A flexible coupling assembly for a power transmission system including a first shaft defining an axis, configured for connecting to a first rotating member, the first shaft adjoining and passing through a first flexible diaphragm coupling and lockably connecting to a quill shaft by a locking flange and the quill shaft being configured for connecting to a second rotating member, including a first mating portion for receiving the locking flange of the first shaft within a circumferential opening, wherein the quill shaft is disposed within a primary diaphragm coupling shaft.