A spring brake actuator comprising, in order to provide sealing: - A parking chamber comprising pressurized air, - An adapter plate containing an intermediate shaft, - An emergency diaphragm pushed by the intermediate shaft, - A flange that pushes the emergency diaphragm, - An emergency spring that pushes the flange after the pressure inside the adapter plate drops, - An intermediate shaft flange that is pushed by the flange connected to the intermediate shaft, - The intermediate shaft pushed by the intermediate shaft flange, - A service chamber inside which the service diaphragm moves, - A service diaphragm pushed by the intermediate shaft - A shaft pushed by the service diaphragm, - A return spring that brings back the shaft characterized in that it comprises: - a two pieced center bearing comprising two types of bearings having different hardness and materials, one of which is the rubber bearing means comprising an outer sealing ring and an inner sealing ring, providing sealing, preventing the contact of the intermediate shaft and the adapter plate; and the other of which is the rigid plastic bearing means which strengthens the bearing of the intermediate shaft in the adapter plate, decreases the lateral forces and prevents force losses, limits the flexibility of the intermediate shaft and strengthens sealing, and - the rigid plastic bearing member has an "L" shaped section which enables form-fit connection on adapter plate in order to ensure that the rigid plastic bearing member located at the side of the parking chamber and/or the service chamber do not dislocate from the slots due to pressure or friction forces, and - a mounting groove that enables the mounting of the rigid plastic bearing means having an "L" shaped section located at the side of the parking chamber and/or the service chamber. - A parking chamber comprising pressurized air, - An adapter plate containing an intermediate shaft, - An emergency diaphragm pushed by the intermediate shaft, - A flange that pushes the emergency diaphragm, - An emergency spring that pushes the flange after the pressure inside the adapter plate drops, - An intermediate shaft flange that is pushed by the flange connected to the intermediate shaft, - The intermediate shaft pushed by the intermediate shaft flange, - A service chamber inside which the service diaphragm moves, - A service diaphragm pushed by the intermediate shaft - A shaft pushed by the service diaphragm, - A return spring that brings back the shaft characterized in that it comprises: - a two pieced center bearing comprising two types of bearings having different hardness and materials, one of which is the rubber bearing means comprising an outer sealing ring and an inner sealing ring, providing sealing, preventing the contact of the intermediate shaft and the adapter plate; and the other of which is the rigid plastic bearing means which strengthens the bearing of the intermediate shaft in the adapter plate, decreases the lateral forces and prevents force losses, limits the flexibility of the intermediate shaft and strengthens sealing, and - the rigid plastic bearing member has an "L" shaped section which enables form-fit connection on adapter plate in order to ensure that the rigid plastic bearing member located at the side of the parking chamber and/or the service chamber do not dislocate from the slots due to pressure or friction forces, and - a two pieced center bearing comprising two types of bearings having different hardness and materials, one of which is the rubber bearing means comprising an outer sealing ring and an inner sealing ring, providing sealing, preventing the contact of the intermediate shaft and the adapter plate; and the other of which is the rigid plastic bearing means which strengthens the bearing of the intermediate shaft in the adapter plate, decreases the lateral forces and prevents force losses, limits the flexibility of the intermediate shaft and strengthens sealing, and - the rigid plastic bearing member has an "L" shaped section which enables form-fit connection on adapter plate in order to ensure that the rigid plastic bearing member located at the side of the parking chamber and/or the service chamber do not dislocate from the slots due to pressure or friction forces, and - a mounting groove that enables the mounting of the rigid plastic bearing means having an "L" shaped section located at the side of the parking chamber and/or the service chamber.