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Do transmission and transfer case fluids physically MIX or are they isolated?
I have a 2010 GLK 300 4MATIC with the 7G-Tronic 722.9 transmission experiencing shudder/vibration when turning at low speeds (parking lots, tight turns).
My question: Are the transmission and transfer case fluid chambers physically connected, or can I service them independently?
If I drain the transmission pan, does transfer case fluid also drain out?
Are there internal passages connecting the two, or are they sealed chambers?
Can I access and change ONLY the transfer case fluid?
Why: I was quoted $1,000 for full transmission service (9L fluid change), but I've heard that transfer case fluid change alone can fix turning shudder issues. If they're separate systems, I'd rather try the transfer case first (~1L fluid vs 9L).
Some sources say "9L transmission + 0.6L transfer case" suggesting separate systems, while others imply they share fluid. I need to know if this is truly two independent chambers or one connected system.
Thanks for any real-world experience!
Last edited by steve_mil; Sep 13, 2025 at 02:16 AM.
There is only one supply of fluid for both the transmission and transfer case. Another good reason to do regular tranny fluid changes!
And like OP said, $1K is a whole lotta money for a glorified oil change. If you're interested in a DIY job (and it's not at all difficult), here's a video that shows you pretty much everything you need to know...
Did you check cv joints , they make sounds when going bad . Do the oil, yes 1000$ is nutz. FCP euro has complete oil kits . I don’t trust mechanics to use the best oils. I bought the kit from FCP and had a mechanic do it for about 300$ the kit is expensive. Did you check the differentials for oil ? Have you changed it? They can make noise also if going bad . The trans really should be done at 40-50000 miles.
$1K is a crazy high price for this service. Was that at a dealer? Suggest pricing at a German car indie specialist or considering DIY.
Hey man, appreciate the reply. I’ve actually been digging deep into this lately and I keep running into conflicting info.
Like yeah, some places (even that FCP Euro article) say it’s a shared system, but then I’m finding Mercedes docs and WIS procedures that tell you to pre-fill the transfer case separately with around 700ml of ATF before even touching the rest of the trans. Also shows different fill plugs. Makes me think they’re technically using the same type of fluid but kept in separate little chambers sealed off with gaskets/seals.
So I’m starting to wonder if they only appear shared from the outside but are actually split inside. I could be wrong, just trying to figure it out. You ever crack one open or service it firsthand?
There is only one supply of fluid for both the transmission and transfer case. Another good reason to do regular tranny fluid changes!
And like OP said, $1K is a whole lotta money for a glorified oil change. If you're interested in a DIY job (and it's not at all difficult), here's a video that shows you pretty much everything you need to know...
Yeah that’s exactly the part I’m still scratching my head about. I keep finding official MB docs that show the transfer case has its own little fill and drain, and you’re supposed to put about 700ml in there separately. That makes it sound like it’s not just one open reservoir but more like two small chambers that happen to use the same ATF.
Not saying you’re wrong, just trying to reconcile what I’m reading with what folks see in real life. Have you actually drained the t-case side yourself and seen it pull straight from the main sump? Would love to hear first-hand experience on that.
Did you check cv joints , they make sounds when going bad . Do the oil, yes 1000$ is nutz. FCP euro has complete oil kits . I don’t trust mechanics to use the best oils. I bought the kit from FCP and had a mechanic do it for about 300$ the kit is expensive. Did you check the differentials for oil ? Have you changed it? They can make noise also if going bad . The trans really should be done at 40-50000 miles.
Yeah the diffs were actually the first thing we did since we thought that was the main source of the noise, but nope, still there.
I’m the second owner so I’ve got no clue if the trans fluid was ever touched. Car’s sitting at around 120k km (about 80k miles). Do you think doing the fluid service this late could cause any issues, or is it still worth going ahead with it?
Replacing the transmission fluid and filter will not cause any damage, its like asking if you should replace the engine oil and filter.
I serviced my transmission in my W204 last fall and it was easy. Just need an obd scanner that can read the transmission fluid temp to properly set the level.
As stated above the transfer case is integrated into the back of the transmission and shares the same fluid. There is a line from the transmission cooler that feeds the transfer case then that fluid goes back into the transmission.
When preparing to service my transmission I noticed the part about pre-filling the transfer case. I did not do that and skipped that part. I think that is if there is no fluid in the system at all, like it was recently overhauled. Im speculating.
Heres some info on how the fluid flows thru the transfer case.
I have some home made wooden ramps I drove the car up on. I feel much safer than way. My parking area isnt that level so I jacked up the front a little bit more, front middle jacking point with jack stands underneath.
I'll show everything I used. Bought a pump sprayer that worked great for filling the fluid. I replaced the pan due to severe rusting. New sprags because the old ones were heavily corroded. When I was done I cut open the filter just to have a look. Everything looked good, no metal shavings or glitter that I could see.
I have some home made wooden ramps I drove the car up on. I feel much safer than way. My parking area isnt that level so I jacked up the front a little bit more, front middle jacking point with jack stands underneath.
I'll show everything I used. Bought a pump sprayer that worked great for filling the fluid. I replaced the pan due to severe rusting. New sprags because the old ones were heavily corroded. When I was done I cut open the filter just to have a look. Everything looked good, no metal shavings or glitter that I could see.
Do you have a lift? How do you do it without a lift as it has to be kept level.
I use the wooden ramps, too. I made 4 of them from 3 2”x12” planks staggered 27”, 24”, 21” lengths and cut 45 degrees so they could be placed in front of each wheel and just driven up onto. The added 4 7/8” height gives plenty of working room.
That’s a big job, was the torque converter drained ? My mechanic refused to drain it , I guess he had problems in the past with the torque converter screw. He drained it a second time after I drove it a few days .
My ramps are 2 planks high then I have more sections I can nail on the bottom if needed. I can only really fit 2 planks under the car if im driving the entire car up. My floor jacks wont even fit under and I have to drive it on at least one plank.
That’s a big job, was the torque converter drained ? My mechanic refused to drain it , I guess he had problems in the past with the torque converter screw. He drained it a second time after I drove it a few days .
I did not drain the TC. It was my first time ever servicing a transmission plus I have a habit of getting side tracked, was checking everything out while under there. It was taking me too long. When I pulled the pan the old fluid looked pretty good so wasnt too concerned, my main goal was to replace the rusted pan.
I figure I have 4 bottles of new fluid left over so will just pull the drain plug, see how much comes out, then add new fluid while resetting the level. Will probably only be maybe 2 quarts.
When I re-filled it the first time I pumped in 8 quarts total but then after setting the level 2 quarts came back out. So basically without draining the TC it took 6 quarts.
I put in 8 quarts because I followed the instructions, 6 quarts first fill then another 2 quarts. But after pulling the pan I only had around 5-1/2 quarts old fluid so should have only pumped in 6 quarts. I also thought the transmission was low due to seepage, but was really only low by 1/2 quart.
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