Differential and Transfer Case Lubrication Service

Words: Mark Yanochko

Differential and transfer case fluid should be drained and replaced on a regular basis as recommended in the maintenance schedule for a particular vehicle. The maintenance schedule to follow, shown in the Owner’s Manual, will depend upon the type of service to which the vehicle is subjected. Replacing the fluid is important, particularly if it is contaminated with water; however, it is also very important to use the correct fluid.

Recommendations for the fluid type can be found in the Owner’s Manual or O.E. Service Manual for the particular vehicle being serviced. A good reference for the different types of differential and transfer case fluids used in Chrysler, Jeep® and Dodge vehicles is in the You Should Know section of this issue on pages 44–45. This article provides an overview of the purpose of these fluids, the different types and general recommendations for each component.

A typical 4-wheel-drive vehicle, like the Jeep Liberty or the Dodge Nitro, will have a front axle with an independent suspension, a transfer case located behind the transmission and a solid rear axle. Both axles have differentials. Let’s review draining and filling the fluid in these three components.

FRONT DIFFERENTIAL

The front differential probably presents the most problems when it comes to changing the fluid. Draining the fluid isn’t the problem, but filling the differential is tricky. Figure 1 shows the bottom of the differential with the drain plug, A, clearly accessible. The plug is removed with an Allen head wrench, allowing the fluid to be drained (Make sure that you can loosen fill plug, B, Figure 2, before drain plug, A).

Filling the differential is difficult as access to the fill hole, B, which is located on the side of the cover, is somewhat limited. As you can see in Figure 2, the fluid bottle, C, (usually Mopar® Gear & Axle Lubricant, SAE 80W-90 GL-5 – see Owner’s Manual for correct recommendation) is almost horizontal as there is little room to raise it. You might spill some of the fluid, D, onto the mounting bracket, E.

If filling the differential in this manner is too difficult, place a plastic tube on the nipple of the bottle. Position the bottle in the open area behind the radiator and direct the tube into the fill hole. Squeeze the bottle to inject the fluid.

Regardless of the method, fill the differential to the bottom edge of the fill hole.

TRANSFER CASE

Draining and filling the transfer case, F, shown in Figure 3, is probably the easiest task of the three components. On the back of the case you can see the drain plug, G, the fill plug, H, and the ID tag, J.

The ID tag contains the transfer case model number, assembly number, serial number (represents the build date) and the low range ratio. This information is valuable when servicing the unit.

To drain the fluid, first remove the fill plug, H, then simply remove the drain plug, G. To fill the transfer case, insert the nipple of the bottle, K, into the hole (Figure 4). Fill the transfer case to the bottom edge of the fill hole, L. Mopar ATF+4® Automatic Transmission Fluid is usually the fluid recommendation.

REAR DIFFERENTIAL

Draining and filling the rear differential is quite easy, but requires a bit more work as the cover must be removed, cleaned, sealed and re-installed. To drain the fluid, remove the cover, M, by removing the cover bolts, N (the number of bolts will vary by design), as shown in Figure 5.

After the cover is removed, the old RTV must be removed. This is quickly done using the grinding wheel, O, on a standard bench grinder (Figure 6). Remove all of the RTV on the sealing surface of the cover, P.

After the sealing surface of the cover has been cleaned, apply a bead of Mopar Axle RTV, part no. 05013477AA, Q, as shown in Figure 7. Smooth the bead across the surface, then re-install the pan. Remember, the pan must be installed within 3 to 5 minutes after applying the RTV. If you wait too long, the RTV must be removed and the pan surface cleaned again. Also, don’t forget to use a criss-cross pattern when tightening the cover bolts.

After the cover has been re-installed, fill the differential with fluid, usually Mopar Gear & Axle Lubricant, SAE 75W-90 or synthetic SAE 75W-140. Insert the nipple of the bottle, R, into the fill hole, S (Figure 8). Fill to the bottom edge of the fill hole.

Note: When servicing differentials or transfer cases be sure the fill plug can be removed easily before removing the drain plug to let your customers know of a potential delay in service completion.