I would like to strip down and replace components on my old 1994 Trek 950 mountain bike, primarily to replace the drive train, brakes, shifters and wheel sets. I would like to go from a 3x8 to a 1x11. What constrictions or constraints do I need to be aware of? Any advice?
At minimum you require:
- new hub in your rear wheel that will take an 11 speed cassette. May be cheaper to buy a complete new wheel, but 26" and 11 speed hub would be relatively rare combination
- new cassette, 11 speed
- new 11 speed derailleur with the same mount as your current one
- 11 speed chain
- single front chainring and spider and cranks to suit your current bottom bracket interface, which is probably square taper.
- 11 speed shifter for the bars
Probably wise to replace your shifter cable inner and outer while doing this - they're cheap.
You may need a new bottom bracket cartridge that fits whatever interface your new cranks have.
You can probably continue to use your pedals.
Price all that up as new parts, and you could easily exceed the cost of a nice non-BSO MTB. I'd strongly recommend you fix up this nice old bike as-is and just ride it.
There's nothing better than riding your old bike and keeping up with a modern bike, except for passing and dropping a modern bike.
A couple of things to add to @Criggie's answer:
You bottom bracket bearings may well be worn out, so factor a new BB unit in.
If you are replacing both the BB and crank you will probably want to consider an outside bearing unit rather than square taper. If you do this you will need to understand how to select a suitable crank to maintain the correct chain-line.
If you are thinking of keeping current cranks and running a single ring on the middle position you'll probably want a new narrow-wide chainring. You will have to find out if you can get one that fits the crank bolt circle diameter. You will also need replacement shorter chainring bolts.
Factor in the cost of tools you will need: both common tools like hex wrenches, or pliers if you don't already have them; and bike specific tools such as a chain-whip, cassette tool, square taper crank puller and bottom bracket tools.
One thing not mentioned is the rear spacing on the frame. It will likely be 135mm. It's not the rim size that matters, but the hub width. There are still plenty of 559mm mtb bikes on the market, but most of them no longer use 135mm rear hub spacing. 11 speed cassettes increase the possible complications; Shimano MTB 11 speed cassettes will work with a "normal" 8,9,10 speed freehub, 11 speed road cassettes will not.
You can get an 11-40 or 11-42 rear cassette and either use a double or single up front. A 10 spd cassette will fit on 9 speed hubs, so you should be able to find a reasonably priced replacement wheelset.