07 S550: front and rear differential fluid change

[kevm14]

Rear is pretty typical. Fill plug and drain plug. However, they take a 14mm allen. I do have it but man it was a tight fit. I had to really clean the plug to get it in and even then it was super tight. The other issue was for the fill plug there was no room to attach the ratchet to the socket once it was in the plug. Ended up slipping a box wrench onto the 14mm shank of the socket, sticking the socket into the plug and then doubling up wrenches to get enough torque to loosen it. I did not have a traditional 14mm allen key which may have worked with a cheater bar.

Ended up using this type of tool (essentially a large syringe) to inject the new fluid. Not my favorite because it takes a lot of muscle to pump 85W-90 gear oil.

To fill it up I ended up transferring the gear oil into a clean and empty washer fluid bottle. Next time I'll just yank off the stupid straw from the Liqui-Moly bottle. The straw seems helpful except it doesn't go into the container so you still have to squeeze/pour into the diff. That's impossible because of the height of the fill plug. Quite a workout to suck up gear oil and dispense it into the diff. Rear diff holds around 2 quarts which was like.....3 refills of the tool I think. I feel like the factory used sealant on the plugs but that seems silly so I didn't use any.

The front diff required a little more ingenuity. There is either no fill plug or it's buried by the subframe. So the process is simple: drain the fluid and pump a measured amount back into the drain hole (just like the transmission it turns out).

I attempted to measure the fluid (very sloppily) and ended up with 520 mL plus a little spillage. Factory spec is 600 mL (someone on the forum said 650). So a little low but not bad at all. Maybe the weirdest thing is that the fluid was hot. At first I was like....oh no is this transmission fluid somehow? But no, it was the diff. It is bolted to the oil pan or something and may be intentionally (or unintentionally) heated by the engine coil. So for gear oil it was alarmingly thin. Glad I changed it I guess.

To fill I made quart container (old ATF container) available, one that had the level window and also graduation markings. I filled to 800 mL and the plan was to pump up into the diff until it showed about 150 mL remaining. That's about what I did plus another pump or so. Might be a touch over filled but probably not by more than 100 mL or so. Oh I also bought a kit of threaded adapters for filling transmissions and stuff. It turns out the thread is M12x1.5 (I think) and that was one of the fittings in the kit. It threaded right into the diff drain plug hole, then I slid the pump hose into the adapter. Pretty simple.

[kevm14]

I did the front again, unplanned, at 96k. It did not need it. I was trying to determine if fluid was leaking. It was not.

600 mL came out and that is what it is supposed to have.