I have a 1994 Trek 850 that I really like. It fits me, we've been many miles together, etc. However, the shifters don't work well any more, the chainwheel teeth are wearing, and on and on. If I replace the current drivetrain with say an SLX group, is it just a matter of taking the old stuff off and bolting on the new? I'd be willing to spend the money to buy a new group if I don't have to do any modifications to the bike itself. Am I going to have wheel trouble putting on the SLX cassette?

You're talking about an old school MTB with a rigid fork. They're great bikes. You're likely better off posting this in the C&V forum with a few pictures particularly of the drive side. Folks there can help you figure out what to do at the lowest possible cost.

Bottom line is that the bike is worth fixing but you obviously don't want to sink too much money into the project. If the wheels are good, I'd stick to the 3 x 7 gearing but replace parts as needed.

I have a 1994 Trek 850 that I really like. It fits me, we've been many miles together, etc. However, the shifters don't work well any more, the chainwheel teeth are wearing, and on and on. If I replace the current drivetrain with say an SLX group, is it just a matter of taking the old stuff off and bolting on the new? I'd be willing to spend the money to buy a new group if I don't have to do any modifications to the bike itself. Am I going to have wheel trouble putting on the SLX cassette?

I posted this in the mtn bike section and they recommended me to post it here.

It sounds like you just need to replace the worn chainrings, clean/lube the mechs and shifters, and adjust or replace the shift cables. Basically an overhaul job that would cost less than replacing the entire drivetrain.

My project is a early 90's that's been through a dorment period. Exposed to the northern Indiana winter. Most of the drive train is rusted together or, missing. What would be a good replacement front derailleur for a Trek triple????

Worth reading

https://www.sheldonbrown.com/k7-7.shtml

If you stay with a 7 speed transmission group, upgrading is a no brainer. Cassette removal is simple requiring only 2 tools.

catbackr, If there is not a 4.5 mm spacer behind the cassette, you have a freehub that is too short for 8+ cogs at the rear. If the chainrings are riveted to the crank arm's spider, you will need a new crank set. Otherwise a basic overhaul looks good from here.

Brad

Depends on what generation of SLX. Some SLX is 11 speed. That won't work on your wheels. Details on what is currently on the bike?

If you have never upgraded the wheels, then you will either have to replace them or stick with 7 speed. The 94 850 came with 7 speed Alivio.

Why not just replace the Cadette and chain rings. I'm sure the cables and brakes need to be done as well. All in all maybe 60 dollars if you do it yourself. 150 if you take it to a shop.

Replacing the chainrings isn't that expensive if you know what you're looking for. Mine isn't top end by any means. Depending on what BB you've got I have a square tapered shank. The crank I found is Sugino GP 170mm cost me $56 used. I found a new set of 50t and, 40t Specialized aluminum chainrings for $60 and, 30t Sugino granny ring for $15. Not bargain basement but, I thought I did ok. Mine is a early 90's 800 antelope that I'm converting into a road bike. If I would have gone used ot probably would have cost half that.

But replacing the wheels is a lot more expensive... generally speaking.

If you're stuck with 7 speed and needs a good derailleur buy a shimano zee.

When members ask you to post again in a different forum, please ignore them and contact staff by PM or you can flag yourself (that is not an offense). Posting in two forums creates confusion and two different streams of comments which have to be resolved by the staff and combined.

I agree... doesn't matter the age... you find a bike that fits... ride it and replace components as needed.
I wouldn't worry too much about it being a 26"... even though the industry has been trying to push away from that size for a while. I don't see anything wrong with it personally...and can still easily get replacements if needed. It's all what works for you and the bike they're on. I've upgraded my now vintage Klein several times over the years and still love it. Plus new FS/fullys demand a decent chunk of coin. Not saying some may not be worth it... but to me, don't know if I'd really enjoy mountain biking that much more than I already do. I've tried some new bikes, but for the money.. none have made me think.."I've gotta have it" and fork over the cash, compared to my older bikes.

Way more!!!

Appreciate the comments. Turns out I can still buy replacement parts for the original equipment so that is the easiest and cheapest way to go.