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700-R4 legnth v.s. TH-400

Discussion in 'The Garage' started by blackblazer717, Mar 13, 2005.

  1. blackblazer717

    blackblazer717 1/2 ton status

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    ok i know the 400 is a stronger tranny.... i have a blown up 700 im removing from my 88 k-5 i want to put a 400 in it because of the fact its stronger

    do i need to do any crossmember mods

    would the 208 case bolt to the 400 tranny

    how much shorter or longer is the 400 compaired to my old 700.

    will my d-shafts be too short/long

    thanks any help would be awesome... its my DD and i need to get this fixed soon

    LUKE any help would be awesome
     
    Last edited: Mar 13, 2005
  2. jekbrown

    jekbrown I am CK5 Premium Member GMOTM Winner Author

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    The TH400 is 24.25" long, the TH700R4 23.4" long... atleast thats what marks4x says.

    j
     
  3. blackblazer717

    blackblazer717 1/2 ton status

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    so that 3/4 of an inch would help with my rear shaft a bit heading into the case more which is good, but will the 208 bolt to the 400?
     
  4. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    the np208 from your 700r4 won't but you can get one that will (32 spline input)

    if you get a th400 and np208 combo, you won't have to change driveshafts, they are the same lenght.
     
  5. blackblazer717

    blackblazer717 1/2 ton status

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    sweet

    so if i find a 208 and a 400 set ill be able to make them work with the shafts i have now.
    awesome ill keep y'all posted on the buildup and ill find a link or somthing for pics
    luke
     
  6. 83ZZ502_Jimmy

    83ZZ502_Jimmy 1/2 ton status

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    A quick search of a few keywords resulted in one of my old posts.....:rolleyes:

    ~~~~~~~~~~

    I have done this swap, however, I removed the tbi equipment at the same time. I dont think that will be an issue because the speed sensor is on the t-case. Be aware that you will have an extra plug left over, b/c the 700R4 has a lockup convertor and needs the plug for it. (no biggie, just zip tie
    it to the frame)

    Things you will need~
    1. T-400 Tranny with a 208 output shaft.

    2. 208 t-case with a 32 spline input. The input on your current 208 is 27 spline and will not work. However, you can buy a special output shaft from Advance Adapters, but its pricey and you still have to take the trannyapart to install it. My advice is to get a 400/208 combo already together.

    3. The above suggestion will give you the correct adapter between the t-case and tranny. If not, you will need the adapter for a 400/208 case.
    Two versions were used, the short and the tall foot. You will have a short one in your truck because of its year. These are plentiful and shouldnt be hard to find.

    4. With the correct adapter the length of the tranny and t-case will be the exact, and I mean exact length of you current setup. The adapter makes up for the difference. You will not need to change any driveshafts at all. Your current crossmember should be fine also.

    5. Your shifter should hook up with no problems. The indicator on the dash will not be look right b/c it will now only be 3 speeds. This is no big deal as long as you can feel what gear your going into.

    6. You will need to install a kickdown cable. This is electric and easy to do. The throttle pedal already has the holes for it and the switch can be bought at GM. You'll need to wire it into an ignition switched power source. Then hook the switch to the terminal on the tranny. (NOTE)~~~you
    can run without this hooked up and it will do NO damage to the tranny. You will just have to manually downshift at higher speeds.~~~~

    7. You will need a converter for a turbo 400, as the one with your current tranny will not work. The flexplate on the engine should not be a problem.

    8. You will need a dipstick and tube for a 400.

    9. You will need a gasket for the adapter to tranny, and the adapter to t-case. You can use RTV on the adapter to t-case, but NEVER, EVER use it on the tranny side of the adapter. RTV is VERY BAD on auto trannies.

    10. The original cooler lines will also work just fine. Just make sure you are running an external cooler in conjunction with the one in the radiator. HEAT is the #1 killer of auto trannies.

    That is all I can think of for now. I hope it helps. I'm fairly sure
    this covers it all, but its easy to miss some things..

    ~~~~~~

    Hope this helps..

    John
     
  7. blackblazer717

    blackblazer717 1/2 ton status

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    thatnks buds i really needed the input and you answered my question about RTV on the adapter between the tcase and the tranny

    i need a new gasket b/c i recked the old one and i can use the RTV method because i never took the adapter off the tranny just off of the t-case so i should be alright
    thanks a lot guys !!!
    luke
     
  8. R72K5

    R72K5 Banned

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    shift indicator plate is no big deal to swap, its simple,, two screws and cable

    good luck
     

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