sleeve 24 deflecting one pair of the inwardly curved flange portions 14 the spring 40 is compressed laterally and assumes a configuration as shown in fig8 wherein the surface contact between the spring 40 and the sides of the coupling sleeve splines 22 is minimized this feature is deemed advantageous in that the resistance to sliding of the coupling sleeve 24 toward and away from the gear 28 is minimized this eliminates the problem encountered with the first embodiment wherein as shown in fig4 a line contact tends to be generated at the position indicated by 34 c 34 and by which the return of the coupling sleeve 24 toward its home position is somewhat resisted in this embodiment the axial length 34 w 34 of the tang like portion 42 is arranged to be essentially equal to the distance defined between the inboard surfaces 44 45 of the baulk rings 26 27 which cooperate to define the aformentioned recess 34 as will be readily appreciated from fig7 the tang like portion 42 of this embodiment is essentially as wide as the main body portion of the spring and thus able to stably exert force on the inboard surfaces 44 45 of the baulk rings viz a force which acts normally to said surface further as best seen in fig7 in this embodiment the inwardly and outwardly curving flange portions are formed in 34 mirror image 34.