High mileage 6L80, perhaps I saved it?

[redhat]

Mom's 2018 Tahoe, 154k on the odometer with about 300 miles on the new L83 DOD-deleted engine and the OE 6L80E. With the truck now having a DOD-deleted engine, the transmission calibration has TC lockup turned off for 1st-4th gear, and all TCC slip zeroed out.

I have been driving this truck since last Saturday after finishing up the engine swap... putting miles on it/breaking it in as per the engine builder. I replaced the engine cooler and transmission cooler lines when the motor was swapped as (A) easiest time is without an engine in the bay and (B) hose/metal crimps were seeping. The transmission cooler lines were replaced with GM lines and the thermostatic assembly was bypassed with a TransGo kit. When replacing the lines, the fluid coming out of the lines was pretty dark and brown. Prior to the engine swap, when I drove the truck, the transmission surprisingly shifted excellent. TC locked up well, perhaps a touch of shudder when/during the lockup, but nothing horrible. After the swap, to top off the transmission, I added an entire 15oz bottle of Lubegard Platinum. After adding the Lubegard, I noticed the shudder while the TC was locking up was gone. That got me thinking, perhaps this transmission, while definitely high mileage, is still OK but the Dex VI being pretty worn out is not doing me any favors. I am of the opinion that, even though the situation can be a big bummer, if you service a transmission and it fails, it couldn't have been that great to begin with. I decided to service it.

With over 150k on a stock 6L80E, with AFM operating for the time -- up until this point and stock cooling characteristics I am a bit in the "I am not sure how long this transmission will last" mindset. Perhaps some saving grace is that the transmission was serviced with a pan drop, fluid and filter at around 45k when the truck was bought used and around 110-120k by a mechanic my Mom frequents. Additionally she drives like a 71 Y/O woman would drive... think Miss Daisy.

My back has been messed up for weeks now and I did not have it in me to drop the pan and throw filter and fluid at it. I proceeded to use my pneumatic fluid extractor and sucked the pan contents out via the dipstick tube. About 5-6 quarts came out. Dark brown and definitely aged, but I did not see any metallic bits or shimmer in the fluid. Just oxidized and used dark fluid.

My process was:
- 5-6 quarts aged Dex VI sucked out through dipstick
- Refilled with 6 quarts O'Reilly Dex VI/Merc LV, started engine, idled and ran through gears
- Sucked pan contents again
- Refilled 5 quarts O'Reilly Dex VI/Merc LV and 1 quart Valvoline MaxLife ATF, idled
- Sucked pan contents again
- Refilled 6 quarts MaxLife ATF, idled
- Sucked pan contents again
- Refilled 6 quarts MaxLife ATF, idled, set rough level, went for a drive and set final level

I drove the truck for about a half hour now on this new fluid, about 20 miles. Shifting feels great, crisper than before, TC lockup is excellent, still no shudder while locking up at all. Fluid on the dipstick is bright cherry red/pink. Temps in our ambient 50-ish degree weather didn't go above 145F.

So I guess we'll see how it does... probably if all is well come spring, I will drop the pan and do a full service, filter and fluid. Mom knows that anything is possible and if it happens to be the 6L's time, it is what it is.

Perhaps I saved it in time?

Initial fluid pull

2nd fluid exchange pull

 

[AZjeff]

You ended up with around 94% new fluid. Good thinking putting the Maxlife in the last 2 fills. With any luck it will last mom until she's done driving.

 

[jetman]

Torque converter is on borrowed time, change it before it takes out the transmission.

 

[JavierH19]

That definitely helps it. So you left the old torque converter on it? At that high mileage with the known issues I think I would have ponied up the few hundred extra to not have to drop the transmission for at least another 150k. But maybe it'll be fine for another 50k i've read of these lasting a long time even with minor shudder and a fluid change. With 5th disabled so only 6th has lockup for highway use i'd be more confident in it.

I believe it's better to use Valvoline Extended Protection ATF as it has a different additive pack and less broad compatibility than maxlife but meets GM HP unlike maxlife so I imagine the additive pack has whatever extra in it to prevent the torque converter shudder. 5th is 0.85 and 8th in the 10 speed is also 0.85 and i think i'm in 8th once i'm going 44 mph so I imagine the 6l80 goes out of 5th and into 6th once you're doing 55 or so. I never cruise for long below 55 so i'd leave lockup only to 6th if it was mine if i was using the old tc.

 

[redhat]

I considered a torque converter but to be honest I really wasn’t sure how well the transmission was before I started and didn’t want to wing a new TC at it with a transmission on its way out or shock something into failure.

I think I’ll re evaluate this come spring but as it stands I understand it’s on borrowed time and whatever happens is what it is. I’ve also heard some not too terribly confidence inspiring posts of putting a TC on an already 150k transmission is a questionable move as “how is the rest of the unit”, etc.

Delay the inevitable I guess. At least if mom can get a bit more time until the when.

 

[SShooterZ]

Crazy that I had a 2004 Suburban, with the 4L60, that dumped all over itself at 100K miles while the engine, pre AFM didn't use a drop of oil up until I sold it at 150K miles. Then I had a 2012 Yukon XL, with the 6L80 that never gave me an ounce of issues, even hauling a 21' Crownline and multiple snowmobile trailers, but the engine stuck a lifter at 144K thanks to the AFM. If only GM could get it right one way or the other. I'd say you're probably OK with what you've done as I found the 6L80 to be much more stout in how it shifted and ran when pulling. Hopefully you avoided any issues down the line with the fluid changes.

FWIW, my dad has a 2001 Suburban, 4L60 and pre-AFM 5.3L with 235K on it and it still runs just fine. He's not exactly Miss Daisy, but he definitely doesn't push it and the only hauling he's ever done with a 16' runabout every year for 2 miles to the boat launch and 2 miles home at the end of the season. Go figure.

FWIW - We are both believers in regular maintenance meaning those transmission fluids were probably changed every 40-50K miles. Sometimes it works, sometimes it doesn't I guess.

 

[Donald]

As they say time will tell. But certainly changing the ATF was the proper thing to do even if the transmission needs replacement in the future.

 

[redhat]

It has been really good so far. Mom doesn't beat on the thing, and she's been super good about following my aggressive maintenance schedule.

Time will tell.