1965CS wrote:

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The number on my 12B diff is 3852980. Can anyone identify it as good bad, ugly.....or does it matter? Also has 1343 on tube.

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 Here is what I have, did not come out very nice

 They say on the bottom in the attached pic, but it is usually on the front side of the tube facing towards the front........ Even though it says '66-'67, it will be the same...

Steve

I am no expert on decoding casting numbers, but I thought rear end casting ID's were a two letter combination - like these for Full Size Chevrolet from the Camaro.com site:

This is a listing of only the "B#"

Model Year Description Code
1965 Chevrolet 3.08 BA
1966 Chevrolet 3.08 BA
1965 Chevrolet 3.36 BC
1966 Chevrolet 3.36 BC
1965 Chevrolet 3.08 Posi. BE
1966 Chevrolet 3.08 Posi. BE
1965 Chevrolet 3.36 Posi. BF
1966 Chevrolet 3.36 Posi. BF
1965 Chevrolet 3.55 Posi. BG
1966 Chevrolet Small Ring Gear, 3.55 Posi. BG
1966 Chevrolet 3.55 BH
1965 Chevrolet Metallic Brakes, 3.08. BJ
1966 Chevrolet Metallic Brakes, 3.08. BJ
1965 Chevrolet Metallic Brakes, 3.08 Posi. BK
1966 Chevrolet Metallic Brakes, 3.08 Posi. BK
1965 Chevrolet Metallic Brakes, 3.36. BL
1966 Chevrolet Metallic Brakes, 3.36. BL
1965 Chevrolet Metallic Brakes, 3.36 Posi. BM
1966 Chevrolet Metallic Brakes, 3.36 Posi. BM
1965 Chevrolet Metallic Brakes, 3.55. BN
1966 Chevrolet Metallic Brakes, Small Ring Gear, 3.55. BN
1966 Chevrolet Metallic Brakes, 3.55. BO
1966 Chevrolet SHP, Air Cond. 3.31. BQ
1966 Chevrolet 3.07 Posi. BR
1966 Chevrolet 3.31 Posi. BS
1966 Chevrolet Metallic Brakes, 3.07. BT
1966 Chevrolet Metallic Brakes, 3.07 Posi. BU
1966 Chevrolet Metallic Brakes, 3.31. BV
1966 Chevrolet Metallic Brakes, 3.31 Posi. BW
1965 Chevrolet 327cid 8cyl, Powerglide Trans., 2.73. BX
1965 Chevrolet 2.75 Posi. BY
1965 Chevrolet Metallic Brakes, 2.73. BZ

Here's a summary of the numbers on a typical rear end:
http://www.thecamaro.com/Decoding/Chevy-Axle-Rear-End-Decoding/index.php

Hope this helps...

3852980 is the center housing casting number

code you need is located here....

Have my '70 on the hoist and snapped a few pics......... Generally, they are stamped in this area....

It will look something like this:

And, if you lucky, it will have one of these:

2drpost wrote:

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3852980 is the center housing casting number

code you need is located here....

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this is a good post, as it shows exactly where the codes are stamped onto the passenger side tube.  Take a wire brush, and eventually the numbers will appear.   If you've got some chalk, rub some in the area.   If not, just wet your finger a bit and go over the area, the depressions will stay dry and appear.

I've totally cleaned it using drill brushes etc, ...there are no numbers like shown above, just the diff cast number and 1343 on the right tube, ....strange. Did determine ratio, stamped 13-43, so 3:31.  

67Poncho wrote:

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 Ok, so what are you trying to perform here? Are you doing axle seals, pinion, side gears?? It will be easier for me to explain if I know what operation you are performing!! Just gives me a better idea!

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 Almost all of the above, except for pinion.  Found one spider gear washer in the housing, mangled, but intact -  so should replace those gears / washers and thrust washers but problem is that one of the axle gears (the gear splined inside that meshes with spider) does not drop out of the carrier.  It moves a bit but jams.

Everything is apart and marked with the exception of the pinion.  Carrier c/w rign gear, on the bench and only has the one axle gear left in it -  

How do the axle gears inside the diff come out? One side dropped out no prob...the other only moves a bit, then jams, ... aren't they supposed to drop out?  

 Ok, so what are you trying to perform here? Are you doing axle seals, pinion, side gears?? It will be easier for me to explain if I know what operation you are performing!! Just gives me a better idea!

So, axles are out? I so, install the one requires to push out the side gear.. Have you got the carrier out?

It has to tap out! UNLESS, because of the shredded pinnion washer, someone did one to many one wheel peels with it? Brass punch and a BFH!!! (big effen hammer)

I did tap it lightly, moving it an 1/8", but hesitant on hitting too hard since whatever is binding might damage the surface inside - but have to try it I guess....

 That's why I say brass or aluminum... Give 'er...

Lots of good info in this post. Thanks.

 Yup! Figured as much... The dreaded one wheel peel syndrom strikes again!!!

 Find yourself another diff? One with a 3:07 would be better on the highway if you needed.. Here are '66-'67's...

With the chart, you can decode my axle.....

 

Have to replace the carrier,  It's badly scored along with the axle gear from something getting in there, probably part of that spider gear washer laying in the bottom.

1965CS wrote:

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Have to replace the carrier,  It's badly scored along with the axle gear from something getting in there, probably part of that spider gear washer laying in the bottom.

-- Edited by 1965CS on Wednesday 18th of July 2012 07:22:28 AM

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 (lol) I highly doubt anything got in there. It is a high tolerance fit.... The scoring happened when the oil that WAS in there got tossed out during the burn outs and was left to spin dry!

 I have seen a few in my Dealer days!

67Poncho wrote:

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 (lol) I highly doubt anything got in there. It is a high tolerance fit.... The scoring happened when the oil that WAS in there got tossed out during the burn outs and was left to spin dry!

 I have seen a few in my Dealer days!

-- Edited by 67Poncho on Wednesday 18th of July 2012 07:38:48 AM

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 Admittedly, I don't know much, well nothing, about rear ends as is evident in this post.  No idea how that spider gear washer could  come out and cannot see how it is possible, but the washer was intact yet mangled from going thru the gears at some point.  I just assumed it may have something to do with that.  One thing I do know is that I got screwed yet again on buying this rear end in the first place, and can't be certain what it even is with no markings or stamped numbers etc -

 At the rate that they spin compared to the crown and pinion, it has to be twice to thrice the speed...... I have seen the washers weld to the pinion and spun out as well...

 I am not questioning your knowledge on diffs as a subject, not in the least... Just personal visual experience!

 I have also seen the pinions welded to the cross shaft, (pinion pin), the retaining bolt was snapped because of this and a cutting torch, A.K.A Mr. Smoke Wrench, was needed to disassemble... I have also see the cross shaft come through the diff cover and destroy everything in its path!

 I know what it is like when you purchase something that was suppose to be in "perfect" condition! We've all been there at sometime..

 That being said, there should be thousands of these kicking around! Where are you located?

68 427 wrote:

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WHAT'S THE GOING PRICE FOR A USED FULLSIZED 12 BOLT POSI REAR?

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 There's a 4:11 12 bolt posi (crown/gears/carrier) on kijiji here for $300 out of 68 Camaro

 I'm the exception tho, by not wanting posi since I just drive the car and not out for performance so much as driveability.

A dumb question;  Are all 12 bolt axles (full size) the same length and 30 spline?    ..... will need one

1965CS wrote:

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Well I got it out, only to find that it's scored so bad that it's non repairable. Great, now I have to find another carrier, more $$$$

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Do you need a carrier, or just all the gears/shims for inside the carrier?  A 3 series carrier might be a bit tough to find, and it might be easier to find a 3 series posi carrier.   Tom's Differentials in Ponderay Idaho (Sandpoint) will have all the guts for inside the carrier.