unbelievably

My wife has a mountain bike that she uses as a commuter.
It's a to the gym...around town, only when it's not raining kinda' bike.

I changed the tyres today.
And while at it, I noticed a not so good feeling in the spin in the HB-KM40 Shimano hubs.
I imagine that I could service them.
I could also imagine relacing to new hubs...

What would be a smooth spinning upgrade in trems of MTB gear?

This wheel set would never see a rugged trail, let alone a jump,drop or rut.
Pure street...

Am I asking for too much in terms of smooth expectations?
I'm a road cyclist with no idea what to expect...

Thanks

ed 

I would just take the hubs apart, throw in some new balls, and pack with Phil Wood grease.

bikinfool

Doesn't sound worth the trouble to do but what Ed suggested....try this https://www.parktool.com/repair/readhowto.asp?id=105

surreal

let's define a few things, in terms of hassle and what's "worth it"...

rebuilding hubs can be seen as a PITA, but it's cheap and easy and quick compared to buying a new hubset and lacing them up

if you're lacing the new hubs to the old, used rims that came with your 400-level shimano hubs, that would be totally not worth it, as you won't likely build a better wheelset than what you have now

if you're lacing the new hubs to new rims, you could make yourself a great wheelset, but this would be far more expensive and more difficult than repacking/rebuilding the existing hubs

you could just buy a complete new wheelset. This would be almost zero hassle, and you can get good wheelsets cheap these days, but it's way more expensive than some new balls/grease.

me? I'd crack the old hubs open, pull em apart, see if the balls/races are badly scored, and if they look half-decent, i'd just clean everything out really good and repack with fresh grease. but then, i'm a cheapskate. most ppl think it isn't worth pulling a hub apart without putting new balls in there.

hth
-rob