What is a characteristic of sealed wheel bearings?

Sealed wheel bearings are designed as a complete unit that typically cannot be disassembled for individual component replacement or lubrication. This means that once the bearing is worn out or damaged, the entire assembly must be replaced rather than just specific parts. This design leads to ease of installation and maintenance while offering reliability since the components are pre-lubricated and protected from environmental contaminants.

In contrast, the other characteristics listed do not apply to sealed wheel bearings: they are generally not meant to be lubricated after installation, are not adjustable, and are not designed for easy repair or disassembly. This assembly nature simplifies the replacement process and enhances the longevity of the bearing without requiring regular maintenance.