In order to study the nucleus-nucleus interaction in Pb-based cold fusion, we have measured excitation functions for quasielastic scattering of 48Ti, 54Cr, 56Fe, 64Ni, and 70Zn projectiles on a 208Pb target at backward angles. The barrier distributions were derived from the first derivative of measured quasielastic scattering cross sections relative to the Rutherford scattering cross section. The centroids of the barrier distributions show a deviation from several predicted barrier heights toward the low energy side. The shape of the barrier distributions is well reproduced by the results of a coupled-channel calculation taking account of the coupling effects of two phonon excitations of the quadrupole vibration for the projectiles and of the octupole vibration for the 208Pb target.