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Old 12-12-2011, 05:42 PM
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Please help ID my GM 12 bolt

Been searching around the net, mostly here, and can't find much to help me ID this rear end. It came out of my '72 Chevelle, but I have no idea if its original.

The numbers I can find are all on the pumpkin, nothing on the tubes. I found the following (pics below):

GM53
3969278N
12345
67890
H299
00N1 or I

The housing is 55" or 54 1/4" long from dust shield to dust shield.

The cover is 10.5" wide.















The car was wrecked and I'm in the process of fixing it. The drivers axle was bent at the flange and I need to replace it. I'm taking it to Dick Strang in Waukegan, IL for a refurbish, new axle, control arm bushings, wheel bearings, c-clip eliminators, and a disc brake conversion, so I would like to go there knowing what I have and what I need to source for parts.

Thanks, this site has been a tremendous help since I got this car!

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Old 12-12-2011, 06:16 PM
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A quick search shows 3969278N to be a '70-'72 Chevelle 12 bolt. The date code H299 is August 29 of '69, so this would have likely been used in a '70.

There should also be some stamped (not cast like on the center section) numbers on the axle tube.
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Old 12-12-2011, 06:33 PM
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Thanks Cobalt! I'll go have another look on the tubes after I scarf some dinner down, BRB!
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Old 12-12-2011, 07:23 PM
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ok, I found some stamped numbers on the pass side tube front side. Best I can tell it reads: C6H 0909B

I'll let the pics do the talking, maybe I'm reading it wrong.





If there is anything under that cover that will answer some questions let me know what to look for and I'll go pull it off and take a couple pics.

Thanks for the help!
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Old 12-12-2011, 10:09 PM
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You were close- it's actually "CCH". Means it was originally a 2.73:1 posi. The "0909" is September 9, which corresponds to the August 29 casting date.

The "B" is Buffalo, NY assembly plant.
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Old 12-13-2011, 07:05 AM
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Ok, so originally it had a 2 series carrier? If I pull the cover can I id the gear set and carrier that's in there now? What should I look for when snapping pics?
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Old 12-13-2011, 07:35 AM
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The Ring Gear will have the Pinion & Ring gear teeth numbers stamped, Part #'s & Date.
Example 41-11 = 3.73, 41-10 = 4.10, 41-15 = 2.73

Carrier will have:
Casting #-----Series----------Gears-------
ED32088------- 2--------- 2.73:1 & down
30140PM1------ 3-------- 3.08:1 to 3.73:1
EDB30174------ 4--------- 3.90:1 & up
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Old 12-13-2011, 07:40 AM
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Great info, thanks! I'll pull it apart tonight after work and update the thread.
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Old 12-13-2011, 04:51 PM
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ok, pulled the diff cover and I'm a little confused.

it looks like the number on the carrier is ED -32088 which would be a 2 series, but the number on the ring gear is 2 GM 3862525 11 41 3 67 which is a 3.73:1?


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Old 12-13-2011, 05:08 PM
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Someone used a Ring Gear spacer which allows you to use 3-Series Gears in a 2-Series Carrier. Not the strongest method but, they work.
Looks like March, 1967 GM gears.
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Old 12-13-2011, 05:13 PM
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And you're correct on them being 3.73's.
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Old 12-13-2011, 05:19 PM
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hmm, how much power is this setup good to?
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