Bicycle Mechanics - SA 3 Speed Re-Pack of Bearings

Alright first- of late I've started to hear a crunchy/gritty noise coming from my rear wheel when pedaling or coasting. I think this means there's some kind of dirt in the bearings. It seems to be coming from the part of the wheel where the chain drives the cog. Correct me if this assumption of dirt is wrong. This is a Sturmey 3 Speed hub from 1974 by the way.

If that's right, then I figure the solution is to clean up and re-pack the bearings with fresh grease. How easy a process is this, and what procedure do you recommend? I've never done this before (though I've worked on other things quite a bit on this bike) and if it's a hard one then I can pass it off to my local shop. But I'd rather keep my money and get a little good work in if it's an easy one to do. Any thoughts?

Edit: this whole thing assumes that there actually is grease at work here. I always had the understanding that oil was used to lubricate the hub's inner workings, but that grease was used on the bearings in the drive train. If not, then please advise me on it.

If you only hear the noise when coasting, then it's not your bearings, it's the ratchet prawls. But I think you said pedaling AND coasting, so it's probably your axle bearings. It could be dirt, or rust, but if you're hearing crunching, it's proabably a cracked bearing.

The inner workings of the hub should still be okay (by the way, those should take oil). you should only have to disassemble the axel and cones, and bearings (those take Grease). You'll have no problem leaving the gears alone, they're a different assembly to remove.

If you see large chunks of bearing, it'll be obvious you need to replace one/some, but if you don't try counting the bearings to make sure they're all there. I'm not sure how many you need, so try to find a hub/axle schematic for your model (sheldon brown probably has one).

good luck.

This may help:
http://www.toehead.plus.com/stmain.htm

Do a search, there's a lot of info on quick refurbishing of SA hubs around here. It'd be a lot easier to read over the old stuff than re-hash it all. I've asked about this so if you wanted to narrow it down search under my name.