But I need some advice. My work vehicle is a 2021 Chevy Tahoe. I have used Valvoline quick change for the oil changes exclusively since new, not a problem. But this time, Tuesday, the fleet company had them change the rear diff oil as well. All the invoice says is " Valvoline High Performance 80W90 Gear Oil" and now I hear grinding noises when I go around tight corners. Did they use the wrong oil? Forget a posi additive? Advice?

How long before there is real damage if they used/didn't use the right oil?

Thanks!

 

Probably didn't use limited slip fluid or additive. IMO, not overly time sensitive or urgent if it is just clutch chatter. The big question is did they add enough oil?

 

Your boss might want to take the truck into another shop for a second opinion. Was it making the noise before the service?

 

Both the American axle and the GM differential take 75w-90.

Pat

 

What type of diff is it?

I believe the G80 gov-lock takes no additives.

 

Hopefully they actually put the differential fluid back in. Back in my working days they pickup my company truck for service and return it without differential fluid. The differential lasted 640 miles before an axle bearing failure occurred. The investigation revealed that 1 person drained it and went home (end of shift) his replacement figured being the cover was reinstalled that it was completed and never checked it.

 

I had fleet service trucks for many years and they made me use those quickie oil change places and I have horror stories.

In that situation I'd call - or better yet email - the fleet admin and tell them it needs to be checked by a shop. Even if they ignore you at least you CYA when the rear end falls out.

 

You don't need advice, your boss does. Tell him that the company truck is now making noise after the differential fluid change, and let him worry about it. You've done your duty in telling him. You might also tell him that, if the truck continues to be driven as is, damage might occur, and see what he says.

 

Attached is a Service Bulletin (21-NA-028) which appears applicable to your issue. Realizing you're simply looking for advice i.e. not specifically "your" problem. One forum member added a friction modifier which supposedly eliminated the noise. I'm siding w/ Jeff (Sugar Bear) - sounds like clutch pack chatter. Note in the SB recommendation a series of multiple figure eight or lock steer turning maneuvers to work the gear lubricant into the clutch pack.

Rear end issues.

 

We had this problem 25 years ago when I apprenticed at a Ford dealership. We put in the then $25 per liter Ford Motorcraft synthetic 75W90. He came back with clunking and banging in his posi rear end. We figured out the super expensive Ford gear oil didn't have the posi additive. I put in the CRC posi additive with a 85W140 that was supposed to already have additive in my 70 Cutlass S. I did again when I dropped the gear oil shortly after the rebuild. Boy does the posi grip, goes sideways when I floor it. I bet GM now uses a clutch posi and that is your issue. Surprised, supposedly most gear oils supposedly come with the additive.

 

I am responsible for the maintenance of the vehicle. So it is very much my issue. I have fleet cards for fuel and service and anything over $100 needs fleet approval. Tje oil change place called fleet management, they said oil change and diff service. So here I am. I didn't notice the noise until yesterday and I'm trying to find out if that grinding noise would be caused by the wrong oil, or the lack of the limited slip additive.
Guess I need to go back and make sure they put the additive in.

 

After more thought, if the noise is in a straight line it isn't clutch chatter. If it occurs on turns it probably is clutch chatter. Let us know what you discover.

 

I truly appreciate all the input. Pretty much what I expected. The only vehicle I ever owned with a posi was my '82 Trans Am, Knight Rider style. So my experience with such things is limited. It made clunking noises only in reverse. This one has never made noises before. Now it makes noises but only while turning. It is an IRS as well, fixed differential housing and flexible joints on the axle shafts. I'm used to seeing those under the front of cars, not the rear. I'll take it back and get the LSD additive put in.