The JT Gladiator's front and rear Dana 44 axles hold approximately 1.6 quarts of fluid each. Rubicon trims with the factory locker require a friction modifier additive — without it, the Tru-Lok locker chatters and shudders during low-speed turns.
Jeep specifies 75W-140 full synthetic gear oil for the JT's Dana 44 axles. Change interval is 30,000 miles under normal use — or after every water crossing where the axles were submerged. Water contamination in differential fluid turns it milky gray and looks nothing like fresh gear oil. If you've wheeled through a significant water crossing, check the axle fluid within a week. A half-pint of water in a differential will destroy bearings over 5,000–10,000 miles.
**Rubicon locker note:** The Tru-Lok locker in the Rubicon front and rear axles requires Mopar friction modifier additive in the gear oil — or equivalent (Loctite 504821). Without it, the clutch packs chatter during parking-lot turns. This is normal behavior initially after an oil change without additive, but persistent chatter means the clutch pack surfaces are being worn prematurely. Use the additive.
Non-Rubicon JT trims (Sport, Overland, Mojave): standard 75W-140 synthetic, no additive needed.
75W-140 synthetic gear oil: ~$16–20 per quart. You'll use 3.5 quarts for both axles (front + rear). Two quarts of Mopar or Royal Purple covers it if each axle is slightly under 1.75 quarts.
Friction modifier (Rubicon only): ~$12–15 per bottle. One bottle per differential (front and rear each get one bottle).
Gasket kit (Fel-Pro Dana 44, 2-pack): ~$12–15. Reusable RTV silicone is an alternative — Permatex Ultra Black works — but a cut gasket is cleaner and doesn't require cure time before filling.
Total per axle: ~$35–45. Both axles: ~$65–90. A shop charges $80–120 per axle for differential fluid service on a JT. Do both at home in an afternoon.
| Part | Vendor | Est. price |
|---|---|---|
| Mopar Gear and Axle Lubricant 75W-140 (Rubicon limited-slip additive included) | Mopar | ~$18 |
| Royal Purple Max-Gear 75W-140 Synthetic Gear Oil | Royal Purple | ~$16 |
| Mopar Friction Modifier for Limited-Slip Differential | Mopar | ~$12 |
| Fel-Pro Differential Cover Gasket — Dana 44 (2-pack) | Fel-Pro | ~$14 |
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.