Joining the rear diff club

[burgandy25]

When mine was replaced, I think about 1.5 years ago, the part number on the paperwork that dealer used was listed as also fitting the AWD XT4 Cadillac which is still in production so maybe there is some hope (and maybe an improved part).

Did you ever post the paperwork screenshot of P/n? I'll stalk your account and see if you did.

 

[burgandy25]

When mine was replaced, I think about 1.5 years ago, the part number on the paperwork that dealer used was listed as also fitting the AWD XT4 Cadillac which is still in production so maybe there is some hope (and maybe an improved part).

I did find this
P/N: 84672963
Fits: Regal TourX, Regal Sportback AWD 2.0T/3.6 V6. Cadillac XT4.
without RDCM (Rear Differential Clutch Module).

So I wonder if this means they have you re-use the module (which appears to be a computer module). Or if that is ordered separately.

Interesting enough the fitment guide lists both FWD and AWD... I don't see how this fitment would work with a FWD model.

I'll have to verify if this is the actual part that will go in my GS, or the prior one thats showing discontinued. Maybe there was miscommunication between what they're ordering for mine, and what they told me. I hope so, I hope the new P/n is flawless and we don't see any more multiple replacement scenarios that some others in this thread have experiences.

 

[koolhandluke]

We bought our 2018 TourX Preferred red needle with 36.5k in December 2023. It now has 41.5k. 7 year drive train warranty will be in effect until 12/31/24. It should still be well under the mileage cap. I had noticed in the winter cold over the last couple of months the telltale low moaning sound. There are no visible seal leaks. I decided to drain and refill the differential with the recommended AC Delco LS75W90 when performing my first oil change at 5000 miles of ownership. The magnet had around 1/8" of debris on it. Fluid was dark but not terribly dirty. I drained 28 oz out, and pumped the full 32 oz in, which brought the level right up to the fill plug. The noise immediately disappeared. I wonder if it was low from the factory. Another post had commented on the rear sway bars proximity to the upper fill plug. I was able to reach it and crack it open with a 1/4" drive 10mm hex socket on a wobble extension. There is not enough clearance for the 3/8" drive 10mm hex socket. I will monitor this for any leaks or noise before my drive train warranty expires at the end of the year. Thanks to everyone on this forum for their contributions on this topic.

 

[renchjeep]

At 58k on our 2018 TourX white needle, I had the same noise right after we bought it used a couple months ago. I did the same, drained the rear diff and refilled with the AC Delco 75/90LS, and the noise is either gone or much less prominent. My fluid was the same, a bit dirty, but not bad, with the same amount of schtuff on the drain plug magnet. Our warranty is up on like 5/15/24, so hoping for the best! I am thinking MAYBE the rear diff had been serviced at some point in the past, and someone put regular gear oil in it.

 

[fowlparts]

I think I'm joining this dubious club, as well.
I have a 2019 GS. I'm not sure if I'm the first forum member with a GS to report this problem, or not.

I don't have a pinion seal leak, but over the cooler winter months I noticed an occasional "gurrr" on right hand turns. It almost seemed more like a power steering pump noise. I'd also have what felt like a missed shift occasionally. It was always in the morning when I pulled out of my neighborhood onto a 35mph street from a 15mph street. Not sure if it was a 1-2 shift or a 2-3 shift.

During the third week of May and though Memorial day, I drove about 1600 miles. The 'gurring' and 'whirring' noise has been much more pronounced in the days since. Last Friday (5/31) the gear noise was intense as I made 3 slow-speed righthand turns as I circled around a urban residential block looking for a parking spot. The noise was pronounced enough that the passenger in the car asked "What is that noise?" unprompted.

The transmission has had a few hard and/or missed shifts last week.
In hindsight, I may have experienced the differential "pop" or "snap" about 3 weeks ago while making a tight right turn. At the time the event felt like I ran something over that burst under the right rear tire - maybe like running over a capped soda bottle.

I've owned the car 2 years and 5 months. It's a CPO. The extended bumper-to-bumper warranty has expired (5 months and/or 3000 miles ago, I think) but it may still have a powertrain warranty. I'll track that paperwork down this evening.

So far, I haven't seen anyone mention a specialist shop that knows how to deal with these things. It appears the only current solution is R&R. Is that correct?

The most prevalent GM dealership where I live is hopelessly incompetent. I've used two different locations (one near my house; one near work) on two different cars (2012 Regal GS, 6spd and now the 2019 Regal GS) over a 7 year period. In both cases they did more damage initially than they fixed.

Depending on the warranty situation, I may drive the car 30 to 45-minutes to a GM dealership owned/operated by someone else.

The 2019 Regal is my 6th GM vehicle, of which 5 have been daily drivers. Unless this is resolved amicably and with minimal cost to me, this will likely be my last GM vehicle - at least as a daily driver.
There are too many other good options and if I choose wisely I can at least avoid this specific imbecilic dealership franchise. It seems likely that I can get a car with fewer headaches, too.

 

[Jack GS]

The 9-speed is known to have a rough and/or delayed 2-3 shift on a cold day. In my case, when it happens, it is almost always a one-time thing and then it shifts normally for the rest of the drive. My car has done this since new and I don't see it as much of a concern. Just something to be aware of.

The diff definitely sounds like an issue, but you are not the first GS owner on the forum to face it.

If I may ask, what kind of miles does your GS have and have the fluids been serviced?

 

[fowlparts]

The car turned 75,000 miles middle of last week.
Engine oil and filter is changed regularly (when service indicators shows 20% - 25% life remaining). Engine air filter has been changed every other oil change (far more frequently than the service chart recommends).

Driveline fluids (transmission and differential) have not been serviced under my ownership (last ~42,000 miles).

Are these service fluids according to GM? I don't recall seeing service of fluids on the maintenance chart. They have hood and rear hatch gas strut replacement listed for 75k (I think I'll take my chances and skip that until it's a problem), but I don't recall anything about driveline fluids.

Don't get me wrong: I'm happy to change them out (pay someone or do it myself, depending on PITA factor), but in the case of the AWD system, I wonder if it's already too late.

As for warranty...
I tracked down my CPO paperwork last night. The powertrain has an extended 100,000 mile warranty (or expires on 3/20/2026). See below.



So naturally my concern turns to "do they consider a rear differential part of the powertrain." Well, according to the owners manual warranty section, the Drive System is part of the Powertrain. The Drive System coverage includes "All internally lubricated parts, final drive housings, axle shafts and bearings, CV joints, prop shafts..." as shown in the right-most column below.


I should be covered as long as I find rational people that are willing to accept that there is a problem, and are willing to do something about it, and do it right-and-well. I anticipate this is where I'll run into some trouble.

Any words of wisdom or caution from others that have traveled this path?

 

[Jack GS]

Good news on the warranty!

Although the driveline fluids are not listed as a service item in the maintenance schedule, they should still be changed in my opinion. No fluid, in any vehicle, is a lifetime fluid. Transmissions, transfer cases, or Power Transfer Units (PTUs) as ours are called, and differentials should be serviced ever 50k at the very least. For trucks, it is typical to replace differential fluid ever 25-30k miles. In addition to the differential oil, our diffs also have fluid for the clutch packs, so that's another item to keep track of.

Despite being a unique vehicle, the GS has much in common with other products in the GM lineup. The LGX V6 is used extensively, the 9T50 trans is used by the Cadillac XT4, Blazer, Equinox, etc., and the differential is to my knowledge unique to the GS. Saying this just to point out that any GM dealership is capable of working on your GS.

 

[fowlparts]

In addition to the differential oil, our diffs also have fluid for the clutch packs, so that's another item to keep track of.

Glad you mentioned this because I forgot to clarify this earlier. There are a total of 4 different fluids between the transmission, transfer case (PTU), and differential housing?

1. 9-speed automatic transmission fluid - Dextron VI ATF, p/n 88865602 / 10-9395 for gallon container; 8865601 / 10-9394 for quart container
2. Transfer case / Power Transfer Unit (PTU) fluid - GM GL-5 75W-90 Synthetic PTU Lubricant, p/n 19351882 / 10-4105 (1 quart)
3. Differential gear oil - Dexron LS 75W-90 Gear Oil, p/n 8886262 / 40-4034 (1 quart)
4. Differential clutch fluid - Pentosin CHF, p/n 88901975 / 10-5050 (1 liter)

I came across instructions on draining and re-filling each of these units somewhere in the forums last night. I'll have to track those down again this evening. I'll try to remember to come back and consolidate the links, here.

Saying this just to point out that any GM dealership is capable of working on your GS.

Yep. The challenge - at least around here - is finding a combination of GM service center, service manager, & service technician that is even remotely competent or engaged.

 

[Jack GS]

@fowlparts, looks like you have the correct part numbers. If you follow the link below, I have an older post where I attached a photo of the service write-up after having the dealer perform an engine/trans/PTU/diff service.

All of the part numbers and associated costs are shown here:

Rear Diff change 15K

After reading about peoples rear diff's going bad. I decided to change my fluid out. My Tourx is a White needle with 15K with only one mild winter under the car. The fluid coming out was clean beige color. The car took 1 Qt and 4 OZ. (so get two bottles)

buickforums.com

 

[Displayhawk]

I think I'm joining this dubious club, as well.
I have a 2019 GS. I'm not sure if I'm the first forum member with a GS to report this problem, or not.

I don't have a pinion seal leak, but over the cooler winter months I noticed an occasional "gurrr" on right hand turns. It almost seemed more like a power steering pump noise. I'd also have what felt like a missed shift occasionally. It was always in the morning when I pulled out of my neighborhood onto a 35mph street from a 15mph street. Not sure if it was a 1-2 shift or a 2-3 shift.

During the third week of May and though Memorial day, I drove about 1600 miles. The 'gurring' and 'whirring' noise has been much more pronounced in the days since. Last Friday (5/31) the gear noise was intense as I made 3 slow-speed righthand turns as I circled around a urban residential block looking for a parking spot. The noise was pronounced enough that the passenger in the car asked "What is that noise?" unprompted.

The transmission has had a few hard and/or missed shifts last week.
In hindsight, I may have experienced the differential "pop" or "snap" about 3 weeks ago while making a tight right turn. At the time the event felt like I ran something over that burst under the right rear tire - maybe like running over a capped soda bottle.

I've owned the car 2 years and 5 months. It's a CPO. The extended bumper-to-bumper warranty has expired (5 months and/or 3000 miles ago, I think) but it may still have a powertrain warranty. I'll track that paperwork down this evening.

So far, I haven't seen anyone mention a specialist shop that knows how to deal with these things. It appears the only current solution is R&R. Is that correct?

The most prevalent GM dealership where I live is hopelessly incompetent. I've used two different locations (one near my house; one near work) on two different cars (2012 Regal GS, 6spd and now the 2019 Regal GS) over a 7 year period. In both cases they did more damage initially than they fixed.

Depending on the warranty situation, I may drive the car 30 to 45-minutes to a GM dealership owned/operated by someone else.

The 2019 Regal is my 6th GM vehicle, of which 5 have been daily drivers. Unless this is resolved amicably and with minimal cost to me, this will likely be my last GM vehicle - at least as a daily driver.
There are too many other good options and if I choose wisely I can at least avoid this specific imbecilic dealership franchise. It seems likely that I can get a car with fewer headaches, too.

If you can change your own oil, you can change the fluid in the rear differential and front transfer case. I used Royal Purple 75W90 for each one, and put 1 oz. of Motorkote in each one. I got a pump on Amazon to pump the new gear oil in with. So far no whines or noises, and that was probably 20k miles ago. The important thing to remember is to loosen the fill hole nut first before draining out all the fluid. As has been mentioned, the rear sway bar is directly in front of the fill hole, so that might present the most problem for you. But it can be done.

 

[quakerj]

If you can change your own oil, you can change the fluid in the rear differential and front transfer case. I used Royal Purple 75W90 for each one, and put 1 oz. of Motorkote in each one. I got a pump on Amazon to pump the new gear oil in with. So far no whines or noises, and that was probably 20k miles ago. The important thing to remember is to loosen the fill hole nut first before draining out all the fluid. As has been mentioned, the rear sway bar is directly in front of the fill hole, so that might present the most problem for you. But it can be done.

I agree, very easy to do. Even the transmission drain/fill is a fairly simple job if you read and follow the procedure.

You're a brave soul though, one of the first forum posts I read after buying the car in early 2023, was the story of a fella who changed their rear diff fluid out w/ some aftermarket stuff, and within 1K it grenaded. That was enough for me to stick with OEM. But as they say, correlation ≠ causation.

 

[thorusk]

Hey guys,

First of all, thanks to everyone who's helping out in this thread.

I'm from Europe and I own a 2017 Opel Insignia B 2.0t 4x4 with 150k km on it.

I found this thread after I almost went crazy because of some slight vibrations I felt in the steering wheel, gas pedal, and my seat.

The service center changed both front CV axles, two engine mounts, and one gearbox mount. They also balanced the tires twice and put in new brake pads and discs. There was a leak around the front CV axle, so they changed the seals. But I still feel a slight vibration under load at low RPM, and not only then. I took it to another garage, but they couldn't find anything wrong either.

Then I lay down under the car and saw some oil/grease around the rear differential.

The rear differential and PTU haven't had their oil changed.

Do you think I'm joining the "diff club"? Could this be causing the vibration issue? What do you recommend I do?

Thanks!

 

[Jack GS]

@thorusk, welcome to the Buick forum! I have a couple of questions to rule out some of the simple stuff before going down the driveline rabbit hole...

Is your Insignia still on the original tires?

At 150k km, I doubt it, but there's a reason for asking. In the US, some of our Regals were spec'd with Continental's ContiSilent technology. The OE ContiSilent tires have a band of foam on the inside that tends to delaminate. When this happens, the foam collects in one area and causes an imbalance. No amount of tire re-balancing will correct the imbalance until the foam is completely removed.

If you're uncertain about your tires, look for this logo on the sidewall:

 

[thorusk]

@thorusk, welcome to the Buick forum! I have a couple of questions to rule out some of the simple stuff before going down the driveline rabbit hole...

Is your Insignia still on the original tires?

At 150k km, I doubt it, but there's a reason for asking. In the US, some of our Regals were spec'd with Continental's ContiSilent technology. The OE ContiSilent tires have a band of foam on the inside that tends to delaminate. When this happens, the foam collects in one area and causes an imbalance. No amount of tire re-balancing will correct the imbalance until the foam is completely removed.

If you're uncertain about your tires, look for this logo on the sidewall: View attachment 46901

No. Tires are one year old. Hankook ventus s1 evo 3. Hey, so I checked under my car today and noticed that the PTU is shaking and the driveshaft has a little play in it. I can move it to the sides a few millimeters and it shakes too.

 

[Jack GS]

That's a good lead. I don't know what service rates are like in your area, but it might not be a terrible idea to have all of the fluids replaced with the mileage on the car. At the same time, ask the shop to investigate the shaking PTU and driveshaft play.

Fresh fluid can solve some issues (looking at you GM 8L45 trans)

 

[thorusk]

Sending pictures

 

[Greeno]

Hey guys,

First of all, thanks to everyone who's helping out in this thread.

I'm from Europe and I own a 2017 Opel Insignia B 2.0t 4x4 with 150k km on it.

I found this thread after I almost went crazy because of some slight vibrations I felt in the steering wheel, gas pedal, and my seat.

The service center changed both front CV axles, two engine mounts, and one gearbox mount. They also balanced the tires twice and put in new brake pads and discs. There was a leak around the front CV axle, so they changed the seals. But I still feel a slight vibration under load at low RPM, and not only then. I took it to another garage, but they couldn't find anything wrong either.

Then I lay down under the car and saw some oil/grease around the rear differential.

The rear differential and PTU haven't had their oil changed.

Do you think I'm joining the "diff club"? Could this be causing the vibration issue? What do you recommend I do?

Thanks!

Honestly check the fluid levels if you see leakage. To rule out engine vs drivetrain vibration, brake torque to the low RPM in park. If it occurs you know it's motor related. On the highway, go neutral at speed you feel the vibration and bring the engine up to the RPM you feel it. If it occurs neutral when revved up, motor side, if it does it while neutral rolling at speed, you know it's drivetrain.

That said won't rule out loaded up differential vibrations. I'd say definitely have the fluid changed on it all. They should be changed every 20-30K I'd say for sure on these.

It's tough to pinpoint. There are picometer testing options and GM has a set of charts to match to the vibration to know what it is... On these perhaps they don't, but most vehicles it's part of the vibration diagnostic. Could even be torque converter etc. generally if you feel it in the steering wheel its up front, in the ass it's in the rear... A tire rotation after locating and seeing if it changes character and position a good way to rule out tires too.

 

[thorusk]

Honestly check the fluid levels if you see leakage. To rule out engine vs drivetrain vibration, brake torque to the low RPM in park. If it occurs you know it's motor related. On the highway, go neutral at speed you feel the vibration and bring the engine up to the RPM you feel it. If it occurs neutral when revved up, motor side, if it does it while neutral rolling at speed, you know it's drivetrain.

That said won't rule out loaded up differential vibrations. I'd say definitely have the fluid changed on it all. They should be changed every 20-30K I'd say for sure on these.

It's tough to pinpoint. There are picometer testing options and GM has a set of charts to match to the vibration to know what it is... On these perhaps they don't, but most vehicles it's part of the vibration diagnostic. Could even be torque converter etc. generally if you feel it in the steering wheel its up front, in the ass it's in the rear... A tire rotation after locating and seeing if it changes character and position a good way to rule out tires too.

I tried everything you said, but I'm still not 100% sure what the problem is. I can feel it a little bit when I put the car in neutral while driving. It's most noticeable when I'm accelerating at low speeds and especially low RPMs. Sometimes it's more noticeable than other days. Yesterday, when I was driving on the highway with ACC on at 137 km/h, I noticed it like it was coming in waves. I can feel it in the footwell, the gas pedal, and the steering wheel, but it's very slight. It's like something is gently rotating under my feet.

Btw, I replaced my brake rotors and pads with Brembos about 3000 miles ago. But the noise was so bad that I had to switch to softer pads. They lubed them up and now the noise is gone. They brake fine, but they can get a little shaky when they get really hot. But you have to really push them to get them that hot. I thought brakes cause vibrations, but they're fine when braking normally.

 

[Greeno]

I tried everything you said, but I'm still not 100% sure what the problem is. I can feel it a little bit when I put the car in neutral while driving. It's most noticeable when I'm accelerating at low speeds and especially low RPMs. Sometimes it's more noticeable than other days. Yesterday, when I was driving on the highway with ACC on at 137 km/h, I noticed it like it was coming in waves. I can feel it in the footwell, the gas pedal, and the steering wheel, but it's very slight. It's like something is gently rotating under my feet.

Btw, I replaced my brake rotors and pads with Brembos about 3000 miles ago. But the noise was so bad that I had to switch to softer pads. They lubed them up and now the noise is gone. They brake fine, but they can get a little shaky when they get really hot. But you have to really push them to get them that hot. I thought brakes cause vibrations, but they're fine when braking normally.

These cars do hold top gear and grumble in a sense and make that 4 cylinder work until you get enough for a gear change. Could be a misfire or similar if you're feeling it everywhere like that. Could be any sort of mount not isolating something. A scanner on it while it's occuring would be helpful to see if it's knock and or anything is happening that shouldn't engine wise. Chasing a gremlin can be frustrating.