324,086. Wilson, G. Sept. 19, 1928. No Patenb granted (Sealing fee not paid). Locking vehicle wheels by positive detents.-Spragging devices for motor vehicles, of the kind described in Specification 290,320, are arranged for use with a four speed gear box, being controlled by a pair of superposed cam plates with slots so arranged that either plate may be stationary whilst the other is moving with the gear control lever. The spragging action is effected by pivoted detents adapted to engage a. ratchet wheel on the tail shaft of the vehicle, such engagement being controlled by the cam plates and being effective in neutral or neutral and first gear positions of the control lever. In the arrangement shown in Figs. 1 and 3, the detents 9 are mounted in a rotatable carrier 3 with an arm 3<a> engaging one of the cam plates 13 whilst a concentric mask or shield 4 apertured as at 4a for the passage of the pawls is connected through a lever 14 both to the plate 13 and to a second cam plate 16. Engagement of the ratchet wheel 6 by the pawls is controlled by relative rotation of the pawl carrier 3 and mask 4. The cam plate 13 is elastically connected to the gear control lever for first and second forward speeds and reverse, the cam plate 16 coming into operation for third and fourth speeds. The arm 3<a> on the pawl carrier engages a slot 12 in the plate 13 whilst the lever 14, operating the mask, engages slots 15, 17 in both cam plates, these slots being provided with transverse portions 15a enabling either plate to be operative whilst the other is stationary. Fig. 1 shows the arrangement with the gears in neutral, the spragging device, Fig. 3, being in operation and remaining in operation when the plate 13 moves with the control lever to first speed position. On movement through second neutral to reverse, the arm 3<a> is rocked as it enters the raised end 12b of the slot 12 thereby disengaging the pawls, the lever 14 remaining stationary in the straight part of the slot 17. On passage from first, through neutral, to second forward speed, the arm 3a remains stationary whilst the lever 14 is rocked by the raised end of the slot 17. For third and fourth speeds, the plate 16 moves with the control lever, rocking the lever 14 whilst the plate 13 remains stationary. In a modification, the pawls are mounted on a fixed carrier and are provided with tail pieces engaged by a. rotary cam member to effect disengagement, the cam member being rocked in the requisite manner by a single lever engaging slots in a pair of superposed cam plates 36, 37, Fig. 6, functioning in a similar manner to the arrangement already described.