Which brake type is not adaptable to mechanical operation?

The expander-tube type brake is designed to operate using hydraulic principles rather than mechanical means. This type of brake relies on fluid pressure to expand a tube which in turn pushes brake shoes against a drum. Because of this design, it cannot be effectively actuated through mechanical systems like cables or levers, making it particularly unsuitable for mechanical operation.

On the other hand, disk brakes, drum brakes, and hydraulic brakes all have capabilities for mechanical actuation. Disk brakes and drum brakes can be actuated using mechanical linkages in some designs, while hydraulic brakes primarily use hydraulic fluid for actuation but can also be designed with mechanical backup systems. This operational principle highlights why the expander-tube type is distinctly not adaptable to mechanical operation.