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Discussion Starter #1
How does one calculate the final drive on an unknown tranny without opening the case and counting teeth?

I know that some people rotate the input shaft 10 times and see how far the differential has turned. As far as I know, all 1st gears on the L3 transmissions (88-91) are 3.250. How does the math behind that work?

10/3.250/(final drive ratio) = (rotations of differential)?
 

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Brokedick Millionaire
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use 5th gear..........that helps 2 ways...............

First, you could have a STD 4 speed tranny, no 5th!!!!!!!!! dead give away.
Second, if it is a HF tranny, it will be very evident!!!!!!!!

10 / 5th / FD = xxxx

HF
10 / .694 / 3.250 = 4.43 turns of the diff

DX
10 / .771 / 3.889 = 3.33 turns of the diff

Si (big bearing case)
10 / .771 / 4.25 = 3.05 turns of the diff

Now the key is to reverse engineer.

5th gear, 10 turns, # of diff turns, figure out what is closest.
 
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Discussion Starter #3
Ok...so an SOHC ZC from a ZXi would be:

10 / .771 / 4.437 = 2.92 turns of the diff

And a normal ZC would be:

10 / .878 / 3.888 = 2.93 turns of the diff


Hmmm... I'm guessing first gear is the way to go on that set of transmissions.

ZXi in 1st

10 / 3.250 / 4.437 = 0.69 turns of the diff

ZC in 1st

10 / 3.250 / 3.888 = 0.79 turns of the diff

Possibly using even more turns of the input shaft to separate out the results a bit more?
 

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Dab some white out on the diff and case at 12oclock
dab some white out on the input shaft and the case at 12
put it in 2nd

spin input shaft 10 times
if it's 0:15 Min it's an Si 4.25 FD (these came on some of the larger diff trans)
a lil before than it's ZXi 4.437 Territory
A lil after that it's DOHC ZC 3.88 territory

I got a DOHC ZC and the SOHC ZXi, now who's gonna help me swap gears???
 
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