The JK's NV241 (Sport/Sahara) and NV241OR (Rubicon) transfer cases need a fresh fill of ATF+4 every 30,000 miles — under an hour of work that saves a $2,000 t-case.
Both the NV241 and the heavier-duty NV241OR in your JK use ATF+4 — not gear oil. Capacity is right around 2 quarts; you'll know the case is full when fluid starts trickling back out the fill plug. Skip this service and the chain rides in increasingly contaminated fluid until the bearings or chain themselves start to wear. Replacement t-cases run $1,500 to $2,500. A $20 fluid change is not a hard decision.
Pull the JK up on level ground and crack the fill plug first. This is the rule that has saved more drivetrains than any other: if the fill plug won't loosen, you don't want to discover that after the drain plug is empty on the floor. Both plugs are 3/8" square drive — no socket needed, your ratchet fits directly. The fill plug is the upper one on the rear face of the case; the drain is below it.
With the drain pan ready, pull the drain plug and let it run for about ten minutes. Old fluid will be dark brown or black; it should come out red. Inspect the magnetic drain plug — a light fuzz of metal is normal, chunks or shavings are not. Clean the plug, install it, torque to 20–25 ft-lb (don't overdo it; the case is aluminum).
Pump new ATF+4 into the fill hole with a manual fluid pump. Most people use about 2 quarts before fluid starts to weep back out. Buy 2 quarts to be safe. Stop pumping the moment fluid trickles out, let it settle, then install the fill plug at 20–25 ft-lb. Wipe everything down and check for leaks after your first drive.
| Part | Vendor | Est. price |
|---|---|---|
| Mopar ATF+4 (1 quart) | Mopar | ~$10 |
| Valvoline MaxLife ATF (replacement for ATF+4) | Valvoline | ~$8 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.