A rock knocker bracket holds a rock ejector such as a chain or bar that is used to clear debris from the gap between two tires of a mining vehicle. The rock ejector is pivotally mounted on a horizontal, lateral pin that is held at both ends by side plates of the bracket. The pin has a series of holes formed along its length. Bar retainers and washers mounted on the pin allow the rock ejector to be moved laterally along the pin and thereby provide for different laterally spacing configurations of the tires. Fasteners pass through holes in the bar retainers and the holes in the pin to hold the rock ejector at a predetermined lateral location along the pin. Alternative designs for the pin and the bracket include other systems for laterally moving the rock ejector and mounting it in the predetermined lateral position.