Abstract: A seat belt retractor mechanism having a belt reel rotatably mounted on a shaft journalled in a support frame, the reel at each of its ends having a circular ratchet plate. A locking bar parallels the reel shaft and is pivotally mounted in the support frame for movement into engagement with the ratchet plates to hold the reel against rotation in seat belt protraction direction. An inertia sensor comprising a pendulum device is engageable with the locking bar.The improvement comprises a support bracket on the support frame beneath the locking bar for which the pendulum device is suspended. Coacting gimbal means on the support bracket and pendulum device permit swinging movement of the pendulum device relative to the support bracket. The locking bar and pendulum device are constructed and arranged so that during swinging movement on the gimbal means the pendulum device is ineffective to cause movement of the locking bar toward the ratchet plate.