A whole lot of work. Depending on the type of vehicle, it may not even be possible. If you have a vehicle where the 4x2 version and 4x4 versions use the same body and chassis, then you might have some luck. However, if not, you will have very little chance. It would be cheaper, and less of a nightmare, just to trade in your 4x2 for a 4x4. First of all you need to install a transfer case, a front propellor shaft, a front differential and axles. The front suspension would need to be replaced to handle this extra hardware. You would need to make sure that the engine will clear the front axles. You would have to change the rear prop shaft, or shorten it, to compensate for the transfer case. You will probably need to change your gearbox as well, because 4x2 gearboxes usually don't have the mounting points to attach a transfer case to. If the new gearbox doesn't mate up to the engine, you would need to make up an adapter plate to join them, or get an engine that it fits to. You would need to fabricate (i.e. cut) a hole in the floor somewhere for the 4WD lever to go. All in all, unless you have a truck like a Ford F100 or something, where the 4x2 and 4x4 versions shared the same/similar body, then it would be near impossible to do what you're suggesting.

I agree with the other answer. You would also need to see if the frame of your vehicle would support the four-wheel drive conversion. You most likely have to put in some form of a "lift kit" to assist with ground clearance and the additional four-wheel drive components. I think when all is said and done, It would be cheaper to sell the vehicle you have and but a four wheel drive

well I can not see why everyone has a problem with changing over a PU to from a 2x4 to a 4x4 first of all not all PU come in either a 4x4 or a 2x4 and getting the parts and converting it is nothing but time..some work and money you can buy a 4x4 van that has been converted..almost anywere..and they do not come from the company in that form also you can buy 2 1/2 ton axles and put them in from military trucks So there isn't a reason in the world why it can not be done without a major problem..but money...but you will have a better setup than stock when done

get a donor truck of the same year. there are your parts. simple.

You can do it, but why? You can just lift your 2wd and put bigger tires and it will be fine, or just sell your truck if its new. But if its an old truck you can buy another cheaper truck and use the parts off of it. Me and my brother converted a 63 chevy, about 2 years ago, alot of work.

Money

Full size truck: Dana 44/60 solid axle with NP208 Transfer case. CAGE Offroad Radius Arms for coil sprung suspension. or a leaf springs(easiest and doesnt require radius arms) Mid size truck: Dana 28/30 Solid Axle with Borg-warner 1354 Transfer Case (or 1345 T-case i forget which way the numbers go) Jeep Cherokee Radius arms or leaf springs. Get some LOCKING hubs. not vacuum or that other crap. locking hubs are the best. Get Warn hubs so youll never have to replace them. If your using the coils go to Zabeard.com he did a SAS on his ranger theres enough info there for a 4x4 conversion and you could just ask around about installing a Transfer case. Make sure you get your driveshafts at a junkyard unless you plan on spending alot of money. MAKE SURE YOUR GEAR RATIOS MATCH! other wise your drive train will bind when you lock in fourwheel drive and destroy your gears in your axles and transfercase, possibly transmission too. That in a nutshell is what youll need. I suggest reasearching it and talking to alot of mechanics first. be aware that everyone will tell you to just buy a new truck too. Good luck to you and anyone else who intends to do a 4x4 conversion.

I have a 1978 chevy 1ton p/up w a 454 2wd that i have converted to a 4wheeldrive with a 8"lift and 38's, it takes some work but it is really whorth it since the truck is a 4x2 it has never been abused off road and being a 1978 it will be really hard to trade for a 4x4 truck in the same conditions and a good thing is that you could choose the type of suspension,axles,etc you want to use. word of advise,yust go for it! people will tell you over and over to buy another truck, but if you love the truck as much I love my truck and youre willing to take the challenge do it and good luck.

I really don't think it should be too much of an issue. Like some others have said, just buy a dummy truck for parts. Or better yet buy a dummy truck for the chassy, and swap your cab and truck bed to that frame. Any modifications should be fairly strait forward.

I am sorry but for those that say buy a new truck I beg to differ. $3500 to convert a truck to 4x4 not including your labor. http://www.fourwheeler.com/techarticles/129_0605_4wheel_drive_conversions/index.html

I agree with Ofblong I have a 1998 dodge ram that I'm interested in doing this to. The truck has less than 65K on it and is fully paid off . It would cost way more than than the average price of retrofit( about 2.5 K) to trade it in and purchase a 4x4 in EQUAL condition. I plan to keep this baby for another ten years( if the body will hold out) and I know how it hasn't been abused. As much use as it gets, it should last that without any issues. So in my case ( and maybe others as well) it makes more sense to "upgrade" the gently used oldster than to lose money trading it.

it's time and money, i would only do it for a truck with round headlights.

Add 2 more wheels...duh!