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.

[Johnm1]

I am having trouble finding a shop to replace only the torque converter. All the shops want to rebuild. But they all use the same OEM torque converter. The last shop quoted $4,300 for a total rebuild but with only a 12-month warranty. And that was with an oem torque converter rebuilt.

Trying to keep this HP tuner related, it appeared from a post above that there are vendors who will tune your engine / transmission. Is that correct? If so how does one find one of these vendors. Once I have my problem fixed there are still some changes I would like to make.

[gtstorey]

I am having trouble finding a shop to replace only the torque converter. All the shops want to rebuild. But they all use the same OEM torque converter. The last shop quoted $4,300 for a total rebuild but with only a 12-month warranty. And that was with an oem torque converter rebuilt.

Trying to keep this HP tuner related, it appeared from a post above that there are vendors who will tune your engine / transmission. Is that correct? If so how does one find one of these vendors. Once I have my problem fixed there are still some changes I would like to make.

GHuggins, Alvin, and edcmat-l1 (hpt forum usernames) are all professional tuners that spend a lot of time helping on the GM Gen 3,4, & 5 forums.

[Johnm1]

Thank you

I'm still not comfortable with the mechanics of this forum. I've tried to reply with this thank you several times. I suspect I'll find a double post eventually.

[Johnm1]

Thank you

I'm still not comfortable with the mechanics of this forum. I've tried to reply with this thank you several times. I suspect I'll find a double post eventually.

I thought I'd follow up with the group that provided so much good information/help. So, to start with, thanks to all that contributed as in the end it all helped me understand my issues better and come to a conclusion that finally worked.

As I wrote in the above thread, all of the transmission shops here just want to rebuild the transmission and to get their warranty I'd have to live with an OEM torque convertor. That was not an option for me. Besides, the second rebuild had way less than 100,000 miles on it and other than the shudder functioned well. For all of this time I have been nursing the transmission using the magic mystery additive that stops the shudder. I still can't believe that stuff work, but it did for me in my situation. It only lasted a couple of thousand miles each time, but continued to stop the shudder each time it was added. Reality is sometimes it only reduced the shudder, but it reduced it a lot if it didn't stop it. I learned how to drive to avoid the conditions that caused the shudder. I drove it locally to and from work and the terrain here in the Phoenix area if pretty flat. I tried once to take it up into the mountains, but the shudder was significant as well as the increase in transmission temperatures when I did and just avoided mountains. I had also added a transmission cooler for summertime use and that kept transmission temperatures pretty close to normal while driving locally. I found that driving long distances, even on fairly level ground, the transmission would eventually get very hot even with the transmission cooler. That said, the engine functioned well up to 400,000 miles. It never leaked or burned a drop of oil. At 400,000 it did develop a rear main seal leak. That could be fixed if I could find a shop that would replace the torque convertor and while out repair the real main seal.

I was still searching for that elusive shop when at 412,000 miles the 5.3 L engine finally gave up the ghost with a broken lifter. Otherwise, the engine was still running well. But the cost of repairing the single lifter was half the cost of a remanufactured engine. So, it now has a Jasper remanufactured engine in it and the new mechanic I found installed an aftermarket billet torque convertor.

SHUDDER ISSUES ARE RESOLVED!

It was a total guess that the transmission I have in it was still good and the only problem was the torque convertor. But I rolled the dice and this time came out OK. No shudder and no other issues. It shifts well through the gears. Or at least as well as it did when new. The 6L80 was known for 'not knowing what gear it wanted to be in". And it is no different now. But it shifts normally for this truck.

The lifter that broke was one of the four DOD/AFM lifters. I ordered the Jasper engine with the DOD delete and am happy with the decision. Fewer parts to break. There isn't any potential for the computer to mess things up while changing gears at the DOD transition. And the first tank of gas showed a 2 MPG increase in gas milage from 15 to 17! Although I'd like to track that a little further as the exact starting milage was estimated but probably isn't off by more than 15 miles out of almost 400 miles traveled.

Again, I'd like to thank those on this board for all of the help and advice. It helped me make what I think was the right decision. Even though it wasn't a 'HP Tuner' related decision. That includes ordering the remanufactured engine with the DOD/AFM Delete.

[TheDoofus]

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

Hello There,
I know this is an old post, but I was wondering if you still felt this was the case. Can you tell easily via a log if this is problem? I don't know anything about fuel trims and what they mean / indicate. I can see some trim levels on my last log, but not sure what they indicate. Would doing the maintenance you suggest at 100K prevent this, or do you think it would be best to do it before then (80K)?

[LSCALADE]

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

Just wanted to say thank you, I've been dealing with a sawtooth TC lock up and nothing seemed to make a difference and the shudder in 5th and 6th gear were headed for a trans rebuild. I reset the LTFT and my trans completely fixed the shudder. the TCC line pressure now climbs up as high as 90psi and holds the clutch down very well even tho the offset is set to 32psi. Its working amazing and I think all had to do with negative LTFT. The engine also seems to run smoother and I saw an immediate MPG difference. Prior to this I was getting 11mpg highway and city, now I am up to 17mpg without even trying to drive smooth.

[Estep40511]

Ive always heard and seen that when the carbon builds up on the intake runners and valves excessively, it causes the fuel trims to be skewed, thus making trans shudder. Aftermarket intakes and filters even, can cause it. We used to have bulletins at GM dealing with aftermarket intakes causing early/late shifts, taking out clutch packs.

[TheMechanic]

Ive always heard and seen that when the carbon builds up on the intake runners and valves excessively, it causes the fuel trims to be skewed, thus making trans shudder. Aftermarket intakes and filters even, can cause it. We used to have bulletins at GM dealing with aftermarket intakes causing early/late shifts, taking out clutch packs.

Would you happen to have the bulletins you are referencing? I am aware of the Gen5 intake carbon issue but would like to read to the relation with trans issues. If you have the doc# or bulletin#. I have full Techline Connect.

[Estep40511]

Would you happen to have the bulletins you are referencing? I am aware of the Gen5 intake carbon issue but would like to read to the relation with trans issues. If you have the doc# or bulletin#. I have full Techline Connect.

The document number is 6369828. Bulletin would be #04-07-30-013E. It deals with various issues of Aftermarket air filters (especially oil-soaked) causing different issues.