Synchronizer Assembly 12JS160T-1707140

The working principle of the secondary synchronizer in the Steyr Fastrate nine-speed gearbox is to use the friction inside the synchronizer to make the rotational speed of the output shaft more similar to that of the gears, thereby avoiding the generation of teeth-rubbing sounds when the gears engage due to excessive speed difference.

Specifically, when a repair technician disassembles the secondary synchronizer and the high-speed teeth of the gearbox after replacing it, they will find that the secondary synchronizer has already worn out along with the high-speed teeth. In more severe cases, the friction belt of the high-speed ring of the synchronizer may burn out, the driving teeth may turn blue, and the combined layer may be severely worn and deformed. What could be the reason for such a serious problem occurring in such a short period of time? The same assembly and the same components, some vehicles won't encounter such a situation until they have traveled 100,000 or even 200,000 kilometers. In fact, this situation occurred when we just assembled the gearbox, but we didn't see what was inside.

The structure of the Fastrate 12-speed gearbox is very compact. More experienced repair workers will notice that the secondary synchronizer of the Fastrate nine-speed gearbox has a large axial gap between the front and rear axles in the gearbox. When you push it forward and backward, there is at least 5MM of gap. While the 12-speed secondary synchronizer basically just fits between the driving teeth and the reduction teeth, the gap is very small. If the flange rotates along with the movement and the impact force, the secondary synchronizer will rotate along with it and move forward. However! At this time, the driving teeth are not rotating! The high-speed cone ring of the synchronizer has no lubrication and high-speed friction with the cone surface of the driving teeth, burning the friction belt! Colliding with the internal combined teeth of the driving teeth at high speed, because the hardness of the synchronizer cone sleeve is higher than that of the combined teeth of the driving teeth, it will cause the combined teeth of the driving teeth to crack, and also burn the reduction tooth pad and washer, resulting in no low gear (the reduction tooth burns and does not float). Therefore, when repairing technicians replace the 12-speed reduction teeth, pads, combined bearings, and synchronizers, they must not allow the flange to rotate when tightening the nuts to avoid unnecessary losses.

The Fastrat transmission adopts a dual intermediate shaft structure to achieve power distribution. Each intermediate shaft, intermediate shaft bearing, and gears on the intermediate shaft only bear 1/2 of the total power. The gears on the input shaft and the main shaft also bear 1/2 of the total power. Under this design, the force on the main shaft is equal in magnitude but opposite in direction, so the main shaft only bears torque and not bending moment.

This brings many benefits. It eliminates the damage to the gear meshing area caused by the deformation of the main shaft, reduces the noise of the gear meshing in the transmission, extends the lifespan of the gears, can prolong the service life of the transmission and make its operation more reliable. Moreover, the dual intermediate shaft structure can reduce the center distance, decrease the diameters of the gears in each gear ratio, narrow the width of the gears, and reduce the diameters of each shaft, making the axial size of the transmission shorter and the weight lighter. The short axial size is convenient for the overall vehicle layout, and the light weight of the transmission can reduce fuel consumption and improve the overall vehicle performance.