Front Differential Top Cap or Plug?
2010 GLK 350.
Trying to change front differential fluid using procedure of a YouTube video. Alternator is pushed aside to access top cap.
Removed top rubber cap. Tried to put a stick down and expected to find fluid level near the top. Instead, the stick hit something solid plugging the hole. Looked at it with a mirror and with a camera inspection scope and it appears to be a tan coloured plug, with a small hole in the middle. Tried to put the stick in the small hole and again ran into something solid. The scope image appears to show a small “bar” or something across the hole under the tan plug.
I have heard that MB does not recommend changing the front differential fluid, but this seems weird.
Anyone know what is going on here and if there is a technique recommended to change the fluid?
Thanks!
This image below is using a rectangular mirror to look into the fill hole. Red arrow is the top of the front differential. Image at bottom shows the “bar” blocking the center hole, sorry for image quality.
From memory I think there is no fill plug on the W204/X204 front axle and the axle is rather filled through the axle (halfshaft) hole. This requires halfshaft removal.
This video shows a non-WIS workaround:
Does not matter, but mystery is whether MB decided to make filling at the top cap not possible at some point where previously it was possible.
Filling at bottom will be much easier with the right pump equipment.
Thanks!




As others have said I used an inexpensive fluid pump and filled it through the drain plug. I already had the fill adapter for the trans. I didnt have a shut off so used some quick connects, when done pumping pull the quick connect and the fluid wont come back out while your getting the drain plug ready to put back in. Ive since picked up some inexpensive shut offs.








