Ford’s F-250 truck is a rear-wheel drive vehicle--it uses a driveshaft to route the power produced by the engine to a differential, which then transfers that power to the rear tires via two differential gears. To keep the gears cool and lubricated, the differential contains fluid. Over time, this fluid breaks down and must therefore be periodically changed. Fortunately, changing the differential fluid on an F-250 is fairly straightforward and usually takes less than an hour.
If you've driven recently, give the fluid within the differential at least an hour to cool down.
Place a large fluid drain pan below the differential.
Remove all but the top differential cover bolts with a wrench. The differential cover is located on the back of the differential, meaning the side of the differential which faces the back of the truck.
Pry the bottom of the differential cover away from the differential with a screwdriver until the differential fluid begins to drain into the fluid drain pan.
Remove the top bolts from the differential cover with a wrench, then pull the cover off of the differential.
Pull the differential cover gasket off of the cover, then wipe down the gasket’s mating surfaces on the differential cover and on the differential with a lint-free rag. These surfaces must be as clean as possible to ensure that the new gasket seats properly.
Apply a single bead of silicone gasket sealer to both of the cover’s mating surfaces, then press a new cover gasket onto the cover.
Position the differential cover onto the differential, then install and tighten each of the cover’s retaining bolts with a wrench.
Remove the differential’s fluid filler bolt from the driver’s side of the front of the differential with a wrench.
Insert a funnel into the filler hole, then pour differential fluid into the differential through the funnel just until fluid begins to run out of the filler hole.
Remove the funnel, then tighten the fluid filler bolt into the differential with a wrench.
