Anyone knows where is the diff gear ratio tag located? If its not there then how do you determine the ratio whether its 3.9 or 4.1?

 

Ive tried looking at the rear diff but there is no tags or numbers.

 

Block your front wheels

On level ground, put the rear of your car up on jackstands (good ones). Make sure that your car is stable.

Put the transmission in neutral.

Chalk mark the pumpkin and the driveshaft.

Chalk mark a wheel where it will be visible.

TURN THE DRIVESHAFT.

Count the number of turns of the driveshaft it takes to turn one wheel one time.

The number of times (including fractions) the driveshaft must turn to turn the wheel onetime is roughly your gear ratio.

 

^

I've never heard of Mazda tagging the diffs like you'll see on domestics. Turn of the shaft or counting teeth is the only way I know of.