i have a old mountain bike that the chain is rusted and the cassete is rusted, brakes are rusted so i was thinking about making it into a fixie
the cassete on a mountain bike has multiple sprockets on it so could i unsrew the cassete and use the small gear?
but also what would i have to do to fix it all together.
mountain bikes coast, and you can rotate the crank arms backwards on a mountain bike but on a fixie that is how you stop. so how would i go about fixing that problem. im new to this and just wanted to fix up my bike. it didnt feel right to have it sit there rusting away.
any help would be very much appreciated

any ideas on how to do this?
cause im stumped

the way you convert any other bike, starting with a search of the interwebz and our very own forum stickiez

Yeah, you see that **** where it says "Start here?" Start there.

https://sheldonbrown.com/fixed-conversion.html

Here is useful site for beginners. Please note that to turn your mtb into a SW33T FIXAY you will end up replacing the following parts with fixed/singlespeed specific parts

- rear wheel and hub
- crank

Most conversions will run you at least $100, assuming that your frame is compatible and that your parts are in good condition, which they are not.

In all, do more research, and find out what kind of bike you eventually want. There are too many project bikes where the owner had an old frame, wanted something completely different, spent an ungodly amount of money upgrading their old frame only to get a bike that will never meet their expectations.

If you plan on riding your mountain bike in the mountains, don't convert to a fixie. If you have a "mountain" bike that's not technically suited for mountain usage, then by all means, start on the forum's "Start Here" and use the search function.

You almost never need a crank, just a new set of chainring bolts. You will find some trouble finding an appropriate rear wheel; most fixed gear wheels are 700c, while chances are very strong that your mountain bike is a 26 inch wheel. Converting it to fixed will be more expensive, because there is a decent chance you'll have to have a custom wheel made, but fixed mountain bikes with large, slick tires are awesome bikes.

No you can't just take off the cassette and put a single cog on to go fixed, you need fixed rear wheel. You can do SS that way however. There are plenty of cassette SS conversion kits.

Back to fixed...

A lot of times you can run 700c wheels with road tires on MTBs no problemo. Most rigid MTB forks have a hole you can use a nutted caliper on, or even drill out back fork hole for recessed. If you have sproingy fork you'll probably want to replace that. If I had a bike with a sproingy fork I'd just look for another donor bike to start a fixed project from.

If it has a cassette it's probably not old enough to have horizontal dropouts so you'll have to see what kind of magic ratios work or go eccentric somewhere. This is a killer magic ratio finder.

Brakes and cassettes can be de-rusted pretty damn easily. I only go SS if the rear derailer is fubared or missing, stuff like that. But, up to you. Fixed will take more parts and luck than SS will.

this comment is the new kilo tt comment. so much win

Surly fixxer is an option. Pricey, but nearly as much as a wheel build.

i wouldn't recommend a surly fixxer to someone with the OP's level of knowledge unless it was being installed by an LBS