eli5 Why don’t all transmissions have dog gears if you don’t need to use clutch while shifting them?
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Are you referring to automatic transmissions or manual transmissions that you “float” or “double clutch” like those on large trucks with split differentials?
Most automotive and motorcycle transmissions require using the clutch to shift gears unless they have some kind of auto clutch system. You can get away with shifting by rev matching, but it tears up the synchronization gears that act as brakes for the gears, especially with gasoline engines that have a larger rev range.
With larger trucks and tractor/trailer combo trucks, you generally add a clutch brake. At the very bottom of the pedal, you can keep pushing to stop the transmission from spinning. This helps get you into your first gear of choice from a dead stop (r/3-5, depending on your load. 1st and second gear aren’t used very often unless you’re in a dirt lot and you’re not trying to kick up dust, 3rd is a truck stop gear that’s fast enough not to piss off drivers behind you but not fast enough to upset pedestrians). Once you get moving without throttle, you can tap the clutch or do a slight lift on the pedal to release the gear and then increase or decrease engine speed to match the next gear and tap the clutch again or get the rpm perfect to slide into the next gear.
Farm tractors have a clutch brake too, and it’s used to get into gear from a dead stop. The difference is, tractors are geared to go about 25mph flat out. You start it in the gear you want without throttle input and you only use the clutch to start or stop. You’re often running a PTO (power take off) used to run accessories with power taken off the engine on a shaft, usually in the rear to run rototillers, various pumps, flail mowers, etc… (they have a front PTO on some military or heavy duty trucks to run a winch, and tow trucks will use them to run hydraulics). Why mention the PTO? Cause you need to run the engine at a select speed to properly power the PTO. You select your gears for the speed you need to be going while the PTO accessory is being used (like when spraying nutrients/pest deterrents).
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