Which term describes the braking phenomenon where one shoe causes the other to apply in a drum brake system?

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Servo-action is the self-energizing effect in a drum brake where the rotation of the drum helps press the two shoes together, so one shoe’s contact causes the other to apply more firmly. As the wheel turns, the leading shoe is driven against the drum and, through the shoe geometry and pivots, this action pushes the trailing shoe toward the drum as well. The result is an amplified braking force without needing extra hydraulic pressure. The other ideas don’t describe this self-energizing interaction: an energized shoe isn’t a standard term here, an anchor is just the fixed pivot, and a metering valve relates to hydraulic pressure control rather than the mechanical shoe action.