Is there a way to tell what rear diff. I have? I have a 98 F150 with a 5.4l Is there some type of code?

 

look on the back of your differential for a couple of "dog tags". One might say what type of oil to use and the other will tell you some differential information.

 

if you can support the rear of the truck and spin the rear wheels by hand in neutral at the tire. if they spin in same direction you have a limited slip. if they spin in opposite directions you have an open diff.

that dog tag on the diff if you can read it will say a number like 373 or 355 that is the ratio you can also get the axle code off of the door jam sticker and post it here someone will know what the code means