In order to realize a practical hyper-redundant manipulator, a new lightweight wire driven transmission mechanism, named M-Drive, has been developed. This mechanism not only takes advantage of the lightweight properties of a wire and pulley system but also has a unique torque keeping function. The mechanism keeps the joint solid without compliance and not only allows the joint to deform when in contact with an external torque over a threshold torque, but is also able to maintain that threshold torque while deforming. Furthermore, M-Drive also features automatic wire elongation elimination, the fundamental difficulty of a wire and pulley system. Combining two M-Drive mechanisms in a differential configuration, a 2-DOF coupled drive actuator that maximizes power has also been developed for a proposed gravity compensated hyper-redundant manipulator named Float Arm. Experimental results for the M-Drive mechanism and the differential M-Drive actuator are also included.