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I have an SP-PD8 dynamo hub on the front of my tourer, powering an Axa Luxx 70 front and unbranded rear light for 3W nominal. Whenever I put the wheel in, I orient the connector down and back -- 7 or 8 o'clock looking from the right hand side. After a front wheel puncture I did this, and within 20km it was pointing up and forwards (2 o'clock). I opened the (external cam) QR, rotated the hub/connector, and closed the QR tighter. It's as tight as I can reasonably press with the heel of my hand and I might need a cheater bar to open it again*. The connector has rotated again.

This happened before, to the extent that I snapped the dynamo wires on a ride (luckily I had backup lights, but not good ones and not fully charged). Then I fixed it by doing up the QR tighter, but it's already tighter than reasonable. It feels like a hub issue rather than a QR issue.

How I set it up: how it should be

How it soon ends up

how it ends up

The hub was serviced last year and runs nicely (and this is no longer my big miles bike). I'm extremely wary of trying to attach something to hold the connector body in place. The failure modes could easily be painful and the connector isn't shaped well for just putting a thin cable tie round it.

* The mudguard stays get in the way slightly, but finding something to press against is more of an issue. The amount I have to pull to open it feels like lifting about 40kg with 2 fingers.

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  • I should have a picture, but I should have checked it had actually taken before walking away from the bike this morning
    – Chris H
    Commented Aug 22 at 10:35
  • Disk or rim brake?
    – Dan Gao
    Commented Aug 22 at 20:55
  • 1
    @DanGao good point. Disc. And I've got the bike here to take a photo
    – Chris H
    Commented Aug 24 at 17:01
  • The hub has never had an anti rotate washer previously?
    – Warren Burton
    Commented Aug 24 at 17:36
  • 1
    @Noise this is the skewer that came with the hub, but I might switch to a security one. These dropouts are between forwards and down. Old-fashioned steel forks but a nice ride
    – Chris H
    Commented Aug 25 at 8:17

1 Answer 1

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-Idea-
I've had something like this, but it was in the rear wheel.

In my case, the rear QR was backing off no matter how tight it was, which caused the chain to pull the wheel crooked in the dropouts and bind on the frame.

The cause was a combination of a worn/cheap-soft QR nut, and a very hard/smooth dropout face. A temporary fix was to roughen the outside of the dropout face, and to use a small triangular rattail file to re-form the ridges on the QR's nut. Replacing the QR was needed eventually and I also dimpled the dropout-face with a punch to add texture.

However in your case, I can't see what could be adding the rotational force to move the axle in the dropout.

If the hub was exerting a significant resistance to motion, you'd feel it while riding.

Is it possible that the front disk brake is involved somehow? When braking, the rotational force is somehow driving the hub around a small angle? Or maybe there's a three-way triangle with the mudguard stays that allows small rotation over time?

Perhaps in the workshop, slacken the QR slightly and try a bunch of braking actions while looking closely at the axle?

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    I wouldn't be too confident of feeling a resistance while riding - I'm more likely to blame my body if a ride feels hard - but it spins nicely. A short test ride yesterday with the QR normal-tight was fine even under both sharp and sustained braking. I'm away but can use the rack on my van as a workstand so may test with it quite loose. I'm inclined to change the skewer anyway. I've got a pinhead security one I was thinking of fitting. I also can't find the source of rotational force. It feels like it must be that end of the hub. In that case a tight QR might increase bearing load unhelpfully
    – Chris H
    Commented Aug 25 at 7:24

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