Changing the Rear Axle Oil of a Dodge Ram

Changing the oil in the rear axle housing on a Dodge Ram does not have a specific mileage interval determined by the manufacturer. It should be changed any time that a leak occurs--primarily to re-seal the rear and check for wear in the rear due to a low oil condition. Other than that, from a mechanic's standpoint, it is a good idea to change the oil in the rear between 70 to 100,000 miles for preventive maintenance reasons. When the differential cover is removed the differential should be inspected to determine whether it is a limited slip differential. The rear differential uses 80-90 weight gear oil however, but if it is a limited slip, an additive is necessary for the clutches. Without this additive the clutches will slip and the differential will ratchet when making tight turns.

You will need the following tools to complete this job:
Floor jack
Jack stands
3/8-inch ratchet
13mm socket in a 3/8-inch drive
Common screwdriver
Two bottles of 80-90w gear oil
Limited slip differential additive
RTV silicone sealant
Gasket scraper
One can of brake cleaner
Rags
Drip pan

Raise and support the vehicle on jack stands. Place the drip pan under the differential cover. Remove all the 13mm bolts in the cover except for one bolt on each side of the cover. This is so the cover does not come off all at once and splash oil everywhere.

Loosen the last bolt a little bit. Use the screwdriver to slowly pry the cover loose, just enough to allow control of the oil flow into the drip pan. Once the oil has drained out, remove the last bolt and the cover. Scrape the gasket material from the differential cover. Use the brake cleaner to remove all the traces of oil around the outside circumference of the cover and the rim of the rear, and wipe with a clean cloth.

Look at the differential and notice if there is a clutch pack in the center left side. Another tell-tale piece is an S-looking piece between the clutches. If it is not a limited slip all that can be seen is the pinion pin with the pinion gears at either end. If it is an open differential just use the gear oil. If it is a limited slip install the limited slip additive first before filling the differential with gear oil.

Lay a continuous bead of RTV sealant around the circumference of the differential pan. Keep the sealant in line with the boltholes and just angle down with the bead to barely touch the bottom of the bolt hole. After the bead is laid, put a little RTV around the outside each hole in the cover. Wait until the RTV begins to skin before it is installed. Skinning means that the RTV outer layer has dried just enough so that it will not stick to a finger when touched. This helps keep the RTV in place when installed.

Install the cover with as little movement as possible. Install the bolts and tighten.
Remove the filler plug in the front of the differential. Pour the limited slip additive in first if needed followed by the gear oil. Fill the differential until it begins to run out of the filler hole. Install the plug.