Front Dana 30 takes 1.25 quarts. Rear Chrysler 8.25 takes 2.1 quarts. Rear Dana 44a (5.9 Limited and V8 tow package) takes 2.6 quarts. All three want 75W-90 gear oil, and if your rear is Trac-Lok limited-slip you need 4 oz of friction modifier on top.
This is one of the highest-payoff maintenance jobs on a used ZJ — most of them come with whatever fluid was in there when the previous owner stopped caring. Plan on 90 minutes for both axles your first time, half that on the second pass. The cover-off method (no drain plug on these axles) means you'll wipe out old fluid, scrape off the cover, and re-seal with RTV.
Figuring out which rear axle you have: pull the tag on a cover bolt. "8.25" is the Chrysler 8.25 (most 4.0L ZJs). "44" is the Dana 44a (most 5.2/5.9 Magnum ZJs and V8 trailer-tow packages). The Dana 30 is up front on every ZJ — no Dana 44 up front from the factory. The Dana 44a (the "a" is for aluminum center) is lighter than a full Dana 44 but uses the same ring and pinion, so service is the same.
Service interval: every 30,000 miles for street driving. Every 15,000 miles if you wheel, ford water above the diff, or tow regularly. Water intrusion turns gear oil milky — if you pull a cover and see chocolate milk, change it now and check for axle seal damage.
| Part | Vendor | Est. price |
|---|---|---|
| Gear oil 75W-90 (conventional or synthetic) | Valvoline / Mobil 1 / Royal Purple | ~$14 |
| Friction modifier (Trac-Lok only) | Mopar | ~$12 |
| Differential cover gasket (or RTV) | Permatex | ~$8 |
| Cover bolts (replacement, optional) | Dorman | ~$6 |
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.