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Speaker 1: and sign up today. Welcome to brain Stuff from house

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Speaker 1: stuff works dot com where smart happens. Him Marshall Brain

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Speaker 1: with today's question, why does a manual transmission make a loud,

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Speaker 1: worrying noise when it's put into reverse? Manual transmissions use

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Speaker 1: mostly helico gears, but reverse is a special situation that

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Speaker 1: requires a different type of gear, a spur gear, and

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Speaker 1: this is why reverse sounds different than forward in a

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Speaker 1: normal manual transmission car. The gears that make up the

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Speaker 1: forward gear ratios are all helical gears. The teeth on

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Speaker 1: helico gears are cut at an angle to the face

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Speaker 1: of the gear. When two teeth on a helical gear

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Speaker 1: system engage, the contact starts at one end of the

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Speaker 1: tooth and gradually spreads as the gears rotate until the

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Speaker 1: two teeth are in full engagement. This gradual engagement makes

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Speaker 1: helical gears operate much more smoothly and quietly than spur

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Speaker 1: gears do. Also, because of the angle of the gear teeth,

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Speaker 1: more teeth are in engagement at any one time. This

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Speaker 1: spreads the load out more and it reduces stresses, which

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Speaker 1: also reduces noise. The only problem with helical gears is

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Speaker 1: that it's hard to slide them in and out of

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Speaker 1: engagement with each other. On a manual transmission, the forward

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Speaker 1: gears stay engaged with each other at all times, and

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Speaker 1: callers that are controlled by the stick shift lock the

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Speaker 1: different gears to the output shaft. You can go read

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Speaker 1: how manual transmissions work for details on this. In contrast

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Speaker 1: to that, the gears that are used in reverse are

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Speaker 1: normal gears like you see in cartoons their circles with

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Speaker 1: teeth on them. The reverse gear on your manual transmission

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Speaker 1: uses an idler gear that has to slide into mesh

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Speaker 1: with two other spur gears at the same time in

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Speaker 1: order to reverse the direction of rotation. Each time a

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Speaker 1: gear tooth engages on a spur gear, the teeth collide

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Speaker 1: instead of gently sliding into contact as they do on

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Speaker 1: helico gears. This impact makes a lot of noise and

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Speaker 1: also increases the stresses on the gear teeth. When you

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Speaker 1: hear a loud, whirring noise from your car and reverse,

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Speaker 1: what you're hearing is the sound of the spur gear

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Speaker 1: teeth clacking against one another. For more on this and

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Speaker 1: thousands of other topics. Because it how staff works dot com,

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Speaker 1: Streaming TV shows and movies directly to your home is

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Speaker 1: a breeze with Netflix. As a Netflix member, you can

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00:02:54,919 --> 00:02:58,760
Speaker 1: instantly watch TV and movies on your PC, Mac, mobile device,

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Speaker 1: or right on your television. Get a free thirty day

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Speaker 1: trial membership. Go to Netflix dot com slash brain stuff

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Speaker 1: and sign up today.