TH400 2WD to 4WD Question

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Kilian

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Hello. Gathering some information for a possible 4x4 frame swap.

What needs to be done or even can be done to convert a TH400 from a 2WD truck to work with an NP208 transfer case?

My current tranny is good and would like to continue to use it if I go to 4x4 frame. Is finding a donor TH400/NP208 combo enough to get the transmission adapter, etc., to make it all work? Or is there a lot of disassembly required to the transmission needed?

Thanks for the help.
 

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IF I remember right the th400 has a long shaft for the 4wd one and a short shaft for the 2wd. they interchage but the trany need to be pulled apart to change them out.
 

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bucket

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To run the 208 on the th400 output (bolt-on yoke, correct?) you would need a custom spacer to fit between the trans and the t-case adapter.
 

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I was thinking of doing the same thing. But my turbo400 came with the Doug Nash (crash) overdrive. Does anyone know if they used a different tail shaft to tie into that overdrive system?
 

bucket

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I was thinking of doing the same thing. But my turbo400 came with the Doug Nash (crash) overdrive. Does anyone know if they used a different tail shaft to tie into that overdrive system?

That's interesting. I had no idea there was a Doug Nash overdrive that fit the th400. Is it electronically activated?
 

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My friend has an 87 K10 with a th400 np208. 5.0 tbi The truck has about a hundred thousand miles, and is rotted to hell, but he drives it daily. It replaced an even lower mileage 87 2 wheel drive, also 5.0 th400. And far more rotted than the plow truck, which is rotted to hell!
 

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Maybe I'll post some pictures of both trucks, and even make a YouTube video for you guys to salivate over what the coronavirus can do to a Body and Frame
 

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That's interesting. I had no idea there was a Doug Nash overdrive that fit the th400. Is it electronically activated?


Yes it was.
 

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i can't think of any automatic where the output shaft is not the first thing down the assembly line. I could be wrong, I'm old. What about a divorced transfer case?

:cheers:
 

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As was said, if it's the usual truck issue 2wd th400 with a bolt-on yoke, then a pre-'85 (figure 8 style) np205 will bolt right on. To run an np208 or np241, you can have a spacer made like @Honky Kong jr did, or the output shaft in the trans would need swapped out.

Side note, I don't know why there's not a company making a th400 type spacer like they do for the th350/700r4. If he weren't so busy already, I bet @Vbb199 could whip some up and sell a lot of them.
 

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As was said, if it's the usual truck issue 2wd th400 with a bolt-on yoke, then a pre-'85 (figure 8 style) np205 will bolt right on. To run an np208 or np241, you can have a spacer made like @Honky Kong jr did, or the output shaft in the trans would need swapped out.



Side note, I don't know why there's not a company making a th400 type spacer like they do for the th350/700r4. If he weren't so busy already, I bet @Vbb199 could whip some up and sell a lot of them.


Obviously always remember divorced cases either yoke to yoke or with a jack shaft are an option too
 

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