big_block

hey we are checking the gear ratio on a 65 289 8" rear and we have it jacked up and counted the number of turns and we got drive shaft 1 1/2 to tire 1 so what is the ratio 1.50:1 if so is that rare?i thought 2.78:1 is normal the tag reads

wcz v9ma
2.78 8 930a

shatter

Got this off a quick google search:

If the vehicle does NOT have a posi-traction unit, jack one drive wheel of off the ground. Place the transmission in neutral and make sure the vehicle is safe. Place a visible mark on both the tire and the driveshaft so that you can count the revolutions. Turn the tire 10 revolutions and also count the number of revolutions of the driveshaft. As a hypothetical value, if you make 20 turns of the tire and the driveshaft turns 36 times, the number of crankshaft turns divided by 1/2 of the tire turns (10) equals the approximate ring gear and pinion ratio, 3.6 in this case.

So, you got 1 turn of the tire and the driveshaft turns 1.5 times, the number of crankshaft turns divided by 1/2 of the tire turns (0.5) equals the approximate ring gear and pinion ratio, 3.0 in your case.

big_block

so you think i have 3.00:1 or do i have 2.78:1 the tage says 2.78

shatter

Well, that is a good question. To get to 2.78 gears the driveshaft would have to turn 1.4 times to one tire rotation. So, you could see how you could still be at 2.78. You might try to do the trick of turning the rear tires like 20 times and see how many times the driveshaft turns to try and minimize the error.

A second method you can do is if you have an accurate speedo and tach. You can measure your tire diameter and then get your RPMs in 3rd gear (1:1) trans ratio at 60 mph. You can then use that information to also calculate your rear end ratio.

This website will give you the calculators you need to automate the computations: http://www.idavette.net/tech/ratioc.htm

big_block

i think you guys are right ,, now what do you all think about changing out the c4 auto for a stadard trany??? and what would fit as far as late models

shatter

At one time I was going to change out my C4 for an AOD transmission and put 3.55 gears in the back to give me some more oomph. I have 2.79 rear gears currently. In the end, I just decided to leave the car as stock as possible.

So, I have no first hand experience in a tranny swap, let alone swapping to a vintage 4-spd or newer 5-spd transmission. I am sure there are swap kits out there to do it. Have you checked the Mustang Monthly website for articles?

Here is one to swap in a vintage T-10 4-spd into a stang: http://www.mustangmonthly.com/howto/41438/index.html

I am sure the better choice would be to go with a T-5 5-spd: http://www.mustangmonthly.com/howto/...ngs/index.html