Easy step by step guide on how to service an automotive differential, though appearances may very the process is the same on most vehicles.
Difficulty Rating: 4 of 10
Tools and supplies Needed
- Socket and ratchet set
- Gasket scraper
- Screw driver
- Differential cover gasket
- Gear oil
- Shop towels
- Safety eye wear and gloves
Begin by parking the car and level ground, blocking both front wheels to
prevent movement. Also put the transmission in park, with the emergency brake
set. Even though the rear wheels will be in the air and will not help the
vehicle from moving its a good safety habit.
Step 1 -
After the vehicle is safely lifted into the air enough to be able to work on
the differential, start by locating the service cover or drain port of the differential.
Some differentials utilize a drain plug which can be simply removed to allow the
gear oil to drain out. Unfortunately most vehicles are designed with a rear cover
that must be removed to allow gear oil drainage. To remove the cover position a
liquid drain basin directly under the cover and start removing the cover bolts.
While removing the bolts allow the bottom three bolts to be loosened only, this
will help support the cover once the remainder of the bolts have been removed.
Step 2 - Once all other bolts have been removed use a screw driver to help separate the
cover from the differential housing. Once the seal has been broken gear oil will
start to flow out. (Note: position a oil drain catch basin under the differential
Step 3 - Continue this operation until the stream of gear oil has stopped, then remove
the remaining three cover bolts while holding the cover in place. Once the bolts
have been removed allow the cover to fall away from the housing to expose the inner
Draining Differential Fluid (Gear Oil)
Step 4 - Once removed clean the cover by scraping the gasket from the cover surface, also
wipe out the cover while cleaning the particle magnet.
Removing the Differential Cover
Step 5 - Next, clean the differential housing gaskets surface with a gasket scraper, this
will assure a proper seal when the cover is reinstalled.
Metal Shaving in Differential
Step 6 - Once all cleaning processes have been completed its time to reinstall the cover
with a new gasket, install sealer to the cover surface. (Note: apply sealer to the
inside of the bolts holes to prevent leakage.)
Removing Differential Cover Gasket
Step 7 - Once the gasket has been installed, reinstall the cover onto the differential
housing and reinstall the mounting bolts and tighten in a star pattern.
Installing Differential Cover Gasket
Step 8 - Next, locate and remove the differential fill port which is located near or on
the pinion snout. Once the plug has been removed fill the differential with manufacturers
Reinstalling Differential Cover
To check the fluid level use your finger and dip the fluid side of the differential
and continue and do so until the fluid is at the top of the drain plug hole or until
fluid is dripping out, reinstall the plug. The differential fluid change is now
complete. (caution: never turn drive shaft or wheels when checking fluid to prevent
A differential unit is used to transfer energy delivered from the transmission
to the rear axles and then onto the wheels. Inside the differential there is a pinion
gear, ring gear and spider gears. These gears are lubricated by 90 weight gear oil
which loses its viscosity much like engine oil and must be changed. Though the differential
does not have a filter, most utilize a magnet located inside the cover housing which
is designed to trap any loose metal debris that may be suspended in the gear oil.
Most service intervals are between 65,000 and 95,000 miles depending on usage.
Refilling Differential Through Fill Port
- Once the vehicle has been sitting for a while double check the cover plate
- Posi-traction or limited slip differentials use a special fluid that must
be installed or malfunction will occur
- Never turn axles or wheels when checking the fluid level. Internal gears
can be sharp which can cause injury
Article first published 2016-02-04