In this video, the counter shaft is not rotating while a gear slides into place. But if the counter shaft was rotating, wouldn't the gear sliding over have a difficult time engaging with a gear on the counter shaft?


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Yes if the shafts were rotating then it would be difficult - this is why the gears are engaged when the shafts are not transmitting torque or rotating.

If you want to change gears during operation then a constant mesh gearbox is clearly a better option. Usually the gears are not locked to the shaft and they have dogs on their sides. These gears transmit torque by engaging with a hub (that also has dogs) that slides along the shaft but is splined with the shaft.

See the video below starting from 3:00. The purple components are the sliding hubs I'm talking about. They have dog teeth that interact with the dog teeth on the sides of the gears.


  • $\begingroup$ What about this scenario. I've added a pic to my original post...(The gears only engage when the shafts are not rotating). In the top picture, the blue gear is meshed with the green gear and rotates the green gear. Then the blue gear stops rotating and slides over to mesh with the red gear. But since the red and green gears are on separate axles and are no longer aligned with each other, wouldn't the blue gear have a difficult time meshing with the red gear? $\endgroup$ – Nev Sep 12 '16 at 23:47
  • $\begingroup$ Sliding mesh gearboxes are prone to gear tooth failure because of the difficulties you are suggesting. They require great skill to operate smoothly. This is one of the advantages of a constant mesh gearbox - they are easier to operate because it's easier to engage dog teeth than gear teeth so to speak. $\endgroup$ – pauloz1890 Sep 12 '16 at 23:55

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