Spanish translation: tambor (de freno) con zapato primario único
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Explanation: drum refers to a brake drum --> tambor (de freno)
A drum brake with two shoes can have one leading shoe and one trailing shoe where both are actuated by a single brake cylinder (this is the most common arrangement on the rear wheels of automobiles) or two 'leading shoes', actuated by one or two cylinders (this used to be common on the front wheels of automobiles, before the advent of disc brakes).
leading/trailing refers to which end of the shoe is mounted on a fixed pivot and which end is moved by the cylinder; a leading shoe provides more braking force than the trailing shoe because it 'bites' into the drum and rotation of the wheel causes the pressure to increase.