'03 Tahoe 5.3/4L60/NP246 Swap to 6.0/4L80

[ShookieJay]

I have an '03 Tahoe with the 5.3 Flex, 4L60E, and NP246 (auto 4wd) transfer case. I have the opportunity to buy a low mileage rusted out truck for parts and I'm wondering how straightforward it would be to swap the drivetrain from the junker into my Tahoe. The donor is an '06 Silverado 2500 HD with the 6.0, 4L80E. Not sure the transfer case number, but it's the manual one with the stick on the floor. Would I be able to drop that drivetrain into my Tahoe while keeping the 246 t-case? I'm also tempted to swap the axles since the donor has 4.10 gearing. My main concerns are fitment (is it direct bolt in?) t-case compatability, and driveshaft length. I'm sure this question has been asked more than a few times, but I wanted to include details specific to my situation. TIA!

 

[strutaeng]

You have to swap the input shaft of the T-Case to the larger spline of the 4L80e. Or find the same T-Case that was already mated to a 4L80e.

Front driveshaft is most likely going to need adjustment. Is your rear driveshaft 2 piece? If not, it will also need adjustment as well. I'm not sure of the crossmember on the 4x4s, but on the 2wd the crossmember can be modified for the 4L80e.

Some repining and ECU reflash for the new transmission and off you go. Or use the ECU that came with the LQ4/4L80e if it's compatible with your truck.

 

[ShookieJay]

You have to swap the input shaft of the T-Case to the larger spline of the 4L80e. Or find the same T-Case that was already mated to a 4L80e.

Front driveshaft is most likely going to need adjustment. Is your rear driveshaft 2 piece? If not, it will also need adjustment as well. I'm not sure of the crossmember on the 4x4s, but on the 2wd the crossmember can be modified for the 4L80e.

Some repining and ECU reflash for the new transmission and off you go. Or use the ECU that came with the LQ4/4L80e if it's compatible with your truck.

Thanks for the reply! I did not know the input spline was a different size, good to know. Rear drive shaft is 1 piece. I'll have the entire complete donor truck so whatever needs to change won't be an issue as long as it fits the Tahoe chassis. I kinda figured the drive shaft was gonna be an issue

 

[ShookieJay]

Side note: I would not be opposed to swapping only the transmission if possible. Not sure if a 4l80 will bolt to a 5.3... After driving the donor I couldn't believe how quick and firm the shifts were! Makes the 4l60 feel like a real slosh box lol

 

[strutaeng]

Thanks for the reply! I did not know the input spline was a different size, good to know. Rear drive shaft is 1 piece. I'll have the entire complete donor truck so whatever needs to change won't be an issue as long as it fits the Tahoe chassis. I kinda figured the drive shaft was gonna be an issue

I did a 5.3/4L80e swap on my 99 Silverado NBS ECSB 2wd. It originally came with a 4.3...think SLOW!

On those trucks it's very easy because the driveshaft is 2 piece and the center bearing support has slots for adjustments. The only thing different is a special yoke that fits the output shaft of the 4L80e but has the ears for the stock S44 u joint. No driveshaft shortening.

After driving the donor I couldn't believe how quick and firm the shifts were! Makes the 4l60 feel like a real slosh box lol

Haha! We were discussing what you just mentioned on another thread...

 

[ShookieJay]

I did a 5.3/4L80e swap on my 99 Silverado NBS ECSB 2wd. It originally came with a 4.3...think SLOW!

On those trucks it's very easy because the driveshaft is 2 piece and the center bearing support has slots for adjustments. The only thing different is a special yoke that fits the output shaft of the 4L80e but has the ears for the stock S44 u joint. No driveshaft shortening.



Haha! We were discussing what you just mentioned on another thread...

So you know exactly what I mean! At the bare minimum I'd like to ditch the slosh box. Sure it'd be cool to have a little extra power, but the trans alone would be an absolute godsend. Unfortunately the Tahoe has a 1 piece driveshaft (although I haven't gotten underneath the donor to see what it has) but based on what you're saying I'd assume it's a 2 piece

 

[strutaeng]

So you know exactly what I mean! At the bare minimum I'd like to ditch the slosh box. Sure it'd be cool to have a little extra power, but the trans alone would be an absolute godsend. Unfortunately the Tahoe has a 1 piece driveshaft (although I haven't gotten underneath the donor to see what it has) but based on what you're saying I'd assume it's a 2 piece

Most likely 2 piece. What cab/bed configuration is it?

The only thing you have to do is swap the flexplate from the LQ4 to your 5.3. Everything else is pretty much the same.

You can repin the existing round case connector of your transmission to the 4L80e and likewise repin at the ECU connector. It's not bad at all; there's already wiring in the harness you can use. I can send you some information.

Then just get a transmission "segment swap" on your existing ECU.