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Thread: 700r4 to th400 swap

  1. #1

    700r4 to th400 swap

    i recently lost third gear in my 90 blazer. it had the 700r4 in it. i found a th400 that i want to put in it. what type of things am i going to have to change to fit it in with the transfer case and what not.

  2. #2
    The man, the myth, the legend mist8kn's Avatar
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    The tcase you have now will not work with a th400. The spline count on the input is different. 700r4 is 27 and th400 is 32. You should be able to either rebuild your 700 or find a complete set up th400/tcase already together.
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  3. #3
    Enjoying Life Chief Hunglikmule 70-K5's Avatar
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    You need this:
    http://www.advanceadapters.com/products/pn-50-7000/

    It has a new 27 spline output shaft for the TH400. It will also space the transfer case to the correct location so that you will not have to change your drive shafts.

    They did make a 32 spline NP241, don't know what it came in though... Adapter kit for that is:
    http://www.advanceadapters.com/products/pn-50-7000/

    Both kits are pretty expensive and require you to rebuild your TH400 to put the new shaft in.

  4. #4
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    What kind of wheeling you going to do? Do you have a BB? Those 400 take a wee bit more torque to turn them. Have to ask yourself if it's worth the cost of converting that. Sounds like if you don't use the adapter your output shaft will move back. That will give you driveshaft length issues. Or maybe should you build up that 700r4?

  5. #5
    Enjoying Life Chief Hunglikmule 70-K5's Avatar
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    The adapters take into account the different lengths of the 400 and 700, the transfer case will be in the exact same location and will not require any drive shaft modification or cross member relocation.

  6. #6
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    Quote Originally Posted by 70-K5 View Post
    The adapters take into account the different lengths of the 400 and 700, the transfer case will be in the exact same location and will not require any drive shaft modification or cross member relocation.
    IMO . . .If I were going to go with the 400 trans. I would look for one with transfer case on it? (205 or 203?) Why have a bullet proof trans. on a mediocre transfer case when you cane have both with about the same cost. I mean those adapters are $478.

  7. #7
    Quote Originally Posted by Zelda View Post
    IMO . . .If I were going to go with the 400 trans. I would look for one with transfer case on it? (205 or 203?) Why have a bullet proof trans. on a mediocre transfer case when you cane have both with about the same cost. I mean those adapters are $478.

    almost there..... but a damn good answer....

    the th400/203 combo is rare and hard to find.....
    the most common is the th400/np208 which is the same t-case the th700 runs with the exception of the larger input shaft and bearing....
    the th400/np205 carries a price tag because of its bomb proof nature...
    BiggsChevys - KittysKrawlers
    1974
    K5 Blazer
    "Beauty"


    454
    TH400
    NP205
    D60/14B
    1974
    K5 Blazer
    "Beastly"


    350
    TH400
    NP203
    D60/14B
    1968
    el Camino


    400
    TH400
    12 Bolt
    1988
    K3500


    TBI350
    TH400
    NP205
    D60/14B
    No, I no longer have any build threads as they were hosted on another site that unfortunately faded away...


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  8. #8
    The man, the myth, the legend mist8kn's Avatar
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    [/QUOTE]the th400/203 combo is rare and hard to find.....
    the most common is the th400/np208 which is the same t-case the th700 runs with the exception of the larger input shaft and bearing....
    the th400/np205 carries a price tag because of its bomb proof nature...[/QUOTE]

    x2 What he said....
    Freedom isnt free thank a vet

  9. #9
    oh and be careful as to which th400 you get as they all have different output shaft lengths appropriate to the t-case mated to the tranny..... these output shafts can be swapped but they are the last part out/first part in when rebuilding a tranny.....
    BiggsChevys - KittysKrawlers
    1974
    K5 Blazer
    "Beauty"


    454
    TH400
    NP205
    D60/14B
    1974
    K5 Blazer
    "Beastly"


    350
    TH400
    NP203
    D60/14B
    1968
    el Camino


    400
    TH400
    12 Bolt
    1988
    K3500


    TBI350
    TH400
    NP205
    D60/14B
    No, I no longer have any build threads as they were hosted on another site that unfortunately faded away...


    Vote for CK5B!!
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  10. #10
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    Quote Originally Posted by Biggs Chevys View Post
    almost there..... but a damn good answer....

    the th400/203 combo is rare and hard to find.....
    the most common is the th400/np208 which is the same t-case the th700 runs with the exception of the larger input shaft and bearing....
    the th400/np205 carries a price tag because of its bomb proof nature...
    OK, Biggs Chevys what would you do? I'm trying to steer ECOTTON in the right direction.

    It goes back to how hard he's going to wheel his rig. . . . and how cost comes into consideration.
    Is he going to benefit for the work it takes to install the 400 or build and upgrade his 7oor4? I can't see buying a adapter plate to adapt something the factory already has bolted together. For what? just so you don't have to dink with the driveshafts. I'm sure that would be cheaper to have the driveshafts worked on than buying the adapter plate.

    I know one thing, I'll have to start buying up those np205's I've come across. . . .

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