I just did the checking now that my Z3 is up on jack stands, because I wondered if my transmission was properly filled last Fall. When I bought the car I took 2 quarts each of transmission fluid and gear oil to an indie shop and asked them to change those fluids. They gave me back 1 unused quart of each, whereas I thought each cavity took a little over 1 quart. I removed the fill plugs on each cavity; the transmission began to ooze, and I could feel the oil in the differential.
The procedure for filling both the transmission and differential is to make the car level, remove the fill plug, and add fluid until the first drops come out of the hole.
The procedure for checking both is to make the car level, remove the fill plugs, see if any fluid tries to come out, if not put your little finger in the hole, and if you get oil on the fingertip, there is the right amount of fluid.
The car needs to be level to get a good reading on whether either the transmission or the differential have the right amount of fluid. On front jack stands alone, both will flow fluid or oil back out of their filler holes before they have received the right amount.
On front jack stands alone, both will drain well since both drain plugs are at the rear. But don't drain on front jack stands alone, because then you have to fill, and that takes jack stands at both ends.
Last edited by vintage42; 01-13-2013 at 02:45 PM.