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An NP205 In Your Future - 4-Wheel & Off-Road Magazine

There's no doubt the NP205 rules. But, when you decide to swap the king of transfer cases into your fullsize 4x4, you'll need some of his princes and other royal attendants too.

131 9809 An Np205 In Your Future np208 Np203 And Np205 Photo 29437838

For your convenience, we took a look at what it takes to swap an NP205 in place of an NP203 with a TH350 transmission and an NP208 attached to a TH700-R4. The swap is similar for nearly any 203- or 208-equipped truck, but details will differ.

PhotosView Slideshow To mate an NP205 to a TH350 or TH700-R4 automatic transmission, you will need an adapter (A) and drive sleeve (B). These are the same for either transmission, but are different for manual transmissions, which most 205s came behind. Furthermore, 205s mated to manual transmissions came with coarse-spline input shafts, which don't match the fine-spline output shaft of an automatic transmission. Either the 'case or the tranny must be modified. The adapter for the NP203 is also shown (C). Offroad Design and National Drivetrain offer a fine-spline 205 input gear and a fine-spline drive sleeve (shown) to match the fine-spline automatic transmission output shaft, but you'll have to disassemble the transfer case to install the input gear. The other option is to replace the tranny output shaft with a coarse-spline unit from Advance Adapters, but this requires the teardown of the transmission to install. For the TH700, the trans will need a shorter output shaft or an Advance Adapters spacer anyway, so the coarse-spline output shaft may be the better way to go. Early 205 to TH350 adapters have a bearing inside, while later ones have only a seal (shown). The ones with bearings take a different drive sleeve than the seal-only unit, so be sure yours came from the same vehicle, or order a correct sleeve from National Drivetrain based on your adapter. The NP208 transfer cases use slip-joint rear outputs. Most 205s have a fixed-style yoke, although a few later 205s have slip-joints. The NP203s (not shown) have fixed yokes, but the output housing is much longer than those on 205s. The bottom line is that a swap from either the 203 or 208 will require new front and rear driveshafts. All three transfer cases can have different front output yokes depending upon the year and application. Stephen Watson at Offroad Design warns us that 205s have different front-output spline count depending on the year: '69-'78 205s use 34-spline shafts, '79-'81s use 30, and '82-'86s use 24. To switch output yokes, you must get a new yoke with the same spline count as your output shaft. Regardless of which type your truck uses, switching from either the 203 or 208 to a 205 will require a shorter front driveshaft. Shifters on 205s and 203s bolt to the adapters, while the 208 shifter (foreground) mounts to the truck floorpan. With a TH350, the 205 shifter will fit in the hole without modification. With a TH700-R4, you'll need to enlarge the hole in the floor because the transmission is almost 2 inches longer than a TH350. Using the Advance Adapters spacer adds even more length to the assembly. If you're replacing a 203 with a 205 behind a TH350, the 'cases interchange without any crossmember modifications. In the 208 to 205 swap behind a TH700 shown here, the crossmember was moved forward about 1 3/8 inches. Apparently GM used several versions of the 208 crossmember, however, so you'll need to bolt everything up and measure your truck to be sure. Also, the 205 brace rod (arrow) had to be lengthened to accommodate the longer drivetrain package the TH700 created. The speedometer connection was the same on all three 'cases we worked with for this article. You'll have to drive the truck to see how close the speedo gear is to what you need. Replacement gears are available at your GM parts dealer. Later 205s have a plug for a four-wheel-drive indicator light that, of course, doesn't need to be hooked up.

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