Power transmission unit for motor vehicles

A power transmission unit for a motor vehicle comprising:

• an elongated input shaft drivingly connected to an output shaft of an engine through a disengageable coupling;
• a primary transmission having an elongated main sleeve shaft in surrounding relationship to said input shaft, a countershaft arranged in parallel with said main sleeve shaft, change-speed gearing means mounted in association with said main sleeve shaft and said countershaft and selectively operable to provide a plurality of forward speed ratios and at least one reverse speed ratio between said main sleeve shaft and said countershaft, and shift means;
• a final drive gearing drivingly connected to said countershaft to drive a differential gear unit;
• an auxiliary transmission having a sun gear rotatably mounted on said input shaft, a ring gear integral with said main sleeve shaft, a planet carrier integral with said input shaft, a plurality of planet gears rotatably mounted on said planet carrier, said planet gears being in mesh with said sun gear and said ring gears, a selector gear unit comprising a first spline drivingly connected to said sun gear, a reaction member stationary with respect to said auxiliary transmission, a slide solidly engaged with said spline and said planet carrier and also with said spline and said reaction member, said primary transmission being arranged between said disengageable coupling and said auxiliary transmission.