Rear differential maintenance and changing the fluid is not required as much these days as with many other maintenance services on modern vehicles. But completely ignoring the differential is not recommended in case problems should develop.
A regular maintenance routine includes inspecting the gear lubricant level and condition. You can check your owner’s manual for recommended intervals and your auto repair manuals for specifications as well as the types of fluids to be used.
In the case of rear wheel drive vehicles different types of gear oil are used in different makes and models. Since there is no filter inside fluid can become contaminated with metal flakes and moisture.
Most rear differentials will have magnets either mounted inside or as part of the drain plug to help remove metal particles from the circulating lubricant. In some limited slip rear differentials special lubricants that contain a friction modifier are required. Failure to use this special recommended fluid can cause drivability problems, increased wear and annoying noises.
Recommended inspection points
As with many parts on the car rubber seals are susceptible to wear and leakage. The rear differential contains a few of these lip type seals. One area to check is where the drive shaft attaches to the pinion yoke known as the pinion seal. Any fluid leak from this area should be repaired before lack of lubrication damages internal components.
Rear axle seals are also made out of rubber. A leaking rear axle seal can cause the same type of problems with lack of lubrication. But more importantly a rear axle seal leak can dump fluid onto your rear brake pads or shoes.
This type of problem can increase stopping distances and cause other problems. On many rear differentials the cover that fits on the back is another point of a possible leak to develop. This is also a cover that may need to be removed for regular maintenance.
Most differential covers use a gasket. Sometimes auto mechanics will take a shortcut and replace that factory gasket with silicone. This is not a recommended procedure and can wind up causing a leak down the road.
Rear differential maintenance is important because the entire assembly does not carry more than a few quarts of lubricant. Even a small leak that goes unnoticed can cause the fluid level to be low enough to starve axle bearings and cause other problems. An occasional visual inspection of the parts mentioned above can provide an early warning and save you from expensive repair costs.
The drive train subject is not covered on the internet as much as other auto repair information subjects. I decided to put together a section dedicated to these systems on my you fix cars website. You can see this area located in the left hand navigation under manual drive trains.