Bicycle Mechanics - Shorten a Shimano 130mm freehub to 126mm?

My bike is 126mm and I'd rather use a 126mm freehub if that is possible, but the older parts seem to be hard to find. If I have to buy a new part and deal with 130mm I will, but I'd rather not. Right now I'm running old 126mm standard hubs with separate freewheels, and I bend axles too much. My hubs have a lot of wear on them so I thought maybe it was time for new wheels and I could convert to freehubs.

There is a spacer on the NDS side of a 130 that can be replaced to make the hub into a 126. It's hardened, so no point trying to cut it unless you've got fairly exotic tools.
Grinding it down on a bench grinder is possible, but quite a chore.
I'f you're not too considered about seal performance I suppose you could replace the spacer with a stack of washers.
If you've got a friend with a lathe he'd be able to make you a new one in minutes.

Do note that doing this would require the wheel to be built with rather aggressive dishing to get the rim centered right. If it's a steel frame I think spreading it to 130 would be a better option.

You can respace the hub, shorten the axle (axles cut easily with a hacksaw) and redish the wheel if you want to. You must shorten the axle or the ends will stick out past the dropout faces and keep the quick release skewer from clamping on the dropout.

As dabac mentioned, the dish will be rather extreme so you will somewhat weaken the wheel.

I agree, that spreading the frame to accept the 130 mm hub is a better option.

My bike is 126mm and I'd rather use a 126mm freehub if that is possible, but the older parts seem to be hard to find. If I have to buy a new part and deal with 130mm I will, but I'd rather not. Right now I'm running old 126mm standard hubs with separate freewheels, and I bend axles too much. My hubs have a lot of wear on them so I thought maybe it was time for new wheels and I could convert to freehubs.

I think you should be able to get a nice 7 speed cassette freehub new or used through ebay without too much trouble. I assume we're talking about Shimano here which will be the easiest to come by. You can get 105 or Ultegra 6400 series. These come The 6 or 7 speed versions will have 126mm spacing. If you get the 7-8 speed version it will have a wider cassette body and 130mm spacing. Probably better to stick with the 126.
If you do get a hub with 130 or even 135 mm spacing you can have your LBS special order a Wheels Manufacturing brand replacement axle for under 20$. These are very high quality, probably better quality than OEM in my experience. This way you don't need to get out the hacksaw or cut off wheel.

If you are having trouble finding suitable Shimano 105 or Ultegra hubs in the 126mm width, you might seek out older Deore LX or XT hubs. These are very nice, have 7 speed cassette bodies that accept Uniglide or Hyperglide cassettes and its a simple procedure to retrofit a shorter axle and re-arrange the spacers for a perfect fit for your 126mm frame application.

If it's a steel frame I think spreading it to 130 would be a better option.

He isn't spreading it from 120mm to 130mm, he is spreading it from 126mm to 130mm. That's 4mm. I bet he could stuff the hub in without cold setting the frame even if it was AL.

Online this sort of stuff is scarce but around here at least haunting the second hand shops or consignment sporting goods shops can turn up older hubs or wheels of this sort quite often. They'll need rebuilding and re-lubing of course but with a bit of searching and digging you can find the older style stuff in good condition quite often.