Abstract: A tandem axle system has a forward axle system and a rear axle system. A method of selectively driving one or both of the axle systems is described.

Abstract: A tandem axle system has a forward axle system and a rear axle system. A method of selectively driving one or both of the axle systems is described.

Abstract: A method and apparatus for operating a compound transmission automatically prevents a manually selected shift of the auxiliary section from occurring unless the vehicle speed is within a predetermined maximum limit or range. A shift controller initially determines if a request for a shift operation in the auxiliary section has been made by the operator of the vehicle. This determination may be inferred from a change in the position of a manually operable switch. If a shift request has been made, the shift controller determines if the main section of the transmission is in the neutral gear ratio. If the main section of the transmission is not in the neutral gear ratio, then the shift controller takes no further action. When the shift controller determines that the main section of the transmission is in the neutral gear ratio, then it determines if the speed of the vehicle is within a predetermined limit or range to enable shifting of the auxiliary section in a safe and efficient manner.

Abstract: A gear transfer unit for selectively shifting an engine driven vehicle to either a two-wheel or four-wheel drive mode while in motion which unit includes a gear system of constant mesh gears, a synchronizer and means for activating the synchronizer for selective high and low speed coupling of the input drive to the front and rear output shafts of the unit.