Subframe Connectors For StrengthClassic Mustangs suffer from inadequate structural support; they twist and flex under harsh driving conditions. When chosen and installed properly, subframe connectors stiffen the underbody and provide exceptional support. Not all subframe connectors are created equal. Heidt's has designed one that follows the floorpan and doesn't require welding. It's a removable, bolt-on design, however, we suggest welding it for optimum strength.