4l80E/NP205 (Yes, another one)

[ZacharyDouglas1992]

Alright well this is my first time posting anything on here (at least on purpose) so go easy on me haha.

I am seeking any insight as far as how to go about this swap. I've seen 500 million of these online, but rarely does the poster give enough specifics as to the vehicle/parts in possession. I am going to try to be as specific as possible and feel free to ask me anything I have left out.

The truck is a 1983 GMC Sierra Classic crew cab K3500.
454/TH400/NP205-DANA 70HD 4.56. Now you can see why the overdrive is attractive. with 31" tires I am 3000rpm+ at 65.

I just purchased a 454/4l80E/unknown transfer case combo. (I havent picked it up yet and I didn't crawl under the vehicle so it won't remain unknown) However this is from a 1991 Driver side drop, and i would like to stick with the gear driven, bulletproof 205. Honestly the price, to me, was worth the serpentine set up from the engine, everything else is gravy.

I will be rebuilding the 4L80E, or having it redone, and updating it so that the aftermarket tranny controller can be used.

The real question is the best way to go about mating the 4L80 to the 205. I would think the best way to go about that would be to have my current TH400 adapter reworked. Machine work on the indexing ring? If anyone has the specifics on this, or knows somewhere I can send it to have it done, I am all ears. If anyone here has done it, and is willing to do my adapter, name a price and maybe we can work something out. I think going that route involves shaving a bit off the 4L80 tailshaft as well? Again, specifics would be great.

I am especially interested in the input of those who have used the TH400 adapter method before, but I am open to other Ideas.

Also, depending on how this goes, I will be selling the TH400. I just had it rebuild 4000 miles ago. still has a warantee through december. had an HD shift kit installed. It shifts fantastic, I just can't live without overdrive with that gearing. Probably for around 600, about half what I've got in it. And im in central CA if anyones truly interested. On the flip side if this seems to overwhelming I will sell the 4l80 for 150 as a core. Was in good condition when parked, but truck sat for 12 years.

*notes
The truck is one of 5 vehicles and far from a daily driver, so turnaround time isnt a huge concern.

I just had the rearend completely rebuilt, and I was told 4.56 was the minimum I could do in that diff, so changing the gearing is not a route I'm going to take.

[48cj2a]

If you have a driver side drop it will not be a NP205.

The 4L80E/NP205 was offered one year only in the V3500 1 Ton Chevy GMC 4x4.

I've read write ups on the conversion with the computer and harness being the major expense of the conversion.

I bought one in a V3500 Crew Cab a few years ago in a govt auction specifically for the drive train and later had to sell it for financial reasons.

They are out there but not as common as you think.

Here is what to look for in the cab to determine the 205 from a glance: (notice the straight shifter stick in the center floor)






Here is the rare as hens teeth adapter:

[ZacharyDouglas1992]

Thank you for the reply. I wish I could stumble across one of those! And sorry for the confusion, allow me to clear a few things up.

The truck I have is an 83 gmc with a 454, turbo 400 transmission and a NP205, as it came from the factory. It is a passenger drop.

When I said driver side drop, I was referring to the drivetrain I just purchased from a 91 chevy truck, which is a 454/4L80E and a driver drop transfer case, and I do not know for certain what case it is, but it is the 88-00 body style with IFS so Im pretty sure it is a driver drop.

Yeah the electronics are pricey, but im getting the whole set up cheap enough that I am willing to invest a little in it.

So what I would be looking to do is mate the newly aquired 4L80E to the NP205 that is sitting in my GMC already.

[48cj2a]

I knew what you mean't and was referring to you not knowing what T/C was in the 91 donor.

I've been scouring the net since posting to throw you a bone. Pretty hard to find parts but here are some adapter conversion options:

Advance Adapters: http://advanceadapters.com/downloads/50-0410.pdf

Summit lists: http://www.summitracing.com/parts/add-50-0410/overview/

PolyPerformance: http://www.polyperformance.com/shop/...t-p-20755.html

Northwestfab: http://www.northwestfab.com/GM-4L80E...ter_p_273.html

Northwestfab: http://www.northwestfab.com/4l80E-to...pter_p_98.html

[ZacharyDouglas1992]

yeah I figured you did, as your reply was very insightful, I just thought I should clear up a few things for future posts.
Thank you for the links, I will look deeper into them. I also know for a lot of the aftermarket adapters, they are made for the 2wd tailshaft, and the round pattern 205. I will have a 4wd 4L80E, (although I plan to rebuild it so changing the tailshaft isnt a dealbreaker). I do believe, however, that I have the figure 8 style 205. The few sources I have been able to find online say in this instance, my TH400 adapter can be made to work with a little machining, but I am looking for the specifics on that and/or someone who has done this before to possible have me send mine to them.

I will be picking up the new drivetrain this weekend and that will help greatly, as I will have a chance to test fit things and take necessary measurements. Also, whatever I end up doing, I will be sure to keep detailed notes and take pictures of the process, so that at least there will be a source for how to complete one of these many ways to do this swap.

[48cj2a]

The 50-410 adapter is for the figure 8 NP205...but is for the slip yoke 4L80E (2wd).

The adapter assembly fits 1971-79 GM NP205 with a figure 8 front bolt pattern, and is designed to replace the 10 or 27 spline male inputs. If the GM NP205 is equipped with a 32 spline female input, the new 32 spline input that is included in the kit will not be needed. Call our tech line for more info.

If you are rebuilding the transmission I would think a tranny shop would swap outputs if its serviceable and they are rebuilding it for you and getting paid for the rebuild...worth an negotiation tactic.

The GM 4L80 has a case length of 26", 17 bolts for holding the oil pan in position. The rear side of the transmission case
will have a hex shaped bolt pattern that uses 6 bolts. There are several various lengths of output shafts that the transmission
has been equipped with and you will need the 6-1/2" slip yoke output shaft GM# 24218219 (1991 to 1996) or GM#
24204289 (1997 to 2007). This shaft is fully splined. Any other 2WD output shaft will not work.

[1969x11]

I bought the Northwest fab aluminum adapter and I'll change my output shaft. I havent got it in the truck yet so time will tell If I went the right route.

[franken]

Have you checked to see if the NP205 is a round 6 bolt or figure 8 style? I'm thinking 83 would be figure 8 but...
The later TC is most likely a round pattern.
If you have, or can locate a round pattern 205, it may bolt up, or almost bolt up. The round pattern TCs use an ANSI standard round pattern with one bolt hole slightly offset. The thing is, different TCs have that offset hole at different spots--even within GM

[ZacharyDouglas1992]

i am almost certain I have the figure 8 style, as it is the factory set up. That being said, I have read in multible places that the figure 8 style tcase/400 adapter can be re indexed to work with the 4l80E. It takes machining about .0034 off of the radius and .0020 off the height of the indexing ring, and the short 4x4 shaft with .25" shaved off the end, and it will bolt up. Can anyone here confirm that? I will be seperationg the motor/tranny/tcase this weekend and I may figure it out via trial and error before I ever get an answer. If by some miracle I do, I will post plenty of pictures and specs.

[Gobuffalo]

I just started this swap in my 70 Suburban. If I may, here is my 2 cents.
I called Advanced Adapters and asked to buy the proper parts for this. He asked what I already had. A 1982 205 (figure 8) and adapter bolted to a TH400. I'm installing a 4L80E from a 2 wheel drive with 2 speed sensors. He told me as long as it is the full splined shaft, I had every thing I needed. He said cut off 1 1/2" of the output shaft and have a machine shop cut the indexing ring on the adapter to 4.800". You may have to grind on the adapter foot a little if the pan hits.
It worked sweet!

P.S. The machine work, new gaskets and seals cost $100.00.

[Gobuffalo]

Adapter

[Gobuffalo]

The point of no return!

[ZacharyDouglas1992]

Originally Posted by Gobuffalo

The point of no return!

Thank you very much for the post! I have almost exactly what you did. (figure 8 style case and th400). I had heard about re-indexing the adapter, and its nice to see proof that it works! The only difference in my situation is that I currently have a 4x4 4L80E. I have heard that all id have to do is shave the shaft, and I think a much lesser amount than you did your 2wd shaft. And i think more grinding on the adapter feet is required. But at the very least now I know I can hunt down a 2wd tranny if all else fails, and they can be had pretty easily around here.

I was sincerely hoping to have this at least started by now, but work has been really demanding lately-and a lot of my free time has been dedicated to the prep work on my Chevelle to give it a long overdue paint job. And the truck is still far to usefull to me to tear it down sooner than I absolutely have to. When I get to this point on the truck I will post some pictures as well. But now I know what I need to ask the machine shop for and that is a huge help.

[rs74]

I have been told that you can get a 91 year model only from a diesel and it will have a stand alone harness and module. Thats sounds alot better if you could find one. Supposedly 91 4l80e diesels had the stand alone and would bolt to the 205. From what I here anyway.

[Gobuffalo]

Thought I would give you some pics installed.

[Gobuffalo]

Here's the other side without the shifters in the way.

By the way, Northwest Fab makes an adapter that is .600 thick to bolt these 2 together. It what's can be used with a 4x4 trans without cutting the shaft.

[Gobuffalo]

Had to give the adapter foot a trim on the little cast gusset, so the pan won't hit and can be easily removed.

[Gobuffalo]

Been working on this swap some more.
Almost put $400.00 out for a crossmember setup then decided to see exactly why my crossmember won't work. Well, it's too narrow. I did some measuring and found if you cut it right below where the upper and lower pieces bolt together, it dropped right in.

[jjzepplin]

Very slick.

[Myers horsepower]

Watching. I'm wanting to put a 4l80e in my 1990 V3500 truck.

[Gobuffalo]

Finished lower half of crossmember.
After powder coating I'm into this for $65.00 and 8 hours of my time

[ZacharyDouglas1992]

Sorry for falling asleep on this everyone. It still will be done, eventually. The truck is currently completely stripped and being restored. One thing led to another and now it is being painted, power doors, motor rebuild, serpentine, fuel injection, the whole 9. I should probably start a build thread for it, and when I get to the point of installing my 4l80 I will post the details of that process here!

[Pano]

Thanks for this thread. I to am also doing a 4L80e swap and have been searching for all the details so when I start I hope to turn it around quickly. It seems everyone has some variation.

I have an 87 v2500 TBI 350/400/208. I bought a TBI 454/4L80e out of a low mileage 1991 motorhome. I have the computer and complete harness. The harness has some sort of trans module but I havent had the time to study it yet. I havent seen any 208s used with the 4L80 so it looks like I may need to pick up a 205 tcase.

[Duck1]

Originally Posted by Gobuffalo

Finished lower half of crossmember.
After powder coating I'm into this for $65.00 and 8 hours of my time

did you sell this

[Gobuffalo]

It’s bolted in my 70 Suburban.