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TH350 or 400???

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by novaboy71, May 13, 2001.

  1. novaboy71

    novaboy71 Newbie

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    I just got a '70 K5 4X5. It has a rebuilt small block 400 w/ a Holley 600, little beefier cam, and I think the heads have been mildly ported. It has 31 inch tires and 4.10 rear gears. It HAD a TH350, until my dad took it for a spin to show my uncle what it could do. He was standing on the gas pedal and manually shifting the trans, but when it he shifted into third, it broke. My dad's a mechanic so he can replace it himself, but my question is this: will a rebuilt TH350 w/ a kit like TCI's Truck master rebuild kit be strong enough to handle the torque the engine is putting out, or does it need a TH400? My dad thinks it needs the 400 because it would cost more to build a 350 strong enough, but I would think swapping to a 400 would be more expensive. The truck will be used mainly for transportation, with a little bit of mild off-roading. I'm not going to even guess how much torque the engine is making, the info above is all I can offer. Any help would be greatly appreciated, thanks.
     
  2. smp

    smp 1/2 ton status

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    I have a th-350 behind my 400 SB built about the same as yours i abuse the piss out of it and never had any problems i even had it so hot from pulling a stuck truck that it was spueing fluid. I was rebuilding my driveline and took it in to rebuild it since it was out and there was nothing wrong with it. I had the pistons milled to fit another friction and steel in the clutch pack and a few other upgrades and it cost me $400. I think a th-400 is stronger but is not nessary for what you are doing a good built 350 will be more than strong for you.


    <A target="_blank" HREF=http://WWW.SMP.COLORADOK5.COM>http://WWW.SMP.COLORADOK5.COM</A>
     
  3. thatK30guy

    thatK30guy 1 ton status Premium Member

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    Be aware of the output shafts on the 350 and 400! If you replace the 350 for a 400, the t-case wont mate up to it. You would also need a different adaptor, too.
    The 350 has 27 splines and 400 has 32 splines. So, just be aware of what youre getting into.

    When In Doubt, Whip It Out!
     
  4. Roostr84

    Roostr84 1/2 ton status

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    Also remember the th400 takes more horsepower to turn too. If that matters to you or not.
     

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