Abstract: Sudden accidental unintended movement of an automatic transmission into reverse with the engine running is prevented by modifying the usual control rod to provide a cam surface so positioned thereon that as the control rod is moved a predetermined distance from reverse towards park a spring loaded member engages the cam surface and both restrains unintended movement of the control rod back to reverse and positively drives the control rod into its full park position as soon as the parking pawl aligns with a space between teeth of a parking gear. The mechanism may be assembled as original equipment in conventional transmissions or added to existing transmissions with little or no modification in design.