I have a '72 and trying to find the rear gear ratio. The data tag on the door was removed and the metal tag on the pumkin is no longer there. I was able to locate the build sheet and the axle code is "951B". The car is a Sprint, built in Dearborn in June of '72, has a 351C 2v, has a FMX automatic transmission. The car has the special "B" package which included competition suspension, F60x15 tires on Magnum wheels.

Any help would be appreciated.

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Most likely a 2.73:1 ratio. Easiest way is to jack up the rear and turn the driveshaft while counting revolutions on the shaft and wheels (both wheels must turn the same speed and direction to be accurate). Just see how many times the driveshaft turns to make the wheels go around once. That's your ratio.

 

I'll give it a shot. I was thinking it came with a 2.75, but according to the information I have, the ratio could be anything from 2.75, 2.79,2.80,3.0 and all the way up to 3.91. Using the rotation of the driveshaft, it may be difficult to determine if its a 75,79,or 80. I sent a letter to Ford to see if they would be able to determine what was used, but don't give that much of a chance.

You mentioned that the wheels need to be turn in the same direction. If the car only has standard gears and not positrac, shoudn't one wheel turn one direction and the other in the opposite direction?.

 

Only if you turn the wheel and not the driveshaft.