MB W212 Front Diff Drain & Fill

[BHopkins]

Those of you familiar with the MB W212 platform are probably aware that there is no fill plug for filling the front diff, on 4Matic models. I believe the MB method for filling the diff, is by pulling an axle. Consequently, it is not unusual for W212 4Matic owners to neglect changing the front diff.

This guy recommends a method of filling through the drain plug, approximating how much fluid is going in, and quickly putting the drain plug back in. He is a little bit of a hack, as he didn't even bother cleaning off the area around the drain plug, before removing it. But the technique is worth considering.



After watching and learning from his experience, I'm tempted to try something similar myself, as I am one of those that has never changed the front diff fluid in my '14 E350 4Matic. I think I heard somewhere that the front diff drain plug is the same thread size as the transmission drain/fill plug. If this is true, I can use a fill adapter that screws into the drain plug opening, and pump in the right amount of fluid plus 2-3 extra ounces, to allow for loss, while pulling the adapter, and screwing in the drain plug. I would also measure how much fluid came out, so I could verify that I got the same amount back in.

I sure prefer diff fills with a separate fill plug, where it is easier to verify that the fill level is ideal. But It seems to me that this method should work.

What do you think? Would you be willing to do a fill this way?

 

[JHZR2]

I just serviced my 722.9 AT today (just wrote up a thread). I could see the potential to fill a known quantity via the drain plug.

Essentially make a filling attachment like the one for the 722.9, but fitting the differential drain plug thread (assuming it’s different than the AT one, I think my transfer case and differential plugs are bigger, fwiw). Pump in an appropriate amount of fluid, unthread the filler and immediately plug. You could even measure the lost amount to be extra rigorous and compare if desired.

 

[The Critic]

I suppose it's no different than using the "finger method" to do a drain plug gasket swap after an oil change.

Though, according to this video, removing the axle doesn't look very painful at all:

 

[rollins.]

A Stahlbus oil drain valve would protrude appr. 24mm beyond the sealing surface...there might be just enough protecting "fence" around it, difficult to tell by the video . With a suction gun it would make things a whole lot easier to fill with the proper amount .
https://www.stahlbus.com/info/images/Downloads/dimensions_oil_drain_valve-all.pdf

 

[BHopkins]

I just serviced my 722.9 AT today (just wrote up a thread). I could see the potential to fill a known quantity via the drain plug.

Essentially make a filling attachment like the one for the 722.9, but fitting the differential drain plug thread (assuming it’s different than the AT one, I think my transfer case and differential plugs are bigger, fwiw). Pump in an appropriate amount of fluid, unthread the filler and immediately plug. You could even measure the lost amount to be extra rigorous and compare if desired.

My thoughts are very similar to what you mention here, in regards to attempting to capture and measure how much fluid is lost, while swapping from the fill attachment, to the drain plug.

I found another video last night, and interestingly, he shows a fill adapter that fits the 722.9, threaded into the front diff drain plug opening. So it must be the same M12x1.5 threads.

 

[JHZR2]

My thoughts are very similar to what you mention here, in regards to attempting to capture and measure how much fluid is lost, while swapping from the fill attachment, to the drain plug.

I found another video last night, and interestingly, he shows a fill adapter that fits the 722.9, threaded into the front diff drain plug opening. So it must be the same M12x1.5 threads.

Certainly could be.

Thought the plugs on the drivetrain of my w164, except the at pan, were all the same.

I’m not sure it’s m12.

Of course ymmv. Different vehicle.

 

[BHopkins]

Those definitely look bigger than the transmission drain/fill plug. That is the transfer case, right? The transfer case on the W212 shares fluid with the transmission, so no need for a separate transfer case drain and fill, on my E350.

I found a thread on MBWorld discussion front & rear diff, and transfer case fluid changes. Someone there shared a link to another YouTube video of the front diff drain/fill on a W204/205, which shares much with the W212. The guy appears to be much more seasoned and knowledgeable. He also uses the 722.9 fluid fill adapter, and makes it looks very easy. Now I just need to find a p/n for the crush washer.

 

[tcp71]

find a fumoto valve with the long nipple and replace the drain plug with it. attach a silicone hose to it and fill it with the correct volume of fluid. Close the valve and you don't have to play the "How much did I spill" game.

 

[BHopkins]

find a fumoto valve with the long nipple and replace the drain plug with it. attach a silicone hose to it and fill it with the correct volume of fluid. Close the valve and you don't have to play the "How much did I spill" game.

View attachment 298522

A drain valve is not a bad idea, but I don't think a long nipple valve would be the best choice. The valve nipple would be pointing straight down, extending it's full length vertically.

I'm not against drain valves. I used a short nipple Fumoto on the Outback I used to drive. I were to install one, it would have to be low profile. I just looked at the short nipple Fumoto and the ValvoMax, and I couldn't find any dimensions for either.

It does seems unnecessary to install a valve for a fluid change that may be done once every 40k miles, which averages out as being about every 13-14 months for me, just to minimize the risk of how much got dripped.

With some care, it seems that the amount lost when installing the plug should be minimal, perhaps 10 - 30 ml. And a little extra can be added to the fill, to allow for that. Even if none were dripped when installing the plug, an extra 30 ml isn't going to hurt anything.