1. Gather your materials. You will need:
* New differential fluid (SAE 90 GL-4 or GL-5)
* A drain pan
* A funnel
* A 17mm wrench
* A 3/8-inch socket wrench
2. Prepare the mule. Park the mule on a level surface and engage the parking brake. If the mule has been running, allow the differential to cool down.
3. Locate the drain plug. The drain plug is located on the bottom of the differential housing, on the left side of the mule.
4. Place the drain pan under the drain plug. Make sure the pan is large enough to catch all of the fluid that will drain out.
5. Loosen the drain plug. Use the 17mm wrench to loosen the drain plug. Be careful not to drop the bolt into the drain pan.
6. Allow the fluid to drain. Allow all of the fluid to drain out of the differential housing. This may take a few minutes.
7. Replace the drain plug. Once all of the fluid has drained out, replace the drain plug. Tighten the plug until it is snug.
8. Locate the fill plug. The fill plug is located on the top of the differential housing, on the right side of the mule.
9. Remove the fill plug. Use the 3/8-inch socket wrench to remove the fill plug.
10. Add new fluid. Use the funnel to add new fluid to the differential housing. Add fluid until it reaches the bottom of the fill hole.
11. Replace the fill plug. Once you have added the correct amount of fluid, replace the fill plug. Tighten the plug until it is snug.
12. Test the differential. Start the mule and let it run for a few minutes. Then, drive the mule around for a few minutes to distribute the new fluid. Check for leaks and make sure the differential is working properly.
