I bought this truck as my first big boy truck, as I had nothing but smaller cars an S10, and now I currently have a Colorado. I happened to find one with everything I wanted for the right price. Everything except a 6l80 that is. Turns out, I have had a 6l80 sitting around for a couple years now waiting for a home. It has come time to give it its home.



I didn't realize how nice a Duramax is to pull with until I tried using my truck for pulling dads buggy about 70 miles away from home to the closest ORV part. It got the job done. I was getting like 9mpg, and the thing was in 3rd gear most of the time. That sucked.



So ever since that weekend I have been researching what I needed to do, in order to put this super sweet 6l80 in my truck. I looked and I looked and I looked. I got a good understanding of what I thought I needed. Then I called Jesse at TBMotorsports inquiring about his plug and play interface module, and asked more questions along the lines of.... "What do I need to do????"
This guy asked me what I had and the way he responded back with such enthusiasm for how easy it as going to be gave me all the confidence I needed.
Unfortunately for Jesse I am alright with splicing a few wires so I didn't end up buying his product, but I would recommend him to anyone wanting to do this swap. His knowledge along with his products will help you get this swap done.

Here is what TBMotorsports sells for their Plug and Play interface. It takes the spot of your T42 TCM and uses the same factory plug, but only transfers the wires needed to the other plug, which is where you plug your transmission harness into.


I looked at that and though, "Hell, I can make that!" So I went to my pick-and-pull and bought a t42 TCM (same one that's already in my truck) and pulled the back off of it. It looked so pretty inside there. $30 from LKQ if you have one of them near ya.



It had some Jelly like stuff about 3/16" thick over the board. I'm assuming to keep the vibrations from busing a connection loose.


The plan was to remove the chip, solder a wire onto each pin I needed for the new trans, then drill a hole small enough for just the wires to the through and silicone it tight to keep the water out. Then put a male and female plug on the wires and boom. I have that interface module for around $50. Turns out those little wires coming off of the pins break really easy. So I went to plan B.

Bust all of the wires off so it leaves just an empty, watertight, box to act as a dummy plug for the factory TCM plug. From there I will just splice into the wires going into the plug and add that same male/female plug for the new transmission harness. Won't be as clean as the TBMotorsports Module, but it will do the same job, and still around $50 at most.

So now that I knew I could wire it, I needed to make sure it would fit my transfer case. The 6l80 uses a 32 spline output shaft compared to the 4l60s 27 spline. So I need to change the input shaft to the transfer case. That will be a cake walk.

Next I was worried about how much longer it will be, and I will probably have to end up buying new front and rear drive shafts. that would be pricy. I had a 4wd 4l60 in the shop, so I semi-accurately measured it agains the 6l80 and it looks like it will be within 1/2". So at worst I will have to make a new trans mount on the crossmember. That made me extremely motivated because this is looking like a damm near bolt in swap. That's never happened to me before!

Cooler lines will be ran to a dedicated cooler with its own fan to keep the trans as cool as possible. Will most likely be mounted along the frame under the drivers seat of space permits. We'll see.

Now I'm hung up on how to get tapshift to work. I'm wanting to put a corvette tune in the TCM so I can do the one wire setup instead of running it through the BCM like the trucks are setup for. This would mean I have to reflash the BCM, and most likely buy a new gauge cluster that supports the 6l80.
I ordered the shifter a few days ago and it should be here this weekend so I can check the OHMs it puts out per command. If it's close to the corvette's values I'm in business. If not, I'll try to pull the rocker switch off and pull the chip out and put new resistors in it to get it in spec with the Vette tune. If that doesn't work I'll be forced to do the BCM flash and get a new gauge cluster.

That's pretty much it.... All that I can think of anyways. I hope it all goes to plan and it's running after a good weekend of beer and work. Any of you guys that have down the swap have anything to add that might help me?

Thanks,
Branden

 

In for how this turns out.....

 

I used the tbms module as i got it second hand for the 6l90 in my truck. If i had to do it again i would just repin the ecm for the tranny and some can-bus lines.

 

Yea but that won't let you go back to factory(for whatever reason anyone would want to) and it will probably be more work to make it look factory. But maybe not.

How do you like the 6l90? Does it seem to hunt for a gear?

Thanks,
Branden

 

I have 2 6l80 engine harnesses. I was going to pull the 6l80 wiring out of it make it a seperate loom and tie it in. As far as i know with 4.10s and a 6l90 it doesnt hunt for gears it just always seems to have the right gear.

 

Right, which is what I'm going to do, but instead of cutting the factory plug off or leaving it exposed to the elements, make a dummy TCM like I did and tap into the harness before the TCM plug.

And good to know about the gearing. I heard it hunts like crazy but that was without tuning. Who tuned yours?

Thanks,
Branden

 

The tcm harness is only like 6-12" long lol. Just pin it in and avoid headaches. You may want to find some pinouts of both pcms, the one with a pcm&tcm (4l60) and a just pcm (6l80). The only circuits from the tcm connector you will need are the ones for canbus data. The one that gave me the idea was Allen from Nelson Performance which also tunes my truck.

 

I guess I don't understand what is wrong with the TBMS box? Does it not get you the wires you need where you need them? You've got me curious. Lol.

I'll just want to keep the T42 plug on there for factory reasons. If I for some reason want to sell the truck one day but want to keep my 6l80, I want to just unplug it, and put the actual T42 back in there, and put the 4l60 in it. Done deal. No more wiring. I probably won't do that if I sell the truck, but I want the option. To each their own I suppose!

 

In for results, I have thought of doing this if I blow up my 4l60

 

All that work when changing the wiring harness is a 10 minute job and is factory.
Great job thinking outside of the box though i like it