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th400 tranny question

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by reddog64, Mar 6, 2001.

  1. reddog64

    reddog64 1/2 ton status

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    OK... I've asked three times... either no one knows... which i doubt, or no one has read the post...

    I have a th350 tranny and i wanna replace it with a th400 tranny... The th400 is from a 2 wheel drive 1979 truck w/a 454 bbc...
    I have a 350/th350/NP203... will the 400 go into my truck with the stock 350 and np 203???
    My buddy said something about a shorter output shaft may be needed...

    Um... yes officer I know it's too big...
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    I thought I just saw a post where someone got into spline count and such for this exact question? Go back a day or two and check. I can throw my $.02 out though...the 2wd is likely a "longshaft" that uses a longer output shaft, and thus a longer extension housing. You'll need to get the short output shaft, tear down the 400, swap it out, then reinstall. That is of course if the th400 you have is a long tail shaft. The reason I didn't post before is because I am not 100% positive...my friends C30 w/th400 if I remember right was a short shaft though, so who knows. I certainly don't : )

    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  3. ken

    ken 1/2 ton status

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    The 400 won't swap to the TH350 versioned 203 transfer, the spline count is different, 27 for the 350 and 32 for the 400. You must change the input gear in the 203 to a 400/32 spline, or simply just find a 400 version 203. There is a TH400/203 combo for sale in my area for $400.

    ken
     
  4. seattlek5

    seattlek5 1/2 ton status

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    The TH400 is an inch or two longer. The splines are 32 for the TH400 and 27 for the TH350-203 t-case. Also the bolt patterns on the rear are different. The previous owner of my rig swapped a TH400 for the TH350 and used a 2wd short shaft trans (I snapped the case less than a month after buying the truck.) You can get an adapter plate from Advanced Adapters to bolt a TH400 to a TH350-203 or 205 27-spline transfer case. It comes with a 32/27 spline sleeve also. I don't have any part #'s, but that is what I'm running. Hold out for a 4wd K-case TH400 though and do the swap once (twisting the trans in half really sucks.) Boyce Military Equip. sellls good used or check the Buy-n-Sell. Maybe swap the 203 for a 205 while your at it. Happy hunting!
     

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