scole

The lube they put in it here does have the friction modifiers in it but as mentioned it's not supposed to. The G80 rear diff in this truck is the Eaton Locker, not limited slip. See the post about the Eaton service bulletin here

Yes, they drained and filled with the OEM lube. Just got it back yesterday but will post back after a week whether slipping/chatter gone. Their techs said they did not experience it but I've driven that truck nearly every day for over 6 years, 85k miles and I know how it drives.

How does the high end weight of a lubricant affect it's performance? How does a 75W90 behave compared to a 75W140 rear diff lube? I understand 140 is more viscous than 90 but in a multi-weight lube how do they behave?

Supposed to be 75W90

Yesterday when I took it in for service to have them check on the slipping, I told the service advisor I wasn't sure exactly where it was slipping but I thought it was the rear end mainly because the issue began right after they changed the rear diff fluid. He poo poo'd that, said he couldn't think of anything a tech could have done to cause the issue. He said it was probably the transmission to which I informed him the transmission had just been replaced with a new one from GM in March 2022. Well, mid afternoon the service advisor said they could not duplicate he issue. I got pretty mad and may have raised my voice a bit. He recalled I mentioned I always noticed it in the morning when I first drove it and wanted to keep it overnight. I bitched some more about now having to be without my vehicle for another day but agreed. I called back this morning and that service advisor wasn't there today and I'm not sure he properly handed the issue off to anyone. The service advisor I spoke to this morning seemed much more willing to listen, checked on the ticket and saw the other advisor had written it up as a transmission problem so tech was not properly diagnosing the problem. I also made the new service advisor aware that the fluid they said they listed as being used on bill was a 75W140 viscosity, not the 75W90 recommended by GM. The are diagnosing the rear diff now. Question: Can they simply drain the incorrect rear diff fluid, re-fill with correct fluid, see if the fixes the slipping/chatter and and if it does, should it be ok and cause no further issues? I think I've read that if a new fluid doesn't stop the chatter, new clutch kit/pack?

They listed 3 units of 75332 Ultra Guard Perhaps it was this product https://www.bgprod.com/catalog/driveline/bg-ultra-guard-ls-heavy-duty/

The truck: 2017 GMC Sierra 2500 HD CC, 6.0, 4x4, 80k miles, limited slip rear diff G80 locking differential When I took truck in for service there were zero issues the drivetrain. Dealer replaced front and rear differential fluid. The next morning while backing out of driveway and taking off forward I noticed a subtle miss or draintrain slip for the first few minutes whenever I started moving from a dead stop. Did not occur at highway speeds, nor did I notice it after driving a while. It is always there in the morning when first taking off. I've researched this a little and appears slipping/chattering can occur in the rear diff. What could the tech at the dealer have done or not done which could cause this issue? Thanks, Steve

The original problem which started the circus on my truck was the trans lost overdrive. There was no shudder, noise or other symptoms except it would not shift up into overdrive. When the dealer replaced the torque converter, they said they inspected for debris but found none. Of course, now I'm skeptical whether they checked or how thorough they were. That's when the shudder started. No shudder when I brought it in for original problem. Shudder began within a day or 2 of getting truck back. The shudder is a widely known issue with these GM vehicles. It's well documented and but GM is unwilling to admit the problem. I guess it is possible for the torque converters to indeed be the problem, like perhaps none of the new or rebuilt torque converters are exactly the same as the ones installed at the factory and when mated with the original transmission, they just don't work correctly. Dunno. I was fortunate enough to have a an extended warranty in place which paid for all the service work. I feel sorry for those who don't.

After 3 months, 3 "new" torque converters and many days without my vehicle, I called GM Customer Care and got them involved. Shortly after that GM and dealer decided to replace the transmission. No problems after that. The official diagnosis was transmission was not maintaining proper fluid pressures, I think that's what they said.

I don't know what the temps of my transmission were but I could get in it first thing in the morning on a 40 degree day and within a mile of easy driving it would start to shudder.

It had a severe shudder even after the 3rd torque converter. They dragged their feet and mid February they eventually decided the transmission was not maintaining the correct pressures (I think that's what they said) and ordered a new transmission. It took over a month to get it to the dealer. It was installed late March and haven't had any issues since.

RV Johnston, any other follow ups on this issue? Did you experience any shudder in the drivetrain? My transmission issues started with it not shifting into high gear/overdrive and throwing a P0741 code. After the torque converter was replaced it developed a shudder in the drivetrain. They replaced that torque converter but the shudder continued and the dealer thinks it's another bad torque converter. They've apparently had the same problem with torque converters from the same supplier and trying to get one from a different source. My issue here... 6L90 torque converter shudder A big concern I have is whether the shudder has caused debris to be sent through the rest of the transmission and will that cause problems.

I'll pass that info along to the lead tech. There was no shudder with the original torque converter. The symptoms with the original one was it failed to upshift into high gear/overdrive after it warmed up and it threw the P0741 code. The shudder only started with the 2 replacement units and dealer said they've had the same problem with another vehicle. They are trying to get a replacement from a different source.

I have a 2017 GMC Sierra 2500 HD w/6.0L Vortec and 6L90 transmission. At about 69k miles it threw a code P0741 and would not shift into overdrive. Dealer replaced the torque converter, dropped the pan to check for metal debris. Reported no debris. Less than 500 miles later it developed the shudder in the torque converter. Took it back to the dealer for service. They said it was bad torque converter, they would replace it and it was ok to drive until the replacement came in. Dropped it off a couple days later, picked it up a couple days after that. Within a day it developed the same shudder in the torque converter. Took it back to dealer, they verified the issue, said it was another bad torque converter and would need to be replaced. They again said it was perfectly fine to drive until the part arrived. I expressed concern about debris being created and causing harm to the rest of the transmission. They said there was no risk of harm to the rest of the transmission. After a couple more days they shudder was so bad I was concerned about getting stranded somewhere so I dropped off the vehicle at the dealer. I spoke with the lead tech and again asked about debris coming off the bad torque converter. He said that type of problem was not causing debris but he said they would drop the pan and inspect again. I asked to be called so I could see as well, for some sleep insurance. My concern and question is whether or not severe shudder will result in debris that requires service in addition to replacing the torque converter. Other opinions about this service experience welcome also. Thanks, -Steve