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Username Post: Differential Codes        (Topic#77131)
PAINE 
Senior Member
Posts: 118

Age: 57
Loc: Hingham, MA, USA
Reg: 01-13-03
10-06-04 07:01 AM - Post#525022    

1957 Chevy Bel Air. I suspect that this may not be the OEM differential. I'm trying to figure out my rear end gear ratio. On my differential I found the follwing raised codes on the drivers side differential body, facing the front end

D167
8725889 Followed by a large GM

Can anyone help decode this?

 
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Ronnie44 
Senior Member
Posts: 9041
Ronnie44
Loc: Tampa Bay, Florida
Reg: 12-23-03
Re: Differential Codes
10-06-04 07:23 AM - Post#525023    
    In response to PAINE

I'm guessing that the number is 8725899, which is an open axle 1957 rear axle. Those numbers are the casting numbers which indicate an April '57 build date. Your rear axle should be stamped, on the passenger side, front, with a code for the ratio. It will be something like AA BB BC AW, etc.
In memory of George K Fullam(Goodwrench) Died 31 Mar 2005

To view my '57 Bel Air, and my previous '55 & '56 hardtops and '56 Corvette: Click Here


 
PAINE 
Senior Member
Posts: 118

Age: 57
Loc: Hingham, MA, USA
Reg: 01-13-03
Re: Differential Codes
10-06-04 08:50 AM - Post#525024    
    In response to PAINE

So the codes on the differential don't indicate the ratio?

 
Ronnie44 
Senior Member
Posts: 9041
Ronnie44
Loc: Tampa Bay, Florida
Reg: 12-23-03
Re: Differential Codes
10-06-04 09:43 AM - Post#525025    
    In response to PAINE

That's correct, the casting numbers just indicate the type of differential. It's the gears inside that determine the ratio and they will vary depending on the application. Since the case would remain the same on the assembly line, the codes for the different ratios were then "stamped" on the unit after a particular set of gears was installed.
In memory of George K Fullam(Goodwrench) Died 31 Mar 2005

To view my '57 Bel Air, and my previous '55 & '56 hardtops and '56 Corvette: Click Here


 
BR57 
Contributor
Posts: 427
BR57
Loc: Conway Arkansas U.S.A.
Reg: 09-30-04
Re: Differential Codes
10-06-04 10:22 AM - Post#525026    
    In response to PAINE

I just got done going through the same experience. With the help of fellow CT members I was able to locate the #. Even with guidence I almost missed it. I finally found it on the front of the pumpkin,(towards front of car), in line with the passenger side axle housing. The code was stamped very lightly. After I scrapped off all the old paint and sanded lightly I still couldn't see it. I just happened to shine the flashlight down at an angle. Low and Behold!! The number. Someone, I can't remember who , answered with a reply containing info listed below. Hope this helps. I never would have found mine without help!!

Bubba

Pumpkin info


The numbers on the pumpkin are as follows:
Stamped #AB1031
Casting #J236 3725899 GM 14

Numbers were stamped on the front right side of the diff carrier
-------------------------------------------Plant
Description---------------------------Gear&Axle---Buffalo
--------------------------------------------------------
3-speed manual,3.7:1-ratio-55-56---------AA--------BA
3-speed manual,3.55:1-ratio-57-----------AA--------BA
3-speed,3.55:1 close ratio--57-----------AA--------BA
Automatic 3.55:1 ratio-----55-56---------AB--------BB
Automatic 3.36:1 ratio------57-----------AB--------BB
Overdrive 4.11:1 ratio-----55-57---------AC--------BC
Limited slip 3.55:1 ratio---57-----------AK--------xx
Limited slip 4.11:1 ratio---57-----------AL--------xx
Limited slip 3.36:1 ratio---57-----------AM--------xx

Example AA212 would decode a three-speed manual built on february 12 at gear& axle.

BR,
The following is how all your info translates.
First, YES, it would appear that your rearend is original to your car.
3725899=Casting number for your differential case.
J236=casting date-(J)Sep, (23)day, (6)1956.
GM14=is simply the number assigned to the mold that was used
AB1031=(AB)gear ratio code-3.36, made at the Buffalo plant (1031)is the ASSEMBLY date-Oct 31.
As you can see, it was about 5wks between the time the case was cast in the mold and the time it got assembled. The STAMPED information doesn't go on until after assembly (because there is no way to know what gears will go into the bare case when it is cast).
Since all the components which go together to ASSEMBLE a car must be built and shipped BEFORE assembly of the car, and your rearend was built the last day of Oct, then your car could not have been built until sometimein Nov or later. Components such as rear ends, trannys, engines, etc, usually pre-date a car's assembly date by a minimu, of 2wks, but, 6mo has been documented. So, your car could have been built anytime between Nov 56 and the end of 57 production.


 
PAINE 
Senior Member
Posts: 118

Age: 57
Loc: Hingham, MA, USA
Reg: 01-13-03
Re: Differential Codes
10-06-04 11:30 AM - Post#525027    
    In response to BR57

Thanks, I was looking on the passenger side axle. I have a lot of undercoating that I scraped off of the axle, and couldn't see anything. I gather from what you wrote that the number is on the gear housing itself not the axle.

 
gerard55 
Senior Member
Posts: 609
gerard55
Age: 40
Loc: Hamilton New Zealand
Reg: 02-07-02
Re: Differential Codes
10-06-04 11:49 AM - Post#525028    
    In response to BR57

thats was me that gave that info, I hope you all get what you want from it?
Gerard
Save a 55
My restoration journey
http://www.cardomain.com/ride/2611111


 
BR57 
Contributor
Posts: 427
BR57
Loc: Conway Arkansas U.S.A.
Reg: 09-30-04
Re: Differential Codes
10-06-04 03:52 PM - Post#525029    
    In response to gerard55

Thanks again Gerard,for the info. I saved your reply but I forgot to copy who sent it.

 
BR57 
Contributor
Posts: 427
BR57
Loc: Conway Arkansas U.S.A.
Reg: 09-30-04
Re: Differential Codes
10-06-04 03:56 PM - Post#525030    
    In response to PAINE

That is correct. It's on the differential housing.

 
beejay 
Ultra Senior Member
Posts: 12599
beejay
Age: 78
Loc: Pflugerville, Texas
Reg: 06-01-04
Re: Differential Codes
10-07-04 06:58 AM - Post#525031    
    In response to PAINE

Payne,
Thanks for making this post, and to Gerard who had the answers. I've wanted this info, but couldn't find it in a search. Guess I used the wrong words.
Sure is nice being surrounded by a bunch of car-bandit knowledgable people, and THAT'S a compliment.
Bruce

'56 4-door BelAir, 350, Holley 600, Eddie intake, TKO 600, CPP P/S and A arms, Sierra Gold & Adobe Beige
2010 VW Jetta S/W, 2.5, 5-cyl,6-spd auto.
'87 Elkie, 350 with 700r4 tranny B&M floor shift
http://www.picturetrail.com/beejay3/"


 
PAINE 
Senior Member
Posts: 118

Age: 57
Loc: Hingham, MA, USA
Reg: 01-13-03
Re: Differential Codes
10-07-04 09:12 AM - Post#525032    
    In response to beejay

If I were as smart as the rest of the folks in this forum, I would have just opened my Service manual. It has a picture of exactly where the code is. I just have to get the car back up in the air to climb under again and look for it

 
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