yet another gear oil question

[rockyracoon]

most of the cheaper brands of gear oil all say,

" suitable for use in conventional hypoid differentials,and only for top off of limited slip differentials"

is that only because of the fact that they do not have the friction modifier ?
I would like to use a cheaper gear priced oil for the first 500 miles.

 

[bdcardinal]

The Motorcraft fluid does not come with Friction Modifier even.

 

[Kilgore Trout]

Do not use cheap fluids, if you cannot afford to do it right wait until you can.

AFIK only RP comes with the friciton modifier in it and I would not use RP in my lawn mower.

You should be able to use conventional 80W90 gear oil. The newer cars require the 75W140 synthetic. There should be a tag on the diff that says for sure or refer to the owner's manual.