A brake system for a rail vehicle , which brake system comprises: a brake actuator configured to receive a brake command (cmd P ), and in response thereto produce an electric brake-force signal (BF), and a brake unit comprising first and second pressing members and a rotatable member being mechanically linked to at least one wheel of the rail vehicle , which brake unit is configured to receive the electric brake-force signal (BF), and in response thereto cause the first and second pressing members to apply a braking force to the rotatable member , a gear assembly arranged to operate mechanically on the first and second pressing members (211; 212), and a self-locking mechanism configured to lock the first and second pressing members (211; 212) if a supply of electric power (W) to the brake unit fails, characterized in that the brake unit comprises: a stepper motor configured to act on the gear assembly in response to the electric brake-force signal (BF), so as to cause the first and second pressing members (211; 212) to move towards or away from the rotatable member and attain a specified position interrelationship, and a position sensor configured to produce a position signal (P) indicating an angular position of a power transmission shaft of the stepper motor , wherein the brake unit is configured to receive the position signal (P), and based thereon determine whether the specified position interrelationship has been attained; and if so, stop producing the electric brake-force signal (BF) allowing the self-locking mechanism to lock the first and second pressing members (211; 212) in the specified position interrelationship. a brake actuator configured to receive a brake command (cmd P ), and in response thereto produce an electric brake-force signal (BF), and a brake unit comprising first and second pressing members and a rotatable member being mechanically linked to at least one wheel of the rail vehicle , which brake unit is configured to receive the electric brake-force signal (BF), and in response thereto cause the first and second pressing members to apply a braking force to the rotatable member , a gear assembly arranged to operate mechanically on the first and second pressing members (211; 212), and a self-locking mechanism configured to lock the first and second pressing members (211; 212) if a supply of electric power (W) to the brake unit fails, characterized in that the brake unit comprises: a stepper motor configured to act on the gear assembly in response to the electric brake-force signal (BF), so as to cause the first and second pressing members (211; 212) to move towards or away from the rotatable member and attain a specified position interrelationship, and a position sensor configured to produce a position signal (P) indicating an angular position of a power transmission shaft of the stepper motor , a stepper motor configured to act on the gear assembly in response to the electric brake-force signal (BF), so as to cause the first and second pressing members (211; 212) to move towards or away from the rotatable member and attain a specified position interrelationship, and a position sensor configured to produce a position signal (P) indicating an angular position of a power transmission shaft of the stepper motor , wherein the brake unit is configured to receive the position signal (P), and based thereon determine whether the specified position interrelationship has been attained; and if so, stop producing the electric brake-force signal (BF) allowing the self-locking mechanism to lock the first and second pressing members (211; 212) in the specified position interrelationship. <EOS>