A pivot mechanism for a vehicle external rear view mirror assembly, the mechanism including: • a base frame portion integral with, or attachable to, a vehicle-mountable base frame; • a case frame portion mounted to the base frame portion for rotation about a pivot axis, the case frame portion integral with, or attachable to, a case frame adapted to support a rear vision mirror; • a detent operable between the base frame portion and the case frame portion, the detent having: • an engaged position where the case frame portion is held in a selected position with respect to the base frame portion, and a disengaged position allowing the rotation about the pivot axis, the detent including a first set of detent features and a second set of detent features; and • a spring mechanism clamping the case frame portion to the base frame portion and the first set of detent features to the second set of detent features; characterized by • a support arm having an attachment end and a floating end, the floating end supporting the first set of detent features, the first set of detent features fixed against rotation about the pivot axis with respect to the support arm, but displaceable relative to the attachment end in a direction substantially parallel to the pivot axis, • wherein the attachment end of the support arm is fixed to, and is fixed against rotation with respect to, one of: the case frame portion and the base frame, and • wherein the second set of detent features is fixed against rotation with respect to the other of: the case frame portion and the base frame portion. • a base frame portion integral with, or attachable to, a vehicle-mountable base frame; • a case frame portion mounted to the base frame portion for rotation about a pivot axis, the case frame portion integral with, or attachable to, a case frame adapted to support a rear vision mirror; • a detent operable between the base frame portion and the case frame portion, the detent having: • an engaged position where the case frame portion is held in a selected position with respect to the base frame portion, and a disengaged position allowing the rotation about the pivot axis, the detent including a first set of detent features and a second set of detent features; and • an engaged position where the case frame portion is held in a selected position with respect to the base frame portion, and a disengaged position allowing the rotation about the pivot axis, the detent including a first set of detent features and a second set of detent features; and • a spring mechanism clamping the case frame portion to the base frame portion and the first set of detent features to the second set of detent features; • a support arm having an attachment end and a floating end, the floating end supporting the first set of detent features, the first set of detent features fixed against rotation about the pivot axis with respect to the support arm, but displaceable relative to the attachment end in a direction substantially parallel to the pivot axis, • wherein the attachment end of the support arm is fixed to, and is fixed against rotation with respect to, one of: the case frame portion and the base frame, and • wherein the second set of detent features is fixed against rotation with respect to the other of: the case frame portion and the base frame portion. • wherein the attachment end of the support arm is fixed to, and is fixed against rotation with respect to, one of: the case frame portion and the base frame, and • wherein the second set of detent features is fixed against rotation with respect to the other of: the case frame portion and the base frame portion.