700r4/NP208 and TH400 Compatibility

[MtBraun]

My son picked up a 700/208 combo and a some other parts he needed for his 84 swb project for $100. With our goal of a 496BB we know the 700 isn't the ultimate trans option, going to use a built th400. My question, though, is this specific np208 able to be mated to a th400? I am thinking the 700 and th400 have different output shaft spline counts (and lengths), so not sure if it can be modified to work with the th400. I understand I'd probably need a different adapter plate, but I'm curious on the transfer case internals. Thoughts?

 

[84 M1008]

The NP208 had two different versions. 27 spline for the700R4 and 32 spline for the Turbo 400. Just my 2 cents, but as old a design as the TH400 is, it is a far superior transmission to the 700R4 no matter what internals you put in it. Probably the best automatic transmission ever made.

 

[MtBraun]

The NP208 had two different versions. 27 spline for the700R4 and 32 spline for the Turbo 400.

Ok, but can the internals be swapped or is it not worth the effort? I'm having a heckuva time finding a th400/np208 combo so I'm wondering if the current one we have can be used on the future trans build.

 

[84 M1008]

I bought a new 208/32 spline off eBay a few years ago. They are available .

 

[84 M1008]

Ok, but can the internals be swapped or is it not worth the effort? I'm having a heckuva time finding a th400/np208 combo so I'm wondering if the current one we have can be used on the future trans build.

It's possible to change the shaft to a 32 spline, but it's not worth splitting the case, new gaskets, seals bla bla unless you plan on rebuilding the entire transfer case.

 

[HotRodPC]

The adapter isn't going to be cheap either. Seems about $150 or so. Just keep your eyes open for an NP208 for a Th400 and chances are it'll come with the adapter too. Seems they can be found with adapter for $250-$300. They've gone up in price alot. I remember a few years ago I was buying transfer cases for $125-$150 with adapter. Even scored a 89 700r4 K case with NP241 for $100. Hard to find those deals these days.

 

[84 M1008]

My son picked up a 700/208 combo and a some other parts he needed for his 84 swb project for $100. With our goal of a 496BB we know the 700 isn't the ultimate trans option, going to use a built th400. My question, though, is this specific np208 able to be mated to a th400? I am thinking the 700 and th400 have different output shaft spline counts (and lengths), so not sure if it can be modified to work with the th400. I understand I'd probably need a different adapter plate, but I'm curious on the transfer case internals. Thoughts?

I would be weary of putting that kind of power through a chain driven transfer case. Perhaps an NP205 may be a better choice. They were also common behind the TH400.

 

[HotRodPC]

I would be weary of putting that kind of power through a chain driven transfer case. Perhaps an NP205 may be a better choice. They were also common behind the TH400.

I tend to agree somewhat with that. Though if he's using all that power in 2wd, then there's no strain on the chain right??? Those chains are pretty tough too, but no telling how tough it'll need to be for this build, but unless it's in 4wd then it's still pretty much a shaft driven go through isn't it???

However, since OP is likely to be looking for a 32 spline NP208 and Adapter, he could certainly open up to the suggestion of the NP205 also in a 32 spline and Th400 adapter.

 

[84 M1008]

Yeah, but you can still break the housing with the torque that engine will make. It's a bit much for a 4×4 truck.

 

[ajd89]

A later model 4 speed stick is also a 32 spline 208. Cant remember when the changed think they were 11 spline before that. Ive got a steel adapter I picked up for 20 bucks to put my 241/ or a 208 behind my 4l80e. It was out of a early 90s 4l80 241 truck i believe.

 

[4WDKC]

keep your eyes on craigslist you can usually find someone swapping from the 208 to a 205 because they think they are made of glass. I bought a case and adapter for $100

 

[MtBraun]

Thanks for all the suggestions. I've been watching CL for months in a four state area and just haven't been able to find anything. Its probably going to come down to finding a truck we have to buy to get the parts we want.

Despite the engine build, it's not going to be in 4x4 much, if ever. I will expand the search to a NP205/Th400 combo as well.

 

[Camar068]

This may help you as well.....if the TH400 and 4l80 have the same bolt pattern. Edited out incorrect statement. Good catch Hotrod.

http://forum.73-87chevytrucks.com/smforum/index.php?topic=33282.0

https://www.rockauto.com/en/parts/acdelco,15724745,transfer+case+adapter,50338

It looks like it worked for the guy in the first link. Do some research please lol. Just what I found on the web. You can order one, or you can use Rockauto to find out what vehicles it works with and go to the yards.

Don't forget we (GMSB members) get 5% off with RockAuto.

And I'm sure Advance Adapters has what your looking for. They can get steep on their prices though.

 

[HotRodPC]

This may help you as well.....if the TH400 and 4l80 have the same bolt pattern. Of course you'll have to change the shaft on the NP208. Plenty of video's n how-to's on the internet. Doesn't look hard.

I'm curious as to why the shaft on the NP208 would have to be changed if it was off of a 4L80-E? Input shaft??? Both are 32 spline. What might be an issue is the output shaft due to the 4L80-E is going to be a reluctor wheel for Electrnoic speedo, but I think you can swap the reluctor wheel for a driven gear??? , then the drive gear into the tailshaft housing. ???

 

[HotRodPC]

Opening up to looking for an NP205 combo will be good too, but be prepared, it'll be a bit more costly, but worth it in the long run, especially since you're running a BB. The NP has other nice features like the ability to have a Twin Stick so you can have 2 wheel LOW to the rear wheels only, where normally you get 4 wheel low only. Then you have the option for FWD ONLY in both Hi and Lo.