[Hawkynz]

Hello. I am currently doing this exact swap right now. I will try to answer some of your questions and tell you what I did. I have an 89 K5 blazer though but its pretty close. I am also running a 5.3l and swapping the 700R4 out to a 4l80e with NP241 transfer case.


What I know so far is that I will need at least the following (random order):
1. TH 4L80e to NP241C transfer case adapter (GM Part 15724745).
I got this adapter off of Amazon for $36 Dorman part 926-891. Uses the same transmission mount

2. Stand-alone transmission controller (I may go with US Shift Quick 4 Gen2).
I am using a holley terminator x. Uses both front and rear input output sensors on the two wheel drive 4l80e.

3. New cooler lines and bigger radiator.
I am using the stock lines and stock radiator. I might add a cooler later.
The front line on the transmission will retain the stock trans line. The rear line will be too short. I used AN to 5/16 compression fitting and rubber hose to extend the line. (Evil energy 6an male to 5/16 hardline compression fitting off of Amazon).

4. New transmission mount and to relocate cross member.
Use the stock mount and crossmember. Just slide it back and drill new hole.

5. New transmission dipstick. I used the 4l80e stock one.

6. Adjust driveshafts, front and rear. The new set up will be about two inches longer. My front shaft extends enough to use and my rear I think will work, but I also have a blazer.

7. Adjust shift linkages for transmission and transfer case. You will also need to extend the long bar brace that connects the transfer case to the transmission.

You will need to get a new input shaft for the transfer case. The 4l80e is 32 spline. My 700R4 is 27 so I have to change the input on the transfer case.

I suggest getting a two wheel drive transmission because it will have both input and outputs on the transmission and you can use mechanical speedo output on the transfer case tail housing. I was told you will need to change the mechanical to VSS or something in order for what ever system you are using to recognize the correct speed while in four wheel mode.

If you get a two wheel transmission you will need to shorten the output shaft and plug up the freeze plug that lubricates the tailhousing on the two wheel drive transmission. There are videos on youtube.

What I do not know and need info and help about are:

1. Do I need new flax plate for this engine and torque converter combo?
You will need 4l80e flex plate. Some people call them 6.0L flexplates.

2. I have read somewhere that 4WD 4L80e have only one speed sensor, but in this swap to fully work, it needs two speed sensors. Is that true?
This is true because the output sensor is on the tailhousing of the transfer case. Thats why most people get a two wheel drive.

3. TH 4L80e transmission itself. Here I have two options:

3.1 Buy rebuild TH 4L80e from USA (I have some places in mind, will discus this later).

3.2 Buy “rebuild” TH 4L80e from an individual here. As far as know the story, he order it for his H1 6,2 Diesel but never install it.(He is reach guy, changing vehicle often, so, I would believe this story). It sits abandoned for 10 years in his garage. It looks clean. The code on transmission is 8KYP on front label, and KYP on yellow rear label. Unfortunately, there might be some water penetrated in it. There was leaking rain pipe near it and there was water in the transmission transport box. Isn’t it too risky?

I would buy the used one and change all the fluid. Hope this helps.