TH400 2WD to 4WD Question

[Kilian]

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.

 

[climb-101]

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.

 

[nvrenuf]

There are several tailshafts for the th400, you need to identify which shaft you have as some 2wd versions use a compatible tailshaft.

If your trans has a short tail cone approx 4"5" long then you should be able to use a pre 85 np205 tcase.

https://www.offroaddesign.com/tech/...ge/offroad-design-th400-technical-information

 

[bucket]

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.

 

[Justalex]

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]

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?

 

[CORVAIRWILD]

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!

 

[CORVAIRWILD]

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

 

[Justalex]

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

Yes it was.

 

[Rickf]

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?

 

[bucket]

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.

 

[Vbb199]

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