are you sure? based on what I saw, the fluid returns where L3 and L4 are. It comes from transmission onto the upper part of the planetary gear assembley then flows down and goes back at the bottom of L3/L4 area. The sump is a debrie catcher.

 

You say you are not an engineer but based on the work you did in the other forum post you must be very mechanically inclined. Very impressive job indeed.

But back to the axial forces. ..

I was quick in my earlier post as the axial force generated in the mesh between the ring gear and outer planetary gear can be carried as an internal force in the planet rattier-ring gear combination. But what takes the axial force between these two parts as helical gear mesh certainly generates some?

Then, if that is properly managed, what carries the axial force generated at the mesh between the inner planetary gear and the sun gear. If you look at the “planet carrier-ring gear” combo as one unit, the sun gear will either push it out towards the ball bearing or pull it in towards the gear box.

Bassd on the picture of the transfer case I believe this ball bearing carries axial force as at the other side the green ring gear shaft mounts on the transmission output shaft with a spline that is not bottomed out. There is no axial force carry in either direction.

Regardless, if the ball bearing is not the one failing it obviously is strong enough for the application.

By the pictures in the other thread the tapered bearings do not look good as you say. They are clearly under dimensioned for this transfer case. There seems to be overheating issues but one picture with used and new races in it shows small pits in the used race surface. This is clear material fatigue failure that happens under over load very easily but with very old used bearings can be the cause for failure too.

I don’t know at what mileage your transfer case failed but if it happened below 100000 miles I would say the tapered bearings are under sized. I have read in the forums some people have this failure at below 40000 miles so it is a serious design flaw for bearing sizing.

I have mentioned this before in the forum discussions that many bearings with the same mounting dimensions are made for different loads. I don’t know this bearing but there may be another bearing that is made for higher load range.

 

Ha thanks, I just liked to play lego. Cars are just lego for adults.

I had to look up axial load...you mean the shaft moving in and out? I think the shaft can just move inside of the ball bearing. I was thinking you were talking about transverse load (shaft pushing down on the roller bearing) which of course there is some of it (that's why bearing is there) but not much. It probably takes away stress from transmission output shaft. Anyways, that bearing is not problem one.

My TC bearing went at 105k miles. I read some people have driven with the noise for 10k miles before more substantial damage appeared. I only had whine that was noticeable most from 30mph to 65mph. The little sump dirt catcher definitely cought some stuff. The fluid in the transmission was very clean as it only had 14k miles on it. I had one tranny fluid at 50k and then at 91k.
Side note: I also flushed both diffs, and highly recommend doing it around 80-100k or every other tranny flush. Front diff has meager 0.6L of fluid. At 90k miles both had dark fluids.

 

reviewed my pics and I'm pretty sure L1/L2 is where oil enters and L3/L4 is where it exits.
You can actually see oil passage in the diagram you posted next to L2 that sprays fluid into the planetary bearing. The hole by L3/L4 is at lower level controlling for the amount of ATF that is present at any given time.
The exit hole is also closest to the tranny oil pan so I'm guessing the fluid that exits transfer case ends up in the pan and does not flow through the entire transmission.

 

Great discussion all! Thanks for joining and sharing your insights NYCGLK!

 

So after about a nine months after I had my TC rebuilt I started to hear a faint whine and took it back to the indy that rebuilt it. He said he couldn't tell where the noise was coming from but suspected the front differential. It wasn't that bad at that time so I went on with life. I wanted to get the engine mounts replaced mounts which I had already purchased from the dealer for a good discount. The indy that rebuilt the TC would not install my mounts and told me to take them back and he would buy them.

So I phoned another indy in town. By now the whine had gotten worse. The second indy reluctantly agreed to install my mounts. I told him before he installed them to diagnose the noise. I may have mentioned that the TC had been rebuilt and the first indy was suspicious of the front differential. The second indy calls me and says the front differential is bad and he can get me a low mileage used one for a reasonable cost.

Recognizing that I would in essence get the mounts installed for free as the subframe would need to be dropped to replace the differential I agreed. I get a call later where the 2nd indy tells me that they replaced the differential but they still hear a noise. I go there and drive the car and the noise that I took it in for is still present. He takes me over to the bench and shows my differential and removed fluid and the fluid does have tiny bits floating in it and the top of the fluid has a silver color layer. We put my car on the lift and listen using a stethoscope and pinpoint the noise to the transfer case. The 2nd indy claims that the differential was so loud that they could not hear the transfer case over it.

He offered to call the first indy and explain the situation and while the first indy was initially amused over the differential diagnosis he did agree and ultimately rebuilt the TC again indicating that they had had other returns due to setting the bearing clearances too tight.

I really want to believe that the first indy told me a straight story (he genuinely seemed a good guy and has a loyal customer base) but part of me thinks that if you dropped the fluid on any differential of a car with 125K miles it would be silver looking and have bits in it. The other part that bothers me is it had the exact same sound after the replacement of the differential. I would have thought if it was that loud that he couldn't hear the transfer case noise then I would have heard something different.

I am hoping that you guys can say that indy number 2's story was reasonable.

 

#1 tried to cover up a bad job they did with rebuild. They admitted later that they had made mistake of setting bearing clearance too tight for some others so they knew they had done that to you too. Just wanted another job to cover cost to do the rebuild again. This is my opinion.

 

I was hoping that my noise was front diff as it seemed to be coming from the front inside of the car. However, once I put the car on jack stand it was very apparent that the noise was coming from the back end of the transmission. I agree that the noise is faint enough and can be mistaken for normal and gets drowned away by other noises. Once I had the car on the lift I was able to hear noise coming from the front end shaft on TC side, where the failing bearing was. Mind you, I'm not a car technician, I am in finance industry and I wrench for fun. It was pretty clear it wasn't front diff. Draining front diff is easy way to diagnose. When I drained mine, I didn't have any metal but the fluid was pretty nasty (that was at 90k miles).

 

That's why I didn't want some monkey shop rebuilding it. This is not a break job or oil change. This is a tranmission rebuilding service that requires certain skills and patience. This is not a high volume job where you can forget a wrench under the hood.

Contrary to some comments here and in other threads, I don't think there are any clearances being set during assembly. These things are produced by thousand per day. The clearance is set during the car development and then bearing supplier is told what it is. What one should do tho is measure the replacements to make sure you didn't get wrong or defective part. You also need to make sure that the shim/spacer used to set the clearance and the outer race are installed all the way in. It's tight fit and may seem it's in all the way while it's not. In other words, plenty of room for mistakes especially when you are running a shop on an hourly basis. Lastly, did the shop replace all 4 bearings, or only the bad one?

 

Thank you for the replies. Just to be clear what I was really looking for was a weigh in on whether in fact I needed a front differential. I am somewhat encouraged by the report of no metal bits in your NYCGLK.

I would not describe the shop that did the rebuild a monkey shop. They only service Mercedes and have repaired cars including a Mercedes Grosser 600 and have been in business 40 plus years. That said I suspect that the quality of their mechanics may well have deteriorated from what they once were. They had one mechanic who was the local man on Mercedes and I don't think that he still works there. And I suspect that the shop owner has never turned a wrench in his life.

So my options were a) Do what my chief yacht engineer son said to do which was fix it myself. This didn't work because it was cold, I don't have a lift and was imposing on the kindness of a friend at work for his spare car while mine as getting repaired and oh I was under the gun at work and I'm not that great of a mechanic. b) Take it to a transmission shop. The most reputable transmission shop in town refuses to work on Mercedes because they got burned by having to pay to have a transmission reprogramed by the dealership. The guy would get mad when I asked him about repairing it. Though had I gathered up the parts which i didn't feel confident doing he might have reconsidered c) Dealer no rebuild only replace the entire transmission assembly to the tune of $8500. d) Mercedes specialist indy rebuild for $2300 plus a fluid change.

 

I'd probably get a rebuilt unit from Sun Valley or Peter Schmid, and have the Mercedes indy shop swap it.

 

I assume you mean rebuilt the front diff? Yes, or just a used one from low mile car and change fluid.

 

right, the transfer case and transmission are all one unit. if a bearing has failed in the TC, then odds are pretty good the metal chips are all over the innards of the transmission, so the whole thing needs rebuilding.

 

That's actually not as black and white as people make it out to be. TC is attached to transmission and uses the same fluid but it's almost a separate unit with is own housing. Based on benz books you can by replacement TC...but yes I don't see the point in that.
Bearing doesn't fail overnight. As I mentioned, some people drive for thousands of miles with chipped bearing before it gets worse.
There is a little sump for catching debris in the transfer case before fluid goes back to the pan, where there is filter as well.

 

Right since the fluid was due for a change after the first TC rebuild the fluid was changed. Afterward I started to think I was having shifting issues and raised the contamination concern with the indy and he explained and sent a hand drawn diagram illustrating the fluid flow path with the sump in the TC. When it was rebuilt the second time I brought it up and he said the fluid didn't need replacing and the car is currently shifting pretty nicely and I closely monitor the 3rd to 4th shift which had been a little janky.

 

re oiling, that same Intro to Service showed these, first is when the car is stopped, 2nd is when its moving and the TC gears are spinning...

 

Have a look at LCG's post... I think how its described in the document aligns with what I wrote. I suspect the design is the same across platforms... The returns to the main transmission are 5 & 7. Given where their placed, any larger metallic debris I suspect would remain in the sump area of the transfer case and not make it back to the main body of the transmission.

 

Using my own post here for the drawings I posted.

Here is something for all gear heads out there to ponder about the 4Matic function.

Looking at my drawings (upper is easier) and first thinking of the planet carrier (rear wheels) on good grip area and the sun gear (front wheels) on ice. The movement of the ring gear would make the sun gear spin fast while the planet carrier would spin slow or even not at all. This is where the multi disk lock steps in and limits the slip and allows the rear wheels to move the car. This is easy to understand.

But, it becomes a little more complicated when positioning the rear wheels on ice with fronts on good grip.

Looking at the drawings the ring gear applies the force to the outer planetary gear wheel. This same force minus frictions is present between the inner planetary gear and sun gear. Because the forces are the same and the outer gear force is located further away from the center of the planet carrier the planet carrier can only rotate forward. This means that the rear wheels cannot spin faster than the front wheels even without the multi disk lock. They would spin the same speed with fronts in situation like this.

If my thinking is correct this system has a built in lock without the multi disk for situations where the rear wheels are on slippery surface. The system does not allow rear wheels rotate faster than front but it does allow front wheels to rotate faster than rear, which is needed when making turns and really, there is no need for the rear wheels to be faster than fronts in any driving situation.

Wonder if the name 4Matic comes from this “automatic” lock...

A 4Matic driver could perhaps test for this. It would take to find a place where one axle can be placed on ice and one on dry surface. Then from stop do a fast acceleration to see how the wheels behave. Probably need another person to observe or film...

If this all proves right this 4Matic system is very smart, just poorly engineered for bearing strength.

 

the ESP 4ETS is going to take care of spinning wheels in your mixed traction scenario, by using the wheel brakes to slow any wheel that spins.

 

Nice topic, thanks guys
4 MATIC system should be same all around Mercedes-Benz products
For instance: W205 C200 4 MATIC , this car comes with 48V technology but regardless of whatever it comes with I assume it must be the same in regards to how it works

 

Well, earlier 4matic systems were more complex, involving clutches and locking differentials and stuff.

 

I get about a half to one revolution on the backs before the front kicks in, there is no braking of the back involved, it's so seamless you don't even notice, it just goes. If you punch it, the traction control engages, but you really need to step down hard to make that happen. You know what happens when you have the fronts on dry pavement and the backs on ice? Nothing, it just goes. I have also owned Benz's since the early 90's thirty years now and I can tell you I pulled my children out of a lot of snowdrifts in my day with the two wheel drive and brakes for traction control systems, these are nothing like that. One of the reasons I am a proponent for fourmatic. My last 2wd Benz was a '03 S500, since I've had fourmatics

 

“You know what happens when you have the fronts on dry pavement and the backs on ice? Nothing, it just goes.”

The above was what I was thinking. With fronts on good grip and rears on ice both axles go together as they are locked together by the gear arrangement.

I just don’t get the first statement “I get about a half to one revolution on the backs before the front kicks in” because it would not make sense. I would see the fronts turning half to one turn on slippery surface before the rears on good grip start moving the car.

 

Correct, that's exactly what I meant. The backs turn a little, like a half a turn to a full turn before the fronts kick in when all four wheels are on ice.

 

Still does not make sense to me as the rear wheels should not be able to go faster than front.