what is the gear ratio

Somewhere on the driver's door or body area of your vehicle you will find a sticker that has the VIN across the top, GVR, tire size, and other information on it. At the bottom of that sticker it will show an "axle code". Take that information with the VIN number to any dealership and they can get the gear ratio and tell you what type of rear axle is in the vehicle. SOMETIMES, if you crawl underneath the truck, there will be a tag on the rear axle cover (held on by a bolt) and the gear ratio will be stamped into the metal tag.

Why do you say you need to "replace" a new rear end ?

Fordtudor37, Not to dis anyone, but sometimes English writing can be a bit tricky. He may of wanted info on buying the correct NEW rear end for his vehicle because the old one is not working. I know it can be very frustrating at times when questions are asked, but they bring up a host of other questions needing to be answered before a correct one can be given. Hand in there buddy.