Mechanical gearbox of 3.8 T internal combustion heavy balance forklift

The utility model provides a mechanical gearbox of a 3.8 T internal combustion heavy balance forklift. The mechanical gearbox comprises a base, a shell, an idle wheel assembly, a main shaft assembly, an output shaft assembly, a driving shaft assembly, a gear shaft assembly, a gear ring assembly and a separation assembly. According to the utility model, the separating force of the diaphragm clutch is 1200N, and the separating force of the two-claw separating claw is reduced by one third compared with that of a three-claw separating claw, so that the force of an operator for treading a pedal is reduced, and the working efficiency of a gearbox is improved; according to the diaphragm clutch, the contact surface of the separation claw and the separation bearing is increased, the problem that the separation claw is not uniformly stressed when the clutch is separated is effectively solved, the bearing capacity of a gearbox is improved, the pre-tightening force of the clutch is increased, and the phenomenon of fricti