The standard capacity is about 2 quarts and you will need to put in a bottle of friction modifier. When you fill it up, it should reach to the bottom of the fill hole, with the vehicle at normal ride height.
front or rear? the front is slightly higher and rear of the drain... the back has a cover you remove to drain the fluid and a fill on the front of the diff..
Rear diff, 7.9 pints.Front diff, 2.4 pints.
about 3 quarts
there is 2 different ways to change the fluid this is a drain plug on the front of the rear diff or you can take the back of the pumpkin off on the rear diff.
on the rear diff
About 2.25 quarts of 75w90
Rear diff is 1.75 qts of 75w90 or 75w140
rear differential is low on fluid replace the fluid in the diff. or if that dont work you may have to replace it
80w90...with a diff additive for the rear
The fluid is checked through the plug on the rear cover.
i think its above the diff
On a 1999 Ford Expedition : The washer fluid for the rear liftgate is supplied by the same reservoir for the front windshield ( located in the engine compartment )