A viscous clutch assembly adapted for installation in a torque transmission system for effecting a drive connection between a pair of rotary members (25, 26) coaxially arranged for relative rotation. The viscous clutch assembly includes a viscous coupling (10a) arranged for generating a viscous resistance force in response to relative rotation between the rotary members, a first cam mechanism (10c) cooperable with the viscous coupling (10a) for converting the viscous resistance force into a thrust force, a friction disc clutch (10b) arranged to be brought into engagement when applied the thrust force from the first cam mechanism for establishing the drive connection between the rotary members, and a second cam mechanism (10d) cooperable with the viscous coupling (10a) for increasing and decreasing the viscous resistance force in response to a difference in torque between the rotary members.