Abstract: A mobile railway track repair apparatus (10) that includes a mobile unit (11) having a cab (22) rotatably supported on a dual mode undercarriage (21) wherein, a boom unit (12) is pivotally supported by the cab (22) and includes a boom support column (31) pivotally attached to a boom arm (32) having a universal connector unit (13) provided on its lower end (34). In addition, the universal connector unit (13) is operatively connected to an undercutter assembly (50) wherein, a plurality of hydraulic piston elements (35) (35?) and (35?) are employed to manipulate the boom support column (31), the boom arm (32), and the universal connector unit (13) to position the undercutter assembly in a generally transverse relationship to the rail bed (101) to extract weakened ballast (104) from beneath the railroad track (100).