For Dana 44 axles (most common): Jeep recommends a 75W-90 GL-5 gear oil. Many reputable brands offer this, such as Mobil 1, Royal Purple, Valvoline, etc.
Important Considerations:
* Limited-Slip Differential (LSD): If your Rubicon has a limited-slip differential (LSD), you'll need a 75W-90 GL-5 gear oil *specifically formulated for limited-slip differentials*. Using the wrong oil can damage the LSD. Look for this designation on the oil bottle. Some oils are even formulated to work with both standard and LSD differentials, making it a good all-around choice.
* Synthetic vs. Conventional: Synthetic gear oil is generally better in terms of performance and longevity, especially in extreme conditions. However, conventional 75W-90 GL-5 is perfectly acceptable and much less expensive.
* Your Owner's Manual: The definitive answer is always in your Jeep's owner's manual. Check it to confirm the exact specifications and recommendations for your specific vehicle's axles.
In short, while 75W-90 GL-5 is a safe starting point, always check your owner's manual first to determine the correct type and to confirm whether you have a limited-slip differential. If you have a LSD, make absolutely certain the fluid you use is compatible.
