mrslyfox

so i am changing the rear differential oil in my 94 4x4 this weekend. Been a while since I have done this. How full do you fill it? I figured it was like the manual transmission, filled till it started coming back out the fill hole and then it was full. Bought gear oil at Advance Auto Parts yesterday and on their computer it was saying to fill to 1/4" below the fill hole? Is this correct? Why didnt they just lower the hole 1/4", then fill till it started coming back out? Would make sense to me. Anyway, anyone have any input on this? Also, I just bought Mobil 1 75w-150 synthetic, thats all I could find in 3 different stores except store brand, and every place had Royal Purple. Question is... Why synthetic? I changed it shortly after I bought it (new in 1994), pretty sure it has regular non-synthetic 75w-90 Valvoline, but that was 17 years and over 250,000 miles ago. but I read where synthetic wont absorb water, so you could cause rust? Seems regular non-synthetic might be better and change more often.
Anyway, main question is how full do I fill the thing. :-)

DriveAk

to answer your main question fill it till it starts coming back out the fill hole, its not gunna hurt it, the other questions I am not sure about haha

techrep

iTrader: (1)

Synthetic won't hurt it, and the gear oil don't absorb water, it displaces it...and fill it like DriveAK said.

Mass0wnage

synthetic is thinner, but more lubricating, causes less friction, therefore allows gears to spin more freely.