Abstract: A drive line assembly and mounting arrangement for converting a front engine front wheel drive vehicle to an on-demand four wheel drive system. The vehicle rear axle is adapted to be selectively driven by means of a viscous fluid coupling positioned intermediate a forward angled universal-joint drive line assembly and a rear torque tube enclosed longitudinal propeller shaft assembly. An overrunning clutch is rigidly connected intermediate a forwardly extending neck portion of the rear axle drive housing and the torque tube defines a composite torque tube structure. The overrunning clutch is adapted to be locked for a transmission of torque during normal driving. The rear axle drive housing is sprung from the frame by a pair of transversely aligned isolation mounts while the composite torque tube is resiliently secured by a bracket support adjacent its forward end.