NP208 to NP241 Swap with Pictures

[drbeeper17]

So this topic has been covered sporadically in several different posts, but I wanted to make an inclusive one with pictures of the differences between the NP208C and the NP241C.

I recently swapped the NP208 from my 1986 M1008 with an NP241 from an 1989 3/4 ton Suburban. I did this to get a better gear ratio (2.72 in NP241 vs 2.62 in the NP208, better oiling (in the NP241 there is an actual pickup tube that draws oil instead of just the chain slinging the oil as in the NP208, better sealing (the front bolts on the NP208 are tapped all the way through meaning you need some RTV to seal them during install), and better shifting (it is smoother to shift through neutral to 4LO in the NP241). Here are some pictures of it installed.







The NP241C is a direct swap with the NP208C in our trucks if A) it is passenger side drop, B) it is a 32 spline input, and C) it has a mechanical speedometer. Passenger side drops NP241s are only found in straight axle GM vehicles from 1988 (I've heard some information saying it actually started in 1989) until 1991. So this means K5 Blazers, Suburbans, or classic square body trucks. I believe the 32 spline is only found behind the following transmissions: TH400, SM465, NV4500, and 4L80E. I personally have only found them behind TH400s. Usually if the vehicle is a 3/4 or 1 ton, it will have a 32 spline input NP241. This means K5 Blazers all have 27 spline inputs and will not work. Mechanical speedometers are only found in 1988 or 1989 trucks. In 1990 and 1991 they used VSS.

 

[drbeeper17]

I also wanted to physically show the differences between the NP208 and the NP241. The length is basically the same give or take maybe 1/4". This means no driveshaft modifications. You can even use your existing NP208 shifter. I didn't even have to readjust my shifter rod, the end slipped right into the NP241's shifter bracket. The 4WD indicator plug (the only electrical plug on these cases) is also the same. If you didn't look carefully, you would think the NP208 and NP241 were the same transfer cases.

Here are some pictures of the NP241 (dirty brown one) vs the NP208 (clean silver and green one).









When I mentioned better sealing I was referring to the forward facing side of the transfer case - the side that attaches to the adapter with 6 bolts.

Here is the NP208. You can even see it leaking fluid after I thought it was fully drained.



Here is the NP241. It actually has a removable front sealing piece which makes replacing the seal a lot easier.



With regards to the 6 adapter attaching bolts, the NP241 has fully sealed bolt holes. You can look in them and see aluminum so if you used too long of a bolt, it will bottom out. The NP208 has through holes into the main part of the case. This means that fluid can leak out of these holes unless you install the bolts with some sort of sealant. This is something I overlooked a few years back when I reinstalled my NP208. The adapter always looks wet which was probably due to slow seepage of fluid from these holes.

 

[drbeeper17]

Since I happen to have both a VSS (velocity speed sensor, basically an electrical pickup) tail housing and a mechanical speedometer tail housing, I will show those differences as well.

Here they are side by side. Mechanical on the left, VSS on the right.



A couple of different views.





Here is the actual piece that slides onto the output shaft. The metal one is VSS, the blue one is the plastic drive gear for the mechanical speedometer.





Here is a fully dissembled NP241C.



Here is the oil pickup I was mentioning earlier in the NP241.



Since I do have both a 27 spline input and a 32 spline input, here are those pictures.

27 spline from dissembled case.



32 spline from assembled case.



One other difference I noticed between the NP208 and NP241 is the shift lever that attaches to the case with a single nut. They are clocked differently (about 45 degrees), at least on the ones I have. This means these pieces are not interchangeable. The NP241 is on the left, the NP208 is on the right.



A picture of the NP241 shifter.

 

[drbeeper17]

The last piece of information I have is about the adapters. If you are using the stock CUCV adapter it is considered the tall 6 bolt adapter. This is because it attaches to the transmission with 6 bolts. If you are putting a 700R4 into your CUCV, you will need the tall 4 bolt adapter due to the adapter only attaching to the transmission with 4 bolts. These also come in short variants. From what I have found, they starting using the short variants in 1985 with civilian trucks because they had different crossmembers. These short adapters used a different style of rubber mount. I actually have all 4 variants, but no pictures of the tall 6 bolt adapter as it is installed in my truck.

Here is the short 6 bolt adapter with the newer style mount (left) vs the tall 4 bolt adapter with the older style mount (right).



Short 4 bolt (left) vs tall 4 bolt (right).



Short 6 bolt with mount (left) vs short 4 bolt. A picture from the backsides as well.





The 6 bolt adapters, both short and tall measure about 2.5". The short 4 bolt adapter measures about 3.5". The tall 4 bolt adapter measures about 3.25". Here is a side picture of the short adapters. You can see that the 6 bolt adapter (left) is about 1" shorter than the 4 bolt adapter (right).



That's it. All the relevant information I have on this topic. If there is something I didn't cover, I probably know it or can find out for you. Hope this helps someone sometime in the future.

 

[Recovry4x4]

Good stuff. I have a 241C in the shed waiting on it's owner to get one of hisnmany 700R4 trans rebuilt. One day. I can take some pics of the tall 6 bolt adapter as well.

 

[cobaltboatfan]

I'm new to the site, just bought an 84 M1009. Going through and reading all the posts and this is an amazing thread. Great write up and the pics are a huge plus. Thanks!

 

[Cucvnut]

So you used the stock adpater that came with the 208 on yours? I used my stock adapter on my 241 swap and its the 205 style.

 

[EngineJoe]

Hi drbeeper,
Would the NP241c VSS housing you have pictured be for sale? That is a passenger side drop right? Trying to find a replacement one for my 1991 Blazer.
Let me know,
Chad

 

[CowBro55]

Hello Drbeeper

I have a NP241c with the mechanical speedometer and I need it to be VSS. Can I swap them out??

 

[drbeeper17]

Yes you can swap the mechanical for the VSS. All you need is the VSS tail housing and the tone ring. Unfortunately I think only the 90 and 91 passenger side drop GM case have this tail housing. The drivers side drop housing that is very common won't work since it has the cavities in the wrong location. It's a mirror image of what you need.

 

[CowBro55]

Awesome great to know!! Thanks Buddy! The big thing to me was getting the VSS to work, I’m gonna install a SYE on it anyways so finding the tail housing is not a big deal. Thanks again!!

 

[WARWAG]

Thank you for this write up. I am now armed with the information to pick up the correct NP241. Thanks.

 

[WARWAG]

View attachment 530545

Do you happen to have the correctly clocked NP241 shift lever on hand? I am in dire need for one. I need the one on the left in the attachment.

 

[cucvrus]

What year fits that. I have a complete NP241 from a 1988 V3500 cab chassis. The case is split. I can look if you think it will fit.