An adjustable support arm for a vehicle exterior rearview mirror assembly comprising a holder base adapted for mounting to the vehicle; a holder pivotally carried on the holder base; a pivot control unit included in the holder for engaging the holder base to resist rotation of the holder on the holder base; the pivot control unit including: a compression spring disposed within a retainer opening of the holder; a bushing carried on the compression spring for engaging a bearing surface in the retainer opening; and, a retainer carried in the retainer opening and coupled to the holder base to retain the compression spring and the bushing in the retainer opening, wherein the retainer is constructed and arranged to direct the bushing laterally against the bearing surface and the compression spring biases the bushing against the retainer in sliding engagement to resist rotation of the holder on the holder base.