Soft-release wrap-spring brake mechanism with oil-impregnated powerdered metal drum.

The mechanism, eg in a vehicle parking brake, includes a cylindrical drum (26) about which is concentrically arranged a helical clutch or brake spring (30), the coil turns of which are normally contracted radially inwardly into frictional engagement with the outer periphery of the drum. The drum 26 is formed of powdered metal impregnated with damping oil. Owing to the direction of the coil turns, the drum may be rotated only in a first direction relative to the spring, and upon radial outward expansion of the spring, the viscous film of the dampening oil between the outer periphery of the spring affords controlled soft-release of the drum for rotation in the opposite direction. The drum may be formed from elemental iron and nickel powder, with graphite and copper powder; the oil may be a polyalphaolefin.