Abstract: A transmission protection system for a motor vehicle that has a low range of ratios (gears 1, 2, 3 and 4) and a high range of ratios (gears 5, 6, 7 and 8). A selection of gear is made using a gear selection shaft connected with a gear change lever having a preselective switch. An electro-pneumatic valve is directly connected to and acts axially on the gear selection shaft to counteract accidental positioning of the gear selection shaft in a position of the gears 1-2 or in a position of the gears 5-6. An electronic transmission control unit is configured to control the electro-pneumatic valve by an electric signal depending on a difference between a vehicle speed Sv and a first assumed speed S1 for the low range of ratios or between the vehicle speed Sv and a second assumed speed S2 for the high range of ratios.