onevoice

Picked up a low mile L86 8L90 4x4 to swap into a 1972 K10 Cheyenne pickup. Truck is an original paint survivor, i want to keep it relatively stock appearing. Has a mild lift, approx 3-4” done with Off Road Design custom leafs.

onevoice

First problem is where to mount everything. For those unfamiliar with 4x4s, the engine mounts a lot farther back than a 4x2, and the engine mount crossmember is completely different. There are kits available, but i am trying to avoid spending extra $$ for things i can do myself. I got the package with the factory transfer case, with the intent of using it. Probably going to reuse the np205 transfer case i already had after looking at the issues. The factory transfer case is a drivers side drop, which means i would need to swap axles to match, or figure out how to rotate the transfer case. The factory transfer case is activated electrically by a dash switch. It has modes for 2wd, 4wd, 4wd low range and an automatic locking function that reads inputs from the wheel speed sensors to automatically engage 4wd. Mitch at swap time is doing my harness, and he has a controller to make the 4wd functions operate, but the automatic function is just not doable without wheel speed sensors. In have disassembled the transfer case and to switch it to passenger output it would need several mods, like new drain and fill locations, and the trans case would need to move or maybe just elongate one hole because the pattern is not exactly symmetrical. The most complicated problem would be to move the internal oil pump pickup location. None of these are show stoppers, but to use this transfer case i think i would always have to have the hubs locked and the front driveline spinning. The engagement is done by locking up a clutchpack like an automatic transmission pack. Since the factory design is for the front driveline to always be spinning, with minimal difference in speed from the mainshaft, i doubt it would last a long time dragging the front axles constantly. I know automatic transmissions have clutch packs that do similar functions, but this transfer case definitely wasn’t designed to do it. I’ll let someone else be the experimenter.

One of the other issues is to use the new transfer case, i would definitely need new front and rear driveshafts. And by keeping my np205, i can use the factory speedometer. Driveshafts and gauges could easily add up to $1500++

the good thing is that there is plenty of room for the 8l90 underneath with the stock high hump tunnel

onevoice

First try at mounting. 2x4 on factory brackets is close to a 1/2” adapter plate and the 72 cushion. I wanted to use the L86 mounting style, but it would be a project in itself. Too many other things to worry with first. Second picture is a first cut at a mount with the top rear bolt of a old style mount threaded into the top rear block mounting hole. Dont see these mounts used much, but they are pretty easy to work with. They have a threaded hole through the bottom of the mount that takes a bolt through the flat part of the frame mount.

ls1nova71

iTrader: (4)

Nice looking truck, I'll be watching this one.

onevoice

Reusing my np205 transfer case solves some problems, and creates new ones. First thing is there are several varieties of 205’s. Mine originally had a turbo 350 transmission, so it had a male 27 spline input gear. Manual transmissions had a 10 spline male input gear. Turbo 400’s had a 32 spline female input. Later, ie about 1986 - 1990 one tons all had 32 spline inputs and a round pattern front face. Early 205’s had a “figure 8” front face pattern, sometimes called a “racetrack” pattern. There is a short (approx 1 7/16” ) stick out, and a long (approx 3 5/8”) stick out 32 spline inputs. The 32 female inputs also had a different bearing with a larger bore in the case. The 8l90e has a 32 spline male output that protrudes past the end of the transmission case about .530” . There is a lot of confusion and lack of info about bolt patterns, surprisingly hard top get accurate info. Basically most transfer cases started using a “universal “ pattern on the front that is sometimes referred to as a “round” pattern, but is not really evenly spaced. This pattern is used on a round pattern 205, a 208, and many more like a Dana 300, and aftermarket cases like an Atlas. It’s important because the transfer case cant just be rotated on the pattern to change a drivers side output to a passenger output without redrilling holes. The 8l90e uses this same round pattern on its rear, so all that is needed is a spacer to get the proper engagement of the transfer case input to the tranny output.

All that said, i thought i could probably just get a short input gear, get my 205 input bearing enlarged, get an adapter to convert my early figure 8 pattern case to round and bolt it up. Or if i was lucky find a late 80’s round pattern transfer case with the 32 spline input. But one of my desires was to reuse my existing driveshafts, and keep my transfer case shifter in the same position. In order to do that, the engine would have to be so far rearward that the drivers side head would hit the firewall. So i need a long 32 spline input, an adapter to go from figure 8 to circle pattern, and circle pattern spacer 1 5/8” thick. My mockup




yes, that is a 2x8. 😀

its 1.5 inches, plus there is a locating shoulder on the adapter that is 1/8” thick, and the transfer case is bolted to its original frame side brace. Np205 long inputs are on back order till early march and i need to keep going.

I know this sounds confusing, but its not really. Advance adapters doesn’t make a “kit” for attaching a 8l90e to a np205, and depending on who you talk to you might not get the whole story. I called once and got someone who didn’t know how to connect them, the next time got perfect advice.

The other important issue is that the 8l90e case will have to be clearanced to make room for the np205 shift rails, that is what the cutout on the side of the wood block is for. Some 205’s have slightly different shift shafts, but in general they stick out about 2.5-3” max. My adapter is 5/8, and the spacer is 1 5/8, so i will need to grind the case a little. I’ll try to remember to take a picture when i do it.

slickscustoms

any more progress on the 8l90/205 ??

onevoice

This project ground to a halt, because NP205 32 spline female long inputs were unavailable for months, and advance adapters just got them shipping. The 8l90e attaches using a 5/8” thick figure 8 to round adapter, then a 1 5/8” thick spacer. The back of the 4wd 8l90e is large round pattern. A 4wd 8l90e has a seal in the rear so no seal is necessary in the adapter. The shift linkage for the np205 needs to be modified slightly so it will have full movement without needing to cut into the transmission case. Also, the shifter for the 205 is attached to the stock adapter, and a new mount had to be made. The bracket is bolted to the 8l90e and the transfer case spacer. Not much room there, it is where it is, and i will have to cut the shifter handle to go through the floor in the stock spot.

onevoice

The 32 spline input shaft was cut about 3/16” so it wouldn’t bottom out on the output of the 8l90e. Shouldn’t be a problem, there is a large amount of engagement, over 1 1/2”.


This is a complete 2018 Silverado radiator and fan assembly. It fit with a little trimming of the stock radiator support. I will be using a 2018 overflow/expansion tank and radiator holes also.

350SS

iTrader: (38)

cool project

Jimbo1367

yes, very cool
​​​​​​ This should help out others that do similar swaps. Thanks for sharing

iglehart332

Hey Onevoice, cool build!

Hey maybe you could help me out, you seem very knowledgeable on this and I've been very confused. I bought a low mile L83 w/ no transmission. I was planing to put it in my 84 K10 w/ my newly rebuilt NP205 Fig 8 (32 spline from TH400 application) . Will the 8L90 bolt right up to the factory adapter or is it more complicated? I was also thinking about selling the L83 and getting an LS. I have been trying to get my head around this LT swap for a while and it seems complicated. Any input is appreciated.

Thanks!

gagliano7

I have a 2018 gmc sierra 6.2. That thing is going to fly.

onevoice

I think you mean will the 8l90 bolt to the adapter that connects the turbo400 round rear face to the 8l90e. The answer is no. The turbo 400 rear face is round , but it is a much smaller circle than the 8l90. You will need same as mine, a fig 8 to round adapter, then a round to round spacer, and the long 32 spline input with a little trimmed off. The long 32 spline input is needed to make room for the 205 shift rails. There is a picture above of the shifter, you can see that the inner shift rail would go into the 8l90 Trans case without the spacer.

In my case, i got the 8l90 with my engine, and my 205 was a 27 spline input, so to get overdrive, i was stuck needing an adapter and an input shaft. With your 205, and not currently having a transmission, you should look into using a 4l80e. Might be simpler and cheaper.

onevoice

I also have a thread on the 67-72truck board with more pictures. My plan was to have more generic swap info in this thread, and 72 truck specific info in the other one, but life got in the way and neither have been updated much. The truck has been running for a while, and the bugs are ironed out. I love it, it works great. Will try at least do a photo dump into this thread, a picture really is worth a thousand words


http://67-72chevytrucks.com/vboard/s...02#post8893802

ls1nova71

iTrader: (4)

Where did you mount the battery? I have the same radiator and fans, but it looks too wide to fit the air cleaner box and battery? Got any under hood pics of the finished product?

brucebanner

Cool build!

onevoice

Correct. This radiator/fan package is very wide. It might be possible to offset it towards the driver side and have enough room for a battery, but i decided to build a box to mount it under the bed on the passenger side.

onevoice

To expand on connecting the 8l90 to a 205 transfer case. I had originally planned on grinding the extension housing of the 8l90 to make room for the 205 shift rails, but found that the extension housing of the transmission is not solid. The reinforcing ribs are hollow inside. It doesn’t look like an area that you would want to cut strength away from. Also, any trimming would allow dirt to get inside the adapter housing. The rear of the trans is sealed, and the 205 input is a sealed bearing, but it looked like an unnecessary complication and would be near impossible to clean out.

Using the long 205 input and the round to round spacer also allowed making a mount for the stock 205 transfer case shifter, which was important to me because i wanted this truck to look stock from the outside and in the cab.

ls1nova71

iTrader: (4)

Thanks for the pics, they help a lot. I was hoping the battery was going to be on the driver's side though. I think I'm going to have to forgo the factory air cleaner box and move the radiator to the passenger side to get the battery to fit on the left side. Is that an electric power steering pump on your left fender?

onevoice

The power steering pump has been an adventure. There are lots of kits available that honestly look like crap. I didn’t want to redo all the front accessories or use a different water pump/ac compressor, or mount the steering pump on the passenger side. Initially I built a mount for a type 2 PS pump that used the vacuum pump pulley on the crank. Because the crank pulley is only a little over 3”, i needed a ps pump pulley that was about 2.5”. The only pulleys this small are alternator pulleys. When i put it together, there was a groaning from the system and i though i was getting belt slippage so i redesigned it completely.

The second iteration uses a CTS-V/ZL1 balancer to get a larger crank pulley, and a pump with a 6” pulley. It still groaned under load, and i pressure tested the pump and found it was not putting out enough pressure and was bad. I have replaced the pump with a PSC CBR type pump, which is an improved type 2 pump. It all works fine now.

I’m not sure the original setup wouldn’t have worked ok if the pump hadn’t been bad. But it is a a good upgrade anyway because the ZL1 balancer uses a 4 rib belt instead of the 3 rib the original vacuum pump used. This is the first model for the ps pump bracket, it attaches to the holes for the original vacuum pump. The finished one is a little nicer.

This is the 6.2 balancer compared to the ZL1 balancer and the drawing for the ATI balancer i ended up using because ZL1 balancer are back ordered till Jan last i checked. Now it drives the accessories off of the pulley that is for the supercharger, the ac belt off the ZL1 accessory drive, and the PS pump off the ZL1 ac pulley.



The picture also shows the original ps reservoir, which was junk. Get the PSC one with the internal filter. It’s expensive, but it is a quality piece and really works to de-aerate the fluid.

It’s attached to a simple bracket off the cylinder head and also has a fitting for a return from a hydroboost, which is a future project.