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TH400 2WD to 4WD Question

Discussion in 'Automatic Transmission' started by Kilian, Jan 9, 2020.

  1. Kilian

    Kilian Full Access Member

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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.
     
  2. climb-101

    climb-101 Full Access Member

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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.
     
  3. nvrenuf

    nvrenuf Full Access Member

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    bucket, shiftpro and Arkansas_V8 like this.
  4. bucket

    bucket Super Moderator Staff Member

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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.
     
  5. Justalex

    Justalex Junior Member

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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?
     
  6. bucket

    bucket Super Moderator Staff Member

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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?
     
  7. CORVAIRWILD

    CORVAIRWILD Full Access Member

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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!
     
  8. CORVAIRWILD

    CORVAIRWILD Full Access Member

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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
     
  9. Justalex

    Justalex Junior Member

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    Yes it was.
     
  10. Rickf

    Rickf Full Access Member

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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:
     
  11. bucket

    bucket Super Moderator Staff Member

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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.
     
    idahovette and Vbb199 like this.
  12. Vbb199

    Vbb199 B-rate Hillbilly Customs

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

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