6L80 Torque Converter and Tuning

[TransGo Robert]

Sorry for the hijack...but it's a year-old thread, and fits my situation exactly.

(2015 GMC Sierra Denali, 6L80, 148,000 miles.)

Bought my truck with 115,000 miles on it, and had the transmission serviced, including dropping the pan for new fluid. No issues were reported. 20,000 miles later I started to have severe low gear hunting, as well as intermittent rumble strip noises. A trip to the tranny shop revealed much shaving carnage, resulting in a complete rebuild, stem to stern, $4,500, with quality individual parts. The shop explained the problem, and indicated they see it often with the 6L80.

All was fine for several months, until it was not. Repeated but intermittent rumble strip noises kept happening. Back to the tranny shop, where they swapped out both the torque converter and the valve body techum assembly. Again, fine for several months, but the rumble strip noises (TC lock-out?) persisted, as well as some noticeable low-gear hunting.

In an out-of-state location from my tranny shop, we collaborated to find a shop that did an HPtune. All was well on the test drive, I was confident in the discussion with the HPtuner guy, and anxious to drive 800 miles back home. But, alas, while no problems occured below 50 mph, the DAMN rumble strip noises were now occurring at 55, 65, and even 75 mph...depending on rpms and terrain pitch...all the way home!

My original shop (out-of state in another direction) intends to get it right, but I am quite frustrated. Until I can bring it back to them (probably for a third torque converter!), they recommended a Motocraft product called Friction Modifier Additive. Although it appears to be helping, I am not confident how long it may last, or if it actually cures the problem.

In the above discussion, the guy asks if tuning off the lock-out on gears 1-4 works so well, why can't you do the same for 5 & 6?
Is the proper fix to buy the beefier torque converter, or replace it with the 6L90?

First post, so thanks in advance for any opinions or advice on my dilemma.
I love the truck, but am seriously considering a trade-in.

You need the converter to lock or else it would overheat like crazy when you are in overdriven ratios, most of the heat in a transmsision comes from the converter when it is open aka unlocked. The issue you describe is either caused by active fuel management or more then likely the wrong lining used in the converter. The additive will take care of it if it is the wrong lining and surprisingly it will usually work well for a long time.

[ajs67donzi]

You need the converter to lock or else it would overheat like crazy when you are in overdriven ratios, most of the heat in a transmsision comes from the converter when it is open aka unlocked. The issue you describe is either caused by active fuel management or more then likely the wrong lining used in the converter. The additive will take care of it if it is the wrong lining and surprisingly it will usually work well for a long time.

Thanks for the reply, Robert!

The AFM has been disabled. I bought a plug-in when I had the transmission rebuilt, and the HPtuner guy also disabled this useless (and harmful) feature, then he bought my plug-in from me. So, all indications point to the torque converter...again!

If I can get my shop to research and install the heavier-duty torque converter, that would be one option. They are still honoring the original transmission replacement, and vow to "make it right" for me.

Keeping the truck as is, and hoping for the additive to work long-term, makes me less confident...always worried that the problem resurfaces down the road. By then the warranty from my original rebuild will be expired, and I'd be back to square one.

[NCbudgetBuilder]

Your torque converter is probably on it's last leg. I had less than 60k miles on a rebuild and mine did the same exact thing, I narrowed it down to the torque converter and replaced it. No more rumbles now.

[GHuggins]

Root problem on the fifth gens is actually the engine side. Especially with high miles - ever think why they last just fine till they get in the 120,000 range? Then it's repeat failure after failure. I actually hear this a lot with customers.

Look at your fuel trims. Guarantee your injectors are worn and your running rather negative trims. This throws the fueling off which in turn causes fuel to be pulled and inevitably lowers the line pressure on the trans via the new torque model calcs. If you catch it early enough you can sometimes add 5 or 10 % to the torque model and everything will be fine again or you can keep building transmissions.

The truly correct thing to do is to perform a heavy induction clean, swap the plugs and fuel injectors then you're good for another 100k - this of course if you get it before it eats itself

[fer0415]

I did the Mishimoto transmission cooler with included thermal bypass valve delete on 2019 Tahoe at around 60000 and I'm currently at 207,000 miles with the original transmission and torque converter. My transmission temp stays around 143 to 165 but before I would see the transmission hit 220 one night as a uber driver on weekends and had to stop because the transmission would slam in and out gears. And I live in Phoenix, Arizona with temperatures over 100 degrees.

[wayclay]

Just pull the pan. You'll no doubt see carneige. Buy a decent converter, get rebuild no 3, buy HPT and never look back. Cry once, buy once.

pulled the pan and seen gunk from 3 yrs and bad looking fluid and slipping around 60 and would replacing the converter stop it from slipping?

[TransGo Robert]

pulled the pan and seen gunk from 3 yrs and bad looking fluid and slipping around 60 and would replacing the converter stop it from slipping?

In the vast majority of cases the converter is the victim not the cause of the issue. If you just replaced the converter without addressing the root cause of the problem, chances are huge that it will fail again down the road.

[Johnm1]

and hoping for the additive to work long-term

The additive wont last. It needs to be replaced from time to time when symptoms return. It also doesn't fix the problem, just the shudder. I am not a Mystery Oil kinda guy, but I was surprised it did immediately temper the shudder. I've been nursing mine for two years changing the oil and filter twice a year and using the `Instant Shudder Fix` as needed. I suspect I'm down to very little wearing surface in the torque converter. Mine is on its way to another transmission shop hoping all it needs is a new converter. But we'll see. I don't think it will make it through another 115 degree Arizona summer.