A mechanism (19) disposed in a torque converter housing (24) for damping torsionals in a vehicle driveline. The mechanism comprises a viscous coupling (22) including a housing (64) having two sidewalls (24a, 68) defining a chamber (70) containing a viscous liquid, and a clutch member (72) disposed in the chamber for viscous clutching coaction with the housing. One of the sidewalls (24a) is defined by an end wall of the torque converter housing. The housing and clutch member are interconnected by a spring assembly (20) including flat torsion springs (61, 62) which transmit steady-state driveline torque and isolate driveline torsionals. The inner surfaces (24b, 68a) of the housing each include two circumferentially spaced clutching surfaces separated by the clutch member. The clutch member has oppositely facing surfaces (72b, 72c) each which include two flat circumferentially spaced clutching surfaces. When the clutching surfaces of the housing are disposed opposite the clutching surfaces of the clutch member, the clutching coaction therebetween is a maximum. When the clutching surfaces of the housing are disposed opposite the spaces between the clutching surfaces of the clutch member, the clutching coaction is a minimum.