A method controls synchronization of a pinion rotating on a primary shaft driven by a traction machine of a vehicle and rotatably connected to a secondary shaft of a parallel shaft gearbox without synchronization mechanisms. The method includes sending to the traction machine, before coupling of the pinion on the primary shaft, a torque command which depends on a torque signal calculated to minimize a difference between a primary speed and a secondary speed multiplied by a reduction ratio between the primary shaft and the secondary shaft. The calculated torque signal is limited in amplitude when the speed difference is greater in absolute value than a desired accuracy on the targeted primary speed upon completion of the synchronization. The calculated torque signal is saturated on a maximum or minimum torque of the traction machine if the calculated torque signal is not between the maximum or minimum torque.