Tyre building drum with turn-up mechanism

Tyre building drum having a turn-up mechanism for use in building an unvulcanised tyre using rubber tyre components, having two sets of turn-up arms, wherein each set of arms is connected to an axially shiftable arm support. The tyre building drum is provided with means on the one hand for shifting the arm supports in a first direction to move the sets of turn-up arms axially towards each other, wherein the arms are tiltable in radial planes from a starting position to a tilting position, and on the other hand for in a second direction, opposite the first direction, shifting the arm supports to move the arms axially apart from the tilting position into the starting position. The tyre building drum is provided with a pneumatic detection device for detecting whether at least one of the moving parts, such as the arms or the clamping device, are in the starting position, and for giving a detection signal indicating whether or not the arms are in the starting position.