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4L80 to later model 205 mating

Discussion in 'The Garage' started by Leadfoot, Nov 18, 2004.

  1. Leadfoot

    Leadfoot 1/2 ton status Premium Member

    Nov 28, 2000
    Likes Received:
    Western Massachusetts
    My tranny builder is building me a 4L80 (fully manual) to go into the 80 pulling truck (which will see some moderate on road towing duty). I have had no problems with my 700r4/NP205 combo, but I want to install that in the 78. I would like to use the newer round pattern 205 with the short adapter and double hump crossmember but still unsure of EXACTLY what I will need. I know I will need the new style 205 and adapter but don't know which 32 spline input shaft (long vs. short) I will need (or will be ideal if either can be used) and where to get the spacer/adapter (part number, phone number etc.). I'm ASSuming the short input gear is better as the spacer needed would be shorter or non existent. Does anyone have or know of anyone with a 4L80 mated to a newer style round pattern 205 with short input....???????

    There were several posts a while back that I bookmarked, but it didn't seem like anybody used the round style 205, or if they did, I missed it.

    I still need to know what I will need for parts.

  2. nvrenuf

    nvrenuf NONE shall pass! Premium Member

    Jan 7, 2002
    Likes Received:
    Mobile, Al.
    Search for info posted by U2Slow, somewhere he has detailed how to do this.

    Basically, you take a short, round style 400/205 adapter and machine the tranny side to accept an o-ring instead of a gasket and then you have to notch it somewhere on the side to clear the 205 shifter (or rails maybe). The one thing I have never read about is the 4L80E tailshafts, I don't know how many variations there are or which is needed (assuming more than one was used).

    Doing it this way you will need a round pattern 205 with the long input. Once assembled you will have duplicated the OE combo like the one in my 91 3+3.

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