DIFF GEARING

[1969_Mach1 333]

I'm no expert in this area but I think inherent gear noise is more complex than simply gear ratios.  Inherent gear noise with everything setup correctly has more to do with the geometry of the tooth shape and how large the tooth surface contact patch is. I have noticed lower numeric ratios have larger tooth surface contact patches than higher numeric ratios.  I do know gear teeth shaped for increased strength tend to make more noise.  Factory gears rarely make noise that is noticeable inside the car.  Setup has to be extremely far off with factory gears for that to happen. 

[barnett468 418]

21 minutes ago, 1969_Mach1 said:

I'm no expert in this area but I think inherent gear noise is more complex than simply gear ratios.  Inherent gear noise with everything setup correctly has more to do with the geometry of the tooth shape and how large the tooth surface contact patch is. I have noticed lower numeric ratios have larger tooth surface contact patches than higher numeric ratios.  I do know gear teeth shaped for increased strength tend to make more noise.  Factory gears rarely make noise that is noticeable inside the car.  Setup has to be extremely far off with factory gears for that to happen. 

factory 3.91 & 4.11 gears in a ford whine.

 

in a transmission, straight cut gears whine much more than helical cut gears.

[RPM 1,190]

Good info guys, thanks.  I've only used  Ford gears, so I've got that going for me, which is nice. 

[lanky 44]

I have to say that I think that chart is at least slightly off as Ford definitely had more factory ratios for the 9" than those listed in blue. 

[RPM 1,190]

True story Lanky. I ran a set of 2.50 Ford gears  on my trip to Florida. Pretty darn quiet.