Rear differential slipping/chattering after fluid change

scole · September 13, 2023

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

Edited September 14, 2023 by scole

parkermonte55 · September 13, 2023

Sounds like they did not add the posi trac additive. It is like a two or three ounce bottle. It will cause the diff to chatter without it.

rav3 · September 13, 2023

Does the G80 diff require limited slip gear oil?

diyer2 · September 14, 2023

Read this

and

newdude · September 14, 2023

3 hours ago, scole said:

The truck: 2017 GMC Sierra 2500 HD CC, 6.0, 4x4, 80k miles, limited slip rear diff

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

Its the G80 locker, not a limited slip. It does have clutches, however the G80 requires no limited slip additives or friction modifiers.

Go out to an open parking lot and make a bunch of figure 8s and see if that helps the chatter.

Edited September 14, 2023 by newdude

swathdiver · September 14, 2023

5 hours ago, scole said:

The truck: 2017 GMC Sierra 2500 HD CC, 6.0, 4x4, 80k miles, limited slip rear diff

When I took truck in for service there were zero issues the drivetrain. Dealer replaced front and rear differential fluid.

The proper fluid for your differential is 88900401 or 10-4016. It contains the "posi lube" to keep the clutches from chattering. Adding more messes things up, using fluid without it causes chattering too.

Check your receipt for the fluid that they used. 75W90 full synthetic is the spec and that number provided is for 1 quart bottles.

scole · September 14, 2023

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/

Edited September 14, 2023 by scole

newdude · September 14, 2023

6 hours ago, scole said:

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/

75w140? That's not right. Could be causing the issue perhaps.

I'd take it back and have them put the GM stuff in it. 88900401

scole · September 14, 2023

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?

Edited September 14, 2023 by scole

txab · September 14, 2023

Yes, simple drain and refill can be done. Then drive it, see how it does. Others have had issues with diffs after lube changes when incorrect fluid type was installed. So it can be corrected.

Lets see what they come up with

rav3 · September 14, 2023

Fyi, if I recall correctly, your HD truck rear diff takes tge 75W140, not the 75W90 that the 1500 takes. Check your manual to verify. Using a GL5 lube with limited slip additive won't hurt anything. It's just has a friction modifier to allow the clutch disks to slip correctly.

scole · September 14, 2023

Supposed to be 75W90

rav3 · September 14, 2023

1 hour ago, rav3 said:

Fyi, if I recall correctly, your HD truck rear diff takes tge 75W140, not the 75W90 that the 1500 takes. Check your manual to verify. Using a GL5 lube with limited slip additive won't hurt anything. It's just has a friction modifier to allow the clutch disks to slip correctly.

My bad!

scole · September 17, 2023

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?

Edited September 17, 2023 by scole

rav3 · September 17, 2023

14 minutes ago, scole said:

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?

Here's an interesting article about their differences.

75w90 vs 75w140: Head-to-Head Comparison - Oils Advisor