Shrieking hub?

[Claireysmurf]

I have a Shimano dynamo hub on my Croix de Fer. It works really well combined with a USB compatible front light. I'm very happy with it other than for an intermittent screeching or shrieking noise that seems to be coming from the front hub. When it shrieks it normally does so only after speed has hit 20-25 mph and will wail and shriek until the speed drops very low and will restart at maybe 10-15mph. If the quick release is slackened off and readjusted that sometimes helps. If the wheel is dropped out and put pack in that seems to cure it for 30 minutes or so.
When the noise happens, it does so whether the dynamo is on or off. I did wonder if it was something getting caught in the disk brake but it happens too often for that. It's not the mudguard either. It will sometimes go away for ages and then be around for a fair while.
Friends and a couple of bike mechanics have checked to ensure that the QR is not over-tightened. When it is shrieking, having the QR loose seems to stop it, but having a wheel slopping around is dangerous.

Any ideas please?

[MikeF]

In my case I think it's wind blowing across the spokes causing them to "sing", which causes an occasional sound, especially with an angled wind ie not just the movement of the bike through the air.
Which hub do you have? From what you say it might the bearings (not the quick release) are too tight or short of lubricant. Are the cones adjusted properly? Are you sure it's not the disc brake?

[Brucey]

my suspicion is that there is either a fault in the bearings/seals or that there is a load of crud inside the hub.

If it is crud inside the hub then if you stop, turn the wheel backwards a couple of turns, then start riding again, the noise may change or stop for a while.

Another possibility is that the hub may resonate with the forks and this can make a noise too. In this case it will make a noise when the lights are on but not so much when the lights are off.

cheers

[edocaster]

Which USB light? And you say it shrieks when the dynamo is off - i.e. presumably when the light is off and you're not charging anything. Have you tried completely unplugging the light?

[Claireysmurf]

This is the front light http://www.rosebikes.co.uk/article/axa- ... aid:642351

[markfh]

Claireysmurf,

just speculating but I wondered if there was any correlation between the occurrence of the shrieking and the general temperature. The symptoms you describe could be due to something heating up, due to either friction or electrical losses, and expanding to the point that it starts to rub. A higher general temperature would might mean a lower temperature rise would be needed to cause the expansion necessary to "close the gap". Once it has warmed up slowing down would allow it to cool although it might take quite a while to get down fully to ambient temperature which may be why once it is triggered for the first time it then takes a lower speed to re-start the shreiking.

Looking around the web it seems that it is possible to take at least some Shimano dynamo hubs apart but this is probably not for the feint hearted. Such an exercise may let you see what is rubbing against what inside the hub.

Also given that this is a relatively new bike, if I recall your earlier posts about your build, is it worth taking up with the supplier of the front wheel/hub and seeing if they will change it under warranty?

[edocaster]

While I think the others are on the right track in hypothesising heat/friction (especially as you say the problem is intermittent, and can be 'cooled down' for half an hour), it might be worth completely disengaging the light - i.e. unplugging it - to see if that has any effect whatsoever. I note the Axa doesn't really have an off switch - the lights off position makes the USB output available - so it's hard to know if the light is really disengaging all circuits entirely.

[Claireysmurf]

It hasn't truly shrieked for a fortnight now when I was on a night ride from Bristol to Cardiff and it started within a few miles and carried on into the night, although it had been silent for two 5 mile rides earlier in the day.

I should probably contact Rosebikes the German supplier as I don't fancy taking a newish hub apart.

[MikeF]

If you haven't done so already you might want to carry out these simple checks.
Make sure the quick release is tightened correctly (as specified by Shimano.)

Can you detect any sideways play in the wheel by pushing the wheel laterally back and forth near the forks? If you can just feel a very slight movement, it's probably OK, and should indicate the cones are not too tight, but could indicate wear.

Disconnect the light wire plug from the dynohub and make sure it cannot catch in the wheel. Lift the front wheel off the the ground and spin it slowly. Do the brake pads rub? If so it might be a cause of the noise. Then make sure the brake pads don't rub and spin the wheel very gently again. It should spin very smoothly and slowly come to rest with a very slight rocking motion. Try it again in both directions and the same should happen again, and also you might notice that the wheel is probably slightly heavier on one side of the circumference causing it to turn unevenly. This is fine and as it should be.

If the wheel doesn't spin like this then, it indicates that either the cones are too tight or else there is something else causing it to bind. The difficulty is finding out what. I have built only three wheels with Shimano dynohubs, but I found the hubs as supplied (from Rose Bikes incidentally) with the possible exception of the 3N80, had the cones much too tight. I have also noticed that other Shimano hubs are not supplied with the cones correctly adjusted. In fact I wouldn't expected them to be so! Do wheelbuilders adjust hub cones correctly? Probably depends on the wheelbuilder/supplier

You could also try the above tests when the wheel starts shrieking.

The cause of the noise could be something completely different of course, but you can find out only by elimination.