75w-90 or75w-140 rear diff

EvanT08 · #1 11-03-2009, 10:09 AM

I have an 04 f-150 4x4 with the 3.73 ls. My manual recommends 75w-90 but I read all over here to use 140. What difference will the 2 make?

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grizzstang · #2 11-03-2009, 10:46 AM

What manual do you have?

Everything I have read says to use 75w-140 in the rear if you have the 9.75 or the 8.8 diff and the 75w-90 is for the front only. Make sure it is a GL-5 oil.

Since yours is an LS get a bottle of Friction Modifier from Ford and put in in first and then add the oil. If you have the 9.75 diff it should take one bottle of FM and 3 quarts of oil.

glc · #3 11-03-2009, 11:13 AM

Ford specifies 75W140 full synthetic with friction modifier for all rear limited slip diffs.

EvanT08 · #4 11-03-2009, 11:15 AM

This is my manual, should I still use 140?
And I already have the friction modifier, thanks to this forum.

EvanT08 · #5 11-03-2009, 11:53 AM

I called the parts guy at Ford and he said to use the 140, so I guess that's what I'll do.

kingfish51 · #6 11-03-2009, 07:33 PM

Owners manual does say 75w90, but Ford has since change their recommendations and now state 75w140 replace the 75w90.