A seat belt retractor that is sensitive to vehicle movements is provided, having a frame for mounting a reel about which the safety belt is wound. A frame also mounts a pawl which selectively blocks rotation of the reel to prevent payout of a seat belt when a predetermined condition of the vehicle is sensed. The frame includes a support plate integrally formed therewith and including a bearing seat for mounting an inertia member for actuating the pawl, thus locking the reel against rotation. A method of constructing the retractor frame with an integral support for the inertia member is also disclosed.