th400 to 700r4 swap?

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viking2021

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Hi i have a 1988 Chevy 2500(6 lug) with a brand new 5.7 350 4 bolt main with a th400 trans, I think i have the np241 transfer case. I was looking into the swap for overdrive because i drive a lot for work. Was wondering if it will bolt right up or do i have to make some modifications if so what has to be modified. Thank you for your time.
 

stutaeng

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I think @someotherguy has mentioned that he had a bare bones 88 or 89 C1500 that had a TH400. It seems a "few" 5/6 lugs did get the TH400, in the earliest production GMT400s.

I guess to answer OP's question: he's got to change the input shaft of his transfer case, right? Most swaps are actually the other way around, so if find one of those threads on how to do, it's just the opposite. So yes, it can be done. I'm not sure if the driveshaft has to be lengthened? Someone here will know.
 

viking2021

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I think @someotherguy has mentioned that he had a bare bones 88 or 89 C1500 that had a TH400. It seems a "few" 5/6 lugs did get the TH400, in the earliest production GMT400s.

I guess to answer OP's question: he's got to change the input shaft of his transfer case, right? Most swaps are actually the other way around, so if find one of those threads on how to do, it's just the opposite. So yes, it can be done. I'm not sure if the driveshaft has to be lengthened? Someone here will know.
ok thank you
 

someotherguy

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I think @someotherguy has mentioned that he had a bare bones 88 or 89 C1500 that had a TH400. It seems a "few" 5/6 lugs did get the TH400, in the earliest production GMT400s.

I guess to answer OP's question: he's got to change the input shaft of his transfer case, right? Most swaps are actually the other way around, so if find one of those threads on how to do, it's just the opposite. So yes, it can be done. I'm not sure if the driveshaft has to be lengthened? Someone here will know.
Yep, the one I had was an '88 RCSB C1500 4.3/3L80, not even a light duty 2500.

Richard
 

stutaeng

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Exactly! There was a thread (I can't find it now) where I said the 6L90e never came with a 6.6 TD Duramax. I think it was you @Supercharged111 that had asked? I was wrong!

I saw an Express Van listed for sale with that option recently. It was a cab and chassis option. Darn I gotta try to find it now and correct my past ignorant self!
 

Erik the Awful

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I was at LKQ a couple weeks ago and saw an Express van with 8-lug axles and a 4.3. It weirded me out.
 
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