How did GM number them?

[rgshafto]

Here?s a question I have been wondering about: What do VIN and body numbers on 1930s GM cars tell you about its likely date of manufacture?

For example, my 36 Pontiac convertible has chassis (VIN) #29,028, which I believe means it was the 28,032nd Master Six car produced that year. They made 93,475 Master Sixes (no one knows actual production number for the various (7) body styles because all of Pontiac?s records were lost in a fire). Assuming they started production in late August and ended in July, they made them for about ten months. (1936 was the first year for fall introductions: October 26th for Pontiac, late September for Buick). If they produced the same number of cars per month, that would be an average of 9,340 Master series cars built each month. According to that logic, this chassis would have been assembled about three months into the production cycle, or perhaps late November (32% of the way through the 10-month cycle).

The body number is 765. No one knows for sure how many convertibles were made, but let?s assume that Pontiac produced the same proportion of ragtops as Buick or Oldsmobile (0.7%) in that year. Apply that percentage to 93,475 Master series cars and you get 654 Master Six convertibles produced, which is obviously low since I have Body #765. Body #765 would therefore be a very late production convertible, which does not jibe with the chassis number. (It doesn?t have an original engine, so its casting date is unknown.)

My coupe is VIN #8494, body #1894. I know it is an early production car because of the many 35 parts they used up building it (tail lights, horn button, heater, oil breather, etc.). It also had glass dated August 1935 and its engine was cast on July 22, 1935. All those numbers are in agreement: it?s clearly an early production car.

But how did my fairly early production convertible chassis get such a late convertible body number? It doesn?t seem likely they that would have built all the convertibles early in the run, although I suppose it is possible. Or maybe they just sold a lot more ragtops than their Buick or Olds cousins? I would think that production of various models varied according to customer demand, making average figures suspect, but not skewing it this much. Or did they assemble and number a bunch of bodies well ahead of production, then grabbed them in more or less random order when building them?

I don?t know the history of this car, so I guess it is possible that body and frame don?t match (but it is a unique convertible frame), or the tag was changed (no evidence of that). Neither of those things seem likely.

Anyone have any insight about how this numbering business actually worked? I welcome your speculation!

[Buicks Rule]

Bob,

I know that Buick Historian Terry Dunham has spent a great deal of time trying to find a definitive answer to similar questions for Buicks of this same era. Did Pontiac have more than one assembly plant for 1936? You might try contacting him for the full story. I'm working on memory here but this is roughly what he discovered for 1937 Buick VIN issues.

I believe that 1937 was the 'first' year that Buick was involved in a GMAD style plant where multiple GM makes were assembled in two locations other than Buick controlled Flint. The two locations were-I think-Southgate CA and Linden NJ. With 37 Buick Flint last VIN minutes Flint First VIN gives total annual production at all plants. The numbering system was also changed in later years so Terry had to try to understand what was done by a reverse analysis of survivors.

However what Terry discovered was that it appears that Linden/Southgate were assigned blocks of VIN numbers that were re-plenished as they built out their assigned numbers. Since the majority of the production still came from the home plant, and 'early' VIN assigned to CA/NJ would likely have been built later in the calendar year than would have occurred if it were built at the 'home' plant, it becomes much harder to track a build date for an assembly plant car than it is for a 'home'plant car.

Let me also propose the following. I don't know cars of that era well but based on your experience does the following make any sense?

Another issue that might be part of this. The Fisher body number is a production sequence number for Fisher body. At what point did fisher body care that the car was going to become a Pontiac, or within Pontiac which series of Pontiac the car was to become? During the production process at Fisher body? or was this identical body used for more than one GM convertible?

Let me try to explain this idea because I'm not sure I've made my thoughts clear. In 1964, Fisher body had to care whether the A body convertible they were building was destined to be a Chevelle, LeMans, F-85 or Skylark while it was on the Fisher line because the steel body panels welded into the car were physically different panels, even though the cowl and interior structure was the same. So, Fisher style numbers followed by body number became very marque/series specific.

Is it possible that in 1936, this exact same convertible body was used on other GM cars with no structural or 'hard'panel differences in the body itself? Are there press line/character line/or size differences that would make this "A-body" convertible different from the basic body shell on a Chev, Olds or Buick convertible? In other words, from a Fisher body standpoint, was this bare body a 'generic' A body convertible to be sold to whichever division needed it or was it a 'specific' Pontiac master body from the time the body structure started to come together. If the same body could be built out as more than one series of Pontiac or more than 1 GM car line, that would also explain a relatively 'high' body number on a relatively 'early' VIN.

[rgshafto]

Well, Pontiac did as build 1936 cars in both California and Michigan. California cars apparently had serial #s that started with letter "C". Reportly, California-built Master series cars had serial numbers that ran from C-1001 to C-1400, so this car was built in Michigan.

The body is a generic body, used by all GM marques that year. But the tag is specific for Pontiac Motor Division and includes things like the interior trim code and paint code and even a code "V" indicating it had the optional 2nd sunvisor , things that wouldn't have been known prior to it being built.

Too bad some of the guys who actually worked on the line then aren't around to answer these kind of questions!

[Guest]

According to "The Standard Catalogur of Pontiac" 1936 Pontiac Master series were 6BB They do not list a convertable but do list a cabriolet??? It says starting number was 6BB 1001 and the final number was 6BB91362. This would make your car the 28,028th car built. It also says the pacific coast numbers were C1001 to C1400.