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PLEASE HELP!!

20L8TSierra24
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20L8TSierra24 Senior Enthusiast

20L8TSierra24

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Posted (edited)

Long story short, I have 2 vehicles waiting on transmissions at the moment.... A 24 L8T w 20k miles & a 2021 Yukon with 49k miles (converter only). The Yukon also has a grinding rear end when its cold every morning which is what I'm after. The dealership has already changed the fluid once before and the problem came back much worse only 6k miles later. The dealer is telling me they're advised to keep changing the fluid until the part fails per a bulletin. The dealership also told me it's a joke & won't fix the issues but have go go "through the process".

 

I need a corporate contact or a Southeast field engineer, or someone who can do more than GM the CS people. My dealer has been great, but has their hands tied with the rear end repair. They told me to call GM. 

 

My wife and I have wasted probably 30+ hours driving back and forth to 2 different dealers getting these vehicles repaird lately. 

Edited by 20SierraL8T24
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20L8TSierra24 Senior Enthusiast

20L8TSierra24

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  • Author
Posted (edited)
3 hours ago, redwngr said:

Have you been through the steps in the back of the owners manual?

Haven't gone that route quite yet.

 

Dealer is citing 3 attempts required which is lemon law, however mine doesn't qualify for that law anymore. Dealer is essentially agreeing but won't fix it because of the bulletin. 

Edited by 20SierraL8T24
Jay P Enthusiast

Jay P

Posted
Posted

There are some who have added limited slip additive when changing fluid in the SUV diff and solved the cold start groan/noise. The 21+ SUVs don't have the gov lock diff that the trucks have, they have a traditional limited slip with clutches.

newdude Senior Enthusiast

newdude

Posted
Posted

I have to wonder with these SUV rear ends if the dealers are actually following the TSB fully, or they are just draining and filling it and sending it on its way.

 

Here's the TSB - 21-NA-028 1..2

 

Big thing is the procedure to it.  Get it to temp, drain it, fill it, perform multiple figure 8s in the parking lot then let it cool back down.  If it still moans, repeat.  They even state it can take 2-3 drain and fills to resolve this.

 

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20L8TSierra24 Senior Enthusiast

20L8TSierra24

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9 hours ago, newdude said:

I have to wonder with these SUV rear ends if the dealers are actually following the TSB fully, or they are just draining and filling it and sending it on its way.

 

Here's the TSB - 21-NA-028 1..2

 

Big thing is the procedure to it.  Get it to temp, drain it, fill it, perform multiple figure 8s in the parking lot then let it cool back down.  If it still moans, repeat.  They even state it can take 2-3 drain and fills to resolve this.

 

Thank you for your response.

 

I asked this question when I picked it up this afternoon. They said they do it by the book. It has been flushed twice now with a follow up appointment next week because I'm going to drive it over a thousand miles this weekend. 

 

I however have another question. They're adding an "additive" to make the clutch slip more when cold... Now will my rear end not lock up when I need it to because they're compensating for something else?? Is my rear end not working as designed now?

Jay P Enthusiast

Jay P

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15 hours ago, 20SierraL8T24 said:

I however have another question. They're adding an "additive" to make the clutch slip more when cold... Now will my rear end not lock up when I need it to because they're compensating for something else?? Is my rear end not working as designed now?

The additive is a friction modifier.    

https://blog.amsoil.com/what-does-a-limited-slip-additive-do/

20L8TSierra24 Senior Enthusiast

20L8TSierra24

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Posted

Dropped the vehicle off again this morning. Latest oil change did absolutely nothing but make the rear end worse. 

 

This is a complete waste of time and my patience is really running thin.

20L8TSierra24 Senior Enthusiast

20L8TSierra24

Posted
  • Author
Posted

Left the dealer this afternoon after the 3rd fluid change & the grinding is worse than it was when we dropped it off. 

 

I can't believe that GM won't do anything about this. I'm at a loss of words

asilverblazer Senior Enthusiast

asilverblazer

Posted
Posted
57 minutes ago, 20SierraL8T24 said:

Left the dealer this afternoon after the 3rd fluid change & the grinding is worse than it was when we dropped it off. 

 

I can't believe that GM won't do anything about this. I'm at a loss of words

Try another dealer? Have a conversation with the current dealer that something else HAS to be done.

 

20L8TSierra24 Senior Enthusiast

20L8TSierra24

Posted
  • Author
Posted (edited)
22 hours ago, asilverblazer said:

Try another dealer? Have a conversation with the current dealer that something else HAS to be done.

 

I've had it at 2 different dealerships. Victory Layne Chevrolet as well as Dixie GMC. Both dealerships have said they can only change the fluids 3 times per TSB unless the part physically fails. I'm worried my wife will get stranded on a busy road and potentially get in an accident when it does lock up. 

 

I filed a BBB auto claim this morning because it has reached the 3rd attempt without resolution threshold.

Edited by 20SierraL8T24
NorbertDaniau New Member

NorbertDaniau

Posted
Posted
On 1/16/2025 at 9:35 PM, 20SierraL8T24 said:

Long story short, I have 2 vehicles waiting on transmissions at the moment.... A 24 L8T w 20k miles & a 2021 Yukon with 49k miles (converter only). The Yukon also has a grinding rear end when its cold every morning which is what I'm after. The dealership has already changed the fluid once before and the problem came back much worse only 6k miles later. The dealer is telling me they're advised to keep changing the fluid until the part fails per a bulletin. The dealership also told me it's a joke & won't fix the issues but have go go "through the process".

 

I need a corporate contact or a Southeast field engineer, or someone who can do more than GM the CS people. My dealer has been great, but has their hands tied with the rear end repair. They told me to call GM. 

 

My wife and I have wasted probably 30+ hours driving back and forth to 2 different dealers getting these vehicles repaird lately. 






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There are some who have added limited slip additive when changing fluid in the SUV diff and solved the cold start groan/noise

20L8TSierra24 Senior Enthusiast

20L8TSierra24

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Posted
18 hours ago, NorbertDaniau said:

There are some who have added limited slip additive when changing fluid in the SUV diff and solved the cold start groan/noise

If it were out of warranty, this would be the route I'd try. However, GM has had me waste my time with 3 fluid changes and after a couple hundred more miles, it's no better as expected. The rear end feels like I have a truck in 4WD on the pavement while turning now. 

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