A seat belt retractor (22) having an inertial sensor to initiate lockup of the retractor, the inertial sensor including a first housing portion (102) having an actuating arm mounting member (120). The retractor including a first pin (126) cantilevered from the mounting member (120); an activation arm (130) rotationally supported upon the first pin (126), the activation arm (130), when activated, movable into engagement with a ratchet wheel (80), a pendulous vehicle sensor subassembly (150) mounted upon the first housing portion (102), the subassembly (150) and the first housing portion (102) including a support mechanism to rotatably support the sensor subassembly thereon. The sensor subassembly (150) further including a weighted member (152) having a platform for supporting a movable inertial weight (154), the inertial weight movable on the platform in response to deceleration to which the retractor is subjected; a movable arm (156) supported by the weighted member and including a sensing arm (240) having a tip (202) resting upon the inertial weight (154), the movable arm cantilever supported relative to the weighted member, wherein movement of the movable arm causes movement of the sensing arm thereby causing a change in the elevation of the activation arm thereby placing the retractor in a pre-lock mode.