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Th-400 Swap

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by RobbieOH, Mar 2, 2002.

  1. RobbieOH

    RobbieOH Registered Member

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    Since my tranny is shot too, im replacing it as well, this time replacing a th350 with a th400. I'm wondering if it will bolt right up to my 203, or what I will need to do to make it fit.
     
  2. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    Sorry, but it wont bolt up as is. The TH350 has a square, 4 bolt pattern on the back of the case where as the TH400 has an octagon, 6 bolt pattern. Also the TH350 tailshaft is 27 spline and the TH400 tailshaft is 32 spline so the onput shaft on the 203 should be different.

    GM did offer this set up so it can be done but you're going to have to get the TH400 adapter and the correct 203 input shaft. I've never worked on a 203 but I do know a 205 case can be converted from the TH350 to a Th400, so I can only assume the 203 would be the same.

    80 K10 w/ 468 and 1 ton stuff
    You don't scare me, I got chunks of guy's like you in my stool!
    www.nvrenuf.fws1.com
     
  3. mnstr_fx

    mnstr_fx Registered Member

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    You might want to look for TH400 / 205 combo. These are more plentiful than the TH400 / 203's. I think that these were a 1 year only (79' maybe) type thing. I have one that I used to make the 203/205 doubler with my TH400. But I got lucky when I found it.
     

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