Performing a rear differential flush is a fairly straightforward procedure. However, you will need to know a few things before you start. First, the best substance to use to flush the differential is fresh differential oil. Most solvents are not appropriate to use and can damage the rear end during the flush process. Second, examine your owner's manual or contact the vehicle manufacturer for recommendations on which differential oil should be used to refill the differential after the flush. Obtain enough fresh differential oil to refill your vehicle's rear end twice.
Park the vehicle, and allow it to completely cool.
Jack up the rear of the vehicle, and place the jack stands beneath the rear axle. Make sure the jack stands are making contact with the axle and are sitting flat on the ground.
Place the drain pan under the differential in a position to catch the fluid that will drain from it.
Loosen and remove the differential cover plate, starting with the bolts closest to the bottom of the cover. Gently pry the cover loose with a flat-head screwdriver if necessary. Try not to damage the gasket at this stage of the flush. Rear differentials are equipped with a fill hole. Resist the temptation to use a small fluid pump to remove the old fluid from the differential through this hole.
Allow all of the used fluid to drain from the differential.
Examine the bottom of the differential case carefully for a buildup of sediment. If present, carefully clear it away.
Reinstall the differential cover, and tighten it with a ratchet.
Remove the fill hole plug, and fill the differential with fresh differential oil. This oil will be used to perform the flush. Never use paint thinner, fuel oil, or an alcohol-based solvent to flush the differential; they do not provide adequate lubrication during the next steps of the flush process. Also, most of these fluids are highly flammable and dangerous to work with.
Reinstall the fill hole plug. Remove the jack stands, and lower the vehicle to the ground.
Start the vehicle and drive it for several (five to 10) miles.
Park the vehicle, and allow it to cool.
Jack up the rear end, and replace the jack stands.
Place the drain pan below the rear end once again.
Remove the differential's cover plate as before, and allow the used oil to drain completely.
Examine the bottom of the differential case, and wipe away any additional buildup of sediment.
Scrape away the old gasket from the cover plate and its mounting surface on the differential case.
Coat the cover plate mounting surface with gasket sealer. Follow the directions provided with the product you are using. Carefully place the new gasket in place on the mounting surface.
Reinstall the cover plate, and tighten all the mounting bolts.
Remove the fill hole plug, and refill the differential with fresh differential oil.
Reinstall the fill hole plug. Remove the jack stands, and lower the vehicle to the ground.
Start the vehicle, and drive for a few miles.
Park the vehicle, and inspect the rear differential for any leaks.
Discard the old oil safely in accordance with local regulations.
