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Swapping a Th400 in place of my Th350 Whats Needed?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 78Blazer, Apr 22, 2002.

  1. 78Blazer

    78Blazer 1/2 ton status

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    Currently I have a 84m1009 with a 400/350/203 in it and I am gonna be swapping a Th400/208 into it. What will I need to change to make this all work? Can I use the converter and fly wheel from my current setup or will I need something different? I am thinking I have to keep the same flywheel either way becuase it is balanced for the 400? Any help would be greatly appreciated.

    Thanks
     
  2. AZK5

    AZK5 1/2 ton status

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    You need to use the 400's flywheel. Get the 208's crossmember and drill new holes in the frame for it. You'll probably need to modify or cut a new hole for the 208's shifter to fit through. I just swapped a TH400 for my TH350 and the factory linkage worked. You'll have to cut the vacuum modulator line shorter. You'll have to modify the front and rear driveshaft. You'll need a kickdown switch for automatic downshifts. I think the converters are the same but you might check on that. Good luck.
     
  3. 78Blazer

    78Blazer 1/2 ton status

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    Well I should have said earlier the truck origionaly came with a 6.2/400/208. But when I got it it was stripped I added the 400/350/203. So the holes are already in the frame everything else should line right up I think. I do have a rear drive shaft for it already but I will need to get the front one for it. As far as the kick down switch goes where does it go??
     
  4. thebigdaddyof2

    thebigdaddyof2 1/2 ton status

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    The T400 kickdown switch mounts to the gas pedal bracket, under the dash. The T350 and T400 convertors are not the same- but are interchangeable (as long as it is not the T350C- lockup version). When a T350 conv is used in the T400, it gives a slightly better stall because of the smaller diameter.
     
  5. MudbogAD

    MudbogAD 1/2 ton status

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    I'm wanting to do the same thing. I have a 350/th350/205 setup. Will the th400 bolt up to my engine?
     

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