Every XJ has two differentials — front and rear — that need fresh gear oil every 30,000 miles or immediately after any water crossing deep enough to touch the axle housings. Neither has a drain plug. You pull the cover, drain it into a pan, inspect the gears while you're in there, reseal with RTV, and fill through the plug hole. Plan two to three hours if you're doing both at once.
The XJ Cherokee ran two different rear axles depending on year and option package: the Dana 35C and the stronger Chrysler 8.25. The front is always a Dana 30. Knowing which rear axle you have before you start matters — the 8.25 holds more fluid and the fill plug is different. Both rear axles share the same fluid spec and the same cover-removal procedure, so most of these steps apply to either.
Identifying your rear axle: Look for a metal tag riveted to one of the axle tubes, usually on the passenger side near the differential. The tag will list the axle model and ratio. If the tag is missing, count the bolts on the rear differential cover: both axles use 10 bolts on a roughly similar cover, but the 8.25 cover has a slight pumpkin shape with a notch at the bottom, while the Dana 35 cover is rounder. When in doubt, your VIN's build sheet (available through NAXJA or moparinfo.com) will confirm it.
Capacities at a glance:
Axle
Position
Capacity
Dana 30
Front
~1.2 qt (1.1 L)
Dana 35C
Rear
~1.7 qt (1.6 L)
Chrysler 8.25
Rear
~2.1 qt (2.0 L)
Trac-Lok: Some 8.25 rear axles were equipped with Trac-Lok limited slip. If yours has it, add 4 oz of friction modifier to the rear differential fluid — without it, the clutch pack chatters during slow turns. Most XJs did not come with Trac-Lok from the factory. To confirm: raise the rear off the ground and turn one wheel by hand. If the opposite wheel turns the same direction, you have a limited slip. If it turns the opposite direction, it's an open diff.
Change interval: Every 30,000 miles under normal conditions. After any trail run where water crossed the axle housings, drain and refill within a day or two — water emulsifies gear oil into a grayish-brown sludge that strips lubrication quickly and accelerates ring and pinion wear.
Steps
Rear Differential
Warm the gear oil slightly before draining — drive the Jeep around the block or let it idle for five minutes. Warm gear oil drains faster and more completely than cold oil. Don't drain a hot axle straight off the highway; the oil and housing will be hot enough to burn.
Park on level ground, chock the front wheels, and raise the rear of the Jeep. Place jack stands under the frame rails behind the rear axle — not under the axle itself, or the differential will lift off level and oil won't drain cleanly. You can also do this with the Jeep flat on the ground; you'll lose a little less oil but gain better access to the top cover bolts.
Slide a drain pan under the rear differential cover. The pan needs at least 2-gallon capacity to catch both axles.
Remove all 10 cover bolts using a 10mm socket. Work around the cover in a crossing pattern, leaving the top center bolt for last. When all others are out, break the top bolt loose but don't remove it yet.
With the top bolt still threading in, carefully pry the bottom of the cover away from the housing using a flathead screwdriver. Insert the screwdriver in the seam at the bottom and pry gently — you're breaking the RTV seal, not levering against the casting. Oil will begin draining into the pan. Once flow starts, remove the top bolt and let the cover drop into the pan.
Let the axle drain completely. While it drains, inspect the inside of the housing and the gear teeth. You're looking for shiny metallic debris (normal in small amounts — a magnetic drain plug will catch most of it), chunks of metal (not normal — could indicate a failing bearing or chipped tooth), or a milky-gray appearance to the old oil (water contamination). Dark, dirty oil with no metal chunks is a straightforward fluid change. Metal chunks or milky fluid warrant a closer look before reassembly.
Clean the cover: scrape all old RTV off both the cover flange and the axle housing flange using a gasket scraper. A single-edge razor blade works well for the last traces of old sealant on the housing face. Both surfaces need to be clean and flat — any ridge of old RTV will cause the new seal to fail.
Spray brake cleaner into the housing to wash out debris and the last of the old oil. Wipe out the inside of the housing and the cover with clean rags.
Run a 3/16" bead of Permatex Ultra Black RTV around the inside mating surface of the cover — inside the bolt holes, continuous with no gaps. Do not use a paper gasket. The iron axle housing flexes slightly under load and will crack a rigid gasket; RTV handles the flex. Don't use too much RTV — a thick bead squeezes inside the housing and contaminates the gear oil.
Position the cover on the housing. Start all 10 bolts by hand before tightening any of them. Torque to 30 ft-lbs in a crossing pattern, making two or three passes rather than running each bolt to full torque in sequence. Uneven clamping on the first pass can cock the cover and cause leaks.
Let the RTV cure for at least one hour before adding fluid. Permatex Ultra Black reaches handling strength quickly but benefits from a full cure before seeing oil pressure. Two hours is better.
Locate the fill plug. On the Chrysler 8.25, the fill plug is a rubber cap on the passenger side of the differential housing — pry it off with a flathead screwdriver. On the Dana 35, look for a threaded plug on the driver side of the housing, above the axle centerline; it uses the same 3/8" square drive as the Dana 30 front.
Insert a hand pump or drill pump into the fill hole and pump gear oil in until it begins to trickle out of the hole. With the Jeep on level ground, this ensures the axle is filled to the correct level — the fill hole acts as an overflow limiter. Use 75W-90 or 80W-90 GL-5 gear oil. If the axle has Trac-Lok, add 4 oz of friction modifier before adding gear oil.
Reinstall the fill plug snugly. The rubber cap on the 8.25 pushes in by hand. The threaded plug on the Dana 35 should be tight but not overtightened — it threads into the iron housing and can crack it if gorilla-torqued.
Front Differential (Dana 30)
Move to the front of the Jeep. You usually don't need to raise the front — the Dana 30 is more accessible than the rear axle. Slide a drain pan under the front differential cover.
Remove all 10 cover bolts (10mm socket), leaving the top center bolt for last. Pry the cover from the bottom the same way as the rear, let it drain, then pull the cover free.
Inspect the gears. The Dana 30 ring gear is smaller than the rear axles — chunked or pitted teeth are more common on high-mileage Jeeps that have been run with worn tires at aggressive gearing. Note any shiny metal in the drained oil; small particles on a magnet are normal wear, large flakes are not.
Scrape and clean both mating surfaces, apply the same 3/16" RTV bead to the cover, reinstall the cover, and torque to 30 ft-lbs in a crossing pattern.
Let the RTV cure (same one-hour minimum).
Locate the fill plug. On 1996+ XJs (OBD-II era), the Dana 30 fill plug takes a 3/8" square drive — insert a 3/8" breaker bar or ratchet head directly into the plug. On Renix-era Jeeps (1984-1990), the plug may be hex; check the fitting before assuming. The plug is on the passenger side of the differential cover, above center. These plugs can be extremely tight on high-mileage Jeeps — apply penetrant, let it soak for 15–20 minutes, and use a solid breaker bar rather than a ratchet to break it loose. Rounding the plug makes the job significantly harder.
Pump in 75W-90 or 80W-90 GL-5 gear oil until it trickles from the fill hole. The Dana 30 holds about 1.2 quarts — a transfer pump makes this much more manageable than trying to pour from a bottle at an awkward angle. No friction modifier needed; the XJ Dana 30 is an open diff.
Reinstall the fill plug and tighten firmly.
Drive the Jeep gently for a few miles, then park and check both differentials for seeping around the cover edges. A slight weep in the first day is normal as the RTV fully cures. A steady drip means a cover bolt needs another quarter-turn or the RTV bead had a gap.
Dispose of old gear oil at any auto parts store or oil recycling center. Don't pour it on the ground — gear oil is petroleum-based and toxic to soil and groundwater.
Why it works
Extends ring and pinion life significantly. Gear oil breaks down over time and loses its extreme-pressure additive package — degraded fluid causes accelerated wear on hypoid gear surfaces.
Cover-off draining gives you a gear inspection at no extra cost. Catching chunked teeth or metallic debris early lets you plan a rebuild on your schedule rather than on the side of a trail.
Fresh fluid after a water crossing prevents the kind of corrosion damage that rusts bearings from the inside out. The gear oil itself is cheap; the differential rebuild it prevents is not.
Trade-offs
Neither axle has a drain plug, so this job always involves cover removal and RTV work. Budget the cure time — you can't drive immediately after reassembly.
The Chrysler 8.25 fill plug is a rubber cap that degrades over time and can be difficult to reseat if the housing lip is corroded. Inspect it when you're in there and replace it if it looks cracked or brittle (it's an inexpensive part).
If the Dana 30 fill plug hasn't been touched in years, it may be corroded in place. Don't force it with a short handle — rounded plugs require manageable-outs or a welder. Penetrant and time are your friends.
Tools required
Floor jack and jack stands
10mm socket and ratchet
3/8" square drive plug (or 3/8" drive ratchet used as plug tool)
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.