So me and those around me have split open enough aluminum transfer cases that I'm going to try running with an NP205 for a while. I didn't find much information on it as far as what was required to bolt it up, so here's some info on what I had to modify for it to bolt up:

First off the NP205 is a twin shift rail transfer case, and the rear wheel shift rail protrudes slightly into the 6 bolt circular mount, so you have to cut out some of the extension housing to clearance for the shift rail.

Top Left is the cutout to clearance the rear shift rail:


And this is another image showing it. I cut it out initially with a 3/4" hole saw, trimmed the "straights" with a cutoff wheel, blended with a die grinder and smoothed it out with a 90* air sander with a 3" 50 grit roloc. Made sure to keep the webs in-tact and sanded and smoothed the edges:


After you get that clearance cut out the extension *almost* bolts in place, except the four socket head cap screws for the NP205 input hit the extension housing. There's 3 options to remedy this - Grind off the cap screw heads rendering them nearly impossible to later remove, make a spacer plate to gain the approximate 1/4" clearance needed or clearance the cap screws in the extension housing. I chose option 3 so on the CNC machine it went:


And then I machined out with a 1/2" end mill the needed clearance for the cap screws:


After that's done this is what the extension housing looks like with the shift rail notched out and the cap screw clearance machined in:


And looking through the extension housing when it's bolted onto the NP205 you can see the recessed cap screws:


Next up is a transmission oil pan drain and transmission temperature sender, a good bath for the tranny and a new trans filter, then work out the modifications required for the transfer case shift lever. I'll post an update when I get the lever squared away.

Edit: The length from the end of the transmission to the end of the output shaft is 7.25", the distance from the front of the extension to the end of the splines on the NP205 is 7.25". The output shaft's last 1/4" is tapered so the splines end at 7" from the back of the transmission, and the NP205 input splines end at 7.25" but there is an extra .25" or so after the splines before the shaft would bottom out. Maximum spline contact this way.

Chris

 

nice work .

 

Wish i had a CNC mill. I'd be doing all kinds of crazy stuff.....good job bud!!

 

I know its been a couple of months since the last post on this thread, but hopefully someone is still burning some midnight oil out there ....... have a question on the NP205 adapter

In this writing, you used your existing / modern aluminum C6 to NP205 adapter with modifications to get the job done .......... which is what I can do I guess. However, my question is: can someone use the C6 to NP205 adapter from an older / same era 70's adapter and use it in place of the 80's / early 90's adapter?

My truck is a 1988 F-350 with a 460 and C6 tranny and BW1356 TC. I want to intall a mechanical brake system utilizing a rotor set-up that will be employed at the rear of the 205.

So basically I want to change transfer cases .... swap out the BW1356 and in its place install the NP205. If I can find a pre 1980 adapter, is it a bolt in replacement for the 205? Thanks for starting and posting pics for this thread ......... don't see much of the older "bullet proof" iron pieces anymore .......... nice job ............ hope to read reply soon - steve

 

Steve, that's what I was wondering as well - plenty of C6/NP205 setups in junkyards, and AFAIK the C6 didn't change its tailshaft housing bolt pattern, so it should be possible to just bolt up the '70s extension and transfer case to your '80s C6... Unless the output shafts are different length, then you may have to get creative, so make sure you measure both the '70s and your own tailshaft's lengths and compare them.

 

I pretty well agree with what LCAM said. As far as I'm aware there were only 2 lengths of output shafts used on the 4wd C6's. I modified my existing one because I couldn't for the life of me find and older one locally. All the old stuff here got scrapped when the steel prices went up a few years back.

 

And what sucks about a slushbox tailshaft is that it's the first thing to go in the case, and the last to go out - makes the job of replacing one pretty much the same as rebuilding the trans...

 

Hey thanks for the reply's. Here's a link that shows adapter configurations: Woody's 4x4 | Adapters , it states there is an adapter 5-3/4" long and another that is 8-3/4" long (cast iron).
The only mentions shaft length and spline count: Shaft Length - 15-1/2" - T/C 31 Spline. However, the shaft length would reflect the total length of the shaft and NOT the length of the shaft extending outside the tranny case, and I for one would rather not completely disassemble a c6 to figure out if my '88 shaft is 15-1/2". I agree with both of you LCAM and swooshcm. I'm leaning heavily towards the information I've found that the adapaters are 100%, 70's VS 80's pieces. My original main concern was output shaft length and spline count. I'm thinking: find an early piece and it'll bolt in, and hold to my A$$ in hopes that the shaft is correct. BUT, if the adpaters are not interchangable, I would have no problem with the notching the adaptor making clearance for the 205 shift rod, but I gotta tellya, the machine work you did swooshcm is the only way to go and is supurb, unfortunately, many of do not have access to such equipment, to get the job done right. What opinion would one put upon this swap? replacing a modern aluminum tc like the bw1356 with an older technology unit like the NP205, and for the sake of obtaining the right to install a mechanical disc brake setup .......... because rear eldorado calipers equipped with the e-brake system suck, and I'm not gonna pay TSM $320 for a pair at their markup. Thanks again guys ... and gals ..... I'm going to shut up now and will try not asking anymore questions here, since this is Diesel truck stuff here - Steve

 

The quickest way to check is to measure the length of your current BW transfer case adapter and check it to the length of the cast iron unit you're looking at. I think the difference in short vs long shaft is about 2 inches if I remember right.

 

Indeed, the overall length of the tail shaft itself is irrelevant - who cares if it sinks 5" or 7" in the trans when it's the part that sticks out the trans that makes a difference for this purpose. If you have the adapters and T-cases off both transmissions by all means go and measure up how much the shaft sticks out the trans, but as a rough estimate simply measuring the length of the adapters should be good.

 

swooshcm, they made both length versions of the adapter in cast iron and aluminum versions. The aluminum versions are more abundant around here, but I prefer the cast iron piece, which are a little less common. LCAM, I'll measure my adapter tomorrow and post its length ............. 100 on it being 5-3/4 inches. Through some other information I've received, my confidence level of the shaft lengh and spline count are going to be right on the money.

 

i have a 92 ford that i put a 93 cummins with the getrag 360 five speed, it does have a np205, that is the passenger side drop,, now im looking to get the four wheel drive hooked up .. so i have to go with a different transfer case, now is that 6 bolt pattern on the np 205 the same as a borg warner 1356... i know the spline counts are off.. that can be addressed with a new input shaft or possible an adapter ...
if anyone has any input it would be helpful ... thank you

 

Yup, the bolt patterns are the same.