The differential is the part of the axle that directs engine power to the wheels and allows them to rotate at different speeds when needed. The JK Jeep Wrangler differential fluid lubricates the gears that transfer the power from the driveshaft to the wheels. It's important to make sure that this fluid remains clean in order to prevent damage to the gears.
You can replace the JK Jeep Wrangler differential fluid by either removing the differential cover or by the using the differential's drain and fill holes. Removing the differential cover gives you access to the inside of the differential allowing you to inspect and clean the gears.
It isn't always necessary to remove the differential cover to change the oil but it is good practice to occasionally open it up and have a look at what's going on in there. If you find metal chunks on the magnetic side of the drain bolt while changing the fluid using the drain and fill holes, then you need to open up the differential and have a look as this is an indication of damage to the gears.
These instructions will walk you through the process of changing the JK Jeep Wrangler differential fluid by using the drain and fill holes.
Changing the JK Jeep Wrangler Differential Fluid
3/8" socket wrench or 3/8" adapter
Differential oil - 4 quarts of Mopar 8W-90 Gear and Axle Lubricant* or equivalent
*Can be used in both Dana 30 front and Dana 44 rear axles
How to Change the JK Jeep Wrangler Differential Fluid
Step 1 - Remove the fill plug
Park your Jeep on level ground. You're going to have to get underneath your Jeep to remove the differential plugs. Each differential has one fill plug and one drain plug. The fill plug is the higher plug of the two. Use the square head of the 3/8" ratchet or adapter to remove the fill plug first. This will help drainage and ensure that you can actually get the plug out. Imagine draining the oil only to discover afterwards that the fill plug is stuck...
Step 2 - Remove the drain plug and drain the differential fluid
It's a good idea to lay down some cardboard underneath the differential that you are working on for spill protection. Place your catch pan on top of the cardboard and underneath the differential below the drain plug. Use your 3/8" ratchet extension's square head to remove the drain plug and the oil will begin to drain from the differential.
Step 3 - Inspect and clean the drain bolt
The interior side of the drain bolt is magnetic. This is to catch any fine metal shavings produced by normal wear and tear on the gears and prevent the debris from recirculating. You'll need to inspect the drain bolt and clean it off with break cleaner before replacing it.
You may find a small amount of metal shavings attached which is usually normal. If there is a lot of debris or larger metal pieces attached then it is possible that a greater issue exists. You'll have to remove the differential cover to inspect the gears or take the Jeep in for service and have the issue inspected.
Step 4 - Replace the drain bolt
Use some brake cleaner and a paper towel to clean the drain bolt. Replace the clean drain bolt and hand tighten it. You can use your torque wrench with 3/8" extension to torque the bolt to 25 ft/lbs per inch.
Step 5 - Fill the differential with oil
With your catch pan still in place, put the squeeze bottle's nozzle inside the differential's fill hole and squeeze to add oil. Keep squeezing until a small amount of oil starts to drip from the fill hole. That's the indication that the differential is full.
Step 6 - Replace the fill plug
You can clean and replace the fill plug the same way as you did the drain bolt. Replace and hand tighten the fill plug until tight and then use the torque wrench with the 3/8" adapter to torque it to 25 ft/lbs.
Step 7 - Repeat the process with the other axle.
The process is almost identical on the second axle. You may need more or less oil or have to maneuver the squeeze bottles differently but the process is the same.
Step 8 - Properly dispose of the used oil
It is important to properly dispose of your used oil. Most dealerships and garages will accept it and so will some retail stores that deal in automotive products and services. Call first if you're unsure.