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TH350/NP203 to TH400/NP205....Whats the low down?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Zeus33rd, Aug 25, 2002.

  1. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    I'm gettin alittle tired of messin with the 203, So I figured I'd start researchin the swap options. Why the TH400? Easier to find with the 205. Harder to find a 205 behind a TH350. And obviously the TH400 is stronger. Anyways, whats the story on the swap? I assume drive shafts will need lengthening/shortining? Any crossmember modifications needed? Linkage and shifter issues? If I can find a truck with a TH400 and 205, Will that combo bolt right in? Thanks from a guy gettin grey hair from his NP203...... /forums/images/icons/crazy.gif /forums/images/icons/smirk.gif
     
  2. twenty_below0

    twenty_below0 1/2 ton status

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    Just out of curiosity what have you been doing to your 203, I have run one for a while with out problems.
     
  3. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Joe, if you want to swap out your transfer case why not tear apart the 203 and find the correct 205 and double it? Drive shaft mods are in order anyways.
     
  4. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    What have I been doin to it? lol, I guess I've been doin stuff it doesn't like. Got a new shifter for it today. I've got 4 wheel drive now, but thats it. Just Hi-loc and Low-loc. Gonna try adjusting the linkages tommorrow and see if that fixes it...If not...Time to start lookin.... /forums/images/icons/crazy.gif
     
  5. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    I did this swap... only my original combo was a TH350/205! /forums/images/icons/tongue.gif I went to the 400 for its strength. The problem with the 400 is that its the most inefficient auto tranny that GM made. You will probably loose somewhere around 100HP thru the TH400/205 combo! /forums/images/icons/blush.gif But you can't beat the strength... /forums/images/icons/smile.gif

    Drive shafts will have to be cut, the crossmember needs to be replaced with the hump-style CM (check with Westy if you need one), you'll need new mounts... one of which was a dealer-only item when I did my install. You will probably have to drill the holes for the CM in the frame.

    Other than that, it DOES pretty much bolt in. As for the linkage... you will have to lengthen the rod that comes down the firewall by about 5"... but the bracket in the frame can stay where it is. Think that is all I can remember this early in the morning... /forums/images/icons/tongue.gif /forums/images/icons/grin.gif and while you are there, you might as well consider doing the DOUBLER too... that way you can make the shafts once! /forums/images/icons/wink.gif

    Good luck!

    -Dan
     
  6. 77fixer

    77fixer 1/2 ton status

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    I did this swap and all I had to change were the driveshafts and modify the TC shifter since mine came from a 465. Oh, and add the switch for the tranny to downshift.
    That was all after the rebuild for the tranny and bore and rebuild of the TC.
     

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