Has anyone ever swapped their 7 sp Shimano cassette hub for an 8/9 sp one? If so, how did it work? I've got an older MTB with a 130mm spacing and was going to try it. I was wondering about dish and whether it would be too much on a 26" wheel.

7 to 8 is quite possible in road. I simply don't know about mtb. I doubt the dish is a big deal, and it can be redished.

My modifications are road bikes, and I've done it 2 ways:
1-Change a 7-sp freehub to an 8-sp freehub, redish and use a longer axle. I paid LBS $50 total for the change, including parts.
2-Swap out the rear wheel for a more modern one. This is by far the easiest. I generally pay $60-$125 for a wheelset, and sell the older set for $40-$75, sometimes up to $100.

My guess is that if you had a 130mm spaced rear, an 8-sp would fit right in there. I'm not sure when mtb's went to 135, but I don't think it was during the 8-sp era.

I'll yield to the older mtb guys here. You can PM roccobike, he knows that @#$%^& inside and out.

I've made the swap from 7 to 8 several times. It's not difficult. Your 26" wheel will be fine, but it will have to be redished. If you have a Shimano freehub, then the old one unbolts using a hex wrench (10mm I think) and the larger 8/9 speed bolts right in. If it's not Shimano, I can't comment. Some are compatible, some are not.
My only concern is the 130mm spacing in the frame. All the MTB conversions I've done were performed on frames with 135 spacing.
I recall reading a post here on BF the reason MTBs require 135 is due to the chain line being too close to the seat stay causing chain slap against the stay when riding on technical single track.
In theory, the change should work with a 130mm spacing because that's what road bikes have. But I've never made that change.

The bike has 130mm spacing now with a Deore 7 sp cassette. I already have the donor cassette hub with seals. I'm planning on using it more for a city MUP bike. So, there really won't be any rough riding on this one. The only reason I'm looking at 8 or 9 sp is because of the availablility of shifters and cassettes.

7sp parts are still readily available and very inexpensive. For a city bike, I would not recommend going up to an 8 - it's simply not worth it in my opinion.

Shift performance on 7sp index is so reliable and rock steady, even the cheapest triggers work really well. And you could hunt down some old 7sp thumbshifters if you want to!

I have an extra set of 7-speed indexed thumb shifters, if you need them.

I've been torn looking at 7, 8 and 9 speed setups on ebay and it seems that right now 8 and 9 speed are more available and in many cases can be had cheaper than the 7 speed parts.

Don't forget, you can use 8 speed shifters with a 7 speed setup, Just adjust the limit screws properly.

Yes but brand new 7sp triggers start at $30 PER PAIR. Chains $10, freewheels $11, cassettes $15... you can build a very nice new drivetrain for very little money. THe only downside is that new 7 speed is not available in the higher trim levels - XT etc. -- but for city use even the entry level stuffis very reliable. For used/NOS you are probably right - 8 and 9 is easier to find!

According to sheldon, 7speed spacing is 5mm and 8 speed is 4.8 - it will probably work but not be ideal for proper indexing - you have to work harder to keep it in tune.

Option #2 is the way I have done it. The last time, I picked up a $5 donor 8 speed MTB, and just swapped wheels, and all other drive components (I needed them to build up a frame I had).

Good reliable 7 speed shifters are easy to find. I have used the Shimano Tourney ones sold by Niagara for $12 for several thrifty builds. They come complete with SIS housings and cables. Tough to beat!

https://www.niagaracycle.com/product_...ducts_id=15889

Actually, I was looking for barcons. 7 sp barcons are ridiculously expensive. Almost as much used as new 9 sp with cables. That .2mm of spacing can create problems in certain circumstances.

How about this to "trick" 8 speed shifters into working on a 7 speed wheel... get an 8 speed cassette and blow the rivets out. Only put the smallest 7 sprockets on your existing freehub (use a spacer on the inside if necessary). Set your limit screws and tune the indexing based on top gear. The spacing will be correct and you'll be locked out of the lowest gear on the right hand side. Cost=cassette and shifters only. NBo worries about freehubs or wheel spacing.

Or get these: https://www.velo-orange.com/diacosibash.html :-)