a motor - vehicle accessory having a pivotal element that can pivot about an axis on a generally fixed support element is provided with a mechanism having an extension on one of the elements offset from the axis and projecting angularly of the axis and a brake on the other of the elements . this brake has a pair of brake shoes flanking the extension and shiftable between a clamping position gripping the element and preventing movement of the element relative to the brake in at least one angular direction and a release position permitting movement of the element relative to the brake both in and against the one direction .