NP246 to NP208 solid axle swap VSS

Discussion in 'Engine & Drivetrain' started by T-Bagg, Oct 4, 2019.

  1. T-Bagg

    T-Bagg The Esca-Hoe driver.

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    Alright, first, it's been a long time since I've been here.
    Second, I'm finally getting around to this solid axle swap.

    The only front axle I could get a hold of (for not an extortionate price) in SoCal was a passenger pumpkin 10 bolt, out of a 1990 or 91 Suburban, which dictates a passenger drop transfer case. So, I can't do the easy NP241 swap. Instead I got a hold of an NP208 which I've rebuilt. This truck will go from AutoTrac to floor shift.

    My issue, which of the three VSS plugs do I need, which needs to be spliced in somewhere and which can I ignore so that the speedo and transmission work? I'll be getting a cable to VSS converter from someone like Dakota Digital or Autometer.

    20191003_120457.jpg
     
  2. Ryan Buck

    Ryan Buck Full Access Member

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    What’s up buddy, did you get this to work? I need a new t case and want to put in something beefy that can take an ass who open and keep on going.
     
  3. T-Bagg

    T-Bagg The Esca-Hoe driver.

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    I did. I emailed back and forth with Dakota Digital (who were incredibly helpful). I settled on using the SEN-01-1 sending unit, plugged into the aft most pickup on the tail housing and same position as on the 246, and the SGI-100BT to convert the pulse-per-mile signal.
    Got a speedometer signal and the transmission shifts like it's supposed to. I don't know how it will behave in 4-lo yet, since it doesn't have signal from those other speed sensors.

    I'd take pictures for you but the truck is currently at the exhaust shop, since this swap requires an completely custom (not CA legal) exhaust.
     
  4. Ryan Buck

    Ryan Buck Full Access Member

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    Badass! Can you post up photos once you get i back. C the front end as well. What’s up with California and exhaust? Can you not do anything to it?
     
  5. T-Bagg

    T-Bagg The Esca-Hoe driver.

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    1st, the front end isn't done yet. Still need to build the front axle, which requires more money.
    B, California's Air Resource Board doesn't like if you move the catalytic converters from their original locations. Doesn't matter if tube lengths remain the same, if the new cats are more efficient than factory, or it still passes smog. Another example of people that don't know shit about cars making rules about cars.
    Third, pictures:

    https://i.imgur.com/Bh9qwqB.jpg
    Here's the output of the NP208 I rebuilt. If I did it again, I wouldn't use the NP208. Stick with the driver drop NP241. If you do use the passenger drop 208, you'll need a clocking ring to get it over the transmission support crossmember and you'll need to clearance the body with a hammer to get it under the floor.


    https://i.imgur.com/4ZjXUU5.jpg
    Here's the sending unit installed in the tail housing. I also have a slip yoke eliminator from Tom Wood's Driveshaft.

    https://i.imgur.com/Or5BoKk.jpg
    The new floor shifter, stolen from a CUCV and I restored (was rusted to shit before). That's the signal convertor in front.

    https://i.imgur.com/777efNp.jpg?1
    Convertor wiring. Power is coming from the 10A PRNDL fuse. It's grounded under the dash. I cut off the old VSS pug tail, and terminate the ground (I assume signal is grounded through the convertor). Both wires from the sending unit go into the convertor, then one signal wire into the truck harness where the old VSS sensor used to feed.

    But really, if you can, stick with the NP241 if you want a manual shifter, or NP243 if you want push button. They're much closer to bolt in, and will be a lot easier. This NP208 was way more difficult than I anticipated.
     
  6. T-Bagg

    T-Bagg The Esca-Hoe driver.

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    Also, when you mount the adapter to the transmission, and t-case to the adapter you must use gaskets. RTV won't cut it, the transmission will shit fluid all over your driveway as soon as you start it up.
     
  7. drakon543

    drakon543 Full Access Member

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    i second the np241 a good rebuild on a used one with the tcase saver replacing that stupid output shaft snap ring.
     
  8. T-Bagg

    T-Bagg The Esca-Hoe driver.

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    20200119_132105.jpg
    The axle I'm slowly building.
     

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