An automatic slack adjuster for a vehicle brake, comprising: a housing configured for coupling to a brake actuator; a driving worm wheel supported by the housing and configured to engage a brake cam shaft of the vehicle brake; a driving worm screw supported by the housing and defining a threaded portion in mesh with the driving worm wheel and first and second shaft portions (62, 60) extending from opposite sides of the threaded portion, the driving worm screw configured to transfer a brake actuating force, imparted by the brake actuator to the housing, to the driving worm wheel and the brake cam shaft; a spring configured to apply a biasing force to the first shaft portion of the driving worm screw to bias the driving worm screw in a first direction; and, a wear adjustment mechanism including a reference arm assembly configured to be fixed against movement and including a control ring gear; a pinion gear in mesh with the control ring gear and configured for rotation about a first rotational axis, a control worm screw coupled to the pinion gear for rotation with the pinion gear about the first rotational axis; a control worm wheel disposed about the second shaft portion of the driving worm screw and in mesh with the control worm screw, the control worm wheel configured for rotation about a second rotational axis; a clutch ring disposed about the second shaft portion of the driving worm screw on an opposite side of the control worm wheel relative to the threaded portion of the driving worm screw, the clutch ring including a plurality of teeth configured for engagement with a corresponding plurality of teeth on the second shaft portion of the driving worm screw; and, a wrap spring engaging surfaces of the control worm wheel and the clutch ring, characterized in that the control worm wheel and the clutch ring are arranged to ensure coaxial movement and a portion of the control worm wheel and a portion of the clutch ring radially overlap. a housing configured for coupling to a brake actuator; a driving worm wheel supported by the housing and configured to engage a brake cam shaft of the vehicle brake; a driving worm screw supported by the housing and defining a threaded portion in mesh with the driving worm wheel and first and second shaft portions (62, 60) extending from opposite sides of the threaded portion, the driving worm screw configured to transfer a brake actuating force, imparted by the brake actuator to the housing, to the driving worm wheel and the brake cam shaft; a spring configured to apply a biasing force to the first shaft portion of the driving worm screw to bias the driving worm screw in a first direction; and, a wear adjustment mechanism including a reference arm assembly configured to be fixed against movement and including a control ring gear; a pinion gear in mesh with the control ring gear and configured for rotation about a first rotational axis, a control worm screw coupled to the pinion gear for rotation with the pinion gear about the first rotational axis; a control worm wheel disposed about the second shaft portion of the driving worm screw and in mesh with the control worm screw, the control worm wheel configured for rotation about a second rotational axis; a clutch ring disposed about the second shaft portion of the driving worm screw on an opposite side of the control worm wheel relative to the threaded portion of the driving worm screw, the clutch ring including a plurality of teeth configured for engagement with a corresponding plurality of teeth on the second shaft portion of the driving worm screw; and, a wrap spring engaging surfaces of the control worm wheel and the clutch ring, characterized in that the control worm wheel and the clutch ring are arranged to ensure coaxial movement and a portion of the control worm wheel and a portion of the clutch ring radially overlap. a reference arm assembly configured to be fixed against movement and including a control ring gear; a pinion gear in mesh with the control ring gear and configured for rotation about a first rotational axis, a control worm screw coupled to the pinion gear for rotation with the pinion gear about the first rotational axis; a control worm wheel disposed about the second shaft portion of the driving worm screw and in mesh with the control worm screw, the control worm wheel configured for rotation about a second rotational axis; a clutch ring disposed about the second shaft portion of the driving worm screw on an opposite side of the control worm wheel relative to the threaded portion of the driving worm screw, the clutch ring including a plurality of teeth configured for engagement with a corresponding plurality of teeth on the second shaft portion of the driving worm screw; and, a wrap spring engaging surfaces of the control worm wheel and the clutch ring, characterized in that the control worm wheel and the clutch ring are arranged to ensure coaxial movement and a portion of the control worm wheel and a portion of the clutch ring radially overlap.