NP203/th350 swap to th400; adapter ? driveshafts ?

14458 Views 4 Replies 4 Participants Last post by Lil'John, Dec 14, 2006

Fast68

Discussion Starter · Dec 13, 2006 (Edited)

need to knw if the 400 trans was ever put with the 203 case and if so what years

did they use a sleeve or any other parts other than just a basic adapter ?

what all adapter related parts would i need to find in order to swap from a th350 to a 400 with the 203 case

and would this swap affect driveshafts length ?

thanks

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michigander

· #2 · Dec 13, 2006 (Edited)

there is an np203 case just for the TH350, and a diff np203 case for a TH400(same internals except input shaft).

the TH350 and TH400 don't use the same spline output shafts and do not have the same tcase bolt pattern

as far as driveshaft lengths, the TH400 is 2" longer than the TH350... so from a TH350 to TH400 the rear driveshaft will get 2" shorter and front will get 2" longer.

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Fast68

Discussion Starter · #3 · Dec 13, 2006

michigander said:
there is an np203 case just for the TH350, and a diff np203 case for a TH400(same internals except input shaft).

the TH350 and TH400 don't use the same spline output shafts and do not have the same tcase bolt pattern

as far as driveshaft lengths, the TH400 is 2" longer than the TH350... so from a TH350 to TH400 the rear driveshaft will get 2" shorter and front will get 2" longer.

ok well i know all this already, you havent told me anything i didnt already know here..

yes any monkey knows that the case inputs are not the same,,,

i would have to swap the 203 input to a 400 one, thats no big deal, i can do that easily

and usually the difference in length was made up with the adapter length

so i want to find out if swapping to a 400 from a th350 would change the 203 case position or not, if the adapters were different enough length to not change this

they usually were

i need someone to asnwer who knows 4x4 stuff and isnt just guessing and really nows the adapters and the differences between them

GM made lots of different adapter lengths, just because you swap from one model of trans to another doesnt mean that the t-case will move and therefore the shafts would need to be a different length

i know that lots of ppl out there have swapped from a 350 to a 400 trans in a 4x4 and i need to find one of them to tell me if the transfer case stayed in the same location or not,

thats all

yes or no answer needed, real easy

and maybe if someone scould tell me what all adapter related parts are needed to go from 350 to 400 trans, if the 400 used a sleeve with the 203 or not, or anything else that the 350 adapter didnt

thanks

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KWTMECH

· #4 · Dec 14, 2006

The 203 will be moved back b'cuz of the trans length. The 400/203 set uses a direct couple, meaning no adaptor sleeve. The 400 will need a 203 only output shaft. The adaptor is about 1 or 1 1/4 thick, not like the 400/205 which is about 4'' thick. The 203 will of course require a 32 spline input gear which will fit into your exixting 203 (which has the 27) with nothing more than the gear itself and maybe a new seal.

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Lil'John

· #5 · Dec 14, 2006

The TH400 to NP203 adapter is about 1/4" longer than the TH350 to NP203 adapter. IT is also 6 bolt as opposed to the 4 bolts of the TH350. The input gear on the TH400 is 32 spline and a hair shorter than the TH350 27 spline version. It is as simple as swaping input gears on the NP203.

Here is a picture of my spare TH400 adapter:

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