The F150 is a half-ton, full-size pickup truck made by the Ford Motor Company. Gear oil is used in the rear axle differential to lubricate the bearings and ring and pinion gears. F150s that are equipped with four-wheel drive also have a front differential that is very similar to the rear. If a leak is detected, the gear oil should be checked. Low fluid level in the differential may cause it to overheat and fail.
Crawl under the rear of the vehicle. Locate the differential, which is at the center of the vehicle between the front or rear wheels, depending on which differential you wish to check. (Only four-wheel drive F150s have a front differential.)
Locate the threaded plug, which is mounted approximately midway between the top and bottom of the differential at the front.