Joining the rear diff club

[dadiddle]

Well...I have read all 400 posts on this thread, which began years ago with: "For the past 4 weeks i have been getting a noticeable humming sound when driving from 60-75MPH. Only when you coast then feather the gas peddle to stay around that 60-75 mark."

This is exactly what my 85K red needle '18 is doing. The very light rumble-strip hum in top gear and only under light throttle. If you back out of the gas, the noise stops.

It is NOT making any groaning noise when turning or any of the other awful sounds described.

My question is - is the straight line hum the beginning? Will it graduate to the growling when turning, etc., and is that the consensus that the first attempt at resolution should be changing rear diff with GM product, making sure it's totally full and not leaking?

Thanks all. I really love my car, other than this.

 

[remmy]

I would dump the diff fluid, button up with RTV, and replace with GM AC/Delco Dexron 75w 90 or compatible fluid, even if the drive shaft seal is leaking, it’s a slow leak.

 

[94cruiser]

My first failure was the slinger, at under 10,000 miles. The dealer replaced the seal but at the same time banged up the driveshaft and tried to hide this by putting some epoxy or other steel hardening liquid on. Got this verified by my next dealer. Got a new driveshaft out of that.

Some time later, out of the blue noise at tight turns at parking lot speeds. This gets me a new unit.
Then about a year after that I hear a hum at specific mph only. At first dealer agrees, then they play as if they can't hear it. Blow me off and tell me to go to another dealer.
New dealer to me, sees the fluid low and verify hear the hum noise.

New diff here we go.

FSM says if any noise is present, first to do is change the fluid and if noise persists replace the diff.

 

[dadiddle]

Thanks - it's getting the Dexron LS 75W-90 p/n 88862624 / 40-4034 this morning. We'll see how it goes on the way home.

I need it over the weekend to deal with the snow we're getting.

 

[gmtech 2019]

Does my 2019 3.6 Lacrosse all wheel drive have the same diff & problems?

 

[DrFaustus]

Does my 2019 3.6 Lacrosse all wheel drive have the same diff & problems?

No, different rear end.

 

[dadiddle]

Well, I still hear the light growl at light throttle and only between 60 and 70mph. Is that the precursor of what's to come? Of course, I've only driven it 15 miles since the dextron fluid replaced the Valvoline...I wonder if more miles on the new fluid will help...

 

[fredzy]

Well, I still hear the light growl at light throttle and only between 60 and 70mph. Is that the precursor of what's to come? Of course, I've only driven it 15 miles since the dextron fluid replaced the Valvoline...I wonder if more miles on the new fluid will help...

It could take some time for the friction modifiers to work their way in and get to work, yeah. Once upon a time I put the wrong type of gear oil into a manual transmission of mine. GL4/GL5 type mix-up, basically the stuff I put in had modifiers to make things more slippery that the transmission did NOT want. It took about 150 miles for the gears to start grinding due to slippery synchros. Talk about code brown. Then it took another 150 for them to settle back down once I put the right stuff in.

Will be interested to hear how yours goes. I have ~2yr old 88862624 in my diff - it was changed at ~70k miles by a dealer for the previous owner to quiet the noise. I think I'm hearing some growl at 55-60mph now so I have a new bottle sitting for the next oil change in a few weeks.

 

[dadiddle]

It could take some time for the friction modifiers to work their way in and get to work, yeah.

I really hope you're right about that. That noise drives me nuts, both for what it is and also what it might become.

 

[yarden123456]

Hi, I own an Opel Insignia B 2018 2.0 4x4 260hp
When I bought the car almost 2 years ago i noticed the same groaning noise in the rear diff when turning right at slow speed

I have replaced both fluids in the rear diff
1)pentosin chf 11s oil (88901975)
2) Since the original AC Delco fluid (19351882) is not available in my country i replaced it with Motul Gear 300 LS 75W90

The noise was gone after a few minutes of driving.

Now, for a few months, I'm trying to figure out this new vibrating "noise" and feel I'm getting
When I get to around 70kmh(44 mph) and the car shifts to 7th gear (if I'm not mistaken, the car sits around 1100-1200 rpm)
And cruising or with just a small accelerator input, there is a vibration feel until it reaches to around 2000-2500 rpm
if im lowering the gears manually or doing a kick down, the vibration lowers significantly
same on the 8th gear

Has anyone experienced this?
Can it be related to the rear diff? ptu? transmission?

thanks
yarden

 

[dadiddle]

Yarden, that is more like what mine is (still) doing. It's not groaning when turning like some experience. It's almost like lugging under light throttle in high gear - if you give it more throttle, the noise goes away, and of course if it shifts down, it goes away. The fluid change didn't help. I've driven it probably 400 miles with the new fluid. I never noticed any leaks or film at all.

I wonder if my noise could be a vibration of some kind back there. I'm 95% sure it's coming from the rear - not the trans. Sounds louder in the back seat down low.

 

[fredzy]

Yarden, that is more like what mine is (still) doing. It's not groaning when turning like some experience. It's almost like lugging under light throttle in high gear - if you give it more throttle, the noise goes away, and of course if it shifts down, it goes away. The fluid change didn't help. I've driven it probably 400 miles with the new fluid. I never noticed any leaks or film at all.

I wonder if my noise could be a vibration of some kind back there. I'm 95% sure it's coming from the rear - not the trans. Sounds louder in the back seat down low.

How long have you owned your car? I will mention that this car is egregiously bad with engine lugging, because what you both are describing is that gut-wrenching lugging. Engine trying to make too much torque at too low RPM.

I find that this car darts to the highest possible gear at all times and holds onto it aggressively. 45-52mph is the worst as it will try to hold 8th gear uphill at that speed, 1100 rpm. Heinous. I've gone back and forth for a long time with whether I want to do a Trifecta tune just for the improved shift logic, but at this point I am resigned to using manual mode very frequently to keep it from lugging, which is like nails on chalkboard to me whether it is actually hurting the car or not.

 

[dadiddle]

I've had mine for over two years and it's only acted like this for the last couple months.

 

[dadiddle]

Had my (german) shop look at this the past couple days. They could replicate the noise, but the rear-end is silent, wheel bearings are silent, trans is silent. They tried to find some loose thing that might vibrate - nothing. Hmmm...

 

[yarden123456]

I also had my car for nearly 2 years.
I agree that it's possibly because the trans quickly shifts to high gear and keeps the car on very low rpm.
I sometimes manually downshift to 5th or 6th gear when the lugging feels intense

Is this how the car is "designed"? So there is no real issue to fix
I was thinking on maybe doing transmission \ ptu fluid change (i dont believe it was ever done before. Currently, the car is on 180k km (110k miles)).
but im afraid it will be pointless and can cause more harm because i dont have access to the original ACDelco fluid for the ptu.

 

[dadiddle]

I just had all those driveline fluids changed...with OE fluids...in hopes that would correct the noise, but after 500 miles, it has not.

I know that it only started to do this about 800 miles ago. It didn't do it for the first 6K miles I put on the car.

 

[yarden123456]

Can it be related to a problematic Torque Converter?

 

[dadiddle]

Not sure - hard to hear exactly where it's coming from.

 

[Jason J]

Well, I have a heck of a story for this never ending thread. My mother bought a Tour x new in Dec 2019. At 13k it started the groaning. She took it to the dealer and they told her it needed a differential but it was back-ordered.

Told her to keep driving it until one came in. She went in for routine services over the next (FOUR YEARS) waiting for the differential to be available. Finally in 2025 they said they could get one and installed it. Good right, NO. 5 days later, she gets a service AWD notification that keeps popping up.

She takes it to the dealer that installed it and they said the clutch reservoir was low and the gear box was overfilled and the oil is mixed, and the oil pump had slipped. They supposedly fixed this issue then refilled. Good to go right, NO again. Few days later, same (service AWD) code again.

She calls the dealer and they say they will call her back. Meanwhile she gets in a minor wreck where the front bumper and hood are damaged, they total the car with 40k miles. We bought it back and rebuilt it in a few days. Take the car to the dealer. Same thing, clutch fluid low, gear fluid overfilled and mixed. They then say they will not cover it because the car has a salvage title. After a meeting with the GM they now say they will replace it and cover half the cost of the unit plus labor. I believe we will be going to court.