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2015 1500 5.3 6L80 Swap to 8L90

MrRosado

By MrRosado
in Engines & Drivetrain

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MrRosado New Member

MrRosado

Posted
Posted

I apologize in advance if this is covered in a different topic.

 

I've been researching to see if it's possible to swap the 6L80 transmission in my 2015 Silverado 1500 CC 4x4, 5.3 V8 with the 8L90 transmission.  I haven't been able to come up with a definitive yes or no answer. "I'm sure if you throw enough money at something anything is possible".

 

Asking because I have access to a 8L90 and wanted to know if it's a pretty straight forward swap, or is it more trouble than it's worth. If I could get some insight into what would be necessary to complete this swap it would be greatly appreciated. i.e. ECU updates, driveshaft adjustments, wiring harness, bell housing adapter, etc. 

 

Thank you in advance for your time in replying to this post.

 

P.S. I am aware of the issues with the 8L90. Just looking for what it takes to make the swap happen and not a reliability comparison between the two transmissions. 

CamGTP Senior Enthusiast

CamGTP

Posted
Posted

You'd need the harness for it because it uses a different TCM. So the TCM is also needed. I would guess that you need the torque converter obviously and the correct flex plate.

 

The factory computer could be programmed. You would have to use a 5.3/8L90e calibration file. They sold the Denali trucks and maybe even the LTZ/high country trucks with that combo. This would take someone with some know how in the tuning/calibration department and access to these types of files just to see if it could work.

 

Thinking about it more I'd think something with the BCM would have to be re-programmed as well because the clusters manual mode only goes to M6.

 

So if you ask me, yes it can be done but it's not worth the effort unless you have lots of downtime and know a lot of people in the right places to get this job done.

nominion Enthusiast

nominion

Posted
Posted

As noted above, it's possible.  Likely not straightforward though. 

 

Are you considering the 8L90 to replace a failed 6L80?  Or are you considering it as an "upgrade" to a working 6L80?

 

If the later, it's not worth it at all, in my opinion. 

hammong Enthusiast

hammong

Posted
Posted

^^^  This.   The 6L is a superior transmission IMHO, and I wouldn't want to "change" the 6L80 to an 8L80 regardless of possibility or cost.  If the 6L failed, get it fixed or replaced with the same. 

flyingfool Senior Enthusiast

flyingfool

Posted
Posted

Richard Wardell will tell you how to do it, he's on youtube, so you'll have to track him down to get his shop phone number. 

 

L86 All Terrain Senior Enthusiast

L86 All Terrain

Posted
Posted

I have had 2 6L80e's and 1 8L90e. The 6 speed is the better trans. 8 speed is great when it works right but it seems like 1/5 trucks with the 8 speed actually work properly. Not worth the swap IMO, even if free. Never had an issue with the 6L, my 8L needed a new TC then eventually the whole trans was replaced. Shifts nice now, love the trans but the juice isn't worth the squeeze. Going back to 4L85e would be a better mod honestly, you could even put a transbrake in those old units. 

  • Like 1
MrRosado New Member

MrRosado

Posted
  • Author
Posted

Thank you for the feedback. It's greatly appreciated. To answer a few questions. My 6L has not failed. However, I am getting a shutter or shake after the truck is shut off. It doesn't always happen, but usually about 3 seconds or so after the truck shuts down. If a transmission replacement is in my future I just wanted to see my options. I wanted the 8L90 mainly for the fuel economy gains. I don't tow much, but the truck spends a lot of time in 4WD in the winter here. A friend of mine has 2017 1500 with the 6.2 and gets 21 mpg on the regular. Kinda sucks to get 17 mpg on a good day with my 5.3. Thanks again for everyone's input. 

flyingfool Senior Enthusiast

flyingfool

Posted
Posted

you wont gain any mpg improvements by switching to the 8 speed, it has more torque multiplication , so you can put big tires on it, but unless it's a last model trans with the upgrades built into it, your gonna get ****ed on it... your better off installing highway gears in the diff and running a 17" rim on a 33" tire and doing a lowering job on the truck, then rebuild the 6 speed. less head aches.

 

the 8 speed  is just filling in the holes in the shifts more so than the 6 speed with the wider shift pattern.  i agree a beefed up 4L80 would be a better trick.  you might like the wider shift pattern of the 4 speed better.  just re-gear the final to hit your target load and highway speed your after.

flyingfool Senior Enthusiast

flyingfool

Posted
Posted

another post about 8 speeds, these transmissions seem to like to tear up the bushings, and the support for the torque conververter  get's roached. they're also overheating them due to running the thermostat in the cooler line.  sounds like a money pit

 

 

 

  • Like 1
flyingfool Senior Enthusiast

flyingfool

Posted
Posted
3 hours ago, Inacanyon said:

Camaros running 9s on original 8l90 trans no issues. How are they such a problem?

camaros aint pulling trailers or running 35" tires either. its a light weight car so the torque loads are much less.  who knows if the  camaro has better tcu software programming and a deleted thermostat on the cooler. one might want to look into flashing a camaro trans program into the truck tcu. this could improve line pressure and lubrication on the trucks.  

 

truckguy82 Senior Enthusiast

truckguy82

Posted
Posted

I’ve rented a ‘16 camaro ss auto and I’ve driven a 6.2 denali 8sp numerous times. I punished that camaro for a week.

 

both 6.2’s with 8 speeds

 

It is absolutely amazing that it is the same trans. They don’t feel remotely similar. The camaro shifts are so much faster and more aggressive.

 

The 1-2 shift in the camaro feels like you got rear ended by a bus in comparison. 8l90 is amazing in the camaro, I’ve asked numerous people on the differences and nobody knows.

Doublebase Enthusiast

Doublebase

Posted
Posted

6 speeds are no bargain either, there’s a thread on here about how the torque converter shudder tears up the pump, sending metal pieces through the transmission. Two GM techs on that thread say they don’t see 8 speeds in for repair, but 6 speeds all day long. I have the 6 speed it’s starting to shudder with only 47,000 miles (and two transmission services done to it). They both probably suck, pick your poison.

flyingfool Senior Enthusiast

flyingfool

Posted
Posted

higher stall on the camaro Torque converter , bumps line pressure to the trans pump way higher i would imagine, need to data-log the trans on both vehicles to confirm

truckguy82 Senior Enthusiast

truckguy82

Posted
Posted
10 hours ago, flyingfool said:

higher stall on the camaro Torque converter , bumps line pressure to the trans pump way higher i would imagine, need to data-log the trans on both vehicles to confirm

If that’s all it is, anybody who doesn’t tune their 8l90 is missing out big time

 

It’s awesome in the camaro.

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