The XJ's transfer case runs on ATF — not gear oil. One quart, two plugs, and an Allen key is all it takes. Do this every 30,000 miles or after any deep water crossing.
The Jeep Cherokee XJ came with one of two transfer cases: the NP231J (Command-Trac, part-time 4WD) found on the vast majority of XJs, or the NP242 (Selec-Trac, full-time 4WD) which was an option. The fluid service is nearly identical between the two — same fluid type, same plug location, same procedure. The difference is mostly capacity.
**Which transfer case do you have?** Look at your dash shifter. Two positions for 4WD (4H and 4L, no neutral between them and 2H) means NP231. Three positions including neutral (2H → 4H → N → 4L) means NP242. You can also check the sticker on the transfer case itself — visible from underneath on the driver's side.
**Fluid spec:** Both cases use ATF. The factory called for Dexron II originally; current Mopar spec is ATF+4 (part 68218925AA). Dexron-III, Dexron-VI, or any modern ATF+4-compatible fluid is acceptable. Do not use gear oil — it is too viscous, shifts harder, and can damage internal components over time. This is the single most common mistake people make on these cases.
**Capacities:**
| Case | Capacity |
|---|---|
| NP231J | ~2.2 pints (1.0 L, over 1 quart) |
| NP242 | ~2.5 pints (1.2 L) |
Fill until fluid reaches the bottom of the fill hole — the capacity numbers are approximate. Let the case tell you when it's full.
**Service interval:** Every 30,000 miles or 2 years under normal conditions. After any water crossing deep enough to come up to the transfer case (roughly door-bottom height on the XJ), drain and refill within a day or two regardless of when you last serviced it. Water contamination destroys the internals before you'd see any symptom.
**No skid plate:** Unlike the TJ Wrangler, the XJ Cherokee has no transfer case skid plate. Access is straightforward — jack it up and get under it.
**The Allen socket will slip on rounded plugs.** Previous owners who used adjustable wrenches or impact-driven bits on the soft aluminum plugs often leave rounded hex sockets behind. If your plug won't bite, try a new sharp 8mm Allen bit with the torque wrench before resorting to an extractor. Apply penetrating oil the day before if you suspect seizing.
**Check for leaks while you're under there.** Three common drip points on the NP231:
**RENIX-era XJs (1987–1990):** Same NP231, same fluid, same procedure. Nothing changes between RENIX and HO for this service.
**Water intrusion:** If you crossed anything serious and think water got in, the contaminated fluid will look gray or milky. Don't defer this service. Water and ATF don't coexist — the bearings and chain degrade fast.
| Part | Vendor | Est. price |
|---|---|---|
| Mopar ATF+4 or Dexron-VI compatible ATF (1 qt) | any auto parts store | — |
| Speedo sensor O-ring (if leaking at sensor) | Mopar | — |
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.