I have a 89 s-10 blazer, but it is 2 wheel drive. how hard would it be to make it a 4 wheel drive, or is it even possible?  

i have the same problem as you do with my 85 F-150. its a badass 2wd truck but when we out muddin and my friends kick it in 4 wheel i get left behind or have to ride with someone else so it sucks. if you get any info on this email it to me at rhogan568@yahoo.com

Thanks,

FPmudder

JUST BUY ONE THAT IS ALREADY 4X4.  

You will need the T-case with the tailshaft from a donor truck with the same transmission.  You will also need the traction beams, radius arms, front driveshaft, rear driveshaft, and radius arms.  Since the 4x4 F-150s had TTB and 2x4 had Twin I Beam, the pivot brackets are the same, and the radius arm brackets should be the same too, but the arms themselves are different.

If you want more than stock drivetrain, such as straight axle, then you can convert easily.  You should have a 9 inch rear, so check.  You will need the front axle from a 79 or earlier F100 or F150 (4x4 of course), along with the steering linkage, radius arms and brackets, and track bar.  Its a direct bolt in, you will just need to grind off some frame rivets for the TIB pivot brackets and old radius arm brackets, locate the axle under the truck, mount the radius arm brackets, you will need some springs with a few inches of lift to clear the engine crossmember, you will need to build a track bar mount, hook up the brakes, the steering linkage works with the stock box and arm, and you will need to swap a 4x4 tailshaft and Tcase to your transmission.  This will allow you more strength to run larger tires and run in thicker mud, but you can swap in a stock D44 TTB with a lift and that will work just fine, just don't be too hard on it. 

Its a pain but there are ways and my ways are the junk yard ways. You can change the front end to a toy straight axle and be sure to put the same gearing as the rear and adapt a believe it or not a 6:1 samurai transfer case between the tranny and the rear end and have some drive shafts made. Thats how you do a junk yard fab cheap  

I HAVE AN 87 F-150 2 WHEEL DRIVE.  I HAVE ALSO THOUGHT OF MAKING IT A 4 WHEEL DRIVE.  I FOUND ANOTHER TRUCK SAME MAKE MODEL AND YEAR TO SWAP PARTS.  IT LOOKED LIKE IT WOULD BOLT RIGHT UP.  HOWEVER,  I WAS GOING TO HAVE TO GET A DIFFERENT TRIANI.  THE TAIL HOUSING ON THE 2 WHL WAS DIFFERENT THAN THE 4 WHL, AND THE TRANI IN THE 4 WHL WAS BAD.  IT'S POSSIBLE,  BUT MUCH FASTER TO BUY A 4 WHEEL DRIVE.

sell it a get a 4x4 it cost way more to convert rather than buy one already done.  

Might look into an old 4x4 undercarrage and just put your body over on to it. then you can sell or part your old undercarrage and git most or all your money back.

here i'll make it easy for you come take the 4*4 one at my house it's just sitting in my yard holding s10 parts and go ahaed and leave your two wheel drive see problem fixed..... Reallistically though the easiest thing would be to buy a 4by if you like ifs if you want a challenge use a wrangler front axle a s10 transfer case and flip your rear axle under the leaf springs if you want to beef the rear a bit put a ford 8.8 out of an explorer on it same track width and lug pattern as s 10 4by and some one sells a cable activation kit for the wrangler vaccum activated axle I also belive there is some one who actually markets the wrangler swap for the 4 by brackets etc. might work for the 2by . Can't remeber who read it in a magazine somewhwere might be available in back issues.Hope all this rambling helps.