Abstract: An actuator mechanism for a brake having a plurality of friction disc compressed between a pressure plate and a backing plate. The actuator mechanism has a piston located in a bore of a housing. A pin fixed to the housing extends through and locates the piston in the bore. A first tube made of an insulator material is located in the bore between the piston and the pressure plate. A second tube concentric to the first tube has an inwardly projecting flange adjacent to the piston and an outwardly projecting flange. A keeper attached to the first tube cages a spring between the outward projecting flange and the first tube. A third tube which engages the inwardly projecting flange is connected to the pin through a button fastener thereby establishing an air gap between the first tube and the pressure plate. The piston, in response to an operational input, initially moves in the bore by overcoming the spring and brings the first tube into engagement with the pressure plate to eliminate the air gap.