TH400 into 1st gen blazer

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by k2-k5, Jun 24, 2004.

  1. k2-k5

    k2-k5 1/2 ton status

    Sep 30, 2003
    Likes Received:
    Vancouver, WA
    I'm considering swapping in a th400 into my blazer and want to know how easy a swap it is.
    Right now it is a th350 and 205 setup.
    If I got a TH400,adapter and the mating 205 and even the crossmember could I just drill new holes in the frame for the crossmember or would I be better off using my stock crossmember?
    Since I'm going with a 14b FF if i used the drivelines from the th400 said truck would they all bolt to the 14b without the conversion joint. So I would just have to get the rear shortened and make the front longer.

    What other issues will there be?

    The other issue is I plan to go with a doubler in the future as well as a bigblock. For you guys that have put in bigblocks have you moved the motor forward at all? Seems like that would help with the distributor clearance, driveline angles particularly with a doubler. I will have around a 6-7" lift in the back with a doubler setup would my driveline angles be too extreme? Also with the double from ORD's site it looks like I would need to get a np203 th400 for the shortest adaption.

    I'm trying to plan for the future without have the frame full of crossmember holes but maybe I can't avoid that.
  2. Yukon Jack

    Yukon Jack 1/2 ton status

    Jul 25, 2002
    Likes Received:
    Rose Hill, KS
    I am doing a big block swap and had heard that a 2" body lift was enough to clear the big block. Well, that is wrong, at least in my situation. With the 2" body lift in place the valve covers on both sides of the engine caused major interference. Your best bet is to move the engine forward especially if you are gonna change your driveshaft lengths anyway. I will do that in the future. If you search back about a month you will find some pics I posted about my fitment problems.

    I can't speak to the TH400 questions knowledgeable but I know you can make that tranny work. If I recall, it is longer than a TH350.
  3. kennyw

    kennyw N9PHW Premium Member

    Jun 9, 2002
    Likes Received:
    Stevens Pass Highway, WA
    Would you be interested in a strong running Oldsmobile 455 with a rebuilt TH400? I have one for sale for $750 and a local tranny shop quoted me $245 to swap in a 4x4 output shaft (parts included) or they would sell me the shaft for $50 by itself. Then you would just need the TH400-NP205 adapter and matching NP205 (or convert your current NP205 to 32 spline using ORD's kit).

    The distributor in the Pontiac is alot lower than the BBC.

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