Technical Reverse whine

How come cars, new or old, whine when driving in reverse?

 

Not always, does that occur, at least in my world.
The ring and pinion are matched up to mesh with out whine, under power.
They should also mesh quiet when under deceleration.
Not always the case. Depends on the person/method used.

 

Most transmissions I have taken apart have straight cut reverse gears. Ever heard a Pete Jackson gear drive? So I figured it was because of that.

 

Reverse is typically non-synchronized, so it is engaged by sliding an idler gear between the main shaft and counter shaft. Straight cut teeth are easier to engage than helical.
Notice in my avatar that the gears are helical cut except the second from right, which is the reverse main shaft gear.

 

think about how helical gear teeth work...there is always contact between the teeth, the contact point moves sideways along the teeth, engaging the next tooth before disengaging the first one. Compared to straight cut, which engage and disengage teeth all the time.

 

Mostly its because reverse uses straight cut gears on an extra lay shaft for reverse.

A model A ford has straight cut gears for first second and reverse and wines in every gear apart from top which is direct drive

 

As everyone has said, straight cut reverse gears

 

Enihw, whine in reverse.

 

I sit corrected, thanks guys.
Just don't let me set-up your ring and pinion

 

With square cut teeth, a single pair of teeth make a very sudden contact with each other as they engage. Each individual pair of teeth literaly "smack" together as the gears spin. The frequency of these two gear teeth smacking together creates a whining noise as speed increases.

As Squirrel mentioned above, helical ge****ts allow multiple pairs of teeth to be at least partially engaged and allow the load on the gear to be spread out over a larger surface area without shock loading just a single pair of teeth at any one time.

Hypoid ge****ts used in modern rear axles carry this practice even further. Multiple gear teeth sets are engaged slowly to their maximum contact and slowly disengaged while making a moving contact area over the face of the teeth. This moving contact area also attempts to wipe lubrication off the face of the teeth. This is why hypoid rated gear lube is required for hypoid rear axles. When properly adjusted the mating gear teeth never clash or smack together and thus run more quietly and can withstand higher loading.

 

Hypoid gears have the added fun of having the shaft axes not crossing each other, which I think is part of why they have to wipe so much.

Gears are neat.

 

Off topic electrics and hybrids seem to wine backing up. Electric motors?

 

No, that’s just the driver because she thinks everyone should get out of her way…

 

no, it's because they have a speaker playing "motor" noises to warn people that they're moving, because they are so quiet.

 

Cars don't reverse often so they don't need the money put into the reversing gears

 

Quick and easy check to confirm; Back up on level ground, push in clutch, then shift into neutral.
It will whine under load, less while still engaged but no work, and quiet out of gear.

 

It’s like a Beatle album, you play it in reverse and it sounds like you’re at a Satan fest.

 

My sm420 makes that noise in all of em

 

I buried Paul (Cranberry Sauce).

 

Had to look that up. Non-syncro and straight cut first. Since they are engaged all the time, just not linked to the shaft, there's the reason.

 

The new process 4 speed in my 57 does not make any noise when backing up. Then again, I'm 78, maybe I just can't hear it.