Swap from a 700r4/np208 to T400/np208 Whats needed?

Discussion in 'The Garage' started by TecumsehK5, Mar 11, 2003.

  1. TecumsehK5

    TecumsehK5 Newbie

    Feb 9, 2003
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    I Drive a 87 Fullsize Jimmy and the 3rd gear recently went out in my 700r4 and i want to swap it for a T400 also i know that a r4 is 27 spline and T400 is 32 a friend has a T400 mated with np208 and tourqe converter that he will sell me for 350 dollars is this a good deal? and what else might i need to preform this swap?
    Thanks for any help someone can give me
    /forums/images/graemlins/k5.gifWill Austin /forums/images/graemlins/k5.gif
  2. 78Blazer

    78Blazer 1/2 ton status

    Feb 17, 2000
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    Should be a pretty simple and straight forward swap I would think. You should be able to reuse your current drive shafts. You will probably need the flat style cross member to go with the 400/208 you may have to drill holes in the frame for the cross member and u will need the kick down switch for the 400. Thats all I can really think of that you will need.. pretty basic.
  3. 83ZZ502_Jimmy

    83ZZ502_Jimmy 1/2 ton status

    Feb 7, 2001
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    Richmond, VA
    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.. /forums/images/graemlins/wink.gif

    $350 is an ok price if you know that the tranny is in good shape. Leaks are one thing, but a bad tranny is another. I'd offer him $300, and then end up at $325. But thats just me.

    Your best bet is to get the whole combo from him and put it in. Least amount of headaches.

    Sorry for the documentary


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