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4 speed to th350 swap with np205. what output/input shafts needed

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by jimyjamm, Mar 20, 2002.

  1. jimyjamm

    jimyjamm Newbie

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    I have a 85 blazer. I'm replacing my 305cid engine and np208 t case with a 350cid and np205 out of my 73 blazer. wondering what input and output shafts I am going to need? the 73 blazer has a sm465 4 speed. the 85 blazer has a th350 already in it. what about cross member t case support? any other things I might look out for? Any help would be appreciated. thanks
     
  2. 84_Chevy_K10

    84_Chevy_K10 Banned

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    TH 350 is 27 spline output. You'll need that setup for your 205 to make it work.
     
  3. mike reeh

    mike reeh 1/2 ton status

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    before you start, make sure you have the t-case adapter and coupling sleeve.. check the for sale section and ebay, i even heard someone say the dealer can get the adapter if you're feeling real spendy.

    the coupling sleeve is 27 spline (like a th350) and you need the 27 spline input gear. word has it that ORD stocks the input gear you need... once you have those 3 parts, you can start.

    you will have to disassemble part of the t-case to swap the gears, its really not that hard if you're used to working on your truck... crossmember, you should be able to use the crossmember from the '73.

    as for your driveshafts, depending on the rear and front axles, you MIGHT get lucky and be able to use the rear driveshaft.. you see, I did this very same swap recently. I had a shortbed truck with a sm465/np205. I swapped in a th350, and converted the np205 over to work with the th350.. Its still sitting on the shop floor, not ready to go in the frame YET but while I was bored, I started taking some rough measurements.. It turns out, if my calculations are correct, that the length from bellhousing to transfer case are well within 1" (I think it might have been more like 1/2") between the sm465/np205 and th350/np205 setups.... this would mean both front and rear driveshafts from the old np205 truck will probably work.. Im going to take some more precise measurements next time im working on the beast, but one of the things I have to take care of is the damn driveshaft situation with my truck. I thought they were going to have to both be custom, but maybe not.

    mike
     
  4. jimyjamm

    jimyjamm Newbie

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    thanks guys Man I love this site!!!
     

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