (although I really should cut the excess axle length down!)

The wiring runs up to a Busch & Müller OneFive. Pleased with results.

The 'quick release' wire connectors are sparkplug high voltage terminal thumb nuts (BA2 thread).

Has anyone ever measured the efficiency of a Dynohub? Electrical watts per kg are woeful (no neodymium magnets back then) but watts out/watts in, compared to a modern hub?