Downhole vibration tool - having a hollow tool housing (12) which can be lowered into a borehole, - with a tool in the housing (12) longitudinally movable piston (16) having a piston bore (28) and is biased in a first direction that is parallel to the longitudinal axis of the tool housing (12), - arranged with a in a dart valve assembly (50) vibrating mechanism (56, 58, 60), the valve is controlled so that repeated the fluid flow is interrupted and is applied to the plunger a force in a second direction (parallel to the longitudinal axis of the tool housing 12 the fluid flow), and opposite to the first direction, and that repeatedly restored and the force is released to the piston, marked by - passing a tool through the casing (12) housing bore (26) whose diameter corresponds substantially to the diameter of the piston bore (28), and - the dart valve assembly (50) down through a work string in the well bore therethrough is pumpable, the outer diameter of ...