main transmission 8 the main transmission 8 comprises an output shaft 9 a lower 2 speed transmission device a higher 2 speed transmission device and a pair of synchromesh mechanism 8a 8b for selecting the speed change gears and a reverse gear mechanism not shown a drive pinion 10 is secured to one end of the output shaft 9 and the drive pinion meshes with a crown gear 12 of a final reduction gear device 11 the final reduction gear device is adapted to transmit the output of the output shaft 9 to front wheels of the car through the front axle f the output shaft extends rearwardly and a transfer gear 13 is jointly rotatably mounted on the rear end of the output shaft 9 a rear wheel drive shaft 15 is rotatably supported by bearings not shown and a gear 13a engaging with the gear 13 is freely rotatably mounted on the rear wheel drive shaft 15 a rear wheel drive synchromesh mechanism 14 of a second clutch is mounted on the rear wheel drive shaft 15 so as to selectively jointly rotatably engage the gear 13a with the shaft 15 to transmit the output of the output shaft 9 to rear wheels of the car a device for operating the synchromesh mechanism 6 in the auxiliary transmission 4 and the synchromesh mechanism 14 on the rear wheel drive shaft 15 will be described hereinafter referring to fig2 in the auxiliary transmission 4 a first shift fork 25 is secured to a shaft 42 and a lever.