6L80/6L90 Transmission Failures

m.mcmillen

Original poster
Gold Donor
Apr 29, 2016
534
Wisconsin
Has anyone noticed a rash of failed 6L80 and 6L90 transmission? I was under the impression they were pretty solid units but now I’m not so sure.

I changed a 6L90 at my regular job (fleet of mostly Express 3500 vans) in a 2016 Express with just under 130,000 miles on it.

The same week, in my side job (soon to be full time job!) I changed a 6L80 in a 2017 Suburban that had just 101,000 miles on it.

There wasn’t much to diagnose really. They would go into limp mode and have 2nd gear only. I pulled the dipstick on both and used a nice, clean white rag to wipe the dipstick and there was metal in both.

Pulled the pan on both and they had all kinds of metal in them so it was pretty easy to say they’d had a failure.

I’ve done a little checking and it seems that the torque converter clutches have been failing and sending trash through the system. It kind of makes me wonder if one should change the converter on these preventatively or just accept that the trans will fail.

These aren’t isolated to just me. I was quite fortunate that I was able to get the transmissions within a couple days. I’ve heard stories of people in my town waiting a month to get a transmission. I bought both from the local Chevy dealer as they were the same price as all the other remans and come with a 3 year 100,000 mile warranty.

It might also be worth noting that if you get another transmission that it will have to be programmed with a j2534 device.
 

Attachments

  • 69EB880C-5564-4A74-94C7-A45BBF13A019.jpeg
    69EB880C-5564-4A74-94C7-A45BBF13A019.jpeg
    531.4 KB · Views: 13
  • C0D8115D-A91E-4B15-9A5D-91C349184E9B.jpeg
    C0D8115D-A91E-4B15-9A5D-91C349184E9B.jpeg
    288.7 KB · Views: 15
  • 45C2CF96-BE7E-4BC8-ADBE-7A87ACE12850.jpeg
    45C2CF96-BE7E-4BC8-ADBE-7A87ACE12850.jpeg
    436.9 KB · Views: 12
  • CFE6FC97-4DCE-4217-AB64-2D1FE23BED67.jpeg
    CFE6FC97-4DCE-4217-AB64-2D1FE23BED67.jpeg
    641.9 KB · Views: 12
  • 6A074577-F6E6-4495-9F9B-B137F40C7D6B.jpeg
    6A074577-F6E6-4495-9F9B-B137F40C7D6B.jpeg
    572.4 KB · Views: 18
Jul 6, 2014
9,237
The 16 3500 dump we have went out at about 50k last year. GM covered 90% of it. On that truck, it seems there isn't adequate fluid cooling as the temps always ran hot. That trans also felt off from day 1. I haven't driven it since the new unit went in but it's allegedly much better now. Had the feeling of always slipping a little. Then one in the 21 seems better. I don't believe it's related to the HP fluid issue that the 8 speeds had with the TCC clutch but maybe it could be something along those lines? I've heard the fluid change was to mask a defect in the TCC and maybe the 6 speeds have a similar defect and they're just starting to show?

Just out of curiosity, were they all AFM vehicles? I know express can have a smaller 8 but I'm not sure if they have AFM.
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
22,548
Ottawa, ON
Funny you should ask because I have been studying them because the one in my Caprice is also having issues with slipping 3rd gear shifts and wonky TCC operation.

Check out Precision Transmissions on YT for a ton of teardowns of these trannys. The main culprit is the torque converter failing, sending shrapnel through the pump, destroying it, and burning up the rest. Late models have a temperature regulated valve that will bypass the cooler completely until it is hot. Most will remove it and modify it to run like before always send fluid through the cooler. Another major issue is the 3-5 reverse drum that cracks at the hub weld, which is what I suspect I have.

Here's an example:

 
  • Like
Reactions: xavierny25

BrianF

Hobbyist
Jul 24, 2013
993
West central Sask.
I read on another forum that the issue is the DOD tuning and torque converter strategy to minimize vibration. It wears itself out and trashes the trans.
 
  • Like
Reactions: Mooseman

Mooseman

Master Blaster
Moderator
Dec 4, 2011
22,548
Ottawa, ON
Mine was tuned and had the TCC tuned to lock up instead of doing PWM. It's just acting weird where it locks and unlocks constantly. I was going to return my TCM to its OEM tune to see if that fixes it but I'm afraid that I'll have to drop it and tear into its guts anyway :frown:
 

m.mcmillen

Original poster
Gold Donor
Apr 29, 2016
534
Wisconsin
Just out of curiosity, were they all AFM vehicles? I know express can have a smaller 8 but I'm not sure if they have AFM.
Yep, both had AFM. The Suburban had a 5.3 and the Express 3500 had a 6.0.

But yeah, the vans come with 4.8’s. We have two but I always try and get the 6.0 if I can. Pickings are slim lately so I have to get whatever I can find.
 
  • Like
Reactions: xavierny25
Jul 6, 2014
9,237
Yep, both had AFM. The Suburban had a 5.3 and the Express 3500 had a 6.0.

But yeah, the vans come with 4.8’s. We have two but I always try and get the 6.0 if I can. Pickings are slim lately so I have to get whatever I can find.
Wait... they had 6.0s with AFM? That's new to me. But yes, that jibes with the above, the TCC lockup under dod is what seems to cause it.
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
22,548
Ottawa, ON
Both my 2011 Caprice and the 2008 Avalanche had it. Both have the L77 6.0L
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
22,548
Ottawa, ON
I think it's just a problem with the torque converters in general. 6L80 and 6L90. I'll probably have to source one from a ZL1 or CTS-V with the double clutch. The aftermarket ones aren't cheap. It probably helps to turn off the PWM.
 
Jul 6, 2014
9,237
Allegedly the 8 and 10 speeds have issues too. The one in my truck was good after the fluid flush but... who k nows, the damage m ay already be done.
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
22,548
Ottawa, ON
The 8 speeds had issues with shuddering and still is not resolved. I think there's even a lawsuit on this. I have one of the new 10 speeds (the GM/Ford collaboration). Although I haven't had it for that long (just under 10k miles), it's been fine except one time I had to reboot the truck when it was not wanting to go into gear after trying to go uphill with my sled trailer. I was shifting it back and forth pretty hard. Was probably some sort of protection measure. One thing I do worry about is that it has a temp regulated valve for the cooler. While on the drive to Long Island, it was hanging around 200f even in cool weather. I'd rip that thing out so it cools as much as possible but if I get an issue with it during the warranty, I might get denied because I modified it. And it uses a new Dexron ULV (Ultra Low Viscosity). And they might be able to pull the history of the temps and if they see it was lower than normal will point them to it. I like having a new truck but sometimes not.
 
Jul 6, 2014
9,237
I do recall there being some issues with a shudder on the Ford variant, haven't heard much on the GM one. I have the 8 speed in the colorado, after the fluid flush it has been solid. The 6l80 in the tahoe has the same BS shudder the 8 speed in my truck did but because there is no service bulletin for it GM laughed at me. Oh well. If you nail it even leaving from a light it just feels like something is very out of balance and the tach jumps around the 4-500 rpms indicative of the TCC lockup doing something...

The temp valve surprises me. I think the absolute hottest I've ever gotten the colorado was beating the snot out of it max towing in 95F ambient temps. Saw something like 170 degrees which is phenomenal. But the trans cooler on that truck is the size of the condenser cut in half so it should work well.
 

cornchip

Hobbyist
Jan 6, 2013
606
It's a shame GM or Ford couldn't swallow some pride and build a ZF 8 speed auto variant.

Edit....research on Sonnax's website suggets the 6Lxx's are lightly based off the ZF as are the 8Lxx's.
 
Last edited:

Mooseman

Master Blaster
Moderator
Dec 4, 2011
22,548
Ottawa, ON
Or just throw an Allison in everything. May be pricey but reliable AF. It's too bad the 4L60/70 was retired as it was at the point, with proper maintenance, it sometimes outlasted the trucks they were put in.
 
Jul 6, 2014
9,237
It's a shame GM or Ford couldn't swallow some pride and build a ZF 8 speed variant.
The ZF 6 is still probably the nicest transmission gm ever put in a vehicle. But they want full control over everything in it so that's why you get tremec/BW/THMs...

Or just throw an Allison in everything. May be pricey but reliable AF. It's too bad the 4L60/70 was retired as it was at the point, with proper maintenance, it sometimes outlasted the trucks they were put in.
The Allison's in the early Dmax trucks had their issues too. That was eventually worked out. The current 10 speed allison is rebadged 10l80/torqshift... Ford gm partnership trans with an allison badge on it. There are some differences but it ain't an allison like the 5/6 speeds were.
 
  • Like
Reactions: Mooseman
Jul 6, 2014
9,237
Throw the 6l80 in the 1500 in there. Was fine, left a light and was basically neutral then banged into gear...
 
  • Sad
Reactions: Mooseman

Mooseman

Master Blaster
Moderator
Dec 4, 2011
22,548
Ottawa, ON
I've returned my tune to stock and it seemed to help a bit. TCC or still wonky. reading around I might have a bad TEHCM or switch films. Been busy AF and haven't been driving it neither. Wanted to go pick up a used TEHCM at the PnP but just haven't had the chance.
 

ZachW98

Newbie
Jun 20, 2022
1
Bristol, TN
Literally reading this thread after the fact but I am a victim of this "torque converter pandemic" happening to the 6l80s. I own a 2016 Silverado 1500 4x4 and trans went kaput basically without warning at 112k miles which was about 3 months ago. Was out of warranty so had to replace it. Ended up going with a remanufactured one that had an updated TC from these guys, https://reman-transmission.com/transmission-codes/?code=6L80. So far so good on the new tranny but that 2500 bucks plus labor hurt me, especially on a truck with only 112k miles. My old 05 Nissan Titan ran well over 250k miles with no trans issues whatsoever
 
  • Like
Reactions: Mooseman

Mooseman

Master Blaster
Moderator
Dec 4, 2011
22,548
Ottawa, ON
Yeah. Us old guys lasting double that with our supposedly crappy 4L60Es. I still have to rip into mine in the Caprice. Next week, the Sierra is going into the shop to fix my oops in May so I should have the time to do it.
 

mrrsm

Lifetime VIP Donor
Oct 22, 2015
5,984
Tampa Bay Area
Supporting On Topic Documentation:

6L80/6L90 Exploded Component Diagrams and Parts Listings with Observations Made during an ATRA 6L80/6L90 Repair Seminar:





A 6L80/6L90 Transmission Installation Guide:


An ATRA 6L50/6l90 Products and Issues Updates:


Technical Tips for the 6L80/6L90 Transmissions:


Sonnax Aftermarket Parts Listings and Diagram:

 

Attachments

  • 6L80_technical_tips.pdf
    916.1 KB · Views: 0
  • 6l50_80_90_updates.pdf
    3.8 MB · Views: 0
  • NB_31AS_6L80_installation_manual.pdf
    778.6 KB · Views: 0
  • Catalog 6L45 6L50 6L80.pdf
    2.4 MB · Views: 0
  • GM_6L45-6L90_VBL.pdf
    2.3 MB · Views: 0
Last edited:

Forum Statistics

Threads
22,101
Posts
621,842
Members
16,618
Latest member
tskelton205

Members Online

Members Online

Members Online