2019 Regal TourX GKN Twinster fluid change.

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Based on Molakule and Jim Allens' advise in past threads I changed the rear diff fluid early in my new Buick TourX. It uses the GKN Twinster differential with has the ability to send 100% of torque to either axle with computer-controlled clutch packs. The Focus RS uses the same diff and 75w-85 and friction modifier. It still uses Dexron LS in the diff and CHF-11S in the actuator system. The car just turned 6000 miles and based on some issues some are reporting on forums I tackled it myself. There is no service interval on either fluid, and no drain for the CHF11. Capacity is listed at .92qts and fill until it drains out of the fill hole. It was extremely easy needing only one tool, a 10mm hex wrench. The rear sway bar is close to the fill plug so I had to break out the trusty Craftsman ball-end hex wrench and it just fit. The fluid didn't look bad for 7k miles but the drain plug magnet was pretty maxed out. I refilled with Castrol 75w-90LS from a past AZ clearance(good to have a stash) and will report back if it doesn't get along with the clutches. [Linked Image] [Linked Image] [Linked Image] [Linked Image] [Linked Image] [Linked Image]
 
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After reading this I decided to do some research on the Twinster. Very neat how it all works! Also surprised how easy it was to get to, considering how most newer cars tend to be.
 

4WD

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Originally Posted by Leo99
Is that a normal amount of debris on the drain plug for a newish car?
I have always been an early drive line oil changer and it's been common for me to see magnets loaded - and sometimes to actually see metallic particles in the oil.
 
Originally Posted by 4WD
Originally Posted by Leo99
Is that a normal amount of debris on the drain plug for a newish car?
I have always been an early drive line oil changer and it's been common for me to see magnets loaded - and sometimes to actually see metallic particles in the oil.
I agree with 4WD. I have always changed drive train oils on my new cars within 1K miles, and then again at 5K. Diffs were one thing, but I always found it SHOCKING how much metal debris came out of a manual transmission on the first drain! Scott
 
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How is the fluid holding up for you? I'm having a heck of a time figuring out what all this differential actually requires. My TourX just turned 17k miles and your post confirms my feeling that the rear differential fluid needs to be changed now. I was shocked to learn this car has the same rear differential as a Focus RS.
 

LotI

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Just passed 14k in mine, seems just fine. I would change it, like any rear diff within 10k miles, then regular changes. I'm probably going 30k miles between changes since it only needs a quart and is really easy to change. GM says Dexron LS is the correct fluid. 88862624 if you want it from your dealer. It's a 75w-90 made my Mobil with LS additive in it. [Linked Image] [Linked Image]
 
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Thanks for getting me this info. I ended up changing mine this morning. I used Redline 75w85 hypenoid fluid. I already had some from my Toyota. I actually noticed that the driveline seemed smoother from changing the fluid.
 

JTK

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Looks cool! Good write-up. Lotl, is there a PTU, T-case of some sort of center diff oil you can change on your TourX? Reason I ask is, I was disturbed at how horrible the T-case oil looked on my 2019 Nissan Pathfinder at like 25k miles. This little T-case only holds a few ounces of gear oil and has exhaust plumbing near it. The rear diff oil on the other hand looked relatively new yet. No drain plug magnets on either. What i'm getting at is the manufacturers typically list no service interval for these boxes and given the amount of AWD / 4x4's out there these days? As time goes on, you gotta know so many will go to the bone yard because of failed drive system components that cost thousands to replace.
 

LotI

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There is a PTU located behind the transmission that splits the power. It only holds 0.69qts of gear oil but I haven't been able to track down d&f instructions. There may not be a drain. GM p/n 19351882 for those in the US. I haven't talked to my dealer but online it's over $50/qt. It looks to be a 75w-90 GL5 EP lube that's been used in AWD GM vehicles from Germany(Opel) like the Regal. ACDelco: " ACDelco GL-5 75W-90 Synthetic Power Transfer Unit (PTU) Lubricant helps improve fuel efficiency, reduce operating temperature, and improve thermal stability. GL 5 gear oil possesses high extra pressure (EP) effect. It is used in hypoid and other highly loaded gears. This gear oil is a heavy-duty, extreme-temperature-pressure GL-5 axle lubricant. It is designed to withstand the high temperatures encountered during extended high-speed operation and heavy towing while also retaining excellent fluidity at cold temperatures. The fully synthetic formulation offers oxidation and thermal stability. The formula contains superior oxidation resistance and longer seal life. This gear oil also keeps the power transfer unit lubricated to help allow efficient power transfer to differentials. ACDelco GL-5 75W-90 Synthetic Power Transfer Unit (PTU) Lubricant has been formulated to meet your expectations for durability and longevity." [Linked Image]
 

LotI

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Did an oil change today and got a close look at the PTU(literally as I was on my back). There is a drain plug and a fill plug that have a 3/8" square drive head...nice. It means I can DIY. I'm contemplating using my M1 or Castrol 75w-90 but am worried about any proprietary additives that may be in the $50/qt ACDelco fluid. I will probably break down and buy the fluid considering a failure would be much more than $50. I still have a UOA kit from Wix so I think that will be used for it.
 

JTK

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Originally Posted by LotI
Did an oil change today and got a close look at the PTU(literally as I was on my back). There is a drain plug and a fill plug that have a 3/8" square drive head...nice. It means I can DIY. I'm contemplating using my M1 or Castrol 75w-90 but am worried about any proprietary additives that may be in the $50/qt ACDelco fluid. I will probably break down and buy the fluid considering a failure would be much more than $50. I still have a UOA kit from Wix so I think that will be used for it.
Is the PTU live all the time to the rear diff input? Just trying to figure out if it's a simple ring an pinion gear type setup like a lot of them are. Regardless, I'd want to change that oil as well given how little they hold and the heat they're subjected to. The PTU/t-case wasn't fun to get at on my 2019 Pathfinder either. An uncomfortable, contorted reach-around with long extensions to get at the fill plug and I refilled it I-V style with tubing and a small funnel from up above under the hood which was slow. WHen I do it again, it's going to be in warm weather using one of those pressurized garden sprayers to get the new oil back in.
 
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LotI

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The PTU is always live sending power to the rear diff. The GKN rear differential has an active input clutch that can unlock to reduce drag. It's very visible under my car but tight getting to the fill plug. I'm not sure if I have a socket that's low profile enough. I may have to use one of the "square drive socket cap" I got from HF and just use a spanner on it. [Linked Image]
 

LotI

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OP here with an update. My advise is not to deviate from the GM Dexron LS p/n 88862624!

At 33,500 miles my rear diff started making a moaning sound during low-speed right hand turns and was leaking from the pinion seal. The differential is not field-serviceable so GM replaced it under warranty, thankfully. After replacement the noise is gone. It appears that GM is very picky about the oil as this is the diagnostic for "noise in turns":

"Incorrect type fluid

Installation of the incorrect type gear oil may create a "moan" type noise within 7 770–25 900 km (3–10,000 miles). Fluid that is "black" in color is to be considered normal and is darkened by the carbon material in the clutch plates."

It took about 25k miles for my noise to appear.
 
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