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Discussion Starter #1
I've searched the forums and cant quite find the information I'm looking for, so posting here in hopes of an answer. I am restoring a '70 GTO convertible 455 4bbl that I inherited from my step father. I have three rear bumpers for this car, and Im trying to figure out which is the correct one for this car. I can't find anywhere how to decipher the date code.

the three codes I have are 4GB20, 9GB10, AND 1G1B11. I am guessing that the first one is April, Baltimore 2nd shift '70? and the second would be Sept Baltimore 1st shift 70?

How much does it matter if the bumber matches the vehicle for valuation? the reason I ask is the one that is in the best condition prior to being rechromed its the last one. which I am guessing is a 71. I have numbers matching on everything but the engine, which is the correct engine for the car,(same year, same type, etc.) (I have the build sheet), but is not vin matched.

Thanks Much!
 

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Posted the following before on PY forum in response to a no notch ('70 model) rear bumper vs '71-72 notched rear bumper discussion. All I've been able to discern is the trend of date codes to original cars. the preceding letter is the stamping plant, which severàl of us are trying to decode. Ck the top & bottom edges of the rear bumper for the small notches, by doing so can rule out original '71 & 72 cores.

The following are all original as delivered to the dealer, none are replacements

71 Model year timeline:

6JA23 '71 Judge.... 08C Pontiac plant very early car, built 2nd day of production, YES, has notches

//////////Big UAW strike mid Sept 70-mid Nov '70, most suppliers idled//////////

9JA1 '71 T-37........01A Pontiac plant (Note: still using up pre-strike manufactured bumpers)

2GB22 '71 1/2 GT-37 03E Fremont plant

4GB20 '71 T-37......05D Pontiac plant

4B18 '71 1/2 GT-37 06D Fremont plant

72's...........
9JB13 '72 LeMans GT 10C Lakewood plant
 

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On valuation question, it comes down to how high a level restoration is being performed, or if the car is a very very original car. On both type cars, it's advantageous to have the correct dated rear bumper. Short of that, sure its a detailing issue, '70's shouldn't have notched rear bumpers, that noted, there comes a point, a non correct dated one doesn't hurt value.

In the late 90's I got into with a local bumper plating business, as the very clean original rear bumper core I dropped off with them was swapped out after I wrote on the bumper with a paint pen & also had written on the original work order that I needed this exact rear bumper back. The bumper came back with no date code which was unacceptable. Very frustrating as I had emphatically noted the date code when I took the bumper in. The plating job bill ended up being waived, but that meant very little. Fortunately, I was buying a lot of partscars & was able to find another clean core that had the same date coding. Procuring nice clean dated cores, one never knows where one will pop up. Several years ago, a good friend from out of state was down here with me for a week & we were hitting several huge boneyards. The year before I had bought an extremely low mile '72 Lux LeMans 2 door which had been lightly rolled in late '72. Car had set in a detached garage across local metro area for nearly 30 years... Long story. Besides being a killer parts car, it has been a great example car as how mid year '72 Pontiac A-body's were built. As the original rear bumper had not survived the rollover, with the car came a replacement, whicj just happend to be an Oct of '69 stamped rear bumper which perfectly dated my buddy's '70 RAIV GTO. The bumper had been rechromed in the early '70's, wouldn't surprise me if by the same bumper plating shop I previous had the problems with.
 

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Discussion Starter #4
Thanks for the response on this. It doesn't appear from your listing that there is necessarily any rhyme or reason to the date code format? It does appear that I have a match to your bumper code 4GB20 which would appear to be off of a '71 Tempest?

Thanks!
 

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Thanks for the response on this. It doesn't appear from your listing that there is necessarily any rhyme or reason to the date code format? It does appear that I have a match to your bumper code 4GB20 which would appear to be off of a '71 Tempest?

Thanks!
Def date coding system is evident, the first digit is the month, the lasts digit(s) are the day of the month. The letter codes in between signify a stamping plant. There were no stamping plants west of the Mississippi river, so typically there can be a larger lag time from stamping production til installation on Fremont built cars. As far as your 4GB20 dated bumper goes, it could have been mounted on any late '71 model Pontiac A-body. For your '70, the trick would be to find a no notch style rear bumper that predates your cars build by a reasonable time frame. hope this makes better sense.
 
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