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th-350 swap to a th-700

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by k51973, Feb 20, 2002.

  1. k51973

    k51973 Newbie

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    Hi, i am new to this message board. I was wondering if anyone could tell me generally what modifacations would have to be done to make this switch. I am thinking of doing it so that i might be able to keep my same rear end gearing, yet increase my highway speed. Thank you for your help. ps. i have a np 203.
     
  2. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    This is a fairly easy swap. You will need to purchase an output shaft from advanced adapters for the 700R4 then have a tranny shop install the shaft for you. This however is the most expensive part of the swap. Your transmission has to come all the way apart to do this. Once the shaft is installed all you need is to bolt your 203 to the new 700R4. You will also have to have your driveshafts modified, the 700R4 is 1 7/8" longer than the TH350. So your front shaft will need to be lengthened 1 7/8" and the rear shortened 1 7/8". Once you have all this done you need to check your driveline angles and adjust accordingly
     
  3. xnoahx

    xnoahx 1/2 ton status

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    You might also need to do something about the lockup on the 700. Im not sure what ones have it but some are electronicly controlled so you will need to get a kit to bypass it. Hopefully someone else will know a bit more about this. Ive also heard that after 87 they were built better so those would be a better choice. you also wouldnt need to get th output shaft changed if you got one from a 4x4 i think

    My 73 K5 <a target="_blank" href=http://www.geocities.com/xk5blazerx/73k5.htm>http://www.geocities.com/xk5blazerx/73k5.htm</a> 350/TH350/NP203, Edelbrock intake & carb, Vortec heads, 4" lift, and 36" TSL's
     
  4. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Sorry about that, i forgot you are working with an older blazer and wanting to install the 700R4. Yes you will need to purchase a converter lock up kit from someone such as painless wiring. You will however still need to buy the output shaft. The 700R4 from a 4x4 with the 208/241 will have too long a shaft in it. It is not advisable to try to cut it shorter either because the shafts aren't splined down far enough to safely have enough engagement.
     

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