TH400 to 4L80E swap (with computer/harness and new engine)

[MuddiGGEr25]

Ok lets skip the part of everyone saying i need a computer to control it because I already have one, and an engine, and complete harness all from matching truck ( see my thread about Gen V 454 TBI)

I know im not gonna do much better than 7-8MPG towing, not my concern right now, because the 6.2L I was using only got 9 and could barely get up to 50MPH, 45MPH witha headwind and 35mph on hills, so Im going from 240  ft-lb at 2000RPM to 385 @ 1600RPM. thats something like a 60% increase of TQ, but at 400 rpm lower, which is great for towing...


Anyways ive read many thread of TH400 or TH350 or 700R4 to 4L60e and 4L80E, and most of them just stop short and drop off into nonexistance, probably because they gave up after seeing the $1500-$4000 price tag on standalone controllers lol.

I think the adapter that came with it "should" fit my NP208, i will be verifying this probably tomorrow or sunday to be sure.

I need to know, is there a simple linkage piece/plate/adapter that i can bolt onto the 4L80E that will attach to my existing linkage to keep the geometry correct?

Also the consensus was just to use the existing crossmember and drill a set of new holes? that wont make it as whole any weaker by being 4-8" back further?


I found a shop in town that will shorten and rebalance driveshafts for about $70-$80 each and takes em about an hour, so the rear one will be easy, but since the Tcase will now be xx distance farther back im not sure if i can use my old front shaft or not... i did get the old shafts from the donor, it has standard u-joints on both sides, so is there a conersion ujoint that will allow me to put the 95 front shaft onto the adapter that bolts to the NP208?

[Irish_Alley]

I need to know, is there a simple linkage piece/plate/adapter that i can bolt onto the 4L80E that will attach to my existing linkage to keep the geometry correct?

you should be good with the OE, you should be able to adjust it.

Also the consensus was just to use the existing crossmember and drill a set of new holes? that wont make it as whole any weaker by being 4-8" back further?

when i dropped the cummins in my 91 i had to push the trans back 3" so i had to drill new holes and i havnt seen any cracking from that

[MuddiGGEr25]

I need to know, is there a simple linkage piece/plate/adapter that i can bolt onto the 4L80E that will attach to my existing linkage to keep the geometry correct?

you should be good with the OE, you should be able to adjust it.

I dont have the original attachment that bolts onto the side of the trans, there is a "stud" of sorts with 2 "flat sides" so it looks more oval than round, and thats where im supposed to attach im sure, but i dont know what the actual name of said part is to look it up either

Also the consensus was just to use the existing crossmember and drill a set of new holes? that wont make it as whole any weaker by being 4-8" back further?

when i dropped the cummins in my 91 i had to push the trans back 3" so i had to drill new holes and i havnt seen any cracking from that

Well thats good to hear lol, even after cam swap this fall i wont be pushing anymore than 450ft-lbs, bc ive read the 80E cant take much more than 440-460 stock lol

[Irish_Alley]

behind the cummins im prob close to that (stock is 400 but i have a turbo and tune) the weak part to me in the torque converter.

[Irish_Alley]

you should be able to use your old one. idk if theyre compatible or not. the transmission shift linkage should be and ive never seen anyone say theyre not

[MuddiGGEr25]

the linkage should work  but what im talking about is that the connection to the trans is completly different, 1st pic is what my 4l80E looks like and the 2nd pic is what the TH400 linkage looked like, unless i was supposed to remove that piece with the 2 holes from the TH400 before selling it. if so, im SOL and have to order a piece somewhere

[MuddiGGEr25]

I found this linkage kit, says it can do TH350, TH400, 700r4, 4L60/e, 4L80E http://www.shiftworks.com/column.htm#kit

So it should be perfect, i think

[ehjorten]

What you have is a 1997+ 4L80e transmission.  That sensor on the selector shaft provides the Neutral/Park signal as well as a signal to indicate what gear is selected.  You may not have the driver's side, rear speed sensor on the transmission.  1997 and later 4L80e's in 4wds sometimes omitted that sensor and used the one off of the transfer case.  Besides that the main difference is that on the passenger's side, the cooler line input and output are seperated and not side by side.  They re-engineered the fluid passages and routing that resulted in that external change.

[MuddiGGEr25]

What you have is a 1997+ 4L80e transmission.  That sensor on the selector shaft provides the Neutral/Park signal as well as a signal to indicate what gear is selected.  You may not have the driver's side, rear speed sensor on the transmission.  1997 and later 4L80e's in 4wds sometimes omitted that sensor and used the one off of the transfer case.  Besides that the main difference is that on the passenger's side, the cooler line input and output are seperated and not side by side.  They re-engineered the fluid passages and routing that resulted in that external change.

I will go upstairs here in a bit and make sure or take pictures of mine, but it came from a 1995 K2500 with the 454 but the tag i think means that it was rebuilt because the date code is different.

[ehjorten]

I see now...that is not actually a picture of your transmission, just an example.  Looks like it came from the shiftworks website.