Hey all. Recently serviced my rear differential on my 94.5 F250. Was researching online and people recommended 75w 140 (F1TZ-19580-B). So thats what i put in it. Its not a Dana axle its the ford axle with limited slip. After looking through my Powerstroke manual i realized that it called for Premium Rear Axle Lubricant (XY-90-QL) along with 8 oz of friction modifier (C8AZ-19B546-A) the manual also calls for the Premium Rear Axle Lubricant on Dana limited Slip axles slong with 4 oz of modifier. Then its says for Severe Use Dana F-Super Duty Rear Axles to use the 75W-140. It doesnt say to add any modifier for the 75w-140. I had bought some just in case but i ended up filling the axle with less oil than it called for so i figured i would just leave out the modifier and see how she does. I don't notice any difference. Should i be ok? I quess my question is, what have you guys put in your rear diff on your OBS trucks. Also what would some symptoms of not having modifier be? Thanks!

 

If you have limited slip rear you need the modifier if it isn't already in the fluid. A lot of the 75/140 has it already in it. Depends what you got. I run 75/140 in mine also.

 

I bought the motorcraft 75w-140. It didnt say anything about it having the modifier in it. Although the manual didnt say to add any modifier for applications that called for it.