8.5" axle code - ClassicOldsmobile.com


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Old November 14th, 2017, 01:05 PM   #1
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8.5" axle code

Here is a better picture of my axle code. This is on my 1977 Cutlass Supreme with 350/350. Love to find out exactly what gear ratio I have and what the spline is. IS this a series 2 carrier? Can someone run these numbers for me? Looks like they are:
7 AA 0 003
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Old November 14th, 2017, 03:03 PM   #2
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I don't know how to decode those numbers, but a 77 Supreme likely has 2.41 gears.
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Old November 14th, 2017, 06:53 PM   #3
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Axle Codes

For 1977 open differentials

AA 2.41
AB 2.56
AC 2.73
AF 3.08

Convert you differential to 3.23 gears and add limited slip. Best money you will spend today. 3.23 gears are the perfect compromise between performance and drivability with a 3 speed automatic transmission.

Last edited by oldsmobiledave; November 14th, 2017 at 06:57 PM.
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Old November 14th, 2017, 08:05 PM   #4
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Dave thank you so much for clarifying the AA. I have been hoping for that validation. I have plans for a 200-r4 early next year and with that I have opted to purchase a series 3 carrier with 3.42 gears for now. I have a larger tire ( 255/70/r15 ) 29" tall. So from my research I should be just fine with 3.42 until next spring. even on highways.
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Old November 14th, 2017, 09:18 PM   #5
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Gear choice

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Originally Posted by GoolzCutlass View Post
Dave thank you so much for clarifying the AA. I have been hoping for that validation. I have plans for a 200-r4 early next year and with that I have opted to purchase a series 3 carrier with 3.42 gears for now. I have a larger tire ( 255/70/r15 ) 29" tall. So from my research I should be just fine with 3.42 until next spring. even on highways.
With the OD trans you want more gear. Use 3.90 or 3.73s or the recently and newly available 3.55 gears.
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Old November 14th, 2017, 10:02 PM   #6
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I agree - I was thinking about this just this morning.
0.67 overdrive and 3.90 rear gears = 2.61, so similar to what your car currently has and great for highway driving.
On the other end, coming off the line in first gear wold be similar to having 4.30 rear gears with your TH350.
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Old November 14th, 2017, 10:05 PM   #7
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I found a 8.5" posi package with 3.55 gears. Pretty sure I am getting this. Still should be fine to drive for a while in winter with the th350.
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Old November 14th, 2017, 10:15 PM   #8
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Shouldn't be an issue. I drove with 3.23 gears and short 245-60-14 tires for decades. Engine turned about 3200 RPM at 70-ish MPH.
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Old Yesterday, 07:07 AM   #9
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If you're keeping the 28 spline axles, there's a guy on eBay with a brand new Detroit Locker for $470 or best offer. Those things are $650 from Summit. Things to consider instead of getting a no name unit.
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Old Yesterday, 08:43 AM   #10
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Bomber can you give me the link to the Locker on ebay? thanks
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Old Yesterday, 08:44 AM   #11
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Here is the posi package I was thinking about going with...
Amazon Amazon
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Old Yesterday, 01:53 PM   #12
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Wait,,,,just noticed who's selling it. Another member on here "MONZAZ". He does nothing but rear axles. You should realy consider talking to him. Send him a private message on here, he's great about responding. He'll may cut you a deal on here considering no eBay fees.


https://www.ebay.com/itm/10-BOLT-8-5...19.m1438.l2649
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