Question, I am changing my rear axel fluid but dont know which type of fluid to use? my local ford dealer and Oreillys said i need 75w-140 but my owners manuel says to use 75w-90. Which should I use? I have the FX4 with the 9.75 possi rear end.

 

75w140 is correct. I believe some early 04's came with the 75w90 but the spec was later changed.

 

75w140 full synthetic and friction modifier

 

That was over 3 years ago. Pretty sure that he's taken care of it by now. Avoid bumping old threads unless it's actually needed.

FM is required ONLY with LS differentials.

 

Excuuuuuuse me!