Why do automatic cars whine in reverse?
Discussion
"Proper" automatics (i.e. torque converter and epicyclic geartrain) shouldn't whine at all.
I had one that did, but that's because it was old and borked and had gone 190,000 miles without a transmission fluid change before I bought it!
Lots of manual cars do whine in reverse, as someone above said it's down to having a straight-cut reverse gear. Forward gears on most vaguely modern vehicles are helically-cut, which means the gear teeth are angled. Makes for quieter running, i believe at the cost of a little efficiency.
I had one that did, but that's because it was old and borked and had gone 190,000 miles without a transmission fluid change before I bought it!
Lots of manual cars do whine in reverse, as someone above said it's down to having a straight-cut reverse gear. Forward gears on most vaguely modern vehicles are helically-cut, which means the gear teeth are angled. Makes for quieter running, i believe at the cost of a little efficiency.
kev b said:
Because the diff. is turning backwards, same as a manual car.
Manual cars whine because the reverse gear is usually straight cut instead of helical. A diff shouldn't be significantly noisier running backwards unless it's well worn. Can't say I've noticed autos being noisy in reverse generally.I always thought gearboxes were cut helically as its easier for the gears to deal with the load and are stronger for the most part. Dog gearboxes and straight cut gears are costly to produce and fit and in cars are only ever used in Motorsport applications. They also requure fairly regular maintenance. A used peugeot sadev (brand) dog gearbox recently sold on ebay for over 1700.
So llthough they are indeed noisy I dont that was the main reason road cars dont use them.
Straight cut gears are jerky and trickier to engage in road use, clutch generally isn't necessary, at least not when shifting up. I wouldn't want one on a road car, but on the track they are something else in terms of the performance they offer.
So llthough they are indeed noisy I dont that was the main reason road cars dont use them.
Straight cut gears are jerky and trickier to engage in road use, clutch generally isn't necessary, at least not when shifting up. I wouldn't want one on a road car, but on the track they are something else in terms of the performance they offer.
k!Pebbles167 said:
I always thought gearboxes were cut helically as its easier for the gears to deal with the load and are stronger for the most part. Dog gearboxes and straight cut gears are costly to produce and fit and in cars are only ever used in Motorsport applications. They also requure fairly regular maintenance. A used peugeot sadev (brand) dog gearbox recently sold on ebay for over 1700.
So llthough they are indeed noisy I dont that was the main reason road cars dont use them.
Straight cut gears are jerky and trickier to engage in road use, clutch generally isn't necessary, at least not when shifting up. I wouldn't want one on a road car, but on the track they are something else in terms of the performance they offer.
You may be confusing straight cut gears and dog clutches. They are separate things, you could have a helical dog box (though it would be unusual) and you can get straight cut boxes with synchromesh. The gears themselves are always meshed anyway, so any variance shift quality comes from the use of dog clutches or synchromesh.So llthough they are indeed noisy I dont that was the main reason road cars dont use them.
Straight cut gears are jerky and trickier to engage in road use, clutch generally isn't necessary, at least not when shifting up. I wouldn't want one on a road car, but on the track they are something else in terms of the performance they offer.
Mr2Mike said:
You may be confusing straight cut gears and dog clutches. They are separate things, you could have a helical dog box (though it would be unusual) and you can get straight cut boxes with synchromesh. The gears themselves are always meshed anyway, so any variance shift quality comes from the use of dog clutches or synchromesh.
You are correct, I often do as they are used together so frequently.My apologies
Jonny_ said:
"Proper" automatics (i.e. torque converter and epicyclic geartrain) shouldn't whine at all.
I had one that did, but that's because it was old and borked and had gone 190,000 miles without a transmission fluid change before I bought it!
Lots of manual cars do whine in reverse, as someone above said it's down to having a straight-cut reverse gear. Forward gears on most vaguely modern vehicles are helically-cut, which means the gear teeth are angled. Makes for quieter running, i believe at the cost of a little efficiency.
Isnt the Helical cut also there to Aid changinging between gears and make them feel more refined ?I had one that did, but that's because it was old and borked and had gone 190,000 miles without a transmission fluid change before I bought it!
Lots of manual cars do whine in reverse, as someone above said it's down to having a straight-cut reverse gear. Forward gears on most vaguely modern vehicles are helically-cut, which means the gear teeth are angled. Makes for quieter running, i believe at the cost of a little efficiency.
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