A seat belt retractor comprises a main winding spring (36) coupled between the frame (11) and the reel shaft (14) and an auxiliary winding spring (34) coupled between the frame and a rotatable wheel (41). An operating mechanism (42) locks the wheel (41) against rotation when the belt is done up, thereby inactivating the auxiliary spring (34). The wheel (41) is coupled to the shaft by an elongated flexible coupling member (51) wound spirally around a portion (15) of the reel shaft (14) such that it tightens when the reel shaft rotates in the belt-unwinding direction relative to the wheel (41) and loosens when the reel shaft rotates in the belt-winding direction relative to the wheel (41). The member (51) may be made from polymeric materials such as nylon, polyesters and acetals. <IMAGE>
