What size are the differentials on a ford excursion?

The differential size on a Ford Excursion depends on the year and the specific configuration (drivetrain, engine, etc.). There's no single answer. You'll need to check either:

* Your Excursion's owner's manual: This will specify the differential size for your particular vehicle.

* The sticker on your driver's side doorjamb: This sticker often contains information about the vehicle's specifications, including axle ratios (which are closely related to differential size).

* The differential itself: The differential housing usually has a tag or casting number that can be used to identify it. You can then cross-reference that number with online resources or a parts catalog.

Without knowing the year and specific details of your Excursion, it's impossible to give you a definitive answer.