All,
I have a '03 FX-4 F-150. At what mileage do I need to change the rear end oil? What type of rear end oil do I need to use ( I would rather go with Ford Motorcraft brand)? I am almost sure the truck is limited slip. Also I have noticed when I turn sharp @ take off I can feel a viberation in the rear end like the tires are wanting to break loose. Is this normal for this truck? THANKS for any info...............

 

Its either 100,000 or 150,000 miles with synthetic GL-5 fluid. The wanting to break loose in a turn is the rear working properly. The rear tires don't turn at the same pace in a turn, one gets slightly more rotation than the other. Slow down a bit, and you won't hear it.

 

According to Haynes, you're supposed to change the diff fluid every 30,000 miles, and don't forget the friction modifier because of the limited slip. Also, you MUST USE SYNTHETIC FLUID!!!! Any good quality (Royal Purple, Redline, Amsoil) gear fluid should work fine.

 

Haynes sucks. Ford says officially you aren't supposed to service it unless the fluid gets contaminated, like with water when launching or retrieving a boat. But if you really want to, I'd go every 100K or so, maybe 60K if you beat on it real hard, like smashing around offroad a lot or something.