Okay so I don't know a whole lot about bikes but I've learned a little bit on this forum. I've just bought a older trek 850 21 speed mountain bike that I want to convert to a touring bike. It needs a new rear derailleur because a tooth is broken off of the one that's on it (I can still ride it) and I don't particularly like the grip shifters on it, I prefer thumb shifters, so since I have to replace the rear derailleur anyway I was thinking about changing out the shifters too. Can anyone give me ideas about touring friendly derailleur shifter combos I might like?

For one thing you don't have to change the derailleur, you need a new jockey pulley, which is a lot cheaper than a derailleur.

Well that's good to know. Can I keep this derailleur and just change the shifters

I too prefer and still use thumb shifters; I like friction mode which I prefer over index mode.

Thumb shifters can still be found, although most are not inexpensive.

Inexpensive options:

* Check ebay for models or older stock
* Falcon thumb shifters (and similar other models such as sunrace)
Falcon Friction Thumb Shifters
* Sunrace m96 shifters
https://www.benscycle.com/p-4742-sun...r-indexed.aspx

More Expensive options:

* Paul thumbies (or similar such as Velo Orange shift mounts) with various shifter add-ons
Shifters
Shifters - Shifting - Components
* Micro shift
Microshift Flat Bar Shifters > Components > Drivetrain, Brakes and Pedals > Mountain Bike Shifters | Jenson USA
* IRD power shifters
IRD Power Ratchet Thumb Shifters > Components > Drivetrain, Brakes and Pedals > Mountain Bike Shifters | Jenson USA

* Shifters mounted on drop bar brake levers
Shifters Archives - Gevenalle

Actually it looks like most years of the Trek 850 had Rapidfire trigger shifters. Yes you can change to trigger shifters. This one should work: Shimano Altus SL-M310 Rapid Fire Shifter - Right, 7-Speed (make sure and buy it mate too - the left one) or
SRAM X3 7 Speed Trigger Shifter Set | Chain Reaction Cycles . Be careful if you decide to go with something like this: https://www.amazon.com/Shimano-EF-51-.../dp/B00JDA3PCS because you will need to consider the type of brakes you have (long pull or short pull), but if you can determine that this one will work it may be the best option because it comes with cables, which you may or may not have to replace with the shifters above.

The ones above are "cost effective." not sure if quality shifters (more expensive) are available for 7-speed.

Also you may want to read and heed this thread if you are thinking of using 8 or 9 speed shifters:
https://www.bikeforums.net/bicycle-me...fters-mtb.html

Let see a pic of the new baby!

Will those shifters work on a 21 speed bike? And I'm on a android phone so how do I post pics on here

The shimano Altus m310 is a 7-speed shifter.

Trek 850s are wonderful bicycles. I have a few of them.

Yes the ones I posted are all 3 X 7.

You're better off posting/uploading some pics to this site an then asking some questions. As a general rule, when converting a vintage mtb to a touring bike, the gearing is going to be more or less right. You'll need to swap the tires out from knobbies to slicks. And then you need to decide whether to do a drop bar conversion or not. If it were my bike and I was turning this into a touring bike with flat bars, I'd go for trekking bars with thumb shifters. The trekking bars give you more hand positions.

I had considered trekking bars. I'll try to upload pics. On a android the site is kinda confusing

Okay so the only way I could upload a pic of it is to make it my avatar. Hope you can see it.

There is a mobile and full version of this site when you are on a cell phone. Go to the bottom of any page and you will see 'full site'. I find that to be much easier to use.

You can post pictures a couple ways.

1. In the classic view, there is an icon 4 from the right directly above the text box you type in that is for posting pictures. Click it, choose upload from computer, then choose classic uploader. Press browse and find the picture. Then press ‘upload file’. If the picture is too large, it wont post.
2. Post your picture to flickr. Select the picture’s URL address, choose ‘from url’ when you are in the upload picture section, and paste in the web address. Unselect the button that shows you want to retrieve remote file. Press OK.

As for shifters, the below option is more than fine and comes with cables included.
https://www.amazon.com/gp/product/B00...JGVZV0HZY0JBBJ
Only $13 and its 3x7 shifting.

Just a personal preference thing but I would go with drop bars, especially since shifters need to be purchased anyway.