4matic transfer case questions
Thread Starter
MBWorld Fanatic!
Joined: Dec 2020
Posts: 2,412
Likes: 1,482
From: 122W, 37N
2016 E350 4Matic wagon, 2019 Ford Expedition, 2019 Chevy Bolt EV
4matic transfer case questions
do these cars have a center differential? I suppose they have to since they are always in AWD.
and I've read they have a fixed 45-55% torque distribution, wondering how that's achieved mechanically with a simple differential ? I thought diffs were pretty much 50-50 unless there is either a gear ratio difference, or a friction element to limit output. From what all I've gatherred so far, these 4Matic systems use the ESP via the wheel brakes to control slippage.
and I've read they have a fixed 45-55% torque distribution, wondering how that's achieved mechanically with a simple differential ? I thought diffs were pretty much 50-50 unless there is either a gear ratio difference, or a friction element to limit output. From what all I've gatherred so far, these 4Matic systems use the ESP via the wheel brakes to control slippage.
Thread Starter
MBWorld Fanatic!
Joined: Dec 2020
Posts: 2,412
Likes: 1,482
From: 122W, 37N
2016 E350 4Matic wagon, 2019 Ford Expedition, 2019 Chevy Bolt EV
yeah, its the torque distribution I'm not getting. I know how its done on dynamic systems that use clutches or brakes, but this isn't a dynamic system at the differential level. I keep reading articles that describe what torque vectoring or distribution IS, but none explain HOW its done.
MBWorld Fanatic!
Joined: Oct 2010
Posts: 5,141
Likes: 1,293
From: Southern US
2010 E550, 273 Engine: 2012 S550, 278 Engine
yeah, its the torque distribution I'm not getting. I know how its done on dynamic systems that use clutches or brakes, but this isn't a dynamic system at the differential level. I keep reading articles that describe what torque vectoring or distribution IS, but none explain HOW its done.
The torque between axles is set with the diameter difference between the ring gear and the sun gear. I made the two drawings to explain. Hope they help to understand how it works.
Thread Starter
MBWorld Fanatic!
Joined: Dec 2020
Posts: 2,412
Likes: 1,482
From: 122W, 37N
2016 E350 4Matic wagon, 2019 Ford Expedition, 2019 Chevy Bolt EV
so that stilll outputs the same RPM but with different amounts of torque? that was the part I didn't get... increasing the output shaft RPM lowers the torque but if you compensate for that with a different final drive ratio, then you bring the torque at the wheel right back to where it was.
Trending Topics
MBWorld Fanatic!
Joined: Oct 2010
Posts: 5,141
Likes: 1,293
From: Southern US
2010 E550, 273 Engine: 2012 S550, 278 Engine
so that stilll outputs the same RPM but with different amounts of torque? that was the part I didn't get... increasing the output shaft RPM lowers the torque but if you compensate for that with a different final drive ratio, then you bring the torque at the wheel right back to where it was.
then there is that multi disk lock that allows one axle to move the car when the other is in slippery surface.
MB World Stories
The Best of Mercedes & AMG
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun
Verdad Gallardo
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Verdad Gallardo
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine
Verdad Gallardo
Flawlessly Restored Mercedes 190E Evo II Heads to Auction
Verdad Gallardo
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know
Verdad Gallardo
Mercedes EQS Gets A Major Update: Everything You Need to Know
Verdad Gallardo
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve
Verdad Gallardo
Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping
Verdad Gallardo
10 Most Reliable Mercedes-Benz Models You Can Buy Used
Verdad Gallardo
Thread Starter
MBWorld Fanatic!
Joined: Dec 2020
Posts: 2,412
Likes: 1,482
From: 122W, 37N
2016 E350 4Matic wagon, 2019 Ford Expedition, 2019 Chevy Bolt EV
so now we need someone who can get their hands on a blown 7G 4M to crack it open, and take LOTS of photos and measurements of the transfer case mechanism 
hey, I can dream, can't I?
hey, I can dream, can't I?
Thread Starter
MBWorld Fanatic!
Joined: Dec 2020
Posts: 2,412
Likes: 1,482
From: 122W, 37N
2016 E350 4Matic wagon, 2019 Ford Expedition, 2019 Chevy Bolt EV
speaking of... does anyone know offhand if you can still get the "Introduction to Service" manuals for various model years of the 212 ? I have a couple of those for the W124's and they explain a bunch of MY specific stuff that's not even in the factory service manuals.
Thread Starter
MBWorld Fanatic!
Joined: Dec 2020
Posts: 2,412
Likes: 1,482
From: 122W, 37N
2016 E350 4Matic wagon, 2019 Ford Expedition, 2019 Chevy Bolt EV
ahh, I poked around in my new WIS looking for that sort of thing and didn't find this,b ut of course, I was looking for 212.288 related stuffs.
and hah, my picture that I pasteda bove is from page 10 of the firrst of those docs...
and hah, my picture that I pasteda bove is from page 10 of the firrst of those docs...
MBWorld Fanatic!
Joined: Oct 2002
Posts: 4,975
Likes: 1,343
From: Cincinnati
2010 E350 4Matic
Ok maybe this is standard for those in the gearbox industry, but to me its pretty clever.
Having said that trying to figure out which bearings are prone to failure. I think it is one of the main tapered roller bearings. Then the next question is why? Is it simply undersized for the thrust loads?
Having said that trying to figure out which bearings are prone to failure. I think it is one of the main tapered roller bearings. Then the next question is why? Is it simply undersized for the thrust loads?
Last edited by MBNUT1; Mar 4, 2021 at 06:28 PM.
MBWorld Fanatic!
Joined: Oct 2010
Posts: 5,141
Likes: 1,293
From: Southern US
2010 E550, 273 Engine: 2012 S550, 278 Engine
Ok maybe this is standard for those in the gearbox industry, but to me its pretty clever.
Having said that trying to figure out which bearings are prone to failure. I think it is one of the main tapered roller bearings. Then the next question is why? Is it simply undersized for the thrust loads?
Having said that trying to figure out which bearings are prone to failure. I think it is one of the main tapered roller bearings. Then the next question is why? Is it simply undersized for the thrust loads?
The shaft for the ring gear seems to be just a spline fit over the gear box output shaft in the left end. It does nor show bearing for the other end and this is normally not used as the three planetary gears will center it but where does it carry the axial force that is generated between the ring gear and the outer planetary gear? If there is a thrust bearing inside the output shaft where the planet carrier seems to go inside of it then the axial force is carried by that ball bearing at the right side end of the transfer case. Ball bearings do carry axial forces but they are really not meant to be used for that.
MBWorld Fanatic!
Joined: Jan 2009
Posts: 2,780
Likes: 115
From: Northern NJ
GLK 350 / Porsche 993
Pics here...I rebuilt mine. Pretty simple design. Maybe too simple with not enough proper lube.
https://mbworld.org/forums/glk-class...anny-diff.html
https://mbworld.org/forums/glk-class...anny-diff.html
MBWorld Fanatic!
Joined: Jan 2009
Posts: 2,780
Likes: 115
From: Northern NJ
GLK 350 / Porsche 993
The picture does not show all details but there seems to be a chance for a serious design flaw with this. The mesh from sun gear to the front axle seems quite robust with conical bearings. Of course, I don't know what size those bearing are and what magnitude axial forces they need to carry. But what does not seem right to me is the ball bearing at the far end of the transfer case. The planet carrier (red) does not carry axial force as the helical gear mesh forces cancel them out but what carries the axial force of the ring gear (green)?
The shaft for the ring gear seems to be just a spline fit over the gear box output shaft in the left end. It does nor show bearing for the other end and this is normally not used as the three planetary gears will center it but where does it carry the axial force that is generated between the ring gear and the outer planetary gear? If there is a thrust bearing inside the output shaft where the planet carrier seems to go inside of it then the axial force is carried by that ball bearing at the right side end of the transfer case. Ball bearings do carry axial forces but they are really not meant to be used for that.
The shaft for the ring gear seems to be just a spline fit over the gear box output shaft in the left end. It does nor show bearing for the other end and this is normally not used as the three planetary gears will center it but where does it carry the axial force that is generated between the ring gear and the outer planetary gear? If there is a thrust bearing inside the output shaft where the planet carrier seems to go inside of it then the axial force is carried by that ball bearing at the right side end of the transfer case. Ball bearings do carry axial forces but they are really not meant to be used for that.
What goes are the roller bearings. I think the warm style gears put too much twisting force on the roller bearing and ATF lubrication is probably not the best for this. Proper diffs use gear oil and not ATF. Again MB probably tested this and found good enough for 100k miles after which point they don't really care.
MBWorld Fanatic!
Joined: Jun 2020
Posts: 1,363
Likes: 1,012
'11 E350, '11 E550, '98 M3, '95 E320
The 4Matic W221 describes the oil path... when stationary and underway, in both cases the oil enters the L3 / L4 area first. Maybe their desire to reduce windage and increase efficiency, by keeping a small "effective" sump, leads to poor lubrication. Another consideration, is the flow rate is only 100 ml/min into the transfer case and the max capacity is 700 ml. So the fluid is exchanged once every 7 minutes... is that causing build-up of local heat and leading to wear.
