'89 f150 5.0 5 spd. "The rear end... it can be done in your driveway. You will want to raise the rear if you want to spin the tires (by hand) while the cover is off to check the gears."

I just removed my rearend cover and a whole lot of fluid ran out like a waterfall. What type of fluid is it and where do I refill it? I don't see anything unusual, and probably wouldn't know it if I saw it.

 

There's a filler plug on the drivers side. Takes a 3/8" socket extension to remove it if I remember right. Fill 'er up with 80W/90 to within 1/2" of the bottom of the fill hole.

 

x2 but fill it to the bottom of the hole. the 1/2" below is a minimum

 

With gear oil or can transmission fluid be used, Dextorn/ Mercon III?

 

gear oil... 80w90 as mentioned above

 

I have some gear lubricant left in my garage: SAE 85w-140 GL-5. Just curious, what would that be used for??

 

This is used for the older f-250 and the f-450/550 rear ends. The newer superduty's use synthetic oils for the Ford axles, the Dana axles can use the conventional oil.