A cable backplane system includes a backplane having a plurality of openings and mounting locations with guide holes and a datum surface. A cable rack is coupled to the backplane. The cable rack includes a tray having a frame and spacer assemblies coupled to the tray. The spacer assemblies are coupled to the backplane at corresponding mounting locations. Each spacer assembly has a floating spacer and a spring pressing the floating spacer in a biasing direction. The floating spacer is allowed to float relative to the frame in the biasing direction. The floating spacer has a guide pin extending from a front thereof. The spring presses the floating spacer in the biasing direction such that the guide pin is received in the guide hole and the front of the floating spacer abuts against the datum surface.