How to Change Differential Fluid

I will be demonstrating and giving examples on how to change the differential fluid in an axle on my dad's 2001 f150. Although it is not an everyday occurrence, changing the differential fluid in a vehicle is a normal replacement done on types of equipment. Weather on a big rig, tractor, pickup truck, or another vehicle at some point in their life they should have their differential fluids changed to increase their life and reliability.

The differential is what transfers the motion of the transmission or transfer case to the wheels on the ground through gears and axles inside the differential. Depending on the drive of the vehicle, whether it be a rwd, fwd, 4x4, or awd, the differential can be located in the back, front, or in both front and back.

Many manufacturers have a specific amount of time or miles that they would recommend changing differential fluid. Many times on highway vehicles it is somewhere around the 150,000-mile mark. Not everybody changes this as it is not a “necessity”, however like anything over time it becomes contaminated and breaks down, especially if the vehicle has sat for a long period of time and the seals have gone bad on the differential cover.

Before we begin working on draining the differential, it would be wise to look up in the service manual for the vehicle how much fluid the differential takes. If the information cannot be found, looking it up online is the next best thing as long as it is from a reliable source. After finding the given information needed, go to the nearest store and buy the gasket for the vehicle and the differential fluid of personal choice. I would recommend driving the vehicle to the store if at all possible to allow the fluid to warm up in the axle and flow out much easier when removing the differential cover. Weather being brand specific or trying to buy the cheapest fluid possible, it’s all personal preference. Many times true differential fluid cannot be found, a common replacement is to use Automatic Transmission Fluid in its place. It would also be a wise idea to pick up some brake cleaner as well for cleaning the differential cover later on.

After buying the fluid now begins the process of gathering the tools needed for the job. Some of the more common tools needed for this job are

Catch Pan/Bucket

Paper Towels

Ratchet

Breaker Bar

Socket

Pry Bar

Scrapper

Gasket

Funnel

(Helpful but not necessities)

Torque Wrench

Brake cleaner

Ramps

Jack/Jack Stands

An impact driver and impact sockets can also be used if there are some more expensive tools available, but for the average joe at home, these are all the tools needed for the job.

Depending on the height of the vehicle, it may need to be driven onto ramps, or jack up the vehicle to have easier access to the different cover. Once there is access to the cover, begin by placing the catch pan underneath the differential cover, loosen and remove the bottom bolts on the cover, and slowly make way up both sides of the cover. Now that there are only a few bolts remaining, loosen but do not remove them. Now that they are loosened, gently pry the cover and gasket away from the differential on the bottom. The differential fluid will the run out the bottom opening of the differential cover into the catch pan, while the remaining bolts hold up the cover out of the way.

Remove the few remaining bolts completely and begin to scrape away the leftover gasket from the differential and covers mounting surfaces. Continue to clean and scrape away the gasket until both surfaces are few of anything gasket remnants. Spray brake cleaner along the inside of the cover over the catch pan to remove any remaining fluid and contaminants. Dry with a paper towel, preferably with that of a blue shop towel. Spray one of the towels with brake cleaner and wipe down the surface of the differential. Once everything has been cleaned, take a dry towel to both the differential and the cover to dry off both surfaces.

Apply the new gasket and differential cover back onto the differential. Hand tighten all bolts, then torque down to the specific specification given by the vehicle's manufacturer. This may also need to be looked up on the internet to be found. Not everyone is able to have access to a torque wrench either, if there is not one to be used, it is not absolutely essential to use one. As long as all the bolts are tightened down tight using the ratchet with no leaks it will be good to go.

Once the cover is torqued or tightened down, remove the plug on the differential housing, using the right sized ratchet. Depending on the type of vehicle being worked on, the plug could require a 1/4in, 3/8in, or 1/2in. Ratchet. Once the plug is removed, insert the funnel into the hole, and begin to pour in the new differential fluid. In many cases, the amount given by the manufacturer fills almost to where the plug is located on the housing. However, just to be sure of the amount, only add the amount given. Once the correct amount of fluid has been added, hand tighten the plug, then tighten down with a wrench. In some cases, a torque specification is not given for this plug, tighten down the plug till it is tight, snug, and not going anywhere, but be very certain not to over tighten or strip the threads.

After finishing up the differential all that’s left is to hop in the vehicle, drive it off the ramps or lower it off the jack stands, and take it out for a test drive. This will ensure the fluid is lubricating properly and that there are no leaks. After driving around for a few minutes to warm up the fluid, return to your home or shop. Inspect the differential and plug for any leaks, as long as it is dry, and no fluid is leaking the job is now finished.

All that's left to do is clean and pick up tools, throw away garbage, and recycle the used fluid to the correct facility. Now the differential fluid is brand new and good to go for another 150,000 miles. Although it is not a common practice done on vehicles daily, it is a good practice to do every 150,000 miles or so to keep the life of the axles and gears making up the differential in good working order for years to come.