Servo-action in brakes occur when the primary shoe applies the secondary shoe.

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Multiple Choice

Servo-action in brakes occur when the primary shoe applies the secondary shoe.

Servo action is the self-energizing effect in drum brakes where the friction force on the primary shoe helps press the secondary shoe against the drum. When hydraulic pressure pushes the primary shoe toward the drum, the shoe’s geometry and pivots create a moment that also drives the secondary shoe into engagement. This makes braking torque greater than what hydraulic pressure on the primary alone would produce, because the secondary shoe is effectively being applied by the action of the primary. This is why the correct statement describes the primary shoe applying the secondary shoe.

Servo action is the self-energizing effect in drum brakes where the friction force on the primary shoe helps press the secondary shoe against the drum. When hydraulic pressure pushes the primary shoe toward the drum, the shoe’s geometry and pivots create a moment that also drives the secondary shoe into engagement. This makes braking torque greater than what hydraulic pressure on the primary alone would produce, because the secondary shoe is effectively being applied by the action of the primary. This is why the correct statement describes the primary shoe applying the secondary shoe.

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