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Nuts & Bolts: Ford 2WD to 4WD

Posted in How To: Tech Qa on December 19, 2018
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I love your magazine, especially the Readers’ Rides section. Is there a transfer case that would be able to connect to a transmission that was made for two-wheel-drive trucks? I recently purchased my first vehicle, and would like to convert it to four-wheel drive. It’s a 1986 F-250 with a 6.9L diesel and a C6 transmission. What is the difference between a divorced transfer case and a regular transfer case? Would I be able to divorce it myself if it is something that you could do with average tools? How much would all of this cost? I don’t have much in my wallet right now.
BJ W.
Via facebook.com/4wheeloffroad

A divorced transfer case is a standalone unit that is mounted separately from the transmission. It connects to the transmission via a short driveshaft, as opposed to a married transfer case that bolts to the back of a transmission and connects directly to the transmission’s output shaft. Divorced transfer cases were used in older Dodge and Ford trucks, and while they’re not exactly plentiful, you can find them. Although you’d have an extra driveshaft to maintain with a divorced arrangement, the advantage is that you can use any transmission you want with a divorced case. There is no easy way that we’re aware of to convert married transfer case to a divorced case, or vice versa. While the ability to use your existing transmission seems like an advantage on the surface, locating a divorced transfer case (we’d recommend an NP205 from a 1970s Ford truck) and fabricating mounts for it is not going to be easy. It may be just as easy to source a four-wheel-drive transmission and transfer case from a similar year truck and swap it in, as that would be largely a bolt-in affair.

Unfortunately, converting a two-wheel-drive truck to four-wheel drive is rarely a viable option. For the money, hassle, and time, nine times out of 10 you’re better off selling the two-wheel-drive truck and buying a 4x4. This is probably true in your case as well. Aside from the transfer case, you need a front axle. The four-wheel-drive versions of your truck used Twin Traction Beam front suspension and leaf springs. While your truck has suspension beams similar to four-wheel-drive TTB, your truck is coil-sprung. It wouldn’t be a big deal to swap all the axle components of a similar-year TTB system under your truck, but you’d have to either convert the truck to a leaf spring suspension or adapt the F-250 TTB beams to the existing coil spring suspension. Leaf springs with TTB doesn’t work well at all, and grafting the coil spring suspension to the F-250 beams is complicated and not really viable. Using 1/2-ton coil-sprung beams also won’t work because, among other things, the beam lengths are different and converting from five-lug to eight-lug hubs is nearly impossible.

The best option for a front axle is to source a solid-axle Dana 60 from an F-350 and start fabricating, but safely grafting a Dana 60 under the frontend of your truck is going to take a lot of fabrication, tools, and money regardless of the suspension you use. Ford kingpin and ball-joint Dana 60s are also highly sought after and command a premium price.

Since it sounds like you’re a young guy on a budget, the best advice we can give you is to use your truck to get back and forth to school and to a good job, work hard, and save up for a 4x4. That is by far the easiest and least expensive option.

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