i have a 2002 f-150 with 63, 000 miles on it, recently i have heard aliitle howling in rearend area. so i tighten pinion nut. fix that problem, now i look at my manual and it says 75w140 synthetic fluid. i bought 4 qts.
problem being now.
my rear end tags say, ONLY USE FEHP OIL 75W 90..
why does my rearend and book does not match???
here are tags to help this issue out. i hate to run wrong oil and due damage.
i put the 75w140 in it. i hope it does no hurt it. let me know what you think. and by the tags what all can you tell about my truck??
also view of gears, no marks at all on none of them , fluid was pretty clean

 

my truck was wrecked 3 days after it was new in 2002 so i have no idea what they may have replaced it with rearend wise. if any.
it was it in the left rear quaterpanel hard.

 

Use 75W140. 75W90 is being phased out for use in rear axles (it's still used in the front axles of some 4x4 Ford SUVs and pickups) in favor of 75W140.