6L80 Transmission unusual behavior?

9731 Views 20 Replies 8 Participants Last post by Zeeman, May 9, 2022

rviscuso

Discussion Starter · Feb 12, 2022

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

Truth in advertising: I posted this at the gmtrucks site but only got a few responses then I saw all the 6L80 posts here, so here I am.

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, I think; not 100% sure.

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?

Also for what it's worth I found this site this morning:

www.sonnax.com

6L80, 6L90 Transmissions: Consider an Updated Converter in Your Next Rebuild | Sonnax

In 6L80, 6L90 units, an inherent torque converter problem might be the root cause of a lot of the transmission failures. Sonnax has the answer.

www.sonnax.com

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Reactions: 2

1 - 20 of 21 Posts

swathdiver

· #2 · Feb 13, 2022

We generally don't experience these problems with the previous generation. I reckon that you're going to need another torque converter. Your transmission has a thermostat that keeps it as hot the coolant and it's killing these converters and burning up the bands. "Flip the pill" or put in the newly released lower temp thermostat. Run the severe service schedule from now on, earlier if you've been towing.

Best part of my BlackBear tune is in how they tuned the transmission, see if they can do yours.

18silveradocustom

· #3 · Feb 16, 2022

Yeah I have the same problem with my 2018 6-speed how did you get them to replace the converter because I get shovel mine slips sometimes it it doesn't go anywhere I give it gas it hesitates for a few seconds and then it goes and this is only with 28,000 miles on it

18silveradocustom

· #4 · Feb 16, 2022

Correct me if I'm wrong but I thought it has a clutch to clutch or something to something shifting there are no bands in the new 6-speeds . It's direct clutch to clutch or clutch the gear something but there are no bands at least in an 18 that I know of I just googled it

Reactions: 1

swathdiver

· #5 · Feb 17, 2022

That's right, no bands.

RedSLEd

· #6 · Feb 17, 2022

Could it be related to AFM engaging/disengaging, possibly in conjunction with the TCC unlocking and/or the transmission downshifting?

Reactions: 1

rviscuso

Discussion Starter · #7 · Feb 17, 2022

Well I had to go back and read my service documentation. The first time I complained about the transmission, 3791 miles, the service advisor researched and found TSB 17249. This is where "chuggle" came from. The tech reprogrammed the transmission according to 17249 and 18120. This was to prevent a chuggle sensation when limited or zero torque converter slip is commanded. Whatever that means. Well it didn't solve the problem. I returned a few months later at 10,000 miles and the tech confirmed the chuggle. That resulted in the torque converter replacement. The chuggle was very obvious; it felt like the engine was severely missing, lots of stuttering and stumbling under light throttle or inclines or light loads.... as I recall.

I do not recall seeing AFM switching between 8 and 4 while this is happening. I DO know that AFM transition from 4 to 8 is very smooth. I am trying to remember if putting the transmission in manual mode sixth gear made any difference. I will have to try this.

RedSLEd

· #8 · Feb 17, 2022

M6 won't make any difference. Try driving in M5 for a few days to see if anything changes.

Reactions: 1

rviscuso

Discussion Starter · #9 · Feb 22, 2022

Took a drive today. M5, on the freeway, slight acceleration and deceleration resulted in slightly less rpm movement, maybe 100 rpm's, and hardly any lurching. I put on cruise control and M5, no lock unlock, no rpm's moving up/down and no lurching. I don't understand what is happening; why CC and M5 prevents TC unlock/lock.

Regarding AFM and TCC unlock/lock. I tried paying attention to the tach and the V4 V8 indicator; boy it was hard for me to drive and watch the two but it seems like they are related. When I see rpm's rise/fall then try to look at the AFM display it seems like the two were tied together. Seems like, cuz I am not 100% sure.

Reactions: 1

RedSLEd

· #10 · Feb 22, 2022

rviscuso said:
I put on cruise control and M5, no lock unlock, no rpm's moving up/down and no lurching.

That is what should happen. M5 doesn't prevent TCC lock or unlock. Neither does CC. M5 only prevents AFM. Acceleration, depending on conditions, will unlock the TCC. That is likely the 100 rpm changes you observed. On the hwy in M5 and cruise on, your TCC should stay locked unless you're going up a hill or trying to accelerate.

Motion427

· #11 · Feb 23, 2022

On a factory tune, the TCM will let the converter slip in any forward gears for a smooth transition of the AFM on/off and apply/release of the throttle while cruising,etc....For more performance or when a aftermarket converter is installed,the slip has to be reduced(stock converter) or eliminated(aftermarket converter) so that it can do it's job correctly and survive the abuse.

rviscuso

Discussion Starter · #12 · Apr 24, 2022

I kept my eyes on the dash lately watching AFM switch between 4 and 8 at freeway speeds. Sure enough that was tied to the rpm's moving up then down and feeling the lurch. I guess my memory is not as good as I thought it was. Going to the dealer tomorrow for an oil change and to have them check out this problem.

Reactions: 1

Leveled17yeti

· #13 · Apr 24, 2022

Would the latest Tsb fix your issue replacing the thermostat with one that opens at 164 I believe. Instead of the one that opens at 194🤷‍♂️

swathdiver

· #14 · Apr 25, 2022

Getting a lurch with AFM engaging and turning off? How is your driver's side engine mount? I would suspect the VLOM; this can be tested with a bi-directional scan tool like the MDI and a laptop running GDS software.

rviscuso

Discussion Starter · #15 · Apr 27, 2022

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.

Reactions: 2

Leveled17yeti

· #16 · Apr 28, 2022

Prob wouldn’t be a bad idea to have the TSB done for the new trans thermostat 😎

Reactions: 2

rviscuso

Discussion Starter · #17 · 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.

Reactions: 1

Leveled17yeti

· #18 · May 3, 2022

I’m ordering the transmission thermostat .the new one apparently they will run around 135-145 big improvement over 190🤬🥵

Reactions: 2

MikeB

· #19 · May 3, 2022

I modified the thermal bypass valve on my 2016 Silverado 6L80E transmission using the Superior Transmission STL010 valve rebuild kit. My transmission fluid temperature around town used to run 191°. Now it is holding at 144°.

Reactions: 2

Leveled17yeti

· #20 · May 4, 2022

That’s more like it mine is just still within warranty 😂😈

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