Replacing a NP205 with a BW1356 Transfer Case:

You might be wondering why in the world would anyone want to replace their bulletproof, cast iron, time proven, gear driven NP205 with a bulky, aluminum/magnesium cased, chain driven BW1356?? The answer is simple: A 2.62:1 low range gear ratio, vs. the 1.96:1 low range ratio of the 205. Running 4.10 gears with 38" tires was pretty pitiful offroad with the 205 in low range. The cost of buying new gears and detroit lockers for both ends was not a viable option, so I gave this a try.

Here's the math:
1.96 / 2.62 = .748. This means that for every revolution the 205 spins, the 1356 spins .748 times.
4.10 / .748 = 5.48. The extra reduction of the 1356 effectively gives me 5.48 gears in low range when compared to the 205, or in other words, I would have to get 5.48 gears if I was to stick with the 205 to get the same amount of gear reduction. Gears that low have such a small pinion, that the strength of them could be an issue.

Strength:
Some have questioned whether the 1356 can hold up as well as a 205. Although the casing will not take the abuse a cast iron case can, a siimple skid plate can fix that problem. Truck pullers with mega-horsepower use them, so they can withstand abusive power. The chain is considerably larger then a NP208 chain, which is why I didn't consider using a 208. Ford used the behind 460's so Ford must have some level of trust in them as well.

Full Sized Ford transfercase info:
From 1978 though 1996 the 3 most common part-time transfer cases Ford used were the NP205, NP208, and BW1356. They all use the same circular 6 bolt mounting pattern. They also all have the same splined input shaft. This means that all three are interchangable. Of course nothing is that simple, and there are a few gotchas that you need to consider before swapping.

The following picture shows a 1356 adapter on the left, and a 205 adapter on the right both connected to C6's

The 205 adapter has a notch cut in it for one of the two shift rods. If someone wanted to swap a 205 transfer case to a 208 or 1356 adapter, this notch would have to be made. I haven't looked to see if it's possible to do without degredating the strength of the adapter, but the notch is necessary regardless.

The notch in the 205 adapter is not a problem if trying to connect a 208 or 1356 to it.

The 205 uses two shift rods that move front & back relative to the truck in order to shift. The 208 and 1356 use a single shaft that spins in order to shift. Shifter linkage mods are going to be necessary if swapping in a different case then what you started with, but if you can weld it's not a problem.

Top views of 1356 and 205 adapters

The 205 adapter is 9 inches long and made of cast iron, while the 208 and 1356 adapters are each 6 inches long and are mde of aluminum.

Swap info

Here's what I had to do in order to get a 1356 under my 78 Bronco.

Driveshafts
The 1356 is 6 inches longer then a 205 is, and my rear drive shaft is already short enough, so I wanted to go with the shortest adapter as possible to make up for some of that lost length. I ended up having to replace my C6 at the same time anyways, so I just used a C6 with a 1356 adapter already on it to regain 3 inches of lost length. This effectivly shortened my rear shaft by 3 inches, and lengthened my front shaft by 3 inches as well. The cool thing about this is that it makes the front and rear shafts the same length, although I've got a 4 inch lift and a dana 60 rear so it may not be the same for everyone.

CV shafts
The 1356 was only used in TTB trucks and they never used a CV jointed front shaft, so the front yoke on a 1356 will not accomodate a CV jointed shaft. This was easily taken care of by using a non-cv shaft, but I did have to notch the crossmember a little bit in order for it to clear. Even with a 4 inch lift, I have not noticed any angle problems yet.

Shifter
The shifter that came with the 1356 does not clear the hole in the floorpan like the 205 one does. This is exagerrated by the fact that I have a 3 inch body lift. I could have cut the hole larger, but flipping the shifter 180 degrees makes it clear just fine. I plan on making a custom shifter someday, but this works fine for right now.

Frame Clearance
The 205 uses a frame support on the rear drivers side of it, while the 1356 is light enough that it apparently doesn't need one. This support needed to be completely removed in order for the 1356 to clear the frame, which it does by about an inch.

Straight Forward Install
Other then the issues listed above, swapping in the transfer case itself is easy. After putting the truck through a torturous test run with the new transfer case I am totally happy with the way it drives in low range now. Effectively having 5.48 gears in low range with 38" tires and a 460 to motivate it all is simply just awesome! Of course there is no difference with high range, and I have not noticed any driveline angle problems as of yet.