Mud

I'm planning to replace front and rear differential fluid, car has 50k miles. From what I can find, looks like M1 75w90 will do the trick. Front capacity .6 liter, rear capacity 2.1 liter. Non AMG so no limited slip.
Does this info agree with what others have found?
Transmission and transfer case fluid changed at 40k miles.

Oda112

If you still need the info I can check WIS for you.

Mud

All good thank you. I did change the rear diff fluid, the front will take a bit of maneuvering!

Oda112

I looked around Wis and it's saying 0.55 L for the front diff (they're refering to it as front axle gear?) and it should be Spec 235.7 oil (75W85 from Fuchs or Mobilube).
It's definitely going to be a difficult job on the 4matic. A DIY would be nice if you have the time and you'll do it before I get the chance
Good luck with it and have fun!

Oda112

Here's a pic of the front diff, the fill plug is the one to the right of the shaft well and the drain one on the bottom. Idk how you'd be able to reach them without taking the steering rack and axle carrier out.

Mud

Hmm I used M1 75w90 in the rear diff but after doing some research on the 235.7 spec I think I'll get the 75w85 approved lube. I've read that both Valvoline full synth and the M1 have been used but I'd like to ensure no warranty issues since I have the ELW.
I thought about filling the diff from that easily accessible bottom drain hole. The stern drive on our boat was drained and filled from a similar setup.
Thanks for posting that info , Konisteiger had also pointed me to the same reference. Plus you made me think twice about that gear lube, I was thinking a GL-5 should work but not sure of the cross reference to the 235.7 spec.

Oda112

I don't think you should be too concerned with the manufacturer of the fluid, as long as it's a reputable brand it should be fine. Since this fluid doesn't require any specific friction modifier or any sort of complementary additive, the only thing you have to make sure of is getting the right viscosity specification. Also, I don't think 90 over 85 will impact your differential's function in any significant way, but it is best to stick with manufacturer spec on fluids. I think Mercedes uses their 23x.x and other specs like that to make life easier for their technicians and milk the franchise cow a little when it comes to certification sheets for 3rd party manufacturers.
I have used the drain hole filling method you talked about, but only on transmissions, which have an offset tube so it's easier to control the fluid quantity you add. While it's not impossible, I would say it's pretty difficult to do it that way. I wonder if there are any drain adapters like the Stahlbus oil drain valve set, they use them on the oil pan and it's supposedly a mess free interaction. Basically you connect the adapter to your oil drain hole and it only lets the oil go in one way. After that, you just remove the filling hose/adapter setup, put a cap on the existing adapter which remains on the drain hole and you're good.
Attachment 412866

Oda112

I did some more research online and it seems that the drain plug filling method is the best bet. I wrongly believed that the plug in the picture I uploaded was the actual fill plug, but it appears it is not.
User khtruong0615 seems to have done it sucesfully on his S550 4matic.
https://mbworld.org/forums/s-class-w...ml#post6397209

Mud

That's the same thought I had on the fluid, seems that a GL5 would be fine but yes in case of any issues probably better to have the exact spec in there.
I was thinking about that fill method similar to what you posted but I've got an air compressor w regulator handy. May be able to use it to "inject" correct amount of gear lube. Incidentally the fluid I drained from the rear axle looked pretty good at 50k miles.
​​​​​​​Thanks!
Edit, seems that in reading up on this there's quite a few mentions where the dealer uses M1 75w90. I'll ask my service mgr out of curiosity. After I refill with 235.7 spec lol.

Oda112

That's a good idea, see what MB have to say about it.Glad to hear your oil was in good shape, mine is at 90k miles now and I have no clue if the previous owner changed the diff fluid ( I got it at 88k). From the looks of it they weren't car people unfortunately.