Hey, I have been upgrading my trek 850 mountain track. Mostly just single speed conversion. But I was wondering if it would be possible to somehow install disc brakes on the bike without braking out the welder. Are there any effective adaptors out there? Thanks for any help, this has been a fun project so far.

*breaking out the welder

I bought a repalcement fork with disc mount and left the rear brake alone. Surly has a good selection of 1 1/8" threadless disc forks. If you bike has a 1" threaded fork, I'm not aware of any options. If your headset is 1 1/8" threaded, you'll need a new headset too. It'll run at least ~$200 total, you really need to love the frame to do this modification. A new/used bike with exisiting disc brakes is usually a better option.

You'll need a new disc-compatible fork, which are around $50-70 new for a rigid model, and a rear disk brake adapter that attaches to the brake boss and the dropout via a special reinforced wheel skewer - NOS runs about $60 with shipping. Here's one from Chasertech.

I'd recommend mechanical rather than hydraulic - sizing and running the hose is a pain, and it's a lot more money. Avid and IRD have nice mechanical disc setups.

If you have a 1" threaded headset, Suntour makes a low-end suspension fork for $80 or so with disk tabs.

got the "just buy a new fork thing", not welding exactly,
but, to do it right, have to burn Paint clean , down to the metal,
and do Brazing, on the left rear of the frame..

perhaps add housing/hose guides, while you are at it..

You can braze tabs on if you want.You can tig weld tabs on depending on the tubing and you don't undercut the tubing.There are bolt on things for the back,I haven't seen any for the front myself,but I haven't been looking.

You'll need new wheels too. You need disk specific hubs to attache the rotor to. So you could buy complete wheels, or rebuild the old ones with new hubs.
So together, you need new fork(possible headset, and stem), wheels, adapter for the rear,and the brakes.
IMHO, not worth it.

For this frame, it would be simpler to buy a new bike with disc. The 850 was a low end bike, and as Leob1 notes that is a lot of other stuff to get. The most common adapter available, from A2Z is only for Aluminium frames, and to weld a disc mount to the 850 would, after re-painting, cost more than a new frame / go a long way to a new low - mid range bike. For the forks, if they are rigid or suspension, new ones which have been designed for disc would be needed.

/agree, unless you have all the stuff already, and your own welding or brazing gear it's just not worth upgrading bikes to disc, just use the money for some other upgrade.

Assuming you've got cantilever brakes on the 850, replacing them with V-brakes (and brake levers with the right pull ratio for V-brakes) would be a lot cheaper and easier, and would have great stopping power.

Simple answer; Yes it can be done (see above for details)

Reasonable answer; No, it's way too expensive and complicated for what the bike is worth.

Right on, thanks guys. I wasn't aware that my bike was "low end", that is good to know. Certainly I wouldn't put disc brakes on an old ford pinto. . . Sounds like disc brakes will have to be my on next build, with a nicer frame.

The Trek 850 wasn't exactly low end. Many of them had Double Butted Chromo frames. They were better than the 800(sometimes just seat tube cromo) and the 820 830 (usually full cromo but maybe not the fork).The 900 series had better True Temper OX DB tubing- with better- but not great- components.
Still since you can buy a good one for under $150- frequently under $100- kinda pointless spending and $$ on them.
OK frame, but not worth spending any $$ on.None of them are worth converting to disc.
You can get a used 853 -disc- frame off ebay(Jamis Dragon) for about $200.
Good frame - cheapo components= good bike.
OK frame- great components= OK bike.
Cheapo frame- world's greatest components= cheapo bike
Don't bother- you have an ok not bad not great frame.
Charlie

Depending on what one wants out of life, converting an older bike to Sturmey-Archer drum brakes is straightforward and doesn't require "breaking out the welder".

Some models of Pintos had front discs from the factory.

Haven't seen any Pintos around here for a long time.

The original Trek 850 from the early 80s was Trek's top of the line MTB. It used either Reynolds 531 "All Terrain" tubing or Tange "Prestige" tubing, both of which are well regarded still.

https://compare.ebay.com/like/1806602...=263602_309572

Any Trek dealer can get this adapter for about $15. I keep one or two here. Whether it will work with the frame is dependent of the dropout design, but I've used it on late 90's GF's.

Guess it depend on when and what you call low end, when I started MTBing in the early-mid 90's this was at the top of Treks bottom end range, so would still call it low end, US and UK prices were about the same at 460 £ or $, it's not low end as a supermarket bike, but in MTB terms, when bikes then and now were upto 4-5k or more, and mid range is from around 700-2000, it fits in the lower end of the good MTB market

If you go to the vintage Trek web site, you may be able to figure out frame materials and original components by using the bike's color scheme to ID its model year.
I know that for at least some of the late '80s/early '90s, the 800-series frames were made in Taiwan, while the 900-series frames were made in the USA.

My best-ever craigslist purchase (a few years ago) was a '96 Trek 950 for $47; it had a few nicks and scratches and a bit of surface rust on the gears, but a few hours of rehab work along with new V brakes and chain and upgraded (but re-used) derailleurs and it's now a rock-solid "backup" bike.

"Some Pintos came with disc brakes" haha. . . I can't believe no buddy laughed at that.