Why Does the Shift Lever Block When Shifting?

The common manual gearbox always have a synchronizer and gear structure. Shifting is actually a process that the synchronizer combine with the corresponding gear through the pushing or connection of gearbox shift fingers, gearbox shift blocks, gearbox shift forks and other auxiliary parts, as shown simply in the figure below, the synchronizer move left to combine with the teeth. It is noted that the right side of the tooth is not flat, but is slope, the same as the right side of the synchronizer, and there is a synchronizer ring with the similar structure between synchronizer and gear, these slopes have leading-in effect, but also increase resistance in shifting.

Left： Gear  Right: Synchronizer

If the shift lever unusually blocks when shifting, in addition to check the friction and the like in the transmission system, the main possibility is that the synchronizer and gear are abnormal, such as the unmatched size, angle and the like. Some worse cases, for example the shifting is significantly worse than the other models of the same car, and even having the significant two shifting, often less appear if the gearbox parts are produced from the stable and normal processing.