Factory diff gear ratio

[fireguyfire]

I'm trying to figure out what rear diff gear ratio my 73 challenger came out of the factory with to make sure she still has them.
I have the factory build sheet from under the rear seat but I'm not seeing any reference to rear gear ratio.
How can I find out what it came out of the factory with?


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[Cuda Cody]

Post a photo of your sheet.  It should be in the axle box and it's a code that will translate to a rear gear.  The sheet will not list the gear number (like 3.23) instead it lists the axle code.

[fireguyfire]

Axle code is 979


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[6bblgt]

979 is an 8-3/4" rear axle 3.23:1 ratio w/sure-grip & 10" drum brakes

[anlauto]

So with the car jacked up, both rear tires off of the ground ...Mark the tire and have someone turn it exactly one full revolution. While that's happening, count the revolutions of the driveshaft at the rear yoke. The drive shaft should turn 3.23 revolutions or roughly 3 1/4 turns.

[Burdar]

Only two ratios were available in a 340 car in 73. Standard was an open 3.23. A 3.23 sure grip and 3.55 sure grip were available.

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[fireguyfire]

As suggested I did the rest, and indeed it does take exactly 3.25 revolutions of the pinion to rotate the tire once.
I guess that means I have factory gears in my car!


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[fireguyfire]

Thanks for the info Burdar


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