Ever wanted to know why your car whines in reverse?

[YeuEmMaiMai]

Originally Posted by hurleyint Congrats on having quiet cars, but to say only I4 honda's whine in reverse is a bit much. I know for a fact I have heard toyota's, VW's, and nissans all make the same whining noise. I read about this a few years ago, you guys are way behind. I said "the only cars that I had that make that noise...." I did not say that only I4 hondas do it......

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[YNG]

Why not use a helical gear for reverse as well?

[johnlear]

'Proper' racing gearboxes use straight cut gears on all gears, which is why dedicated racing boxes can make as much noise as the engine (scream like a banshee...).

The reason for using straight cut forward gears in racing boxes is that they are inherantly stronger because the full width of each tooth is contacting the full width of the other tooth (on the corresponding other gear). With helical gears the tooth contact is only ever over part of the teeth on each gear cog at any given moment, so is inherantly weaker (but a LOT quieter!).

Also, helical cut gears are always trying to slide laterally out of mesh with each other when under load. This is because the angle of the teeth creates a side thrust that must be resisted by thrust bearings (usually semi circular metal plates, more a flat bushing than a bearing), and this creates friction which means at least some loss of power in the box and increased gearbox temp. Using straight cut gears eliminates this side thrust and the associated side effects.

Reverse gear needs to use straight cut teeth because to engage / disengage reverse, the gears need to be able to slide into and out of mesh at the teeth (there are no 'dog teeth' associated with reverse as there are with the forward gears). But, helical teeth can't slide into or out of mesh at the teeth, so reverse can't use helical teeth.

The forward gear cogs are always in mesh and engaged / disengaged with 'dog teeth' in the synchroniser assemblies, so the forward gears can use helical teeth. The forward gears all use only two gear cogs for each ratio, but to engage reverse, a third cog (the 'reverse idler gear') is moved into mesh with two other gear cogs. This third gear is required to create the reverse rotation at the output shaft.

All manual gearboxes, whether FWD or RWD or 4WD, use straight cut gears in reverse. This is because of the need to use the third cog to create reverse shaft rotation. Some older gearboxes use straight cut gears on 1st gear only because 1st is the most highly stressed gear, and straight cut teeth are stronger.

PS The only gearboxes Iv'e ever personally worked on that use forward gears that are NOT in constant mesh (i.e. where the gears engage / disengage at the cog teeth) are the gearboxes from old Grand Prix racing Bugattis (Type 35 and 37), which used straight cut teeth (and howled like banshees!).




Modified by johnlear at 11:24 PM 9/10/2008

[sxm5369]

Originally Posted by 02 accord

Now you know.

and knowing is half the battle GI JOE!!!!

[TOAB]

Originally Posted by YeuEmMaiMai

that's funny becasue the only cars that I have had that make that whine in reverse are I4 hondas

my V6 accord didn't do it
my CL type S does not do it
None of my american FWD cars did it

Sable
Cutlass

Were they automatics with a planetary setup?

[rhdins]

Originally Posted by sxm5369

and knowing is half the battle GI JOE!!!!

GI JOE is awesome!!!!

K someone explain this one. My dad has a mazda protege, 95, maybe 96, I'm not sure, it whines in first gear. It's always done that and as far as he can tell nothing is wrong. Does it have a straight cut gear for first?

[rodneylynn1977]

Ok now my whining questions have been answered... Now tell me why all hondas vibrate so bad in reverse. Sometimes it makes my teeth hurt!!1 ha ha ha

[johnlear]

Originally Posted by rhdins

K someone explain this one. My dad has a mazda protege, 95, maybe 96, I'm not sure, it whines in first gear. It's always done that and as far as he can tell nothing is wrong. Does it have a straight cut gear for first?

Without knowing anything specific about these cars, I'd be very very surprised if it did (i.e. almost definitely not).

Straight cut gears on 1st would probably have been last used in the 60s I'd think(?), for cars like Austin Healey Sprites and MG Midgets (to my knowledge). The gearbox internal arrangement in these boxes is a bit different in that 1st uses part of the mechanism invloved with reverse, the gears involved with 1st engaging / disengaging at the cog teeth rather than with 'dog' teeth (which are used for 2nd, 3rd, 4th), and 1st thus having no synchromesh (but 2nd, 3rd, 4th do have synchro).

[doug118]

just for the hell of it.. my buddy's all motor mustang with straight cut gears which sort of makes it sound supercharged which almost everyone around here likes to argue about

http://videos.streetfire.net/v...2.htm

EDITED to fix the improper english


Modified by doug118 at 3:08 AM 9/13/2008

[ricin4ever]

cough they're called straight cut gears cough

[doug118]

what??

[ricin4ever]

Originally Posted by doug118

what??

sorry i only read the first post but what i was getting at is the reason your transmission whines in reverse is because it has straight cut gears and is perfectly normal. but i read and like 3 people have already said this lol.

[YeuEmMaiMai]

Originally Posted by TOAB

Were they automatics with a planetary setup?

I believe that Honda automatics are of a constant mesh design

The american cars use planitary gears to create the proper gear selection

[Katman666]

For some weird reason i like the sound of cars in reverse
lol

[Accord tuner]

that is some old information and basic tranny info. my only question is it the same setup on an auto as a standard? i know my accord makes that whine and its a standard as does my jeep but do autos do it as well? i havent heard many.

and you are correct with the grinding. it may also not go in completely because of the lack of syncros. you might have to hold reverse until you start slipping the clutch...

[Accord tuner]

Originally Posted by rodneylynn1977

Ok now my whining questions have been answered... Now tell me why all hondas vibrate so bad in reverse. Sometimes it makes my teeth hurt!!1 ha ha ha

thats a good question but it must be a local incident. i have never had a vibrating honda just in reverse. good question. id like to know an answer if you get one...

[garciasa0290]

Nice Good To Know I Like The Sound

[nus_dogg]

Yup. Good info.