6L80e to 4L60e

[xKingdom]

Hello everyone, I have a 2008 and 2009 Avalanche LTs. (I know it’s not a Silverado but I really need some help here) my main issue is my 2008 has a built 5.3 and a built 4l60e. My 2009 is rust free and I’m currently installing my 9 inch lift on it. The only issue is the 6 speed transmission is junk, it has no gears besides park. Is it possible to swap the 2008 motor and 4L60e into my 2009? I’m hoping it’s going to be as simple as a normal motor swap but I’m not sure what all it entails. I’m sure the cluster is different but besides that can I just transfer my ECM and tcm over? Or will I need to do some programming to my bcm and such. Thank you in advance!

[davester]

Motor will be straightforward, the transmission won't be, because there are a bunch of other stuff that need to be changed, like the steering column and instrument panel.  The IP in particular probably will be a problem to get working right.  And with gmt900's, it's not just swapping computers like you could with gmt800's, a lot more stuff is vin-locked, and there can be more variations in other parts, such as abs controllers for example.

[CamGTP]

The 6 speedo is a far better transmission than the 4L60e when it comes to lifts and big tires too.

 

The long gear changes of the 4 speed will suck and you need less rear gear with a 6 speed because of the mechanical advantage the 2 extra gears give you.

[xKingdom]

44 minutes ago, CamGTP said:

The 6 speedo is a far better transmission than the 4L60e when it comes to lifts and big tires too.

 

The long gear changes of the 4 speed will suck and you need less rear gear with a 6 speed because of the mechanical advantage the 2 extra gears give you.

So your thinking I should have the 6 speed rebuilt and call it good?

[davester]

Yes, that would definitely be the way to go, IMHO.

[xKingdom]

5 hours ago, davester said:

Yes, that would definitely be the way to go, IMHO.

I called a few transmission shops and none of them really wanted to work on 6L80s, that’s why I wanted to swap my 4l60 in

[davester]

That's nuts.  Do they just not work on vehicles newer than 10 years old?j

[xKingdom]

On 3/4/2025 at 9:47 PM, davester said:

That's nuts.  Do they just not work on vehicles newer than 10 years old?j

Well from the 5 shops I’ve called in my area (100 mile radius from my house) all of them told me the 6l80 is junk and to just keep my 4 speed. My 4 speed was rebuilt buy my local motorsports shop and they didn’t really want to do it but they threw all billet parts in that’s why I didn’t want to keep the 6l80

[CamGTP]

The 6L80 is a far better transmission, those transmission shops just don't like doing the work. The only downfall of the transmission is the stock torque converter, once that is replaced, they are really good transmissions.

 

I also don't really trust those shops if the first thing out of their mouth is that the 6L80e is junk, why would they not want to take someones money for a rebuild that they can do. That just tells me they are lazy and not worth my time if they don't want to fix the thing that needs repairs.

 

At this point I'd be ordering a transmission online from someone, lots of places do it. Then all you'd need is the transmission programmed after you install it.

[xKingdom]

2 hours ago, CamGTP said:

The 6L80 is a far better transmission, those transmission shops just don't like doing the work. The only downfall of the transmission is the stock torque converter, once that is replaced, they are really good transmissions.

 

I also don't really trust those shops if the first thing out of their mouth is that the 6L80e is junk, why would they not want to take someones money for a rebuild that they can do. That just tells me they are lazy and not worth my time if they don't want to fix the thing that needs repairs.

 

At this point I'd be ordering a transmission online from someone, lots of places do it. Then all you'd need is the transmission programmed after you install it.

I was thinking of buying one from oreillys. Like I said though would it be a simple swap to just put my motor and trans out of my 08 truck into the 09? I could definitely keep all the 6l80 parts but I’d really like to utilize my built 4l60 since I already spent the money to have it all gone through.

[CamGTP]

The engine transmission swap is simple but that's it.

 

The wiring and programming is your problem. Different wiring harness, different fuse blocks. The 4L60e is a external TCM the 6L80e is an internal TCM. The other modules on the CAN-BUS are technically programmed to match everything with a 2009 truck with a 6 speedo auto. So things like ABS and all that other stuff may not work again because of the calibration mismatch going on.

[xKingdom]

3 hours ago, CamGTP said:

The engine transmission swap is simple but that's it.

 

The wiring and programming is your problem. Different wiring harness, different fuse blocks. The 4L60e is a external TCM the 6L80e is an internal TCM. The other modules on the CAN-BUS are technically programmed to match everything with a 2009 truck with a 6 speedo auto. So things like ABS and all that other stuff may not work again because of the calibration mismatch going on.

I’ll try to call my local dealership and see what they can do for me. If they can’t do anything I’ll cave and pick up a 6 speed, the nice part is I have a whole donor truck so it’s not like I’ll have to pick up many parts in terms of any wiring harnesses

[newdude]

You'd be much better off rebuilding the 6L80 or buying a rebuilt upgraded one.  

 

4L60 is ran off an external TCM, 6L80 is an internal TCM so the truck would be wired differently between the two and would require some big efforts to swap it to the 4L.  

 

[swathdiver]

In order to downgrade your truck to a 4L60 you would have to swap in new wiring harnesses and multiple programming operations and a new cluster, shifter, cross member, etc.  

 

Less expensive and aggravating to just overhaul the 6L80.

[swathdiver]

On 3/4/2025 at 5:16 AM, davester said:

Yes, that would definitely be the way to go, IMHO.

 

Seems like we're getting this question every week now Dave!