Having purchased a posi rearend out of a basket-case 59 a friend had, I am just now getting around to cleaning it up and detailing it before installation. The stamp on the left hand side of the gear case is "AM 1024" and the gear case part number cast on the right side is #3743833. I have searched Noland Adams restoration book and the Hollander interchange manuals, but can't find any info on these markings. Spinning the driveshaft yoke and watching the axle shafts, it appears that it is a 4:56 to 1 ratio. A large "P" is also cast into the housing on the right side of the gear case. Any help on ID?
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Re: 1959 Differential code?
I have some info but not all of the info, as it came from a gentleman that was interested in buying my Corvette posi 4:56 pumpkin (still for sale). The right side STAMPED markings he listed are "AH" as 3:70, "AN" 3:70 posi both for manual trans only. "AP" for 4:11 (no non-posi 4:11 avail). I don't have a source for the stamped markings. My pumpkin stamped markings are "FM 6 20" which he told me is 4:56 posi with big brakes.
Your cast #, 3743833, is the same as mine. The other cast # is only a date.
C Ya, Joseph Rock -
Re: 1959 Differential code?
AM is likely a passenger car application. What are the casting dates next to the 3743833? That will get you into the ballpark as to the year. Sorry, but I don't have my reference books here at work.Comment
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Re: 1959 Differential code?
That's a '57 to mid-'61 Posi case, but I don't see "AM" listed for Corvette; it's probably out of a passenger car.Comment
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Re: 1959 Differential code?
That's kinda what I was thinking. I searched the 1958 and 1959 rear axle listings in Noland Adams book and never found an "AM" listing. However, he uses "AM" in an example below the listings to explain the date codes that follow the two letter plant of manufacture. Go figure. Reading the Hollander listings gave me a headache!!! Thanks for the help. By the way, how difficult is it remove the axles from the housing?Comment
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Re: 1959 Differential code?
Yep, passenger car, 3.36 Posi, Detroit Gear.Comment
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Re: 1959 Differential code?
Well, I'm closer, I think.....to deciphering the codes on the pig. J1857 is cast into the gear case above the part number 3843833. I believe it stands for June 18, 1957. The tall letter "P" is also cast into the case indicating it is a Posi unit. But.......the AM still eludes me!! I know that of the AM1024 stamp, the 1024 stands for October 24th of, I assume, 1957. Any additional help to be had? Thanks.Comment
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Re: 1959 Differential code?
Mark -
With that date code format (2-digit year code), that's a passenger car case, cast October 18, 1957 at the Tonawanda foundry and machined/assembled at Chevrolet-Buffalo on October 24th; it will also have a "thick" "P" instead of the "thin" "P" that appears on Corvette cases cast at Saginaw and machined/assembled at Detroit Gear & Axle.Comment
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Re: 1959 Differential code?
John, thanks for helping me. I'm still going to use the differential as it is in better shape than the one currently in the car that is non-posi. Thanks for your help.Comment
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Re: 1959 Differential code?
John,
If your information is correct, I'm confused. All my rear axle code listings indicate that a suffix beginning with an "A", such as AB, AM are Detroit Axle, and all such codes beginning with a "B", such as BB, BM are Buffalo units. Can you clarify?
Thanks
VerneComment
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Re: 1959 Differential code?
Verne
I believe you are mixing up the "cast" markings VS the "stamped" markings.
C Ya, Joseph RockComment
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Re: 1959 Differential code?
Actually, no sir. I'm referring to the stamped suffix codes on the right side of the housing that denote ratio, posi, metallic brakes, etc.Comment
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Re: 1959 Differential code?
Verne -
I'm not familiar with the passenger car codes, but many "A" codes were used on Corvette cases; the "AM" code, however, was never used on any C1 Corvette. There were many C1 Corvette codes that started with characters other than "A", such as L, M, F, and C. I don't think the first character of an axle code necessarily has any connection to either Detroit G&A or Buffalo as the manufacturing source, but was just assigned to identify the ratio/diff carrier/brake type, regardless of where it was produced, as they were all functionally interchangeable. The 2-digit casting date year code positively identifies this one as a Buffalo axle, and Buffalo only supplied the passenger car plants.Comment
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Re: 1959 Differential code?
John,
I was still confused, because I remembered the axle code lists in the General Information section of my P&A catalogs as always listing the "A" codes as Detroit Axle and the "B" codes as Buffalo. Well, I went back to those lists, and lo&behold, all the "A" codes are under a column headed "G&A", and all the "B" codes are under a column headed Buffalo. For the passenger applications, beginning with the 4.11 and 4.56 ratios, there is a "dash" in the "B" column. Those ratios are only listed as "A" code assemblies. This also holds true of all the ratios when equipped with posi and metallic brakes. I don't know if the dashes indicate there were no Buffalo assemblies of those ratio combinations, or that the dash means those Buffalo assemblies also used the "A" code, from the first column....
I understand the rationale behind the distinction of one or two digit year casting dates being a good indicator of the foundry source, but the assembly code stamps still lead me to confusion. I wonder if it's likely that a Buffalo casting was assembled by Detroit G&A? That's the only rational explanation I can think of. Your comments would be appreciated
VerneComment
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Re: 1959 Differential code?
Verne -
There may well have been a relationship between the axle code and the source, but I can't imagine raw diff castings being shipped from New York to Detroit Gear & Axle for machining and assembly when Saginaw was only an hour and a half up the road. But, who knows?Comment
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