What gears?
 

I would like information to find out the gear ratio and/or gears that I have in my 1970 Mustang Mach1 w/351 Windsor. Can this be done by using the VIN number? If so, how does that work? If not able to use VIN # how would I go about getting the info? Any and all help would be greatly appreciated. Thank you in advance.

Stryfe,
The VIN # won't help you here you need to look at the door tag. There should be an axle code there. If you give me that code I can tell you what was originally in the car.

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69 351W Sportsroof deluxe

Couple of simple ways. First look for a small metal tag on one of the diff bolts - would have 2 numbers that divided into one another would give the ratio. If no tag, jack both back wheels up, chalk mark at bottom of one of the tires and the driveshaft or U-joint, then rotate the driveshaft till BOTH wheels go around once (easy if posi). The number of times the drivehshaft goes around is your ratio.If you don't have posi and only one wheel goes around, multiply the driveshaft rev's by 2 to get the ratio. Just make sure only one wheel moves .You'll likely end up with a number in the 3's - like about 3.2, 3.08, 3.5, 3,9 etc.

Hey, if this doesn't work, I've got a formula written down somewhere that works with tire diameter and rpms and mph. email me if you need it.

To decode your door plate, go to www.classicponycars.com
They have a very useful decoder to determine the original specs of your car