What is the correct lubricant for a rear-wheel-drive car's front axle?

The appropriate lubricant for a rear-wheel-drive car's front axle is wheel bearing grease. This type of grease is specifically engineered to handle the conditions present in wheel bearings, where there is a need for durability under high loads and resistance to moisture and corrosion.

Wheel bearing grease maintains its consistency and adhesion properties, ensuring that it stays in place, which is crucial for maintaining proper lubrication and minimizing wear on the bearings. It provides effective lubrication at the high speeds and temperatures typically experienced by axle components.

Other lubricants listed in the options, such as engine oil, transmission fluid, and brake fluid, do not exhibit the necessary properties for axle lubrication. Engine oil is formulated for internal combustion engines and lacks the thick consistency needed for wheel bearings under load. Transmission fluid is designed for the movement of gears in a transmission, while brake fluid is formulated for hydraulic brake systems. None of these alternatives can provide the level of protection and performance required for the front axle in a rear-wheel-drive vehicle.