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How to Put Gear Oil in a Rear Axle

by John Walker

A rear differential transmits power from the transmission or transfer case to the wheels. A transfer case is used on all-wheel drive and four-wheel-drive vehicles to split the power between a front and a rear differential. The construction and maintenance of front differentials mirror that of the rear on the same vehicle. Most differentials call for SAE 75w90 gear oil, however some heavy-duty and limited-slip differentials need SAE 75w140 gear oil. Consult your owner's manual for the proper weight oil to use.

Park the vehicle and engage the emergency brake. Raise the vehicle with a jack under the axle for each side of the vehicle, if necessary. Place jack stands beneath the axle for safety.

Remove the differential fill plug. Most plugs come out with a socket wrench. The head of the wrench fits into the fill plug. The plug is typically located on the front-side of the differential on either side of the drive shaft. Some vehicles use a rubber plug on the differential cover. Use a screwdriver to pop out the rubber plugs.

Push the screwdriver into the fill hole and spin it around some. The differential is full if the tip of the screwdriver comes out with fluid on it. Fill the differential with gear oil if the tip comes out clean.

Attach one side of the tubing for the siphon to the bottle of gear oil. Insert the other end of the tubing into the fill hole. The hand pump will have arrows showing the direction the fluid will flow. Point the arrows to the differential and fill the unit until a small stream of oil comes out of the fill hole.

Reinstall the fill plug into the differential. Lower the vehicle one wheel at a time removing the jack stands as you do.


  • You should check the fluid level in the differential every 3,000 miles.

Items you will need

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