Combine cola and teriyaki sauce in a shallow dish or large zip-top plastic freezer bag; add London broil. Cover or seal, and chill 24 hours, turning occasionally.
Remove London broil from marinade, discarding marinade.
Grill, covered with grill lid, over medium heat (300° to 350°) 12 to 15 minutes on each side or to desired degree of doneness. Let stand 10 minutes; cut diagonally into thin slices across the grain.