The 2005 Ford F-150 came equipped with an 8.8-inch rear differential. The rear axle ratio indicates how much the rear differential changes the turning speed of the engine and transmission. A rear-axle gear ratio of 3.08-to-1 indicates that the driveshaft must turn 3.08 revolutions for the axle to turn make one complete revolution. The easiest way of identifying what ratio the rear axle gears, also called ring and pinion gears, are is to read the coded tag bolted to the differential cover.
Block the front wheels of the F-150 using wheel chocks. Roll the floor jack under the center of the rear end and raise the rear of the truck until there is room to crawl under it. Slide jack stands under both rear axles for added safety in case the jack slips while you are under it.
Locate the metal tag attached to the rear end cover by one of the cover bolts. Clean any dirt and grease build-up off the tag using spray parts cleaner and shop towels.
If the bolt head is covering the numbers on the tag, remove the bolt using a 13-mm socket and ratchet. Read the bottom set of numbers on the tag. They will indicate the gear ratio and size. For example, the tag code 3L08 8.8 indicates a limited slip differential, marked by the letter L, with a 3.08-to-1 gear ratio and an 8.8-inch ring gear.
