i recently bought a 12 bolt rearend in a package deal got a gas tank rearend and front disc brake conversion kit for 400 bucks

i was wondering what was the gear ratio of a 1970 442 because i heard they were a limited slip differential and im getting ready to do my rearend i was thinking of 3.55 but i rather go with what the 442 originally had

hope someone can help me out

 

Most common was 3.23 with some 3.42 and as stiff as 3.91 in some 4-speed cars. Remove the cover and divide ring gear teeth number by pinion teeth number to see what you got.

Hope this helps

 

An easier way to figure out the ratio is if the axle is a posi turn the axle one full rotation and count the rotation of the pinion. If the differential is open then fix one side of the axle in place and turn the other side two full rotations again counting the rotation of the pinion. If the pinion turns three and a half rotations, your gears are 3.50 to 1. This is much easier than taking things apart.

 

Unfortunately, it can sometimes be difficult to tell the difference between 3.23 turns, 3.31 turns. and 3.42 turns. I turn the pinion until the axle shaft turns ten times. It's much easier to tell the difference between 32.3, 33.1, and 34.2, for example.

As for available ratios, it could have been anything between 2.73:1 and 5.00:1.

 

You're right, that is a better idea, and then divide by ten. Good thinking!

 

Again if you are going to rebuild it you might as well crack it open ...that fluid should be changed after 30 years anyway...lol.