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gear ratio

457 Views 2 Replies 2 Participants Last post by  camachinist
i'm trying to figure out what kind of gears i have installed in my 70 mustang, 302 2v, C-4 trans. the door tag is gone, so i can't get the code from there. i found the tag on the pumpkin and this is what it says:

3.00 8 931A

does this mean that i have 3.00 gears? i am not sure if this is the original rear end or not. any help decoding this tag will be greatly appreciated. thanks.
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Probably 3.00, you can put the car on stands and spin the tire(s). If the driveshaft spins 3 time to the tires 1 revolution then you have 3.00...
Jack up one rear wheel so you can spin it...chock the front tires first *G*...put the trans in neutral. Try to spin the tire by hand. If it spins, go to step one below. If it doesn't, jack up both wheels and go to step two.

First...Mark tire with chalk or other marker on inner sidewall; crawl under car and mark differential yoke and pinion housing where they meet.

Step one...rotate tire one revolution, noting revolutions of differential yoke. Multiply yoke revolutions by 2. This is your gear ratio.

Step two...same as step one except that the actual yoke revolutions are your gear multiplying..

If you can spin the tire when only one is in the air, you have an open differential. If you can't, you have some sort of a limited-slip differential and it should require 40-60 lb-ft at the axle CL to overcome the differential when only one tire is in the air...

Remember, make sure the trans is in neutral and the parking brake is not set...

Good luck!
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