Vortec 5.7 4L80E Swap in M1008

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NWM1008

New member
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3
Location
WA
I wanted to make a thread describing my recent swap into my CUCV. I bought my M1008 about 2 years ago off GSA. Initially, I was going to just use the axles for my 1970 shortbox, however after driving the truck around for a bit, I liked it and decided to save it. Living in Western Washington the biggest challenge I found with it was keeping up with traffic. My answer to this was to swap in a Vortec L31 5.7 and 4L80E to gain overdrive and also fuel injection. The internet has a lot of info on different aspects of the CUCV with swaps, I just had to piece a lot of different info together to make it work for my particular one. Hopefully, I can point people in the right direction and list part numbers and other relevant info in one spot. While the purists may not like what I have done, the truck serves my needs perfectly. After the swap, it runs about 2500 rpm at 75 on the freeway.

To start the swap, I bought a wrecked 1997 K2500 suburban that had a running Vortec 5.7 and 4L80e. From the donor rig, you will want the complete motor, ECU, air box, transmission, transfer case adapter, rear driveline, pressure line from PS pump to hydroboost . The exhaust manifolds and motor mounts off the suburban will not work with the squarebody.

I sent the ECU off and had it reflashed to delete the emissions, EGR, EVAP, ABS and limit it down to 2 oxygen sensors. This costs around $85 and was well worth it. This eliminates false check engine lights for systems that no longer exist.

For a motor wiring harness, I used painless # 60212 . Overall it fit ok, just make sure to follow the instructions for repinning the transmission plug for use with the 4L80. Don't be afraid to call their tech line if necessary. The instructions for this are somewhat vague. Due to lack of space on the inside firewall, I placed the ECU and fuse block on the driver side inner fender. I bought a small pelican box (1120), drilled a hole with grommet and placed the fuse block in it to keep it away from moisture and dirt. See pics below. From the 6.2 diesel wiring, I used the big red wire on the injection pump to provide power to the painless harness as it has power in the "on" and "crank" positions.

I used a 20 gallon fuel injection tank (Spectre part # GM1C)/sender (Spectre part # FG05M). For the fuel pump, I used Bosch part # 69225. It will provide the necessary 57 lbs of fuel pressure. I used Earl's fittings AT165006ERL and AT165056ERL from the sending unit to transition to -6an PTFE hose all the up to where it enters the fuel rails at the back of the intake manifold. Fuel filter between tank and fuel rail I used is ACDelco GF652 with Russell fittings 648060 to adapt to 6an fittings. To adapt the fuel sender to AN fittings search YouTube "1984 C10 LS swap part 3 by Lonnie's garage". It has a great step by step video.

The stock 1997 suburban alternator was simple to wire up. Just buy the Holley part # 197-400 , plug it in and provide a switched power source to the Holley plug. Lastly, connect a power lead (large gauge wire) from the power stud on the alternator to the distribution block on the firewall.

The stock 6.2 diesel M1008 motor mounts bolt right up to the vortec.

My donor suburban had hydroboost brakes so use the pressure line from the suburban, it screws right into the CUCV hydroboost and is the correct length Gates part # 365470. Just remember if you replace the PS pump (Cardone 20-8739F) or steering box, before you start it lift the front tires off the ground and move the steering wheel in both directions (lock to lock). This helps bleed the system and eliminate a dry first start.

For a radiator, I used a Spectre CU730 with the fan shroud GM part # GM3110122. You will need to use the stock 6.2 radiator mounts and move them into the "narrow" setting. Replace the rubber mounts while you are at it Prothane part # 7-1712. It also has a transmission cooler. I bought AN adapters for both the transmission side and radiator so I can run custom copper/nickel 3/8 transmission lines that will not leak.

For the transmission/transfer case I pretty much followed True Knights info on his thread mythological 4L80e swap. The one difference with mine was that I used the original transfer case adapter. This saved me from having to build a spacer. My father-in-law runs a 5 axis milling machine so he was able to mill down the flange to fit in the 4l80. He said it was pretty simple for any experienced machinist to do even on a lathe. In the pic below (before milling) you can see the difference in diameter from mounts. Transfer case adapter to transfer case gasket is part # 24245110.

Shifter linkage for transmission and transfer case need to be lengthened about 1.5-2 inches. The transmission cross member needs to be moved back a couple inches. I also had to massage the floor pan above the transfer case to get it to fit.

The ECU needs a Vehicle Speed Sensor from the transmission/transfer case to shift properly. Ideally it should be in the transfer case. The NP 241 available in early 90's 2500 series trucks/suburbans have the VSS in the transfer case. The only downfall to this is that you will lose you mechanical speedometer. I wanted to retain the np208, so I had a 2wd VSS and tone ring installed in the 4wd transmission when I had it rebuilt. Some say the way I did it may affect transmission shifting while in 4 low. But I haven't noticed it. I also had the splined output shaft (that slides into the transfer case) shortened about 5/16 of an inch to match the th400 length when it was getting rebuilt.

For drivelines, the front one needed to be lengthened and I used the donor suburbans rear driveline, which was the perfect length.

For exhaust I used Summit Stainless Steel headers part # SUM-G9006-SS along with dynomax exhaust system # 89004 and SUM-638221 mufflers. For a "universal" squarebody kit it fit extremely well. No complaints, especially since the exhaust pipes were about $120 shipped to the house. Most exhaust shops wanted $750 for it.

Lastly, make sure to wire in the proper brake switch AC- Delco D850-A to the painless harness. When the brakes are applied, it disengages the lockout on the torque converter.

I've put about a 1,000 miles on the swap so far. It shifts well, has plenty of power, fires up instantly and most importantly can go on the freeway with ease. The fuel mileage has definitely dropped, but I assumed that going into it. All my original parts I removed were sold to a CUCV collector so they are being reused in trucks he is restoring to stock specs. In the future, i plan on swapping out the NP 208 and replacing it with a NP 205 that was out of a M1028. Also the box on my truck in in bad shape so I plan on putting a flatbed on it. Feel free to ask any questions and I will do my best to answer them. Thanks!
 

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ehuppert

Member
166
8
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Location
Upstate NY
Nice write-up! I also have a 350 in mine, but a "simple" gen 1! I retained the stock radiator as mine was still good. I spliced hoses with appropriately sized exhaust pipe swedged as needed as i couldn't justify spending money on a smaller radiator!

The purists won't love it, but simple and turn key is a good thing in my opinion. These trucks are beasts, little more power and overdrive is desirable...
 

Chaski

Member
659
6
18
Location
Burney/CA
Thanks for posting the write up. Good job on calling out part numbers, those Prothane radiator isolators look pretty good. I think I’ll order up some for my ride to replace the cobbled together isolator setup l’m running.
 

NWM1008

New member
6
1
3
Location
WA
Very nice! I would of used either a Holley Sniper of Fitech if I didn't need the original computer for the 4l80. I'm pulling about the same RPM as you with the 4l80, 4.56's and 235/85/16's so I don't think you would gain much. I just didn't want to try and do carrier swaps for the 60 and 14 bolt. My buddy is the head mechanic at a local Chevy garage so he rebuilt the trans for $750 (including parts and labor) so I couldn't beat it. Looks like you did a nice job on yours!
 
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