Differential fluid question
I'm going to be changing the oil in both the front and rear diffs (7.5 non LS, don't remember the gear ratio). I bought this truck a few months ago and I don't know if it's ever been changed.
I bought some 75-90 synthetic for the rear. It recommended it in the owners manual. However I've read where Ford now recommends 75-140 in the rear diff.
Will using the 75-90 hurt anything? Will it matter if it's a full synthetic?