Anyone know how to open the front differential file plug? It looks like a piece of plastic cap with a round piece of felt inside another piece of plastic. I don't want to break these plastics without knowing if this is the fill plug.
Help! I have replaced the fluid in the transfer case, the transmission and the rear differential. This 2017 C300 has over 80,000 miles. It's time to replace all the fluids.

 

It is well documented on the forum that there is no fill plug but only drain plug. Dealership fills it by removing the half axle. DIYer's will fill it by pumping the oil up thru the drain plug. The transmission filling adapter fits the drain plug and works well. If you do it, please document by taking pictures to help others. Be safe when under the car.

 

Thank you for your reply a4ncar! You mean the front differential does not have a fill plug either like the transmission? Can you give me more information or point me to the forum where this is discussed? The transmission filling through the drain plug was fairly easy. The following tools made it easier:
Performance Tool W54170 12V Oil Extraction Pump for Automotive, Farm & Marina Use
Basically:
I drained 4 quarts from the torque converter. The drain plug for the torque converter is located around the 5 o'clock position. After removing the drain plug and after the oil stop coming out, rotate the torque converter to the 6 o'clock position to get the rest out.
I drained 1 3/4 quarts out by removing the drain plug on the transmission pan. Drained another 1 3/4 quarts by tilting the green filling adapter inside the drain hole with out breaking off the filling adapter.
Then removed the transmission pan, which has another 2 quarts. If you add up all the above, you get 9 1/2 quart or 9 liters of dirty oil.
To fill it, I used the 12v oil extraction pump to pump 5 liters through the drain hole, then start the car for 15 seconds to let the some of the oil get pushed to the torque converter. Then stop the car and pump in another 2 quarts.
Then start the car again and pump in the rest of the 2 quarts. With the car running, remove the Filler Adapter and screw in the drain plug. Torque to 22 NM.
Tips and Tricks:
When draining the torque converter, I rotate the crankshaft a little at a time. When I hear the oil stop coming out, I rotate the crankshaft a little bit more. Repeat this until I cannot hear or see an more oil coming out. You should have 4 quarts of dirty oil from the torque convert.
To fill:
I gave the Oil extraction pump rest (like 2-3 minutes) when pumping to make sure it does not over heat and quit on me, since I don't how durable this pump is.
By not running the car long, I am not heating up the transmission oil. Then I do not have to worry about measuring the temperature of the oil or oil pan to 45 degree celsius.
Since I measure 9 1/2 quarts of cold oil coming, I am putting back 9 1/2 quarts of new oil.
The trick is be mindful of how much dirty oil you drain out. To do that I used a clear plastic 12" x 16" container and clear gallon jugs to save all the dirty oils that came out.
Torque the transmission pan to 5 Nm. I read the spec is 4 Nm, but my torque wrench start at 5 Nm.
Torque 10 Nm on the torque converter drain plug.
Torque the transmission drain plug to 22 Nm.
I got the "Mercedes C-Class ATF Transmission Fluid Change Kit - 2010-17 - 7 Spd 722.9 Blue" from Blauparts.com

 

Yes "no" fill plug, unlike the rear differential. I don't have the links handy. But do a search on all platforms you should be able to find it. If you are still having problems finding it, I will help locate it. Many thanks for the transmission fluid DIY, I am sure it will come handy for the members. My service is also coming up soon before the summer is over that I would like to tackle myself.

 

Here is one thread....

https://mbworld.org/forums/s-class-w...il-change.html


Also, see this video for W204


Hope it helps....

 

Here is the screen


shot from EPC that does not show fill plug on the W205 4matic.

 

Thank you for your information a4ncar! I guess it will take some practice to perfect this kind of refill method of switching from pump to plug without loosing too much oil! I will take a deep breath and give it a shot!
I guess if MB cannot find a good spot to put the refill plug. This is better than having a refill from the top with the risk of people over filling the front differential. Thanks again!

 

Update on the front differential. I drained and filled the front differential from the same bottom drain plug yesterday. To pump the 75w85 oil back in, you need the filler adapter and a gear oil bottle hand pump. The spec calls for 0.6 liter, so I pump in 0.8 liter to anticipate loosing some oil when switching the filler adapter with the drain plug. With my plastic 12"x16" container underneath, I can measure how much came out during the switch. Then I can slowly open the drain plug to let out more if needed until I measure 0.2 liter total that came back out. To my surprise, if you have everything ready and carefully discount the pump hose from the filler adapter first, then with a finger at the bottom of the filler adapter discount the filler adapter and quickly connect the drain plug, you should only loose 50 ml or less. So, I had to slowly open the drain plug to let out about 0.15 liter into a measuring cup. My thought was, if I pump in too little and it drained out more than I expect during the switch, then I have to start over, since I cannot add a bit more from the top like the good old days.
So, refilling from the same drain hole, you have to be precise, since you don't have the luxury of filling it until it overflows from the filling hole like the rear differential.

 

Great to hear that you were able to do it. Did you measure how much actual oil came out when you first drained it? Did you use any additives on the refill?

 

Thanks for your youtube link. I didn't think it was possible to refill the differential from the bottom. The old school says always make sure you can loosen the filling plug before touching the drain plug!
0.5 liter came out, but passenger axle connecting to the front differential looks little wet. So, I suspect that 0.1 liter might have seep out over the years. I have read anything site that it takes 550 ml. I figured if the spec calls for 550 ml, over filling it by 50 ml won't do any harm. I am having a tough time finding any kind of Mercedes specs on this 2017 C300 4matic on the internet. I see some repair workshop manual disc for sale on ebay for $24.95. Do you know any good repair manuals for this model?
I refilled it with SAE 75W-85 (GL-5) febi bilstein for the front and rear differential. Am I suppose to use additives?

 

I was jut wondering about additives, nothing more. Yes, eBay maybe one of sources for WIS/EPC and you will need it if you do your own work.