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I am making this thread for anyone who may have this issue in the future and uses the search option for the symptoms. If this is you, this thread is born out of this one after going down the rabbit hole: https://mbworld.org/forums/gls-class...luid-type.html
Mine: A 2020 GLS 450, owned since new, 93k miles (today - April 2026). All fluids/filters/plugs changed at 50k tip to tale with MB fluid in 2022. Never towed anything. Always garaged and pampered, so much so that rarely has ever seen 4k RPM. It does not have the off-road+ package (other than off-road setting in the menu that lifts it up, which we all have as standard).
Symptom: At parking lot speed, or accelerating from a stop in a turn (like at a stop light) - a humming noise from what sounds like the rear / center of the car. The sound fades away as the car straightens out, and is not heard when at speed while making turns. One would automatically assume the rear differential.
The outcome (likely): The conclusion to my journey ended up being the transfer case, and have learned today that is a relatively common issue known by Mercedes Benz on my car. I am not sure if this applies to later model years of the X167 platform (and GLE sister). It's not a common topic at this point on the boards.
The cause of the noise is the clutch packs in the transfer case. They are slipping with the strain during the low speed turns. The rear differential is not a limited slip setup in the normal 450 variant (only the AMG version is the limited slip differential). BUT, the transfer case IS known as a "limited slip" setup, with clutch packs that move the power front/back in the driveline in real time. Some note the transfer case as the "center differential".
The remedy: As of current, there are no repair "kits" available for the fix. Instead, it is a new transfer case in its entirety from Mercedes. My quote today for a new one was approximately $8k for just the part.
Our conclusion: Ignore it until it really becomes a problem. You'll know it's a growing problem if the sound starts to happen when going straight, or you hear clunking / banging. But a slight humming noise on hard turns, is just the clutch packs slipping a bit. It's not going to leave you stranded.
Mercedes: Perhaps Mercedes will acknowledge the issue and issue an extended warranty for the part. Don't hold your breath however. To replace the transfer case today, means putting in the exact same part that is failing in your car again, meaning it may do it again. Until there is a revised transfer case developed, it is a waste of money to replace it, in my humble opinion.
Feel free to read the other thread, but the conclusion to the issue was not the differential, or the brakes, or tires. It was the transfer case.
Honestly cars have become so complex I don't see any modern car living to 100k miles without some expensive repair potential, even Toyotas nowadays...
I agree!
I don’t mind an expensive repair, like replacing a worn bearing in a driveline. But I’m tired of this “just buy a new driveline” as the answer.
since the old fluid that came out with 40k miles in it, was like new, no sparkles or burning evidence. Gives me comfort in that the slipping isn’t actually chewing up the clutch plates. I “think” this is more of a fluid issue than anything else. I’m hopeful the LS additive will help to prove that idea correct. I’ll know on Sunday when I can get back to it.
I bet it has a lot of life left in it still, if you don’t see any metal in the fluid. Fingers crossed for you!
Thanks amigo! Ultimately, I think this is more of an annoyance than a pending mechanical failure, and hopefully was corrected in the following model years. Just wish Mercedes would offer a reasonable fix for it, instead of a full replacement for the entire thing. They have kits for other transfer cases across the brand, but not for this one, which is also in the GLE's too.
I'll be interested to see what the Lubegard limited slip additive does for it. If it's a winner, then I'm going to pass that along to my shop guys. I trust Lubegard products. Same maker of the hvac cleaner, and have some of their product in my Bronco 10-speed transmission (which is notorious for issues across both Ford and especially GM). The Bronco is smooth as glass with its shifting for the last 20k miles.
When I was looking at the GLS initially, and coming from the W212 sedan where the transfer case was inside the transmission and couldn't be serviced / repaired separately, it was a selling point to me that it was a separate unit onto its own. Turns out that really hasn't mattered.
The one thing most brands seem to have that MB isn't really strong with - aftermarket help! For $1,500 you can buy a new aftermarket Billet valve body for the 10 speed transmissions that eliminates the issues entirely. In MB land, we can't even get aftermarket silicone windshield wipers. Reminds me of Apple vs Microsoft. You can build a Microsoft computer from grass clippings and balsa wood, but can't do a damn thing with an Apple. Yet, Apple is all this family uses and easy to live with.
Ultimately I think we'll buy a cheap 3rd car and reserve the GLS for highway duties. Something fun and easy to repair. We're thinking about a VW EOS for about $10k. I understand VW like the back of my hand, and know what they need to be brought back to new, which isn't all that much.
Yeah that is interesting that there really isn't much aftermarket support. Maybe as these age there will be...
I'm going through this right now with the Pacifica, the lease is up in September and I'm not really sure what to do. Nothing out there really excites me, I love the GLS but thats a huge jump in price and I never really envisioned having two 6 figure cars lol. We like the Lexus TX but my wife wants the PHEV which is $85K and the lease is actually $200 a month more than the GLS, so I'd have to buy that. Right now EVs and Hybrids are sold out everywhere because of the gas prices and all the deals have evaporated...so I'm considering buying the Pacifica out and keeping it, but keeping a hybrid Chrylser out of warranty isn't something I normally would do lol
100% FIXED!!!! The Limited Slip Modifier / Additive into the transfer case was EXACTLY what it needed. I have no more noise, but more importantly, no more vibration from the slipping clutch packs. Silent as the day it was brand new. Thank God!!! This was absolutely eating away at me (I hate defeat).
The conclusion: The Mercedes Benz Gear Oil specification of 239.41 for the transfer case may be fine and dandy for when the car is new. But as they age, its limited slip properties are clearly not good enough anymore! I am surprised they have not included an additive after a certain amount of miles to be used during maintenance cycles......
Actually. I'm not surprised. Why let a $10 bottle of additive stand in the way of selling an $8,000 part (or, just buy a new car, because hey, it's got 100,000 miles, so it's probably time for a new one, right?)...
This is the one I used, but there are many Limited Slip Modifiers out there. I'm sure LiquiMoly probably has one too (they're German). But I trust this brand, have no complaints.
The bottle says drive it for 20 miles to let it mix in and set in. Do some Figure 8's and what not. I just drove it for about 10, hard. Cul-de-sac spins, slammed on the gas from dead stops and while rolling. Worked that car like it owed me money. It is now dead silent. No more humming on parking lot turns or full steering lock spins. What noise I do hear, is absolutely fat tire related as they grip/slide on the pavement in those situations.
From now on - NO more Mercedes Benz fluids for me. Will be changing the transmission fluid this summer, and will be going with the LiquiMoly fluid. MB lost my trust on their fluids after this.
Took it out again this morning for some errands in the rain. The noise is definitely gone. But something else has appeared (I think, could be phycological at this point). I swear, it's down shifting as we come to the gentle stop much smoother now too, not lurching as bad as it used to into 3/2/1. Time will tell if this was just a fluke, or due to rain, or mental games. But if the clutches in the transfer case aren't properly lubricated to glide effortlessly in general, and are perhaps grabbing just a little hard or soft as you're slowing down, I could see where resistance through the driveshaft back into the transmission could occur. It's such a Jekyll / Hyde thing with these cars, I'll have to give it more time to see if it's a real effect or just "a good day".
Took it out again this morning for some errands in the rain. The noise is definitely gone. But something else has appeared (I think, could be phycological at this point). I swear, it's down shifting as we come to the gentle stop much smoother now too, not lurching as bad as it used to into 3/2/1. Time will tell if this was just a fluke, or due to rain, or mental games. But if the clutches in the transfer case aren't properly lubricated to glide effortlessly in general, and are perhaps grabbing just a little hard or soft as you're slowing down, I could see where resistance through the driveshaft back into the transmission could occur. It's such a Jekyll / Hyde thing with these cars, I'll have to give it more time to see if it's a real effect or just "a good day".
That's why I said it'll take more time to determine if it's helped on that aspect as well. But when driving it this morning, it was practically coasting to a gentle stop on a couple of procedures in comparison to how it's done normally when it gets all lumpy/bumpy.
Went down the AI rabbit hole last night and found this. MB calls for a “Dual Flush” procedure on the transfer case. If you ask it what that means, you basically sacrifice the first fluid change as a cleaning agent to the clutches via a series of figure 8 driving procedures, get it hot, then change it again. This would make sense as to why a normal change procedure would not fix the issue. I had no idea about this when I did mine. Nor did my shop apparently. Someone on the other thread did mention a case where someone had issues with the Fuchs brand and switched at it went away. That would be a dual flush scenario.
So, according to MB - if you don’t succeed the first time, keep doing it until you do.
This makes sense to me now on why the Lube Gard has worked so well. It has a cleaning agent in it, which likely has cleaned off the varnish and grime from the two clutch surfaces (one for the front wheels, the other for the back), and therefore has returned a clean surface for the the clutches to grab instead of slip (droaning noise).
Going forward, I will try the dual flush next time. I may pull this current fluid out and go back to 100% MB soon too, but want the Lube Gard to have more time to clean it up.
What is interesting to me, is the old fluid with 40k on it, looked brand spankin’ new when it came out. But, was red like transmission fluid instead of honey like the 239.41 fluid. So I am thinking the Lube Gard as a cleaning agent may indeed be necessary for mine, as perhaps the wrong fluid was in there for 40k miles.
TOD (torque on demand) - reading about it, we definitely have it. This isn’t a standard limited slip, but instead has electronic actuators that push/release the two clutches as the computer anticipates slippage in either the front or rear. Makes perfect sense as to the low speed turning now with the droaning noise. It’s probably at a 50/50 split of power in that scenario to prevent a fishtail issue.
long (but interesting to me) story short - the transfer case in the X167 is just fine. No need to buy a new one. Just need to understand the procedure better to change its fluid. These cars are now entering the “tinkering” phase for ownership. Info like this will be important for the next round of owners who buy a used one and spend some time servicing it.
My understanding is that heat and contaminents induce discoloration (neither one which is good), but fluid that retains its color and translucency is not a reliable indication of its integrity. Without lubricants, metal surfaces would take a beating. So it's the lubricants that suffer the damage in protecting the metal. Fluids can deconstruct in the same way solids do, and lose their efficacy. Heat and contaminents worsen matters (which justfies 5K oil changes for me).
Regarding flushing, not a bad idea, but I think putting a few hundred miles on the fluid and then replacing it a second time might be more effective than drain-fill-drain-fill in a single servicing.
OP: thank you for an excellent thread and for posting your observations as you go. Please post more after a few thousands miles.
This is more common in the X7 and X5 (much much more common than the GLS)... the solution proposed also is similar, and it was actually BMW's service bulletin recommendation to change the oil to another one with new spec. In fact BMW started to fill in Transfer Case with a new oil for used cars that is different from brand-new ones. Sounds like this is what you are doing, except that you found your own new oil spec that is better than the factory-filled one, cause Mbenz hasn't figured out that yet or don't have service notes for this issue. I think you are on the right track.
The only issue though, is that almost all the cases that I read for the X7/X5 with similar issues ended up with the shudder and noise on turn returning after 5K miles and needed the same oil change trick. There is a very nice track sheet that the community created and I think there is more than 50 cases and people who contributed to it (again it is much more common with the X7). Let's hope that in your case, things continue to operate as normal even after 5K miles.
There are also similar olded threads for the torque converter in many cars that starts to cause some shudder. Lube Gard came up with a small tube additive that fixes that shudder. The way it works for the torque converter is similar to what you did for your transfer case, except that Lube Gard in that case had just a small tube that you add to the oil for the torque converter. Nice chart below (and also link) on how it works for the torque converter. Again the issue that also in the case it is often a solution for 5K miles or 10K before the physics takes over and mechanical/parts wear and tear become too much to overcome even with additives like this.
These guys (lube Gard) have done soooo well, that at some point around 10 years ago companies like GM even included this solution as part of their official internal service bulletin. Again this is for the torque converter, not transfer case, but the way it works is similar to your solution. Many enthusiasts from the BMW community also used it around 10 years ago when torque converter failure was very common for some older 5 series vehicles.
These guys (lube Gard) have done soooo well, that at some point around 10 years ago companies like GM even included this solution as part of their official internal service bulletin. Again this is for the torque converter, not transfer case, but the way it works is similar to your solution. Many enthusiasts from the BMW community also used it around 10 years ago when torque converter failure was very common for some older 5 series vehicles.
If the claim to fame is ten years old, I'd treat it as Old News. It seems to be directed at GM and Ford.
Chemistry has changed so much in that time, that my first go-to would now be the most recent factory spec. I'm still reluctant to use additives that might dilute the fluid.
Since I'm near my transmission fluid change, my current question is: Does the 9G Speedshift transmission (on my '21) have a torque converter drain plug? I have mixed responses.
Does the OP change @10 liters, or just 5?
Thanks guys, if anything, this info at least goes against the idea of needing to replace the transfer case when these sounds show up, which truly didn't make any sense to me at all, given how gentle and well maintained our GLS has been treated. I haven't even taken rubber cover off the trailer mount one time since new.
Streborx: I 100% agree on the idea of letting it cycle through for a while before changing it. Mine is due for an oil change in about 3k miles. I'll likely change out the transfer case fluid again and just go with the MB 100% until the problem arises again. To Mikepen's point - it is an additive that MB doesn't endorse, and we know how finicky MB's can be sometimes. If the problem comes back after that, then I'll just put the Lube Gard back in and leave it for good.
S_W222: There is a theory in life that I learned over 30 years ago that has ALWAYS proven to be correct. It's called the "million rednecks" theory, and it suggests that when in doubt about something, trust that "a million rednecks can't all be wrong", and do as they do. There are thousands upon thousands of Chevys, Fords, Jeeps, etc. still roaming the planet because of some bottle they picked up at Walmart for their truck. I learned this lesson in my early 20's when buying a stereo for the house me and my two buddies lived at in Wilmington, NC. I went with some fancy Klipsch speakers that sucked. Returned them and learned this lesson. I still have those Pioneer speakers to this day, and they still rock.
What I used was a small bottle (4 oz) and added it with the MB 239.41 fluid that is in the transfer case that I put in a couple of weeks ago. It's basically 2oz of Lube Gard per bottle of gear oil. This transfer case takes about 1.4 liters, and I had a little bit left over of the Lube Gard.
Ultimately at the end of the day, I think the Lube Gard is acting more as a cleaning agent to the clutch packs, than a lubricant. I think this cleaning aspect is responsible for eliminating the clutch chatter, allowing for a better surface for them to engage with each other. It sounds like Mercedes thinks their fluid does the same with the dual flush procedure. I suspect when I drain this current batch out in 3k miles when I do the next oil change, it'll be black as midnight, which would be good to see!
mikepen: That's a very good question on the torque converter drain plug. I think it might if memory serves correct from the last time I was under there for the oil change (have to remove the engine cover to see it all), but do not quote me on that. When I do the transmission fluid this summer, I am going to buy enough fluid to have the whole thing flushed with it, then I will do a traditional service where you have to buy the new pan for the new filter and fill it from the drain port like typical with MB. My shop has the ability to flush through the cooling lines for about $150 with whatever fluid I bring to them. That way I'll know everything got flushed and a new filter. I did this on my 2014 W212 with Amsoil ATF, and man what a difference that made to that 7g transmission! Night and day in terms of smoothness! I will say, ours with now 45k on the fluid, still shifts like glass going up the tree. But still lumpy/dumpy when coming back down. Guess I will need that software update one day after all. Considering the car needs a visit for two recalls, one being the transmission control unit, I'll do it then, if ever.
If the claim to fame is ten years old, I'd treat it as Old News. It seems to be directed at GM and Ford.
Chemistry has changed so much in that time, that my first go-to would now be the most recent factory spec. I'm still reluctant to use additives that might dilute the fluid.
Since I'm near my transmission fluid change, my current question is: Does the 9G Speedshift transmission (on my '21) have a torque converter drain plug? I have mixed responses.
Does the OP change @10 liters, or just 5?
The 10 years old is one example out of many model examples for service bulletins that referencing this additives. Also, many brands have subcontracts with Lube Guard to white-label the additives like Ford and Lincoln, so you will not track all of that by searching the brand name. Use your own judgement to use or not use such additives, but it will not change the fact this stuff has been used with some good results for more than a decade now.
As for the torque converter, interesting question, cause unless the 9G is different from ZF…. In the case of ZF transmission: the oil for the torque converter is the same oil loop for the transmission. You just add that to the transmission fluid with a tube.
Thanks guys, if anything, this info at least goes against the idea of needing to replace the transfer case when these sounds show up, which truly didn't make any sense to me at all, given how gentle and well maintained our GLS has been treated. I haven't even taken rubber cover off the trailer mount one time since new.
Did you have it looked at by a dealer or an independent mechanic?
IMO this sounds indicative of the "replace first" mentality dealers have today, just replace stuff vs trying to find a working solution. Thats fine when the manufacturer is paying...but not when I'm paying...
As for the torque converter, interesting question, cause unless the 9G is different from ZF…. In the case of ZF transmission: the oil for the torque converter is the same oil loop for the transmission. You just add that to the transmission fluid with a tube.[/QUOTE]
I think what he's asking about is if we're able to drain the old fluid out of the TC when we do the overall transmission fluid service, or does the old fluid stay in the TC (which can be a significant amount) and thus dilutes down the new fluid being introduced into the system via the transmission pan replacement procedure. I know on the W212, this was a big topic as you could not easily drain the TC, thus really only changing about 60% of the total transmission fluid at the service intervals. Seems like the game of diminishing returns to me. If the manual calls for changes every 60k miles (as an example). The miles between 60k - 120k would thus be on only about 50% new fluids...
Did you have it looked at by a dealer or an independent mechanic?
IMO this sounds indicative of the "replace first" mentality dealers have today, just replace stuff vs trying to find a working solution. Thats fine when the manufacturer is paying...but not when I'm paying...
It was at my indi, but they reached out to see what Xentry was showing for the issue, which appeared pretty common with no solution given. BUT, it also didn't show the dual flush procedure either, which I think is key to the service in general for all of our transfer cases regardless of model. I'd say that if you have 4Matic and a separate transfer case (instead of inside the transmission itself), then a dual flush procedure is likely the best route to take.
As a DIY myself on this (it's soooo friggin' easy on this car), knowing what I know now - I would probably introduce the Lube Gard into the transfer case a few hundred miles before the service, let it clean the clutch plates, then do the service. If you still had the humming, then do it one more time (dual flush).
I absolutely 110% agree on the "replace first) approach! For many, this is the reality and perception of the brand. But for the mechanically inclined, it really doesn't make much sense and is maddening! Really a shame to think an otherwise perfectly running and maintained GLS at 95k miles would need to be traded away because of a $8,000 part that shouldn't need to be replaced. But, we all know the game. There isn't a salesman alive that would whisper in your ear to "do a dual flush" or "add some $10 Lube Gard LS additive" to fix it. I really hate this "throw away" culture we've adopted lately for pretty much everything. Honestly, I don't know how anyone in the middle class can get ahead without having some DIY skills anymore. Everything is financed to the rafters and designed to fail shortly after it's paid off. When it comes to this GLS, having spent some time poking around it now, I'm of the opinion that is should absolutely last 300k+. Hell, it still has about 35% of the ORIGINAL brake pads left on this thing at 95k miles with no skipping / warping, etc... That's insanely impressive!! And this 3.0t I-6 engine. Easily the best 6 cylinder engine I have ever witnessed. The way it revs up like a sports car, 0% vibrations, etc... just an absolute gem! Only other 6 cylinder engine I can think of that I've experienced personally would be the old school Nissan 3.5's of the late 90's early 2000's.
I think what he's asking about is if we're able to drain the old fluid out of the TC when we do the overall transmission fluid service, or does the old fluid stay in the TC (which can be a significant amount) and thus dilutes down the new fluid being introduced into the system via the transmission pan replacement procedure. I know on the W212, this was a big topic as you could not easily drain the TC, thus really only changing about 60% of the total transmission fluid at the service intervals. Seems like the game of diminishing returns to me. If the manual calls for changes every 60k miles (as an example). The miles between 60k - 120k would thus be on only about 50% new fluids...
If that’s what the question was, then most likely the answer is no. Again no direct experience with 9G, but for the ZF transmissions which I know very well, when changing oil, about 30-70% of the oil remains trapped inside the torque converter, valve body, and cooler depending on the model. The transmission oil change amount in manuals (and also manufacturers like ZF) already accounts for the remaining oil in these other parts. Some cars like M-cars, Alpina (and I assume AMGs) also come with an extra oil-cooler for the transmission and that traps additional oil. It’s fine though, some manufacturers claim that transmission oil is lifetime but I do not follow that. My Alpina B8 had claims for lifetime transmission oil and same for the M8. To get all the oil out, some folks use a flush machine to exchange the fluid while the engine is running, but it’s not an easiy DIY and many shops don’t even offer than. 2-3 oil changes back to back is the only reasonable method to get most of the old oil replaced with newer one.
For example, with ZF 6HP21 (E70) and 6HP28 (E65) that I had, the typical port will drain about 4 liters. If you remove the valve body all out (normally you would not), drain it and leave the remaining tranny to drain, the total fill can go up to about 9 liters, and the torque converter would still have oil. But again, am not sure if mbenz 9G has a magical solution to extract all the oil that is typically trapped in the torque converter, coolers and valve body. A port is not the issue… it’s the geometry and how oil is trapped in these parts.
RE: 9spd (AMG Speedshift specifically) - A couple years ago it was said that when changing fluids, once the pan is removed, you could rotate the torque converter to expose a plug and drain it. Now it's now a question.
One of my Indy's asked the local MB parts department how much fluid was required so he could verify his bid on my job, and after he provided my VIN (he hadn't earlier) they said 5 liters, so he revised his bid downward, but said he'll still pick up 10 liters just in case.
I haven't called my Dealer yet.
RE: 9spd (AMG Speedshift specifically) - A couple years ago it was said that when changing fluids, once the pan is removed, you could rotate the torque converter to expose a plug and drain it. Now it's now a question.
One of my Indy's asked the local MB parts department how much fluid was required so he could verify his bid on my job, and after he provided my VIN (he hadn't earlier) they said 5 liters, so he revised his bid downward, but said he'll still pick up 10 liters just in case.
I haven't called my Dealer yet.
W212 7g could do this too. You’d turn it to a point where, through a look hole, a bolt would appear that you could drain the TC. Almost nobody would do it though. I remember asking my indi about it, and he said would be much easier and cheaper to just use the flush machine through the cooler lines.
I wouldn’t flush if you had like 90k on the fluid. But if you had like 40-50, then I have no problem with a flush. It’s the ones who never did anything to their car, then starts having transmission issues and decide to flush, that tend to see the problems. Not sure why (other than debris?)
I do know my shop owner has an older G wagon, he flushes.
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