99 ML 430 Diff plugs - sizes?
 

What size hex (allen) do I need to go buy to remove the plugs to change the diff fluids? It looks BIG.

Thanks.

It's not a hex ... it is square

You simply use your standard 3/8" extensions...

The more challenging aspect of this service is getting fluid into the differential

I checked and it is a hex. I know, most diffs use the square of a rachet (usually 1/2") but my plugs on the front (drain and "check") are both hex, no doubt about it.

I changed the fluid in my diffs and transfer case this weekend, and thought I would answer my own question here in case anyone down the road is searching for the knowledge.

The front and rear differentials use a 10mm hex head (allen) for the fill and drain plugs on both.

The Transfer case plugs use the 3/8" rachet extension square.

One more tip--the diffs hold a bit more than the manual says. I originally bought 3 quarts of fluid, but ended up needing about 3 1/4 quarts, so plan accordingly!