I have recently tried repacking my hubs, but they keep making a roaring noise. I have reopened them to see what’s going on: number of balls correct, was no initial pitting to races or cones, added more grease as perhaps the bearings were a bit dry. Yet they still roar and I can feel the vibrations through the fork! I have honestly no clue what’s going on. Any thoughts?

Bearings too tight maybe?--may seem "free' with the wheel off the bike, but a quick release, or nut (if not a qr axle) may tighten them up a bit. Is the cup securely locked against the lock nut? Here's a good ref--might want to start at #6 https://www.parktool.com/blog/repair...and-adjustment

The (solid) axles have slight play in them, as otherwise they would bind slightly and feel a bit scratchy. The rear hub is quieter than the front, but still has noticeable noice when spun fast. The front hub is the worst, and is much louder than the hubs on other bikes in the garage - including one that I also repacked myself.

When in the frame, the wheels spin for a long time by themselves and rotate when still so that the valve/reflector are at the bottom. I'm a bit scared to ride the bike in case I do permanent damage to the bearing surfaces!

Are bearings, cones and races expensive in the UK? Once you've seen it done it's fairly simple to replace them.

So don't worry if you permanently damage them. Consider it a learning curve.

Oh, in my post above, I got the idea you where talking about axle bearings in the wheel hub. If by chance hub meant free-hub, then changing the lube in that might significantly change the sound you hear it make and it not be an issue other than not as quiet as before.

I am, there’s no freehub on this bike. I’d really rather not mash up the races as the wheels are vintage French ones which have good condition hubs, and I don’t have much confidence in my wheel-building abilities/enough cash if it goes completely wrong

Are some hubs just noisy? I don’t think they can fit more grease, and as mentioned I couldn’t see any significant physical issues with the parts.

I'm having a hard time imagining any sound they could make that sounds like a roar. You said that you added grease? You didn't take them completely apart and clean them? Perhaps by adding only, you pushed some contaminants such as sand into the path of the bearings themselves.

Didn't change the bearings out and get the wrong size or perhaps lost a bearing?

So basically when I spin the front wheel in the forks, I get a loud, low “whooosh” sound accompanied by a slight vibration feeling up to the handlebars which I don’t get with the other bikes. It’s not really loud, but it’s noticeably louder than other hubs.

When I did the overhaul, I thoroughly cleaned out all the components with solvents (degreased the axle, cones, races, hole for axle) and wiped them down and let them dry before reassembling with new bearings (correct size as far as I could tell and 10 in each side of the front hub, 9 in the back). When I added grease, it was after a really short test ride where I quickly noticed that the hub was quite noisy.

I just can’t work out what is causing the noise or what I’m doing particularly wrong

First thing I think of has already been mentioned, way too tight a bearing preload.

When teaching first timers to adjust their cup and cone bearings I tell them to start with too loose an adjustment, as determined after the wheel is secured in the frame. Feel the rocking side to side at the rim to confirm too loose a setting. Remove wheel from frame, readjust slightly tighter and recheck in the frame. It's far easier to feel a slight rock from a slightly loose an adjustment then to feel the slightly too tight condition. Andy

Thanks for the suggestion. When I take the wheel from the frame and turn the axle by hand, it sounds noisy both when the cones are loose with lots of play or tight and starting to bind.

Am I perhaps using the wrong grease? I’m using Weldtite Lithium Grease (white in colour) which seemed fine for the other hubs I’ve done.

I doubt that your grease has anything to do with the noise, except to slightly quiet it. One could experiment and try other grease of none at all to see what sound/feel changes happen. The second thing I think of has also been mentioned- too many balls or the wrong size. Andy