Wash cells in ice-cold water. Transfer cells to a conical-bottom 50 ml Falcon 2098 tube. Keep on ice. Vortex at maximum speed on a healthy vortexer for 30 sec periods. Chill on ice for at least 30 sec between episodes of vortexing.
Breakage is most efficient when the entire contents of the tube are lifted by the swirling action.
I also find that erring on the side of having too many beads aids in breakage. It doesn't matter if a few beads get transferred. Pool and spin at 8 K in an SS-34 rotor for 20 min. Incubate at 37 o for 1 hr. The supernatant should have only minor turbidity.