when i went to decode my rear for my 73 it told me i had a 2.73 gear but with my tach reading 2400 and some change at 60 it tells me i have 3.08 gears.... i dont think my tach is off by 500 rpms and my tires are 245/60 on 14 inch rallies and that shouldnt make a difference that much......and as far as i know the gears are the originally but i might be wrong?

I have used 2 different factory tachs, and they both gave different readings from a "real" tach.
The only sure way to get rear ratio is to count teeth, unless you have an aftermarket tach.

i have an aftermarket sunpro tach...........would that make a difference

If its a good tach and hasnt been sitting around for years, it should be accurate.

Diesel,

There are two surefire ways to know exactly what you have. The messy way is to remove the differential cover and count the teeth (not recommended) or the clean way of rotating the rear wheel exactly once while counting the number of rotations the driveshaft makes. However many rotations that is will be the same as the rear end ratio.

Okay, I am confused. I have a '80 Z-28 that I am working on. I have been wondering what type of rear end it has in it and what the gear ratio is.

I jacked up the back and whe I spin one wheel the other rotates the other way. If I put one wheel on the ground, I can still turn the other wheel. So I figure it must have an open rear end.

The I try to figure out my gear ratio. WIth one wheel on the ground, the driveshaft turn appr 1 3/4 turn to one turn of the wheel. Now what's with that? There no such thing as a 1.75 ratio, at least not that I'm aware of. Does anybody have an idea what this means?

Oh, where is that 3 digit code suppose to be? I have scrapped and wire brushed the front of the passenger side axle tube and don't see anything.

Thanks for any help you can offer,
-Bob George

I have a 3.08 open rear end. I get about 1.5 driveshaft rotations. Bet you got a 3.42, also bet it is a limited slip. When I spin one wheel the other doesn't move at all.

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Black 81Z, shift kit, duals no cats, restoration in progress

Not allways, my open spins the other wheel the oposite direction too when I was checking ratio. On the posi I had with one wheel on the ground made it difficult to spin the other.
Steve

Bob, the axle code is on the top of the passenger side axle.

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1971 Z28 Camaro
http://www.usfamily.net/web/grafix/camaro.html

Grafix,

Is it near the center section or out near the backing plate?

Thanks for your help,
-Bob George