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700r4 swap

Discussion in 'Automatic Transmission' started by curse, May 12, 2019.

  1. curse

    curse Member

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    kyle
    Truck Year:
    79
    Truck Model:
    c10
    Engine Size:
    350
    I've done some reading and not really finding a good answer for my situation. I bought a crate 350 hooked to a remanufactured th350 for my 79, 2 wheel drive short bed if it matters. I found out the th350 is really a 700r4. I'd like to use the reman 700r4.

    I've done some reading and some say to swap tail housing and output shaft etc.

    If the driveshaft slides onto the 700r4 why would anything need swapped? Wouldn't shortening the driveshaft be enough? Maybe swap speedo gears if they are different?
     
  2. 84 M1008

    84 M1008 Supporting Member Supporting Member

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    6.2 diesel
    The overall length of the short housing TH350 is 27 5/8. The 700R4 is 27 3/4. There is no need to alter the driveshaft if this is the TH350 you have.
     
  3. C10MixMaster

    C10MixMaster Member

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    my 700r4 went rite in with the original driveshaft for the th350. i believe my th350 was the medium length tail housing 9" comes in 6' 9' 12' for a turbo 350.If your donor transmission uses a speedometer cable your good to go if it is the electronic type you need to do a cable type tail housing and reluctor wheel swap or do an electronic speedometer upgrade. i did have to elongate a few cross member bolt holes. overall i bolted in fairly easy. but there are a couple of things you need to make it work rite. 700r4 uses a a throttle valve cable not a kick down cable it must be set up correctly. i ended up buying the throttle backets to make sure the geometry was correct. if you want the lock up converter to work you will need to rearange a couple wires inside the transmission and add circuit to the truck if it didnt already have a 350c with a lockup converter. if the transmission doesn't shift correctly STOP IMMEDIATELY you can do a lot of damage quickly..
     
    Last edited: May 13, 2019
  4. curse

    curse Member

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    Engine Size:
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  5. curse

    curse Member

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    And yes I am familiar with the tv cable and its adjustment. Does anyone have a link to how to wire the lockup without buying the kit?
     
  6. curse

    curse Member

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    350
    My 700r4 is about 30 3/8 inches. the th350 looks like it's 27 5/8 inches.
     
    Last edited: May 13, 2019
    84 M1008 likes this.
  7. C10MixMaster

    C10MixMaster Member

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    IMG_0531.JPG


    there are 20+ versions of wiring from GM for the 700r4 this pic is not mine but a good reference. i rewired mine starting from the bulkhead terminal ran a wire to the 4/3 pressure switch then to the tcc solenoid then to the 4rth gear pressure switch which is the ground. ( 4/3 pressure switch is optional. ) some transmission only have a 1 wire tcc. In that case the wiring would go from the bulkhead connector to the 4rth gear pressure switch then to the tcc solenoid which is grounded. (I was able to reuse all the internal wires didn't have to make any )

    the wiring for the truck will start with ignition power+ , connected to a brake switch that conducts current when the brake pedal is in the up position, then to a vacuum switch , then to the transmission bulk head connector. the vacuum switch is 14032087 found in mid 80s c10s it will allow the torque converter to unlock on acceleration. and the brake light switch disconnects it when stopping.
     
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