trans an case question

[Gearz]

I have a bran new 400 mated too 203  and a 400 too a 208. Don't feel like splitting them too find out if spline count is the same. I'm guessing there different. Would like too take 203 and adapter off and put 208 and adapter on. would it work or is main shaft in the 400 203 different than 208. 

[7387chevynut]

Difference will be in tailshaft length..............400/203.........used a thin adaptor plate so you have a ( short output shaft)

400/208 used a longer T-case adaptor.........so (longer output shaft)

400 turbos are 32 spline.....so any T-case that came behind a 400 turbo is gonna be 32 spline

[Gearz]

let me get this strait so the splines are the same but the length of the shaft in trans is different from one too the other. Probably different length on the 400 205 I got too. Not that I would split that up. So all three set ups are different shaft lengths and  non interchangeable cases. Because of the differant adapters that go between them.

400/203
400/205
400/208

[chevystudz7105]

when u say no interchangeable cases are you saying that you cant take the guts out of one trans and put that into another?  if thats what you mean that isnt true.  u can takes parts from one 400 and put it into another.  so u could take the tail shaft you need for a 208 and put it into the brand new 400 that you have if u want.  and if that isnt what you ment then im sorry

[Gearz]

That's Kind what I met I have too use the shaft that matches the case I'm using. Just have too put right shaft too match the case I'm using. Its probably a big deal too change the main shaft too I suppose. But there definitely compatible just the main shaft has too be one for that trans case your using.

[BIG DOG]

  not to get picky   but i heard it could be  3/8  of an inch differents      cut or grind that  much
  im lookin at a 400 203   goin 208  lookin at same thing    also still checkin into it myself

[Gearz]

  not to get picky   but i heard it could be  3/8  of an inch differents      cut or grind that  much
  im lookin at a 400 203   goin 208  lookin at same thing    also still checkin into it myself

I just don't want too sell a trans that would work with my 205 and it sounds like all three trans I have will work just have too change main shaft from the 400/205 when it goes too the other trans.

[BIG DOG]

TRUE  THAT   

[7387chevynut]

Okay.. I can narrow down the 400/T-case set ups that you as to what years they were used........and we will figure this out.

400/203.......this has to be out of 77-79........because 77 was 1st year U could get a 400 turbo in a GM 4wd 3/4 ton or 1 ton truck......................and 79 was the last model year GM used the NP203 T-case.............This 400 turbo has the SHORT Tail SHaft...........a 208 will not bolt up to it.....unless you make a special adaptor.........or swap out the output shaft for a longer one.

400/205.........this has to be out of a 1980-91. GM did not offer a 205 behind a 400 automatic tranny before 1980 (1979--back........ all 400 Auto trannys came with the full time Np203. My question to you.......does your NP205 have the BLUE ID tag just below shift linkage coming out of the case? (might be covered up with dirt & crap)...........should be stamped in center what year it was made.......that'll help also.  Does your 205 have a Slip yoke rear outputshaft on it??.......I am gonna guess that it does.  GM Np205s used a splined coupler inside the adaptor........to spline it into the T-case....and into the tranny.......so this is a short tailshaft trans.

400/Np208..........this would be out of a 1981-87 3/4 ton. This has the long rear output shaft coming out of the tranny.....This trans will only hook up to a 208..............unless you swapped out the trans output shaft for the shorter version, OR cut an inch or so off the shaft.........then it would bolt up to a 203 or 205.

So what you want to do.............is keep the spare 400........that would work with the T-case that you are presently using?

[Boggen Joe]

cut it, its easy, just like using a 2wd th350 to a 208, have to cut 1 1/8" off. I did it ease to do if thats the way

[Gearz]

That's great  Thanks for all the info 7387chevynut really appreciate it A LOT.

[BIG DOG]

hey    i just took off my 203  witch had a 1 inch adapter     and (yes) put my 208    with its   3-4 inch adapter  and mount   on to my 400           
       my 208 has a 3"  spline   sleeve                my 400 had 1 @ 1/2 in   stub     same spline count
BUT    it only gos in about 1 inch        out of 3 in         i guess most it would do is  twist the spline faster maybe because not in far enough  ?  ?

[Gearz]

hey    i just took off my 203  witch had a 1 inch adapter     and (yes) put my 208    with its   3-4 inch adapter  and mount   on to my 400          
       my 208 has a 3"  spline   sleeve                my 400 had 1 @ 1/2 in   stub     same spline count
BUT    it only gos in about 1 inch        out of 3 in         i guess most it would do is  twist the spline faster maybe because not in far enough  ?  ?

Sounds like your the guinne pig for this one I will be watching . Hope it holds