In order to improve a master unit for vehicles, in particular for vehicles steered by a handlebar, comprising a housing, a master cylinder unit provided in the housing, an actuation unit for manually actuating the master cylinder unit with a push lever pivotable relative to the housing about a push lever pivot axis and with a push element transmitting a movement of the push lever to the master cylinder unit, which push element is provided on the push lever and, when the actuation unit is manually actuated, acts, via a pressure surface at a contact point, on a contact surface of the master cylinder unit, such that an optimal adaptation to the particular circumstances is possible, it is proposed that, in order to adjust a transmission ratio of the actuation unit with which the actuation unit acts on the master cylinder unit, a lever arm effective in the event of the actuation is adjustable between the contact point and the push lever pivot axis by means of an adjustment device.