1973 Frame Stencil

[Wayne F.]

I am trying to get information on the suffix GM used on the frame stencil. The 1973-4 Judging manual shows the frame stencil for a 1973 with stick shift transmission and the suffix used is 150. The part number for the automatic transmission frame is 330970 - ???. Is the same suffix used for the frames with automatic transmissions?

Thank you,

Wayne Foss (2823)

[Tom R.]

Wayne
Frame stencils were stamped with part number, lot # and date code. Part numbers differentiated a manual transmission frame assembly from an automatic...so two different part numbers. The Suffix is a production lot # of which there would be a series that represented a particular model year. Frames wee assembled for a particular vehicle, then made for another model. Each stamped with a lot #. The only way to pin down a lot # is to know other frame assemblies with same part # and when they were assembled and record their lot #, if that makes sense.

I've done this with 78 Pace Cars and four speed frames. By 78, buyers preferred automatics so when Pace Cars were being built, their was a backlog of manual tranny frames. Early Pace Cars have frame assemblies dated in December 77...while later built Pace Cars has frame assemblies that were about a month prior to their assembly (the vehicle). I can estimated rather precisely their lot #'s as a result of that frame assembly survey. The point of which is that lot #s changed and a challenge to pin down unless you have a series of frame stencils to survey.

So, what you are looking for are 73 automatic cars that have a build date around the same time your 73 was built. Identify the lot # and use it...that is the best method to get close to the original lot#

[Wayne F.]

Thanks Tom,
Sounds like a research project! I know there were two different part numbers for 1973 frames, and most likely all frames from 1963 to 1982 with part numbers to differentiate between manual and automatic transmissions. The question then becomes, was each type of frame manufactured in batches (i.e. auto versus manual trans), or mixed together as demand from consumers would dictate type of transmission, hence type of frame? Another question that arises was the batch number related to the type of frame manufactured, or the time period in which it was produced or both, or was the batch number simply a model year numerical number?

If any of you who are reading this have a C-3 car with a legible frame stencil I would like to hear from you with the frame stencil numbers (including the suffix and date) the VIN number of the car, and the date of vehicle manufacture (trim tag data date) With this data, maybe I can correlate suffix codes to GM part numbers and dates.

[Tom R.]

I'm speculating but would believe it related to a time period. You would have to collect a whole lot stencils to reconcile lot #s for both tranny types.

I've attached a summary of 78 stencils, all of which are Pace Cars. You can see the lot # by transmission type. I suspect these jobs were scheduled well in advance with orders from manufacturers by vehicle and transmission type.

stencil summary.png

[Wayne F.]

Hello again Tom,

Your limited data set would suggest that the suffix code is related to the date of manufacture of the frame and not the year of the frame. It also suggests that there is a different code sequence between auto and manual transmissions. It may be difficult to obtain a large enough survey to actually develop some meaningful conclusions as these cars are 50+ years old and many have spent their entire lives in wet climates.

Once again, my plea is to any who read this and have a C-3, any year with a legible frame stencil, please respond to my request for data. Thanks

[Alan S.]

Hello Wayne.

1971 coupe 4-speed 350/270....
Original Frame

3987882-110
10-26-70

F14
....6589

Regards....

[Wayne F.]

Thank you Alan. One is a start!

[John S.]

Wayne, here’s the data on my ‘73 as shown on page 228 of the 3rd Edition TIM&JG Fig. 13.1.

1973 Coupe L82 M21
Original frame 330960-150
Build date Dec. ‘72
Vin 409909

Let me know if you need any further information.

[Wayne F.]

Thank you John. I appreciate your input.

[Robert R.]

Wayne,

The frame stencil for my 74 automatic car is also pictured on page 228 of the JG.
VIN. xxx25194
Trim tag date. 25 apr 74
Frame stencil. 339720-203. Dated 4-3-74

my other 74 is a 4 speed car.
VIN. xxx14949
Trim tag date 21 Jan 74
Frame stencil 339719-192. The date is illegible.

Bob R.

[Wayne F.]

Thank you Bob. Every little bit of information helps!