fig5 may for more reliable operation comprise plural elements of slightly differing lengths is pivotally mounted upon the uppermost one of a plurality of studs 96 carried by and projecting forwardly from the face of the gear box 18 the free end of pawl 91 engages teeth provided about an adjacent part of the peripheral surface of ring gear 74 such engagement prohibits counterclockwise rotation of ring gear 74 but permits its clockwise rotation studs 96 also serve to support disc 92 which is formed of material having a relatively high coefficient of friction between radially extending surfaces provided upon the confronting faces of ring gears 74 76 engagement between friction disc 92 and the aforesaid surfaces of ring gears 74 76 is maintained by the second disc 94 and biasing means associated therewith disc 94 loosely encircles that portion of the hub of planet carrier 80 intermediate pick gear 66 and the adjacent radial surfaces of the hubs of ring gear 76 and shroud member 68 pin elements 98 fig5 project forwardly from disc 94 into cooperating bores provided within the rearward radial face of pick gear 66 and secure disc 94 and pick gear 66 for rotary movement in unison with one another while permitting movement of disc 94 in the axial direction of shaft 16 housed within suitable recesses also provided in the rearward radial face of pick gear 66 are a plurality of compression springs 100 one of which is shown in fig5 which bias disc 94 into engagement with.