WEBVTT - Why does a manual transmission make a whirring noise?

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<v Speaker 1>stuff works dot com where smart happens. Him Marshall Brain

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<v Speaker 1>with today's question, why does a manual transmission make a loud,

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<v Speaker 1>worrying noise when it's put into reverse? Manual transmissions use

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<v Speaker 1>mostly helico gears, but reverse is a special situation that

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<v Speaker 1>requires a different type of gear, a spur gear, and

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<v Speaker 1>this is why reverse sounds different than forward in a

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<v Speaker 1>normal manual transmission car. The gears that make up the

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<v Speaker 1>forward gear ratios are all helical gears. The teeth on

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<v Speaker 1>helico gears are cut at an angle to the face

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<v Speaker 1>of the gear. When two teeth on a helical gear

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<v Speaker 1>system engage, the contact starts at one end of the

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<v Speaker 1>tooth and gradually spreads as the gears rotate until the

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<v Speaker 1>two teeth are in full engagement. This gradual engagement makes

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<v Speaker 1>helical gears operate much more smoothly and quietly than spur

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<v Speaker 1>gears do. Also, because of the angle of the gear teeth,

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<v Speaker 1>more teeth are in engagement at any one time. This

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<v Speaker 1>spreads the load out more and it reduces stresses, which

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<v Speaker 1>also reduces noise. The only problem with helical gears is

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<v Speaker 1>that it's hard to slide them in and out of

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<v Speaker 1>engagement with each other. On a manual transmission, the forward

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<v Speaker 1>gears stay engaged with each other at all times, and

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<v Speaker 1>callers that are controlled by the stick shift lock the

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<v Speaker 1>different gears to the output shaft. You can go read

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<v Speaker 1>how manual transmissions work for details on this. In contrast

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<v Speaker 1>to that, the gears that are used in reverse are

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<v Speaker 1>normal gears like you see in cartoons their circles with

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<v Speaker 1>teeth on them. The reverse gear on your manual transmission

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<v Speaker 1>uses an idler gear that has to slide into mesh

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<v Speaker 1>with two other spur gears at the same time in

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<v Speaker 1>order to reverse the direction of rotation. Each time a

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<v Speaker 1>gear tooth engages on a spur gear, the teeth collide

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<v Speaker 1>instead of gently sliding into contact as they do on

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<v Speaker 1>helico gears. This impact makes a lot of noise and

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<v Speaker 1>also increases the stresses on the gear teeth. When you

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<v Speaker 1>hear a loud, whirring noise from your car and reverse,

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<v Speaker 1>what you're hearing is the sound of the spur gear

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<v Speaker 1>teeth clacking against one another. For more on this and

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<v Speaker 1>thousands of other topics. Because it how staff works dot com,

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