This payer investigates the mode splits of the bending coupled modes of a rotating shaft with multiple flexible disks, in which the disks are rigidly attached to the rigid shaft supported by bearings. The bending coupled modes, in which shaft bending modes are coupled with one nodal diameter disk modes, are classified as the balanced and unbalanced modes. The mode splits of the balanced modes are the same as those of pure disk modes since the shaft does not experience any motion. On the other hand, the mode splits between pairs of the forward and backward unbalanced modes are found to be dependent upon the disk/shaft configuration and the shaft support stiffness, as well as the rotational speed and the ratio of polar to diametrical moment of inertia. (C) 1999 Academic Press.