Bicycle Mechanics - replace steel fork with supension fork

I have a older mountain bike with a chrome moly fork and want to put a front supension fork on it. It's a 1' threaded fork I think is it as simple as finding a 1" threaded shock and swapping it out or is there more to it, or do I need to convert it to threadless?

Thanks

Why do you want to convert front to shock ?

won't it ride better on the trails?absorb the bumps?

If you want a fork that's even remotely modern, you'll need to go threadless, and even then there are few forks available in 1".

If you must have a threaded 1" fork, a new old stock or slightly used fork off ebay or craigslist might be your only choice.

I have a older mountain bike with a chrome moly fork and want to put a front supension fork on it. It's a 1' threaded fork I think is it as simple as finding a 1" threaded shock and swapping it out or is there more to it, or do I need to convert it to threadless?

Thanks
Yes you can replace a 1 inch threaded rigid fork with a suspension fork. But you need to be aware of the problems and issues it will cause. Attached is a picture of a 89 Nishiki Ariel converted to suspension using a Suntour SR 3000 fork. The shock was obtained from NYCBikes.com and costs a modest $35-40 with shipping. This shock has only 40mm of travel, but in this type of conversion, that's a good thing.
As for the problems, the shock will lift the front of the bike anywhere from 1 to 2 inches, more if you purchase a high end fork with 80mm of travel or more. Changing the geometry can affect how the bike steers. If you have cantilever brakes, you'll need to purchase a fork that has a brake cable attachment, or you will have to build your own clamp since these are not commercially available independent of the fork. I built one for the Nishiki below. If you have V-brakes, no special cable handling is needed. You will have to be sure you purchase a fork with adequate steer tube length, but not too long or the threads will extend beyond the frame head and you won't be able to secure the fork. The Nishiki below has a small spacer since I did not want to cut the steer tube.
The net result is the bike will take small technical stuff like logs, much better than before and your arms, neck and back will thank you for it. I'm not sure I would try jumps with the Suntour fork. The handling of the bike will change. It may not degrade the handling, but it will change.
If I had it to do over again, I would still make the change to the Nishiki. But I'm glad I did not purchase a high end fork for big $$$ because at the end of the conversion, this is still an old bike and a suspension fork does not make it equal to a new, quality entry level mountain bike.

What kind of bike exactly are you trying to upgrade?

Here's the thing, echoing roccobike, your geometry does not support a suspension fork. Your head tube angle will be off, and much of the riding characteristics that you may or may not enjoy (i.e. handling, handlebar rise, stem rise, et al) will be totally changed. Since we don't know what bike you're "upgrading", not much more can be said, but just keep in mind how much your ride will change (though, not necessailry for the bad)...

Nice examples of fully ridgid MTBs are becoming rarer. They make excellent commuter/tourers. If you do switch, keep hold of the fork.

thanks for all the help so far, the bike is a early 90's or late 80's, mongoose iboc comp with full shimano lx, chromally frame and fork 7speed if i can I will post a pic

Thanks, Mike