What is the gear ratio and if it’s a Posi - Chevelle Tech
Transmission & Driveline Transmissions and Differentials

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post #1 of 11 (permalink) Old Sep 1st, 19, 3:00 PM Thread Starter
 
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What is the gear ratio and if it’s a Posi

3969278nf I have this differential and it looks like it’s from a Chevelle 70 - 72 but I don’t know the gear ratio or whether it’s a Posi. It has KDC344 1 and CON2 and GM52 it also has the numbers from 1 2 3 4 5 6 7 8 9 0 on it but I don’t know what that means can you tell me what the ratio is and posi?
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post #2 of 11 (permalink) Old Sep 1st, 19, 3:27 PM
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Re: What is the gear ratio and if itís a Posi

I think it's originally a 71 273 open rear end build in Buffalo NY. https://www.chevellestuff.net/1971/rear_axle.htm

344 means it was built on the 344th day of the year.
3969278nf is the casting number that comes back to a 12 bolt rearend.
Can't help with the rest of the numbers.

Spin one axel and watch the other. If they both spin in the same direction it's a posi. If they spin in opposite directions its an open diff.
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post #3 of 11 (permalink) Old Sep 1st, 19, 8:26 PM
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Easiest way is break it open (it can probably use some fresh oil anyways) and find the stampings on it and look at the numbers, find the separate ones (example 41-12) and divide them, that will give you the gear ratio, the carrier will have 2 springs if it’s a posi
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post #4 of 11 (permalink) Old Sep 2nd, 19, 7:55 PM
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Re: What is the gear ratio and if itís a Posi

[QUOTE=Kjames;11136600]Easiest way is break it open (it can probably use some fresh oil anyways) and find the stampings on it and look at the numbers, find the separate ones (example 41-12) and divide them, that will give you the gear ratio, the carrier will have 4 springs if itís a posi[/QUOTE]

Just a fyi!

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post #5 of 11 (permalink) Old Sep 3rd, 19, 9:08 AM
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Jeff
 
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Re: What is the gear ratio and if it’s a Posi

If you don't want to break it open mark the yoke and block one axle so it doesn't spin. Rotate the other axle exactly 2 times and watch the # of turns the yoke makes.

2 3/4 turns = 2.73
3 turns, 3.08
3 1/4 turns, 3.23, etc.

I don't know chevelle ratios that well so I may be off.
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post #6 of 11 (permalink) Old Sep 3rd, 19, 1:18 PM
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Re: What is the gear ratio and if it’s a Posi

I'm not knowledgeable about 12 bolts rears, but, when I opened the rear end of my El Camino with a 10 bolt, posi unit, the ratio, 3.36, was stamped in the ring gear edge.

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post #7 of 11 (permalink) Old Sep 4th, 19, 2:00 AM
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Re: What is the gear ratio and if itís a Posi

One thing to be aware of, is that with these assemblies being 48+ years old, they have often been altered from the original configuration... So even if the codes indicate a certain ratio and positraction, your really need to verify by either spinning/counting or pulling the cover...

I have seen many people buy rearends, Muncies and engine assemblies based on codes of seller's info, only to later be disappointed when things aren't as the were thought to be, and usually in a less desireable configuration.

Once you go RAT, you never go back...
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post #8 of 11 (permalink) Old Yesterday, 11:24 AM
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George
 
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Re: What is the gear ratio and if it’s a Posi

Mine isn't listed... The first 2 characters on my 12 bolt is CC

It reads CCW 102431
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post #9 of 11 (permalink) Old Yesterday, 3:53 PM
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Jack
 
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Re: What is the gear ratio and if it’s a Posi

Standard ratio for 1970's was 3.31...Both manual and automatic...

For 1971/1972...Manual 3.31 ...Turbo 400...2.73

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post #10 of 11 (permalink) Old Yesterday, 4:12 PM
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Gene
 
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Re: What is the gear ratio and if it’s a Posi

Peggles, the original gearing wil be stamped on the forward part of the pass side axle, near the wheel end. For a list of those visit www.chevellestuff.com Mine, for eg, is a 1967 and stamped CF.

Hotwire has the quick and dirty method of checking ratios. Best way is to pop the inspection cover and count gear teeth, and then simple divide ring by pinion. Also gives you a visual inspection of the gearset.

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post #11 of 11 (permalink) Old Yesterday, 4:15 PM
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Gene
 
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Re: What is the gear ratio and if itís a Posi

Quote:
Originally Posted by spaceace77084 View Post
Mine isn't listed... The first 2 characters on my 12 bolt is CC

It reads CCW 102431
I happened to pull up 1969 @ www.chevellestuff.com , and CC code is 3.73 , the W means built in Warren MI.

Gene
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