How To Service Vehicle Differential System

Car Differential Service

Helpful Information

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 lose metal debris that may be suspended in the gear oil. Most service intervals are between 65,000 and 95,000 miles depending on usage.

Best Practices

• Once the vehicle has been sitting for a while double check the cover plate for leaks
• 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

Step by step guide on how to service an automotive differential. This is a general guide that covers most vehicles.

Difficulty Rating: 2 of 10

Tools and supplies Needed

• Socket and ratchet set
• Gasket scraper
• Screw driver
• Differential cover gasket
• Gear oil
• Shop towels
• Safety eyewear 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.

Differential Cover

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 cover.)

Draining Differential Fluid (Gear Oil)

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 workings.

Removing the Differential Cover

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.

Metal Shaving in Differential

Step 5 - Next, clean the differential housing gaskets surface with a gasket scraper, this will assure a proper seal when the cover is reinstalled.

Removing Differential Cover Gasket

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.)

Installing 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.

Reinstalling Differential Cover

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 recommended fluid.

Refilling Differential Through Fill Port

To check the fluid level use your finger and dip the fluid side 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 driveshaft or wheels when checking fluid to prevent injury.)