Abstract: A four wheel drive vehicle comprising an engine, a transmission connected to the engine, a front wheel drive line, a rear wheel drive line, and an automatic switch mechanism for operatively connecting the front wheel and rear wheel drive lines to the transmission to selectively provides a two wheel drive mode and a four wheel drive mode. The front wheel drive line and the rear wheel drive lines are constructed such that front wheels are driven at a lower speed than rear wheels. The automatic switch mechanism includes an input portion connected to the transmission, a first output portion connected to the front wheel drive line, a second output portion connected to the rear wheel drive line, and a clutch for connecting the first and second output portions to the input portion. The clutch is operable to disconnect the first output portion from the input portion upon receipt of a torque exceeding a predetermined value.

Abstract: A transmission system for a tractor comprising a double clutch for transmitting engine output to an inner shaft consitituting part of a propelling line and to a tubular outer shaft constituting part of a power takeoff line. The double clutch includes a first and second flywheels, and the second flywheel defines a boss for relatively rotatable supporting a forward end of the outer shaft therein. The transmission system further comprises a propelling line change speed mechanism including a reversing gear and a reversing shaft for supporting the reversing gear. A rotational resistance applying device is provided on the reversing shaft for applying a rotational resistance to the propelling line by frictional engagement with the reversing gear.