A machine operator or service person is alerted to the excessive wear condition of friction discs in friction couplings or brakes of construction machinery by being provided with a visual indication of wear of the friction discs in one embodiment, a wear indicating pin element is shifted axially by a brake piston and the position of the end of the pin element is visible through a window in a brake housing, thereby providing a visual indication of the wear condition of the friction disc. In a second embodiment of the invention the excessive wear condition of the friction discs is revealed by a signal light which is activated by a pressure switch responding to the pressure of the fluid delivered to a brake cylinder when the brake piston moves a predetermined distance in application of the brake.