The invention relates to a transmission module (10) for an engine-transmission unit, said module comprising an input shaft (11) for connecting to a heat engine, an output shaft (12) for connecting to a gearbox, and a clutch (30) connecting said two shafts. The inventive module also comprises: an independent casing (16) comprising a first half-shell (17) and a second half-shell (18), said two half-shells forming a sealed receiving element (22) containing the clutch (30) which is naturally in the engaged position; a mechanical element (35) for maintaining the clutch (30) in said engaged position by means of a piston in the form of a disk; a hydraulic control circuit (40, 41) for acting directly on the piston against the mechanical element, in the disengaged position of said clutch (30); and a hydraulic circuit (50, 52, 53, 55, 56) for lubricating and cooling the clutch. The invention can be applied to an engine-transmission unit for motor vehicles.