A counterweight assembly for a vehicle comprising an open-end support frame anchored to the vehicle chassis and extending longitudinally from the latter beneath the overhang of an engine supported on one end of the chassis. A plurality of weights 21 are suspended from the support frame. Co-acting means 25-26 on the support frame and the weights 21 provide for self-alignment of the weights upon insertion of the latter through the open end into the support frame. The co-acting means are constructed and arranged to provide line contact between portions of the support frame and each weight to minimize sliding resistance as the weights are moved in the direction of the chassis toward locating stop means 31. Securing means 28 lock the weights in place on the support frame.