A spindle motor assembly for a hard disk drive which has a fluid filled tube that dynamically balances the spindle motor. The assembly may include a hub which is rotated by an internal motor. A plurality of disks may be coupled to the hub and separated by a number of spacers. In one embodiment, the fluid filled tube is attached to the hub. In another embodiment, the fluid filled tube is attached to the spacer. The fluid within the tube is allowed to move during rotation of the hub. Movement of the fluid may dynamically balance the spindle motor.