How to Change The Gear Oil in Your Cars or Trucks Rear Differential

The rear differential is a sealed unit, however, the differential oil will become contaminated through worn parts. This takes some time to develop unless the vehicle was used for heavy hauling. There is no hard fast schedule for changing the differential gear oil. The general consensus is to change it at 60,000-mile intervals. This will serve two purposes: It will clean out all the floating metal particles and aid in determining if there is an impending wear problem with the differential.

Things You'll Need

• Floor jack
• Jack stands
• 5 pints 80/90-W gear oil
• 1 bottle limited slip friction modifier (if applicable)
• Ratchet
• Set of sockets
• Drain pan
• RTV silicone sealant
• Set of wrenches
• Torque wrench
• Common screwdriver
• Can of spray brake cleaner
• Rags

Instructions

1. Raise the rear of the vehicle with the floor jack by placing it under the differential. Place a jack stand under the axle tube on both sides of the differential. Lower the vehicle so it rests on the stands and remove the jack. Block the front wheels with some wood or whatever is available.

2. Place the transmission in Neutral. Spin one of the tires and watch the reaction on the opposite tire. If the opposite tire spins in the opposite direction the vehicle has an "open" rear. If both tires spin in the same direction it is a limited-slip -- or positraction -- rear. The limited-slip differentials need to have a friction modifier added to the oil.

3. Place the drain pan under the differential. Loosen the filler plug with a wrench to be sure you can get it loose before draining the differential. Remove all the bolts surrounding the differential cover with a socket. Pry the rear cover off using the common screwdriver. Allow all the oil to drain.

4. Scrape all excess gasket material off the cover and the differential-case mating surface using the screwdriver. Hold the cover over the drain pan and spray it with the brake cleaner to rid the surface of all oil. Do the same to the case and wipe both off with a rag.

5. Apply a ¼-inch continuous bead of RTV sealant around the mating side of the cover, making the bead slightly overlap the inside of the bolt holes. Lay the cover down and allow it to set up to the point that it will not stick to your finger when touching it. As soon as it reaches the point it will not stick to a finger, install it and the bolts. Torque all the bolts to 40 foot-pounds with the torque wrench.

6. Remove the filler plug using a wrench. Fill the differential with 4.8 pints of 80/90 W oil. If the differential is a limited slip, add the friction modifier first. Fill the differential until the oil is level with the filler plug. Install the filler plug. Place the jack under the differential and lift the vehicle and remove the jack stands and lower the vehicle.

Tips & Warnings

• If your vehicle's differential has a drain plug, skip Steps 3 through 5, and simply use the drain plug. Always loosen the fill plug first, though, to make sure you'll be able to fill the differential.