6L80 Transmission unusual behavior?

rviscuso · February 8, 2022

2017 Silverado LT 5.3 4X4 6speed transmission 51,000 miles

When I first bought the truck the transmission suffered from severe bucking or shudder under light load. GM calls it chuggle. The cause was "intermittent tcc delamination causing scoring on fluid pump". They replaced the torque converter, cover housing and pump cover along with a flush. This was at 10,000 miles. That seemed to solve the chugging problem.

For the last year or so I have noticed that the torque converter unlocks and locks frequently at freeway speeds. When it locks, following an unlock, there is a noticeable lurching forward. This is not neck snapping but is definitely noticeable. This lurching motion also occurs when upshifting 4/5 or 5/6.

While driving at freeway speeds (65 70mph) when I slightly let off the accelerator the rpm's rise about 200 then settle down. If I should slightly press down the same thing happens. However, when driving at a steady freeway speed, and holding steady on the throttle, on level ground I can feel this unlock/lock along with seeing the engine speed move up then settle down. If I engage cruise control on level ground it is worse and occurs more often. But, with cruise control on and there is a slight road incline there is no unlock or downshift. When I press hard on the throttle then it downshifts and accelerates fine.

Locking/unlocking and lurching; I do not recall the transmission behaving like this in the early years. The dealer says if it doesn't throw a code then it is operating normally. I can see that there are times when it should unlock such as when under load, but should it be this happening this frequently and be so noticeable? Or maybe I am being too sensitive?

Anybody experience the same thing? Is this normal transmission behavior?

CamGTP · February 9, 2022

Doesn't sound normal to me. My opinion says that this torque converter is on it's way out too. It just hasn't gotten bad enough to start throwing codes yet.

newdude · February 9, 2022

Torque converter sounds like she toast. Time to drop the pan and look for lots of clutch material.

rviscuso · February 10, 2022

Thanks guys. I purchased the truck on July 2, 2017. With less than 52,000 miles and less than five years have gone by the drivetrain is still under warranty.

How do I get what so far has been a reluctant dealer to take action?

newdude · February 10, 2022

16 hours ago, rviscuso said:

Thanks guys. I purchased the truck on July 2, 2017. With less than 52,000 miles and less than five years have gone by the drivetrain is still under warranty.

How do I get what so far has been a reluctant dealer to take action?

Get them to have a tech or advisor ride with you and show them what its doing. Or, have them throw a data recorder on it. That should be enough to at least get them to drop the pan.

Edited February 10, 2022 by newdude

rviscuso · February 10, 2022

newdude, I like the idea of a data recorder. Thanks! I have an oil change coming up so will double up on that visit.

Jx16ElevationEd · February 28, 2022

Same issue just started this weekend ...

96k miles on the truck.took it to shop metal on pan torque converter plate cracked. Faith full services thru and thru and now it will be $3400 for rebuilding trans and torque converter.. It's a bad issue in the 6L80s. Sadly the newer 8 speed gm trains issues have masked ours..

Caleb Barrett · April 12, 2022

I will say there are better options out there than just taking it to a local transmission shop. When my 6l80 went out completely (I was out of warranty unfortunately) I went to 3 transmission shops, all of which were in the 4-4.5k price range. I ended up just ordering a remanufactured 6l80 which had the factory defects amended (supposedly) with free shipping to my shop for like 2600 bucks. Got it from what's now these guys, https://reman-transmission.com/transmission-codes/?code=6L80. Shop only charged 650 to swap them out so ended up saving some money and it's been a little over a year now without any issues.

swathdiver · April 12, 2022

Forget the warranty and put a billet torque converter in there with a new lockup o-ring. Make sure Sonnax parts were used.

B & I Torque Converters in Oklahoma City are well thought of.

Don't be held hostage by a warranty.

pokismoki · April 12, 2022

the locking and unlocking converter could be the failure of the o-ring seal on the pump stator.. also a big failure point is the PR valve in the pump usually it wears out the lands on the valve, sheds metal, put a 200-300psi pressure gauge on the transmission and note the pressures compare to the specs from a rebuild manual

Edited April 12, 2022 by pokismoki

rviscuso · April 21, 2022

On 4/12/2022 at 8:31 AM, swathdiver said:

Forget the warranty and put a billet torque converter in there with a new lockup o-ring. Make sure Sonnax parts were used.

B & I Torque Converters in Oklahoma City are well thought of.

Don't be held hostage by a warranty.

I found this on Sonnax. Is this what you referring to?

https://www.sonnax.com/tech_resources/845-6l80-6l90-transmission-tech-advisory-consider-an-updated-converter-in-your-next-rebuild

swathdiver · April 22, 2022

7 hours ago, rviscuso said:

I found this on Sonnax. Is this what you referring to?

https://www.sonnax.com/tech_resources/845-6l80-6l90-transmission-tech-advisory-consider-an-updated-converter-in-your-next-rebuild

Exactly!

rviscuso · April 27, 2022

I brought the truck in for oil change and transmission diagnostic. The short answer from the dealer is working as designed. The tech, 30 years experience with transmissions, drove the truck before the oil change then he requested we both go for a test drive afterwards. I pointed out when AFM kicked in/out and the rpm's moved; I could see the smile on his face. Yes that is normal. He went on to explain the balancing act between engine/transmission for optimum fuel combustion. These transmissions are constantly adjusting. I have faith that there was no BS here. No codes were present. His parting words, again no BS, was that my truck drove better than 90% of the trucks he sees in the shop. I will add here that they waived the $199 tranny diagnostic fee.

I have 43,000 miles on the TC replacement. With two months left on the warranty, I will bring the truck in for a transmission pan drop fluid/filter change. If there is excessive metal then we will discuss what action to take.

rviscuso · May 3, 2022

I had the transmission serviced today; new filter and six quarts. The technician let me in the shop while the pan was down. The old filter inlet looked clean. The magnet had a collection of normal clutch wear material. All is well. I guess I'm getting a bit sensitive in my older years. He said to come back in a few years and get the fluid changed.