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When I got a manual transmission car (2003 Kia Rio) I noticed that it makes a winding sound in the reverse gear.

Here is an example video that I found that demonstrates the sound. http://www.youtube.com/watch?v=mi2t_VT6YWg

Why do manual transmission cars make this noise in reverse gear? Does it work differently than the forward gears?

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1 Answer 1

up vote 27 down vote accepted

In manual transmissions, the reverse gears use a different type of gear teeth than forward gears. Forward gears are helical gears, which have teeth that are pointed at an angle. When the gears rotate, most of the load is evenly spread due to the angles.

Reverse gears are cut into spurs, which don't absorb the load quite so well. As a result, there is more of a whining noise. The reason reverse gears are spurs is because reverse requires an idler gear to prevent accidentally shifting into reverse while moving. This is what is known as the gears not being synchronized, and this is also why you cannot shift into reverse when you're moving.

What you may find interesting is that my 1987 Ford F-150 4x4 makes this same sound when moving forward in low 1st gear. The 4 speed granny low first gear is also using this same technology as it's only designed for towing or going up or down really steep hills.

For more information on transmission gears, check out Why does my manual transmission car make a loud whirring noise in reverse?

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Awesome Thanks! –  James T Mar 21 '11 at 6:12
    
@James - You're welcome! –  jmort253 Mar 21 '11 at 6:15
    
Note that some cars do have a synchro and helical gears on reverse. See the "Reverse" section of the Wikipedia Synchromesh article: en.wikipedia.org/wiki/Manual_transmission#Reverse –  Sean Reifschneider Mar 22 '11 at 11:04
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Amusingly, after watching Mad Max when I was much younger I did manage to practice the change from 3rd to reverse while driving forwards at speed. Wouldn't recommend it as it can easily damage the entire engine, transmission and gearbox - but it is good fun. You need to ensure you pop the clutch in, change to neutral and lock the wheels up (this works best at over 60 so you have time to wait for the synchromesh to wind down) then change into revers, run the revs up near the redline and dump the clutch hard. Don't blame me for any damage:-) –  Rory Alsop Aug 16 '11 at 20:40
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Only killed one. First attempt sort of worked, second attempt was perfect, third attempt destroyed the car. Heh –  Rory Alsop Aug 17 '11 at 7:48

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