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Replace 3 speed auto with 4 speed auto on a 1987 Dodge Dakota 3.9?

Discussion in 'Projects, mods, restoration' started by WalterLeeJackson, Oct 10, 2017.

  1. WalterLeeJackson

    WalterLeeJackson Active Member

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    Has anyone replaced the 3 speed torqueflite automatic used only on the 1987 Dodge Dakota with the 4 speed automatic used on the 1988 to 1996 models?

    What year should I focus on?

    What do I need to complete the conversion?

    TIA

    --Walt Jackson
     
  2. valiant67

    valiant67 Rich Corinthian Leather
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    It will bolt right up to the engine, but the transmission mount needs changed and the driveshaft shortened. You could get parts from a 88-up truck with the same wheelbase and rear axle type as yours.

    But your 87 has a carb, the ones with the OD had fuel injection and a different computer system. So you are left with two options:
    1) Convert your truck to fuel injection with the newer electronics. If you are going to do this, you may as well use a 92-96 to get the more powerful Magnum engine for your conversion.
    2) Run a 88-95 transmission and manually switch OD and lockup converter.
     
  3. WalterLeeJackson

    WalterLeeJackson Active Member

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    "...Run a 88-95 transmission and manually switch OD and lockup converter..."

    The 88-91 trucks have an overdrive switch on the dash. The 87 transmission already has an electronic lock up torque converter controlled, I assume. by the computer. Thus, you may be correct that all I need is the later transmission, the transmission crossmember, the shorter one-piece driveshaft to replace the two-piece 87 shaft, and the wiring and in-dash switch for the overdrive activation.

    I understand that the later transmission are controlled by the computer, which is not the case with the 87-91 vehicles. Or have I got this wrong? Any input is much appreciated.

    --Walt Jackson
     
  4. valiant67

    valiant67 Rich Corinthian Leather
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    The OD button on the dash is to lock out the OD, not to enable it. Without requiring, you won’t engage OD.

    The 1987 lockup may be mechanically enagaged rather than electronic, since it has a carb. I don’t know about Dakota but in the cars it was mechanical.
     
  5. 85lebaront2

    Level 2 Supporter

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    My AllData shows a pair of computer controlled solenoids a part throttle unlock for the converter clutch and an OD solenoid for the 4 speed automatic starting in 1988. On the 1987, the part throttle unlock relay is controlled by the spark advance computer. Valiant 67 is correct, the entire system changed in 1988.
     

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