Need Help to Determine Stock Gear Ratio

[RoadRunning]

Hello,

I have a 1970 Road Runner with 383 automatic that came stock with 4 barrel carburetor. Anyone know what gear ratio I have in the rear end?

Thanks!

 

[moparlee]

Jack it up and as someone rotates one of the rear wheels one revolution, count the number of rotations the drive shaft makes. If the drive shaft turns about 2 3/4 turns you have a 2.76 gear, about 3 1/4 turns you a 3.23 gear, about 3 1/2 turns a 3.55 gear, and if it turns about 4 turns you have a 3.91 gear.

 

[RoadRunning]

That is good advice, thanks. Turns out I think I have 3.23 gears. I found this out because the pinion gear on the speedometer is black. Apparently different colors represent different gear ratios. Mine is black so a chart I found shows it has 3.23 gears.

 

[65-440]

unless someone changed rear gears and not the speedo gear .... spin the wheels and count driveshaft revolutions !

 

[hunt2elk]

That is good advice, thanks. Turns out I think I have 3.23 gears. I found this out because the pinion gear on the speedometer is black. Apparently different colors represent different gear ratios. Mine is black so a chart I found shows it has 3.23 gears.

The speedo gear is sized depending on the gear ratio and the rear tire height. It is not possible to determine axle ratio by counting teeth on the speedo gear.

 

[RoadRunning]

The speedo gear is sized depending on the gear ratio and the rear tire height. It is not possible to determine axle ratio by counting teeth on the speedo gear.

It is actually possible to determine the size because I found a restoration guide that indicates if the speedometer pinion gear is black with 32 teeth then it came with 3.23 gears stock. Pretty sure it has never been changed and I can be 100% certain once I see my speedometer is reading correct as I set it with that gear ratio.