6L80 TCC Slip fluctuations

[ksherma3]

Been dealing with and researching this subject for 25mos. Most of the answers have been given in the above replies, hopefully this adds to them? It appears GM set the Torque Converters to sliplock in these vehicles actually starting in 1st gear at a certain throttle position and speed, and starting with too low of a psi to actually attain lock. That combined with the fact that the JMBX TC they chose has a clutch plate and housing that don't mate up well. It's kind of like stacking two dinner plates of different design. Because of that the clutch material doesn't make contact across it's full width. Kind of like dropping the needle in the middle of the music grooves on an old vinyl and only ever playing that portion of the music. IMHO, either one of those flaws could've survived on its own but the combo causes the clutch material to wear off after 80-120k mi and eventually will cause the TC to grenade taking the tran, the lines and the cooler with it.

The quick answer is: It's only going to get worse as more and more of the clutch material wears off. With stock settings you can prolong the inevitable by driving in M5 with tow/haul mode engaged to prevent the TCC from trying to lockup -or- research the settings in either of these attached videos and set yours to what you're comfortable with.

I've emailed and spoken to engineers at Sonnax(multiple), GM, Lube Guard, and Valvoline. Spoken to local dealer$hip along with every trans shop in 50mi radius. Paid $93 for confirmation of problem to the only trans shop around me that was willing to do what I asked: confirm problem, if TC then replace TC, clean and inspect 6L80, add shift kit and add a few other upgrades I wanted in 6L80, and TUNE OUT the TCC lockup in the lower gears and raise the pressure when locking it. Turned out he wouldn't tune the trans after all...smh

In the last year or so I've noticed 6-8 new videos that ACTUALLY SHOW the fix, but none, IMHO, explain it as well as the original. I've got a folder with 12-15 of the best articles and vids I've seen on this subject, be happy to share more if you want? Here's the original vid and prob the best article describing the what's why's and how's of the problem and in the video, the HP Tuners fix used:

26min long but worth every second
https://www.youtube.com/watch?v=XnsdK2N2an4

excellent write up, must click on and enlarge pics to see
https://gearsmagazine.com/magazine/t...om-bob-warnke/

**This subject is how I found out HP Tuners exists and why I'm here. This is my 1st post lol.

Here's a vid I found the other day that may be more applicable to your solution? You may be early enough to not have to have overhaul on your trans? I would bet you are based on your descriptions of vibrations, but only you can decide that? Skipped through this guy's HPTuner settings, but I've watched Hiram's 5-6 times. I may even go one further than Mr Gutierrez and disable TCC lock in 5th gear also?

https://www.youtube.com/watch?v=sag3h2AQ2uU

Good luck and please follow up with what you do and the results....

I feel the need to post here and share that this info seems to have fixed (at least temporarily) my wife's 2017 Chevrolet Suburban with the 6L80.

We first had issues with this vehicle at 120k miles. On the interstate on a 5-6 upshift the transmission gained another neutral and the CEL illuminated. Pulled off to the side of the road, turned it off and back on, and everything was fine. Arrived home to find that we had a P0796 code for Pressure Solenoid C Stuck Off. Started doing some research on this and found mostly "it's toast replace transmission posts" as one often does on automotive forums anytime an automatic has an issue.

I checked the fluid level and condition and it was black and smelt terrible. Parallel to this while researching, I found this post on justanswer.com with GM's guided diagnostics: https://www.justanswer.com/chevy/ij1...olenoid-c.html.

So at this point I order 4 gallons of Valvoline Maxlife Multi-Vehicle Dexron VI and 2 transmission filters and go about doing a flush in my driveway per the GM guided diagnostics. P0796 code is gone, clean fluid, no material in the pan. So then we drive it and start to very occasionally get a rumble strip sensation when lugging the engine at ~1000RPM in 5th-6th. So, back to the internet. I eventually find a thread on bobistheoilguy.com detailing the rumble strip sensation and how GM's fix is to flush 3 times with Mobil Synthetic ATF LV that is specific to Dexron, and one guy added a bottle of Lucas to the fluid and it went away. In an act of desperation I added a bottle of Lucas and while it improved it, it did not fix it. Further research led me to one guy on a forum somewhere say "just turn off lockup in 1st-4th and disable sliplock in 5th and 6th." This was a bit of a eureka moment for me so I download a 6L80 tune from the repository and start investigating how to figure this out.

After loads of research and some help from the above videos I diagnosed our issue as TCC slip, and want to better detail what is going on in this post as the above videos don't do a great job of it. The long and short of it is that GM has calibrated the TCM to pretty much always partially lock the TCC's wet clutch, allowing anywhere between 20-40 RPM of slip when cruising down the highway. Eventually this is causing early TCC's to overheat and warp, thus causing too much slip. GM's factory settings for the PID controller on the modulated line pressure are both too low and too slow to overcome a worn clutch after ~100k miles, and that is why many owners are now having the issue.

So, the tune I have attached to this post disables torque converter lockup altogether in 1st through 4th in an effort to preserve the little bit of life left in this TCC clutch, as well as demanding zero slip while in 5th and 6th lockup. In addition, I have increased the apply ramp rates so that as more slip occurs, pressure is added to the clutch much quicker than factory settings and increased the minimum pressure demand when in lockup to 417-470kPa. There is a noticeable improvement to drivability with this calibration and also very little slip reported by the TCM.

I'm unsure what the root cause of my P0796 code was but at this point it appears to be fixed. My assumption is that the deterioration of the TCC clutch caused the dirty fluid and contaminated the pressure solenoid line, allowing me to find this failure before it reached the point of no return. I don't want to advertise this as a fix once the rumble strip effect is there; I plan to install a new torque converter ASAP. I do feel this will mitigate the TCC clutch issue for the time being and will be utilizing this calibration with our new torque converter.

I also disabled AFM at the same time I changed the TCM settings, mostly just to prevent lifter failure.

I hope this helps someone else who is in the same situation I was 2 weeks ago.

Here is a log file at cruise with factory settings:
Cruise_Factory.png

Here is a log file at cruise with these settings:
Cruise_SlipFix.png

[NotSure]

Take a look at my post in Nov 2020 on TCC Regulator Gain on the topic of tcc slip.

https://forum.hptuners.com/showthrea...0e-in-a-patrol


You also want to be cautious on tcc ramp rates, as I understand that there are mechanical failures with these tcc components as well. I found a youtube video from Southern IL University that discussed this topic, IIRC.

[mikez71]

Hello forum members, new here. (2012 Tahoe) 1 quick question if I may..

How much pressure on a stock 6l80 only locking in 5&6? (I might lock 4th)
Stock is 1.5 regulator gain and 26.69psi offset..

I have disabled TCC in 1-4..(now 1-3, felt like cruise was too slack) mainly bumping up the 0-25% shift schedule and corresponding lockup times in 5&6.
I have heard too much pressure can warp the stock clutch. 203K miles on what I believe to be the original drivetrain. Turned off AFM/DOD.
Very happy with initial results! Thank you HPTuners! Will take any pointers you may have for reliability and bog/lag reduction. Thank you!

Mike

[ksherma3]

I feel the need to post here and share that this info seems to have fixed (at least temporarily) my wife's 2017 Chevrolet Suburban with the 6L80.

We first had issues with this vehicle at 120k miles. On the interstate on a 5-6 upshift the transmission gained another neutral and the CEL illuminated. Pulled off to the side of the road, turned it off and back on, and everything was fine. Arrived home to find that we had a P0796 code for Pressure Solenoid C Stuck Off. Started doing some research on this and found mostly "it's toast replace transmission posts" as one often does on automotive forums anytime an automatic has an issue.

I checked the fluid level and condition and it was black and smelt terrible. Parallel to this while researching, I found this post on justanswer.com with GM's guided diagnostics: https://www.justanswer.com/chevy/ij1...olenoid-c.html.

So at this point I order 4 gallons of Valvoline Maxlife Multi-Vehicle Dexron VI and 2 transmission filters and go about doing a flush in my driveway per the GM guided diagnostics. P0796 code is gone, clean fluid, no material in the pan. So then we drive it and start to very occasionally get a rumble strip sensation when lugging the engine at ~1000RPM in 5th-6th. So, back to the internet. I eventually find a thread on bobistheoilguy.com detailing the rumble strip sensation and how GM's fix is to flush 3 times with Mobil Synthetic ATF LV that is specific to Dexron, and one guy added a bottle of Lucas to the fluid and it went away. In an act of desperation I added a bottle of Lucas and while it improved it, it did not fix it. Further research led me to one guy on a forum somewhere say "just turn off lockup in 1st-4th and disable sliplock in 5th and 6th." This was a bit of a eureka moment for me so I download a 6L80 tune from the repository and start investigating how to figure this out.

After loads of research and some help from the above videos I diagnosed our issue as TCC slip, and want to better detail what is going on in this post as the above videos don't do a great job of it. The long and short of it is that GM has calibrated the TCM to pretty much always partially lock the TCC's wet clutch, allowing anywhere between 20-40 RPM of slip when cruising down the highway. Eventually this is causing early TCC's to overheat and warp, thus causing too much slip. GM's factory settings for the PID controller on the modulated line pressure are both too low and too slow to overcome a worn clutch after ~100k miles, and that is why many owners are now having the issue.

So, the tune I have attached to this post disables torque converter lockup altogether in 1st through 4th in an effort to preserve the little bit of life left in this TCC clutch, as well as demanding zero slip while in 5th and 6th lockup. In addition, I have increased the apply ramp rates so that as more slip occurs, pressure is added to the clutch much quicker than factory settings and increased the minimum pressure demand when in lockup to 417-470kPa. There is a noticeable improvement to drivability with this calibration and also very little slip reported by the TCM.

I'm unsure what the root cause of my P0796 code was but at this point it appears to be fixed. My assumption is that the deterioration of the TCC clutch caused the dirty fluid and contaminated the pressure solenoid line, allowing me to find this failure before it reached the point of no return. I don't want to advertise this as a fix once the rumble strip effect is there; I plan to install a new torque converter ASAP. I do feel this will mitigate the TCC clutch issue for the time being and will be utilizing this calibration with our new torque converter.

I also disabled AFM at the same time I changed the TCM settings, mostly just to prevent lifter failure.

I hope this helps someone else who is in the same situation I was 2 weeks ago.

Here is a log file at cruise with factory settings:
Cruise_Factory.png

Here is a log file at cruise with these settings:
Cruise_SlipFix.png

We've got about 15,000 miles on a new TCC and Sure-Cool thermostat bypass since I made this post, with no new transmission issues.

After replacing the TCC the line pressure and apply ramp rate changes I made resulted in a too harsh lockup. In addition, no lockup in 1st-4th resulted in transmission temperatures getting hotter than I was comfortable with while cruising on backroads when not in lockup gears. I reverted the tune back to factory settings, with the exception of leaving the slip demand at 0 RPM. I've been happy with it since.

[zukirider1]

How did your tune do until you got your new TC? I'm thinking about using your tune example as far as the gain and offset. 75K mile 6l80 in Silverado. So far I've tuned out TCC til 4th gear. Tried zeroing out the slip but it just made the bucking harsher.

[mikez71]

The '15-'18? 6l80 has some tuning differences.

I felt the same as ksherna3 regarding no lock in 4th. In addition to the heat, cruising was less pleasant with it unlocked. (letting off throttle to slow down, then re-applying throttle would then need to catch up to stall speed again. Too much slack in between little throttle changes.)

Slip tables all 20rpm in my 2012, but the newer ones have an area that is 15 and then 10rpms slip at higher torques.

A/C on slip is updated to 3 rpm vs 8 rpm. I've been meaning to log commanded/actual slip with A/C on/off to see what changes.

From what I'm reading in the thread below, the factory clutch material is designed to slip and doesn't hold up well when tuned to 0 slip.

https://forum.hptuners.com/showthrea...ity-and-towing

[hjtrbo]

From what I'm reading in the thread below, the factory clutch material is designed to slip and doesn't hold up well when tuned to 0 slip.

https://forum.hptuners.com/showthrea...ity-and-towing

Don't be spreading internet forum bullshit.

How on earth would a clutch disc destroy itself at 0rpm slip vs 5rpm.

Rob pointed out clamping pressures and apply rates.

[mikez71]

Apologies hjtrbo! Let's clear this up. I was comparing the 20rpm slip vs 0rpm.
Argument I've heard, the cover deforms under too high a pressure.

Perhaps I misunderstood this statement TransgoRobert..
"..requires between 25 and 45 psi to maintain 20 RPM of slip while cruising. In order to make it lock completely, you have to crank up the apply pressure quite a bit, usually north of 65 because the lining is just not meant to do that and never makes a perfect seal against the cover. Many tuners bring it much higher than that because the tuners don't know any better not being well verse into the principal of operation and they hydraulics involve."

Are you saying the stock clutch and cover can handle 0 slip safely? And that he meant tuners who "bring it much higher than that" ~65psi?

Also said this somewhere..
"The carbon woven lining is very brittle and designed to slip without wearing out, but it is super brittle . the extra pressure required to make it not slip and the increase rate of apply is hard on it and it often will crack and lose chunks of it causing the TCC to start slipping after many thousandths of mile with this modification. "

I've seen some cases where people 0 the slip and are happy, then some that 0 slip and claim it's worse.
Perhaps the ones with problems have other issues, as zuckirider1 above mentioned 'bucking' which doesn't sound like a 'too much slip' issue.. ?

Appreciate any clarifications/suggestions you can make!!

2018 TCC settings shown below
2018tcc.png

Looks like 15 and 10 slip at higher rpms, 5 and 0 slip at higher torques.
vs. my 2012 5.3 6l80, which has 20 in all cells.

[hjtrbo]

Robs comments are good. Unfortunately all my comments up until his valued input are likely still to be referenced. He has since made me re-think what I do in the tune.

I have backed a fair bit of pressure out in the load areas where it's not required. All said, I'm still running with 0 slip everywhere, but I plan on re-introducing slip at low load low rpm next time I'm out with the laptop just to kill a bit of the NVH inherent with cammed motors. I call it a compromise.

I have seen logs where the tcc pressure aggressively ramps up and down as the tcc slip saw tooths from 0 to ~20rpm. To me that is one of a myriad of situations where Robs comments are applicable and should not be ignored. WRT a suggestion of a blanket ban on 0 slip being the new forum gospel, until a day comes where I or one of my friends have chunks of friction material buried into every crevice of the transmission, I'm not on board.

[mikez71]

Got it, thank you for the clarification! I feel much better about giving 0 slip a try (without messing with other pressure settings for now!)

Thinking about leaving some slip.. maybe in the lowest torque row, or even something similar to the 15+ to keep from feeling any engagement bump, if you have any tips for that.

Also, I lied about my '12 being 20 slip in every cell..
I may have accidentally compared files after loading the incompatible '15+ tune..
'12 stock slip tables shown below
2012tccslip.png

[mbramlett2]

I am getting a vibration that I believe is a faint TCC shudder. I disabled TCC in normal so I could drive to work and I am pretty sure I am feeling a difference but it can be hard to tell on some of these roads. So I decided to log TCC slip on my way to work today. I had left the TCC active in tow/haul so it is in tow/haul in the log. I seems to me the trans is struggling to control the TCC Slip with all the fluctuations and spikes after going into V4 mode. However, I have not been able to find an example of what TCC slip should look like. Does this look like an issue?

Stock 2016 Silverado 5.3 & 6L80

Thanks

Try this file. I made some basic changes to your file. 16_Silverado TCC disable except in tow haul.hpt

[mbramlett2]

I am getting a vibration that I believe is a faint TCC shudder. I disabled TCC in normal so I could drive to work and I am pretty sure I am feeling a difference but it can be hard to tell on some of these roads. So I decided to log TCC slip on my way to work today. I had left the TCC active in tow/haul so it is in tow/haul in the log. I seems to me the trans is struggling to control the TCC Slip with all the fluctuations and spikes after going into V4 mode. However, I have not been able to find an example of what TCC slip should look like. Does this look like an issue?

Stock 2016 Silverado 5.3 & 6L80

Thanks

I would also recommend you disable DOD in the ECM.