Joining the rear diff club

[quakerj]

As far as the labor... Certainly there are all sorts of fees in the price too. Tax, cost of the fluid to fill the new unit... Dealership labor rates are what? $150 to 200 an hour? For a dealer to install a $1500 to $2000 part a grand total of $3000 doesn't shock me.

I love my TourX but I'm likely to dump it when I've got it paid off. I enjoy the car but not $3000 of love to go to higher miles.

I'm on the fence with mine, but the money math simply doesn't work out letting the Tour-X go after it's paid off. No car payment = zero principal and especially interest (wasted money) paid on a new loan. I prefer to keep that no-car-loan money in the bank in case a failure does happen, which isn't guaranteed. Some folks here have over 100-200K with no diff failures.

 

[2018 TourX in Texas]

Quaker j:

I think you're right - letting a car go once depreciation has occured defeats the purpose of having paid for it, IMHO anyhow.

Back to the diff issue, to repeat myself:

Has anyone tried adding the GM Limited Slip Friction Modifier additive (4 oz bottle) to a "starting to be noisy" TourX diff & have any improvement / elimination of the noise ?

Q2: Is there an exploded diagram of the diff to show how it laid out internally ?

I know it's said there's a 2nd Fluid - Pentosin - in there & I was curious how / if that fluid is what's lubing the clutch packs that (apparently) go bad to cause these crazy failures !

Now that warranties are running out & future failures will be paid "out of pocket" HOPEFULLY some actual "fix the defect for good" solutions will arise - throwing New Diffs at the problem endlessly (that MAY have same effective tendency) is, to my sense, pure bunk.

I'm tempted to contact GKN in England direct & see if / what they'll have to say on the matter.

I'll add some of the Magic Treatment myself first warm day soon & report back.

David in Texas

 

[2018 TourX in Texas]

Edit : "....same DEFECTIVE tendency..."

 

[quakerj]

Has anyone tried adding the GM Limited Slip Friction Modifier additive (4 oz bottle) to a "starting to be noisy" TourX diff & have any improvement / elimination of the noise ?

I've never had a failure, but I'm not confident this would fix it, someone would have to test this. What I'd really like to see is someone having disassembled one after failure and examine what caused it.

I know it's said there's a 2nd Fluid - Pentosin - in there & I was curious how / if that fluid is what's lubing the clutch packs that (apparently) go bad to cause these crazy failures !

To my knowledge the Pentosin fluid is simply a hydraulic fluid to activate the clutches, completely separate from the diff clutches/gears and the working parts. It only holds a few ounces IIRC. There's probably seals separating the two halves, unknown if that is a contributor to failures.

Now that warranties are running out & future failures will be paid "out of pocket" HOPEFULLY some actual "fix the defect for good" solutions will arise - throwing New Diffs at the problem endlessly (that MAY have same effective tendency) is, to my sense, pure bunk.

I've been begging for this since I bought my car lol. I do all mechanic work myself, but threads about failures always end in: "took it in, replaced X,Y,Z under warranty". I'm still debating buying a new diff while they're still available, just to have on hand. $1400 seems like a steal compared to the $3K+ some folks will be paying out of pocket once warranty expires.

I'm tempted to contact GKN in England direct & see if / what they'll have to say on the matter.

I'll add some of the Magic Treatment myself first warm day soon & report back.

David in Texas

Please keep me in the loop if you are able to get any info from them or if your fix works.

 

[Crispy]

@2018 TourX in Texas, you have brought up some stuff I think needs attention. I have just spent hours reading PTU and diff service posts as I’m preparing to do ours. Regarding the rear diff, there is some misunderstanding out there on this forum about the number of different chambers, the fluid in them and what they do.
I have watched this YouTube (

) and it is really good.
Here’s how I read, watch and understand it. Please correct me if I’m wrong.
The rear differential itself has two sections; the forward one with clutches that uses an LS type 75w-90 gear oil and the rear one that houses the ring & pinion which also uses 75w-90 but doesn’t require an LS additive.
The third area is the clutch actuator which uses Pentosin 11S hydraulic fluid and rarely needs service.
Question- It’s often said that the quantity needed is less than a quart for diff service. The front uses .69 qt and the rear uses .74 qt. Does this statement mean that people are servicing the front section with LS type lube and not changing the rear?
The YouTube guy suggests there can be leakage between the two 75w-90 sections and some have suggested using an LS type gear oil in both sections so you don’t have to worry about mixing.
2nd question- Is it OK to use an LS type gear oil in the rear, ring & pinion section?
3rd Question- The YouTube guys says you should fill the front section via the vent line for effective fill. I didn’t read a single other post that mentioned that. Is that technique necessary? Seems like a good idea.

 

[quakerj]

@2018 TourX in Texas, you have brought up some stuff I think needs attention. I have just spent hours reading PTU and diff service posts as I’m preparing to do ours. Regarding the rear diff, there is some misunderstanding out there on this forum about the number of different chambers, the fluid in them and what they do.
I have watched this YouTube (

) and it is really good.
Here’s how I read, watch and understand it. Please correct me if I’m wrong.
The rear differential itself has two sections; the forward one with clutches that uses an LS type 75w-90 gear oil and the rear one that houses the ring & pinion which also uses 75w-90 but doesn’t require an LS additive.
The third area is the clutch actuator which uses Pentosin 11S hydraulic fluid and rarely needs service.
Question- It’s often said that the quantity needed is less than a quart for diff service. The front uses .69 qt and the rear uses .74 qt. Does this statement mean that people are servicing the front section with LS type lube and not changing the rear?
The YouTube guy suggests there can be leakage between the two 75w-90 sections and some have suggested using an LS type gear oil in both sections so you don’t have to worry about mixing.
2nd question- Is it OK to use an LS type gear oil in the rear, ring & pinion section?
3rd Question- The YouTube guys says you should fill the front section via the vent line for effective fill. I didn’t read a single other post that mentioned that. Is that technique necessary? Seems like a good idea.

That doesn't look like a GKN Twinster rear differential. And holy rust bucket, that looks like an older vehicle.

The front PTU doesn't do anything special, just transmits power to the rear at all times and takes a costly Synthetic PTU fluid from GM.

 

[Crispy]

That doesn't look like a GKN Twinster rear differential. And holy rust bucket, that looks like an older vehicle.

The front PTU doesn't do anything special, just transmits power to the rear at all times and takes a costly Synthetic PTU fluid from GM.

Well dang. Does that mean a Twinster rear diff is a simple drain-and-fill with Dexron LS? No need to fill via the vent? One section or two?

 

[quakerj]

Well dang. Does that mean a Twinster rear diff is a simple drain-and-fill with Dexron LS? No need to fill via the vent? One section or two?

Correct, one section only with separate drain & fill plug. Super easy service except one of the plugs (fill IIRC) requires a very short hex socket / wrench to remove.

The hydraulic portion is off to the passenger side and takes the Pentosin CHF fluid.

 

[2018 TourX in Texas]

@2018 TourX in Texas, you have brought up some stuff I think needs attention. I have just spent hours reading PTU and diff service posts as I’m preparing to do ours. Regarding the rear diff, there is some misunderstanding out there on this forum about the number of different chambers, the fluid in them and what they do.
I have watched this YouTube (

) and it is really good.
Here’s how I read, watch and understand it. Please correct me if I’m wrong.
The rear differential itself has two sections; the forward one with clutches that uses an LS type 75w-90 gear oil and the rear one that houses the ring & pinion which also uses 75w-90 but doesn’t require an LS additive.
The third area is the clutch actuator which uses Pentosin 11S hydraulic fluid and rarely needs service.
Question- It’s often said that the quantity needed is less than a quart for diff service. The front uses .69 qt and the rear uses .74 qt. Does this statement mean that people are servicing the front section with LS type lube and not changing the rear?
The YouTube guy suggests there can be leakage between the two 75w-90 sections and some have suggested using an LS type gear oil in both sections so you don’t have to worry about mixing.
2nd question- Is it OK to use an LS type gear oil in the rear, ring & pinion section?
3rd Question- The YouTube guys says you should fill the front section via the vent line for effective fill. I didn’t read a single other post that mentioned that. Is that technique necessary? Seems like a good idea.

Hi Crispy -
To Quakerj & any reading the mail:

I'll watch the video I need to be "up" on my AWD Doctrine - even IF the GM AWD diff there isn't our GKN Twinster model - we can still learn.

On the fluids - I agree with the post after yours - the .69 fill is actually at the Front of the car it's the "Elbow shaped PTU small diff" - it takes normal GL-5 75w/90 Gear oil - per other oil industry sources it's ok to use any brand GL-5 (synthetic) gear lube.

At rear of car the main chamber uses LS Gear Lube - also a GL-5 but GM sells the fluid under their label so I used that.

Much to my surprise the funny noises upon turning R or L at low speeds began manifesting probably 3-5k miles later - I don't & can't know if they were going to crop up anyways or not.

Part of me asking about adding the small 4 oz bottle of extra Limited Slip Friction Modifier Additive to see IF it quiets these "noises of impending mechanical doom" is my educated guess that PERHAPS the prior fill of fluid in my TourX was containing a Higher % of said LS Additive, which I drained out & maybe the bottle of GM brand LS Gear Oil I purchased at the dealer contained none or too little a %.

(I've worked in chemical formulation environments & can EASILY picture that happening).

So just an idea & about $10 to try it out.

We actually - us affected TourX owners are "in the dark" in terms of the Nitty Gritty details of how PRECISELY these units are failing.

Time for that to change !

Btw - I did try to download the .zip file on the site here that has the Service Manual for the Holden Commodore version of our car - but Firefox browser on my phone couldn't open it.

Has anyone successfully opened & read this FSM .zip file ?

Godspeed to all & good night.

 

[Crispy]

Don’t be afraid to ask as someone here suggested. A stealer said to me yesterday, “that will be $40.48 each” for Dexron LS. I looked at him with sad eyes and asked if he could do any better. Paid $36.43. I was there, the juice was there on the counter, want to do it this weekend…, so I paid-up. Just an FYI.

 

[2018 TourX in Texas]

Don’t be afraid to ask as someone here suggested. A stealer said to me yesterday, “that will be $40.48 each” for Dexron LS. I looked at him with sad eyes and asked if he could do any better. Paid $36.43. I was there, the juice was there on the counter, want to do it this weekend…, so I paid-up. Just an FYI.

I just paid $15 for the small 4 oz bottle of GM Friction modifier.
They asked $20 and I showed them $10 online & they met me halfway.
I'll add it soon & see if any difference happens to the excessive clutch noise.

Cheers - David

 

[fowlparts]

Curious about your 100,000 mile warranty. Did you purchase an extension? My 2018 TourX with 70K miles is starting the same drone/humming noise, and bumming out reading this thread since I am out of warranty.

Sorry I never replied to this before. My car was a GM CPO, purchased in January of 2022. The warranty was extended 3 years (I think) or 100k miles.
I believe I am now out of the extended warranty period, but I am "only" at 88,500 miles.

The next significant repair on this car - and the first one that I'll be on the hook for - will probably be the only one. After that I'm probably joining the Honda/Toyota/not-GM club for my daily drivers.

 

[adam728]

Guess I haven't been in here for a while. At 18,200 miles I had a pinion leak, dealer replaced the seal under warrenty and changed fluid.

Fast forward, and around 77k the rear diff was making significant groans in slow, tight corners (like intersection, parking, etc). Changed to Valvoline full synthetic fluid with friction modifier, and at the same time ordered the right AC Delco fluid. The ~60k mile fluid that came out did not look bad at all, and only a little slurry of metallic sludge on the magnetic drain plug. New fluid did nothing for quieting up the diff. Put about 1000 miles on in the 2 weeks I was awaiting the factory fluid and free time to change it.

Changed to the AC Delco fluid, instantly quiet. Went from groans you could feel shudder the car in slow lefts to nothing. 4k on it since, zero noise or issues. And I have been testing the AWD often. Car will do some nice, big long drifts with traction and stability control off.....

Fingers crossed as I await noise to return.

 

[2018 TourX in Texas]

Guess I haven't been in here for a while. At 18,200 miles I had a pinion leak, dealer replaced the seal under warrenty and changed fluid.

Fast forward, and around 77k the rear diff was making significant groans in slow, tight corners (like intersection, parking, etc). Changed to Valvoline full synthetic fluid with friction modifier, and at the same time ordered the right AC Delco fluid. The ~60k mile fluid that came out did not look bad at all, and only a little slurry of metallic sludge on the magnetic drain plug. New fluid did nothing for quieting up the diff. Put about 1000 miles on in the 2 weeks I was awaiting the factory fluid and free time to change it.

Changed to the AC Delco fluid, instantly quiet. Went from groans you could feel shudder the car in slow lefts to nothing. 4k on it since, zero noise or issues. And I have been testing the AWD often. Car will do some nice, big long drifts with traction and stability control off.....

Fingers crossed as I await noise to return.

Wow great result.
Any chance you have the part # of the GM fluid you used ?
Maybe I got the wrong stuff or bad batch - but I'd love to get your results.
It's either that or be a member of the New Diff Club lol !
Thanks in advance - David in Texas

 

[Clifford]

I understand that the 2018 and 2019 model years had 6 yr/ 70k mile powertrain warranties but the 2020's had 5 yr/ 60k warranties, right? Has anyone had trouble getting their diff replaced under warranty during these timeframes?

 

[Crispy]

2018 TX with 64.5k miles. I did the rear diff gear oil change today with Dexron LS 75W90 from the stealer. It took less than one quart and the job was easy just like everyone has said.
I have a couple observations and wanted to show my gear oil transfer rig.
Our car had the pinion seal replaced at 18k so fresh oil at that time. There was a normal furry deposit on the magnet drain plug. I couldn’t get a 10mm (.394”) hex key to fit the fill or drain, too big. I used a 3/8” (.375”) hex key which was a bit loose but worked fine. Maybe when the pinion seal was done, the dealer replaced the drain and fill with Merican ones, I don’t know. I did not have sway bar clearance problems with a normal Allen wrench.

This is my fill rig. I’ve done this for many years. The squirt type gear oil tops are a little easier because they’re tapered and you just cut at a good spot for the tubing to be a real tight fit. For this screw cap, I drilled a 15/32” hole in the cap and pushed the 1/2” vinyl tubing through. If the tubing has a cast in it, steer it toward the corner and you will get almost every drop. You squeeze the bottle to deliver the gear oil. It’s a little annoying squeezing the bottle and you do have to take gulps of air 5-6 times as the bottle collapses. You don’t have any pump cleanup and no waste. I left the gear oil and tubing on our furnace the night before to warm it up for easier squeezing. Works great.

 

[quakerj]

2018 TX with 64.5k miles. I did the rear diff gear oil change today with Dexron LS 75W90 from the stealer. It was easy just like everyone has said.
I have a couple observations and wanted to show my gear oil transfer rig.
Our car had the pinion seal replaced at 18k so fresh oil at that time. There was a normal furry deposit on the magnet drain plug. I couldn’t get a 10mm hex key to fit the fill or drain, too big. I used a 3/8” hex key which was a bit loose. I did not try a 9mm. Maybe when the pinion seal was done, the dealer replaced the drain and fill with Merican ones, I don’t know. I did not have sway bar clearance problems with a normal Allen wrench.

This is my fill rig. I’ve done this for many years. The squirt type gear oil tops are a little easier because they’re tapered and you just cut at a good spot for the tubing to be a real tight fit. For this screw cap, I drilled a 15/32” hole in the cap and pushed the 1/2” vinyl tubing through. If the tubing has a cast in it, steer it toward the corner and you will get almost every drop. You squeeze the bottle to deliver the gear oil. It’s a little annoying squeezing the bottle and you do have to take gulps of air 5-6 times as the bottle collapses. You don’t have any pump cleanup and no waste. I had the gear oil and tubing on our furnace overnight to warm it up. Works great.
View attachment 48138

Great suggestions. I have one of those clear tubing setups with a connector that fits small diameter oil bottle threads and the larger ones like the GM Dexron LS oil pictured. It's a crazy angle you have to get the bottle up into to get it all out, and lots of squeezing and time wasted waiting for the bottle to fill back up with air so you can squeeze again.

 

[Crispy]

Great suggestions. I have one of those clear tubing setups with a connector that fits small diameter oil bottle threads and the larger ones like the GM Dexron LS oil pictured. It's a crazy angle you have to get the bottle up into to get it all out, and lots of squeezing and time wasted waiting for the bottle to fill back up with air so you can squeeze again.

I keep the bottle upright, it feeds from the bottom. Look at my pic, I set the depth before putting it in the bottle. No hassle at all getting to the fill hole. You can sit the bottle on the floor if you want to. Only the tube has to find its way to the fill hole. It gets almost every drop. The gulps of air take about 3 seconds. The whole fill process took about 8-10 minutes max. Warming the oil is helpful. I have a Mityvac transfer pump but this is easier at less than a quart.

 

[Clifford]

Just went under contract for a 2019 TourX with almost 53k miles. Though there were no signs of ever having had a diff problem, I asked the dealer to change the fluid and to take pics. Here's the drain plug showing very little debris on the magnet. I also have a video of the fluid draining but I don't think a 3gp file can be uploaded here. But I'll say that it looked very clean and translucent.

 

[Chef jpd]

This diff issue is turning into the Porsche IMS bearing lunacy.