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I dun learned sumthin
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Discussion Starter #1
How do I know what rear end I have in my car. It is a 1970 Nova SS with 2.73 gears-posi. I don't know if it is an 8.5 or an 8.2 or what it is. How do you tell and what do you measure. I am getting a set of 3.73 gears for it but don't know what size to order. Had the diff cover off the other day but don't know what to measure to get the correct size. Ive heard that its the ring gear but how do you measure that with all the the spider gears and other stuff in the way?
 

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I dun learned sumthin
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248 Posts
Discussion Starter #3 (Edited)
So if i see this right the 8.5 inchers have the square lugs off the bottom. Mine has those so i think that narrows it down.

Also I saw that you can get 3.90 gears this seems like a good comprimise between the 3.73 and the 4.11. Why isn't this gear ratio as common.
 

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Here's a pic of an 8.5


An 8.2 should have a big wave in the cover, similar to a 12-bolt. If it's an 8.2, your posi carrier won't work with 3.73 gears unless they're specially made for use with a 2-series carrier.

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I dun learned sumthin
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248 Posts
Discussion Starter #6 (Edited)
Im almost positive that it is an 8.5 inch because it has the square lugs in the bottom and doesn't have the wave in the cover. It is an aftermarket chrome cover thought and has another bump in the cover to the right of the ring gears bump.

Also what about 3.90 for a gear ratio. This seems like a good comprimise between the 3.73 and the 4.11. Why is this not a commonly used gear ratio.
 
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