I'm learning about how dog clutches work particularly in sequential transmissions.

I'm having a hard time understanding the principle which ensures dogs will always mesh correctly. I can easily imagine a situation in which dogs will collide and switching gears will not work such as when the speed of the input shaft matches the speed of the intermediary shaft and dogs are aligned together or when the engine is off and the vehicle is not moving then dogs can again collide.

I'm designing my own clutch-less transmission using dog gears, because I thought they are most appropriate, so I'm trying to understand the principle, not so much the example cases I mentioned above.

  • $\begingroup$ If this is for race cars, the speeds of the shafts will only match briefly; then the dogs will un-collide and the gear can be slid home. From a stop, if the thing won't go into gear you'd just pop the clutch, push it in, then put the thing in first while the input shaft is still spinning. $\endgroup$
    – TimWescott
    Sep 26, 2019 at 21:53
  • $\begingroup$ Some dogs do collide $\endgroup$ Sep 27, 2019 at 12:05

2 Answers 2


Usually because dog clutches are engaged when the shafts are stationary - lathes are a good example as they change speeds when the work is stationary and the tool dis-engaged.

  • $\begingroup$ Well in automotive application such as a gearbox the majority of the time at least 1 axle will be rotating if not both and at the same time one side of the dog pair will be freely spinning. I'm not sure if I understand what you mean. $\endgroup$
    – php_nub_qq
    Sep 26, 2019 at 15:15
  • $\begingroup$ Then, in automotive, the dog clutch has a synchromesh unit and that solves that problem - having stripped and rebuilt more than a few gearboxes... $\endgroup$
    – Solar Mike
    Sep 26, 2019 at 15:18
  • $\begingroup$ Regular ones do, but from what I've seen from my researches I'm not quite sure sequential aka dog boxes have synchros, am I wrong? $\endgroup$
    – php_nub_qq
    Sep 26, 2019 at 15:31

I appear to have found an answer but I can not find the source to give credits.

As the shafts are rotating there is a chance the dogs will collide but assuming there is lubrication, they will just slide on each other until they eventually fall into place and engage the gear.


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