Transmissions

May 21, 2004 4:00 PM

Every manual transmission car I've ever driven makes a strange high pitched whining noise when going in reverse at more than about ten miles an hour. They don't make the same noise at the same revs in any forward gear. So why the difference? These are UK / European transmissions if that makes any difference.
posted by twine42 to Travel & Transportation (15 answers total)

Reverse is a very low gear, you are basically winding it out. Try taking your car up to 30mph/50kmh in first gear and I'm sure you'll hear a somewhat similar sound.
posted by mathowie at 4:05 PM on May 21, 2004

what mathowie said
posted by matteo at 4:08 PM on May 21, 2004

1st & reverse = same gear, different directions.
posted by Shane at 5:12 PM on May 21, 2004

All I can say is that you should not be reversing any faster than 10 mph unless you're a stunt driver for a movie. :)

It whines by design, my friend.
posted by madman at 5:26 PM on May 21, 2004

ever need to bump start your manual? do it in reverse.
posted by Frasermoo at 5:42 PM on May 21, 2004

Trivia: In the old old days when cars were big and underpowered it was not uncommon to go up the steepest of hills in reverse, as the lower gear gave the extra edge needed on certain vehicles.
posted by wackybrit at 3:14 AM on May 22, 2004

The reason why it whines is because the reverse gear is a straight-cut gear, not helical like the forward gears.

Shane, reverse gear is a totally separate gear than first. I've never heard of what you've described.

And mat, if you hear a whining in any of the forward gears then you'll need a new gearbox soon :) I think the whine would your hear would come from the 7000rpm+ you're doing in first gear!
posted by derbs at 4:23 AM on May 22, 2004

The reason why it whines is because the reverse gear is a straight-cut gear, not helical like the forward gears.

brilliant! seeing that made me realise i've had a subconscious desire to know what helical-cut gears were all about for years.... seriously. thanks!
posted by andrew cooke at 6:14 AM on May 22, 2004

What derbs said, seconded. Helical gears don't contact along a whole tooth at one time; they gradually engage. Straight cut gears engage one whole tooth at a time. Straight-cut gears are much easier to manufacture, and since we use reverse infrequently, that noise is not a problem factor.
posted by notsnot at 7:16 AM on May 22, 2004

derb thirded. The whine isn't so much about rpm as it is about a different gear mesh.
posted by five fresh fish at 9:29 AM on May 22, 2004

this page has a wonderful diagram that shows the reverse gear with different teeth, and how it's not normally running, while all the others are, continuously (read the text from the page before to understand how that makes sense).
posted by andrew cooke at 10:18 AM on May 22, 2004

(although there's another diagram, lower down, with reverse continuously connected via an idler gear, with helical teeth - do modern transmissions not make the whining sound, because that diagram seems to contradict everything here...?)
posted by andrew cooke at 10:22 AM on May 22, 2004

Shane, reverse gear is a totally separate gear than first. I've never heard of what you've described.

Very often nearly the same gear ratio, derbs, and sometimes exactly the same in trucks or serious off-road vehicles.

Not that I'm a truck enthusiast, or much of a mechanic.
posted by Shane at 12:38 PM on May 22, 2004

brilliant! seeing that made me realise i've had a subconscious desire to know what helical-cut gears were all about for years.... seriously. thanks!

Wow, he was serious.
posted by Shane at 12:41 PM on May 22, 2004

I think the whine would your hear would come from the 7000rpm+ you're doing in first gear!

Some new sportbike motorcycles redline at nearly 16,000rpm... the noise at the speed is more like a scream than a whine.
posted by letitrain at 12:56 PM on May 22, 2004