Having a tough time tracking down the fluid capacity of the rear diff on a regular non 4x4 f150 (1998). I found the tag says 75w140 synth, but how much of it?

sorry for the n00b question!

 

I will assume the axle is the regular 8.8" C-clipper....same axle as used in my '97 F150: My Alldatadiy.com manual shows a capacity of 5.5 pints.

The tag is correct: Do use only a good grade of 75W140 full synthetic GL5 or better. I like Valvoline (mainly because it's readily available).

The differential is nominally full when a crooked finger stuck into and downward into the fill port can bring out a drop or two of oil on its tip.... and DEFINITELY full if the oil begins to run out of the port as you fill it.

Of course the truck will be on level ground during the fill process. (Slap me on the back of the head for that comment.)

 

is it possible to overfill the thing? I didnt have the equipment to fill it properly, so I had to take a hand soap pump and some 1/4" tubing - I put my finger in the diff, angle it down and touch liquid, so I assume that is good eh?

 

Yep, the crooked pinky with the oily tip says the level is good.
The diff can be overfilled, but you have to work at it.... (1) Jack up the left rear wheel.
(2) Squirt lots of oil into the fill port then stick the plug in before the extra can run back out the port..
..just two ways to do it.