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:
Input shaft seal — the shaft that connects to the transmission output. Oil drips onto the transmission tailshaft. Look for a wet ring forward of the transfer case.
Rear output shaft seal — drips onto the rear driveshaft. Common after high mileage.
Speedo sensor O-ring — the small sensor on the tailhousing. A dark ring around the sensor base means the O-ring is shot. Replace it before it turns into a weep-onto-your-driveway situation. O-ring is Mopar part 83503064, under $3 at any dealer.
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.
Steps
Warm up the vehicle. Drive for 5–10 minutes before draining. Warm ATF flows out faster and carries more suspended wear particles with it. You don't need it hot — warm.
Raise and support the vehicle. Use a floor jack and place jack stands under the frame rails at the factory jack points. The transfer case sits under the center of the vehicle, behind the transmission. You need enough clearance to work and to get a drain pan underneath.
Locate the plugs. The transfer case hangs below and behind the transmission tunnel. Both plugs are on the rear of the case and use an 8mm hex (Allen) drive — the same tool as your differential plugs if you've done that service. The drain plug is at roughly the 5 o'clock position on the back face. The fill plug is at roughly the 9 o'clock position.
Remove the fill plug first. This is not optional sequencing — if the fill plug is seized and you drain the case first, you have no way to refill it. Break the fill plug loose before you crack the drain. If it won't budge, stop, figure out the fill plug situation before draining anything.
Pull the drain plug and drain completely. Position your drain pan and remove the drain plug. Let it drain until it slows to a drip — usually 5 to 10 minutes. Inspect the fluid as it drains: dark brown and smelling burned is a warning sign. Metal shavings on the drain plug magnet (if equipped) or suspended in the fluid means something inside is wearing hard. Clean the plug and reinstall.
Note what you see. Fresh ATF is red or pink and smells faintly of ATF. Old fluid goes dark brown. Black, gritty, metallic, or water-contaminated fluid (looks milky or gray) tells you the case has bigger problems than a fluid change will fix.
Reinstall the drain plug. Torque to 18 ft-lb (15–25 ft-lb acceptable range). Do not overtighten — the case is aluminum, the threads strip easily.
Fill through the fill hole. Use a fluid pump, squeeze bottle, or large syringe to push ATF up into the fill hole. Keep filling until fluid runs back out of the hole. That's full. Expect to use over 1 quart for the NP231, up to 1.3 quarts for the NP242.
Reinstall the fill plug. Torque to 18 ft-lb. Same caution about overtightening applies.
Lower the vehicle and check for leaks. Run the engine, shift through all 4WD positions (2H → 4H-Hi → 4H-Lo on the NP231, or the full range on the NP242), then park and check the plugs for seepage.
Why it works
One of the cheapest and fastest drivetrain services on the XJ
Catches output seal and speedo sensor leaks before they drain the case dry
Fresh ATF keeps the shift mechanism smooth — sloppy or notchy 4WD engagement often improves after a fluid change
Trade-offs
Access requires lifting the vehicle — not a parking lot job
Rounded fill plug is a real risk on high-mileage XJs; have an extractor ready if the hex is already damaged
Does not address worn chain, bad bearings, or shift fork problems — if 4WD engagement is grinding or the case howls, fluid alone won't fix it
Tools required
Floor jack and jack stands
8mm hex (Allen) key or socket — drain and fill plugs
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.