An isolator comprising a shaft, a pulley journalled to the shaft, a first torsion spring engaged between the shaft and the pulley, a second torsion spring engaged between the shaft and the pulley, the first torsion spring and the second torsion spring wound in opposite directions, the first torsion spring engaged to transmit a first torque in a first direction from the pulley to the shaft, the second torsion spring having a passive engagement with the pulley during transmission of the first torque, and the second torsion spring engaged to transmit a second torque in a second direction from the shaft to the pulley, the first torsion spring having a passive engagement with the pulley during transmission of the second torque.