The mythical CUCV 4L80E swap

True Knight

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San Pedro, CA
I just swapped out the TH400 in my M1028 for an electronic overdrive 4L80E. It’s great because I can now drive the truck at 65 on the freeway and the engine is at about 2,000 RPM with the torque converter clutch locked. Here is what it took:

I got the 4L80 from the junkyard. It was in a ‘96 2500 4x4 Suburban with a 454. I highly recommend rebuilding the transmission. You never know what could be wrong with it straight out of the junkyard. Get it rebuilt by a good shop that knows how to make the small improvements to factory setup. The output shaft needed to be shortened about 1/8” to match the 400. This is easily done when the trans is being rebuilt. They also supplied me with a torque converter for the 6.2/4L80 combo. I also had the transfer case rebuilt because it needed a new shift fork and would slip out of 4WD high at some times.

The 4l80 will bolt right up to the 6.2. The dipstick tube from the 4l80 needed just a slight bend to make it bolt up in the same manner as the 400’s tube. The 4L80 has a 32 spline output shaft, and the NP208 transfer case that most of these trucks came with have a 32 spline input, so they will bolt together with no modification.

As for the pedestal mount that bolts between the trans and transfer case, I had to use the one that was factory on the 4L80 out of the suburban. It is about 3.75” shorter than the factory 400 pedestal, but bolts right up to the 4L80 and NP208 and it requires no machining. The 400 mount would need to be machined to fit into the recess on the 4L80 trans. So I took two pieces of 2” square tube and two pieces of 3/8” x 2” steel plate and built a stand to take up the 3.75” between the 4L80 pedestal and the stock transmission mounts on the cross member. I had to notch the top piece of steel plate to clear the bottom transfer case bolt.

Overall, the transmission and transfer case was about 2” longer than stock. This required the cross member to be moved back and new holes drilled in the frame. I was still able to use the all stock 400 shift linkage after I lengthened the rod about 1” with round bar welded into the middle straight section. I also moved the shift linkage support that is bolted to the frame back about 2”. The shift bracket off the 400 was used on the 4L80 and bolted right on. The shift linkage for the transfer case was also lengthened about 1” with round bar welded in the middle. The front driveshaft needed to be lengthened and the rear shaft needed to be shortened.

For the trans cooler lines I ditched the factory setup because the factory lines were smaller diameter and I did not want to run into any cooling issues. So went with all 3/8” rubber trans cooler line, which I connected to the factory 4L80 quick connect fittings from the suburban that cut to about 2“ long, and ran the lines along the top of the passenger frame rail to an aftermarket B&M Super Cooler (PN#70266) in front of the radiator. It’s rated at 20,500 BTUs which will keep the trans plenty cool.

I purchased the trans controller, wiring harness, and remote throttle position sensor from TCI. It is very programmable and I like the way it works. The TCI unit works best with a RPM signal to decide wide open throttle shift points, but can be made to work solely off of the throttle position sensor. I replaced the vacuum pump on the engine with an engine speed sensor from the 6.5 but the sensor signal was not strong enough. So I used the output from the Dakota Digital DSL-2 flywheel tach interface for the tach signal. The flywheel sensor mounted to the torque converter cover. The cover itself had to be modified because it was hitting the starter. I just ground down the cover until it cleared the starter and bolted right up.

For the TPS I made a simple bracket that mounted between the two rear intake manifold bolts (going across from one side of the engine to the other.) Then I mounted one end of the remote TPS to that bracket and routed the cable straight to the throttle linkage on the injector pump. The other side of the cable mounted to the inner fender and connected to the actual TPS.

To finish it off, I got a gear shift indicator out of a late model truck with overdrive. (I don’t remember what year it was.)

So that was about all it took to get it done. It's a fairly big project, but overall not too difficult. I finished the swap in Oct 2010, so its been 3 months with no problems at all. Overall I am very glad I made the swap to the 4L80. And sorry if the pictures are a bit dirty, This was after some extensive 'testing' of the new set up.:driver:
 

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True Knight

Active member
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Location
San Pedro, CA
Great writeup. Good job.

What was the total cost for this setup?

Trans from junkyard: $100
Trans rebuild (w/performance adjustments) : $1,400 (they threw in a new TQ)
Transfer case rebuild: $400
Trans controller and wiring: about $1,000
Driveshaft shorten & lengthen: $300
Fluids: about $50

So all together your looking around $3,250.
 

motorman

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Loganville GA
mythical . . . just like smaug

nice job. some may think the cost is prohibitive but to combine highway drive-ability with the M1008 working capacity you have quite the formidable beast. makes the guys driving the 50k trucks on the road look penny wise / pound foolish . . . naw just foolish!!!

what happened to your fuel consumption?
 

Cucvnut

Well-known member
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Carver, Oregon
Nice dude! Sweet build I want to do the same thi.g just with a klune and a 205. The controller company I am going to use is about 500
 

True Knight

Active member
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Location
San Pedro, CA
Yeah it was a lot more than I paid for the truck itself. It is much more comfortable to drive, especially on long trips. And the fact that I can cruise at highway speed is worth it by itself. As for mileage, I had just moved back into a populated area, so the city driving really kills mileage for a 6,000lb truck. But I have noticed an improvement when I have taken some longer drives.

Also, a lot of money can be saved on the trans itself if you get one that you know is good working order. $1,400 in my case. The reason I had mine rebuilt is to guarantee reliability. It would really suck to put in one of unknown quality and have to yank it back out again to rebuild it after something goes wrong a few weeks down the road.

In all it has made my truck more fun to drive. And knowing there is a near bulletproof trans in there that is not going to fail makes it worth it.
 

Ambulancechser

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edmonton ,alberta
Congrats...i got mine running way back in 2007...only i went with an np-205 for a transfer case.you can make a thm-400/np-205 adaptor (super common) work with a 4l80 with a little machining.

my truck is currently down for a 6bt/nvg-4500 swap.(tons of work!)

as an aside...i recall my milage going up quite a bit with the over drive.
from 10 mpg to about 14 if i was nice to it...cheers
 
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True Knight

Active member
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Location
San Pedro, CA
Thanks Ambulancechser. I read up on the information you posted before I got started. I decided to stick with the 208 mostly because of the cost and because I wanted to get it done quickly. I believe it is quite capable of handling the trucks capabilities.

I did notice a bit better gas mileage, but i need to go easier on the accelerator, then I'm sure my mileage will soar!

Good luck on your project!
 

allenhillview

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Jonesborough, TN.
86m1028,Can't wait to follow this rebuild. You did say vortec , right?, plus the 205 tc?

This is what I'd like to do to my 1008, keep us posted. Thats going empty your pocket-book. Maybe?
 

K10A

Member
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Location
Western Co
I was told by a highly reccomended trans guy to run hard lines as much as possible. The hose is not as nearly as durable and it can also get vaccumed shut or explode if some thing went wrong. Possibly blowing oil over hot exhaust or burning the trans due to no cooling.


No problem. Glad I could help.

As an update, it's been 1 year, 5 months and over 11,000 miles, and I have had a total of ZERO problems with this set up. I am very glad I took the time and effort to do this upgrade.
 

86m1028

Active member
1,691
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Murphy TEXAS
86m1028,Can't wait to follow this rebuild. You did say vortec , right?, plus the 205 tc?

This is what I'd like to do to my 1008, keep us posted. Thats going empty your pocket-book. Maybe?

I posted on here to complement True Knights write up & detail not to hijack his post. I will start my own build thread soon.

Back on subject:

Whether your doing a diesel or gas build, I think its much cheaper to buy a complete vehicle. (im not knocking True Knights way of building.)

I was lucky to find a wrecked low mileage truck for cheap.
The truck was 2wd but I already have the 205 t-case.
I did sell off parts to offset the cost of the truck.

From the research Ive done I think it will be easier to adapt to the 2wd trans than a 4wd trans. It will make the adapter a little longer & give more clearance for the frt driveshaft to trans pan. In looking at True Knights pics he has plenty of room.

Once again GREAT write up & pics.
 

True Knight

Active member
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Location
San Pedro, CA
I was told by a highly reccomended trans guy to run hard lines as much as possible. The hose is not as nearly as durable and it can also get vaccumed shut or explode if some thing went wrong. Possibly blowing oil over hot exhaust or burning the trans due to no cooling.
I asked about hard lines when I was getting the trans rebuilt. (The guy I used does some drag strip cars too.) When I asked he said for what I was doing and the amount of rubber hose, it would not cause any issues. I made sure to run the rubber hose away from anything sharp, hot, or anything that could eventually rub through it.



Great write up.

I just started a vortec 350/4l80/205 repower & after seeing yours, I cant wait to get it done now.
I am looking forward to that build thread. I want to keep mine diesel, but I would like to put a modified 6.2 or 6.5 with turbo in mine.
 

Dave Kay

Member
485
14
18
Location
Kingman AZ
This is a great thread--- thanks to ALL you guys!!! Was considering 4L80E swap sometime ago but instead went with the Gear Vendors install to my 1008, finally, and it's a wee-bit disappointing that with the TH400/GVunit, you really only gain about 8-10 mph speed increase in overdrive. So now instead of screaming along with high RPM's to do 50-55 mph, I now can cruise an easy at 60-65 turning 2350-2500rpm, not bad for the slow truck lanes, but still not fast enough and more RPM's than I want to maintain engine's longevity.

Am currently driving the truck daily, 100 mile round trips.

This result makes now me ready for next logical step--- 4L80E swap, which will boost my final output to something like 2:62 to 1, as per GV's trans/gearing chart. So my next step is finding the trans locally, then a reputable builder, and with this and a few other good write-ups, plus the obligatory 2-3K OR MORE in $$$, BINGO--- I'll finally have a low-geared off-road capable, highway cruising, fuel pinching truck to expedition with... BTW; the GV unit helped truck gain in fuel milage with a combined city/highway of 17MPG, using GPS for accuracy. Looking forward to better!

P.S. Anyone's thoughts on an NA 6.2L/NV5400 swap instead?

Ciao~!
 
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