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th350/np203 - 700r4/np208 Conversion

Discussion in 'The Garage' started by joeysworld, Oct 15, 2005.

  1. joeysworld

    joeysworld Registered Member

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    Has anybody done this conversion to a mid seventies K5, or K15?

    1976 GMC with a 400/th350/np203
    Would like to put a 700r4 in the vehicle, but I also figured to scrap the np203, for a np 208, or possibly np241.

    Would drive shaft alignments be off on with the 700r4/np208, or 241?

    Would I need new drive shafts, or would I need to shorten, or lengthen the drive shafts I have now?

    Crossmember: would this be an issue?

    Is there an article out on this project?
     
  2. Hossbaby50

    Hossbaby50 3/4 ton status

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    If you are converting a K5 then you need to get the driveshafts from a K5 that had the 700R4/208 combo. If you have a shortbed you need driveshafts from a shortbed, etc. The front shaft from that combo truck should bolt right in. The rear shaft would need a conversion ujoint at the rear axle pinion because the 12 bolt that you have uses a different ujoint then the 10 bolt that the 700R4/208 trucks have.

    As long as you get all the parts the swap shouldn't be to involoved. The other thing you must worry about though is you will need to connect up a TV cable for the 700R4. You old kickdown cable won't work. The 700R4 uses a special Throttle Valve (TV) cable that tells the tranny what to do. Without this cable your tranny won't act right and will burn up in no time unless you use a manual valvebody in the 700R4.
     
  3. joeysworld

    joeysworld Registered Member

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    I need to start looking for parts then!
     
  4. gauder

    gauder Banned

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    Also need to use a torque converter lock-up wiring kit.
     
  5. seschev3

    seschev3 1/2 ton status

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    You will also need the cross member out of the parts rig and the column marker that has the overdrive selection. Check out Bowtieoverdrives.com for the tv cable stuff. I put a 700r4 in my 75' blazer years ago with out to much problem. Make sure you get a good trans cooler as well. You may also think about the np241 for the slip yoke conversion factor. Tom Woods makes excellent cv type driveshafts with the slip yoke if you go with a np208. From my experience, if you buy a 700r4 and have to rebuild it, just by one built from Bowtie and be done with it. You will also need to get new hubs to convert from the full time 4 wheel drive.
     
  6. UD0MEILLD0U

    UD0MEILLD0U Registered Member

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    LOL, I am seeing this 700R4 swap more and more lately. I had a 700R4 in my 91 S-10 Blazer. Keep in mind the 700R4 is concidered a medium duty tranny just like the 350. I am assuming you want the 700R4 for the overdrive (only reason any1 does this swap) but keep in mind if you ever hafta do a rebuild on it it will cost allmost twice as much as a 350.
     
  7. seschev3

    seschev3 1/2 ton status

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    And the low 1st gear. Plus the 700r4 can be built for heavy duty.
     
  8. UD0MEILLD0U

    UD0MEILLD0U Registered Member

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    Why would you spend twice as much BUILDING a 700 as you would just getting/keeping a 350? All that money just for overdrive? Why not keep the 350 and get a gear vendor overdrive kit? If you wanna spend money thats the way to go! They can handle like 1200HP, and you can overdrive every gear. :D. You'll have 1st, 1st o/d, 2nd, 2nd o/d, 3rd, 3rd o/d. It will run ya right around 3000.00 though. Hmmmm Never mind DAMN thats alotta money. Well looking up those prices shot my arguement straight to hell =). Hope I can convince and unconvince ya again sometime real soon =).
     
    Last edited: Oct 17, 2005

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