65-66 Power Brake Master Cylinder Julian Dating

[Laura L.]

It has been my understanding that the Julian dating on these master cylinders is a 3 digit embossed number formed during casting and located on the outboard side near the rear. While the 1966 NCRS Judging Guide does specify the location, it does not specify the number of digits. A supplier of reproduction master cylinders told me the Julian dating is a 4 digit number, which I questioned. He emailed me a file with what appears to be a copy of a portion of a GM drawing depicting the Top View of the master cylinder. There is a note pointing to the face of the front brake line port stating, "STAMP (4) .06 HIGH FOR LAST DIGIT OF YEAR FOLLOWED BY (3) DIGITS REPRESENTING CHRONOLOGICAL DAY OF YEAR MANUFACTURED." This note is marked as Revision M. The title block of the drawing is not shown, so there is no way to know the date of the revision or even if the revision is legitimate.

Can anyone out there shed any light on this?

[Gary B.]

Re: 65-66 Power Brake Master Cylinder Julian Dating




I think the supplier that you spoke with is making the mistake of believing what is written on some undated GM document, without consideration of what is found on original cars. Whereas the writers of the JG used what they saw on actual cars as the basis for the description in the JG. Some people make the same mistake in believing everything that appears in the Assembly Instruction Manual (AIM). There are known examples where the AIM was simply not followed by the workers on the assembly line.





Gary

[David B.]

Re: 65-66 Power Brake Master Cylinder Julian Dating

The supplier document is probably legit and correct re: 4 digit Julian date code revision. The mistake he might have made is not indicating the date the revision was made possibly long after 1966. Later master cylinders in '70s etc. use a 4 digit Julian date code. Year first followed by 3 digit day of year. (Stamped not forged). Would not beat him up too much.

[Gary B.]

[Dave S.]

Re: 65-66 Power Brake Master Cylinder Julian Dating

[James W.]

Re: 65-66 Power Brake Master Cylinder Julian Dating

Here are pictures of my '65 PB master cylinder. Sorry for the picture orientation, know matter what I did they will not upload corretly.

James

[Dave S.]

Re: 65-66 Power Brake Master Cylinder Julian Dating

It has been my understanding that the Julian dating on these master cylinders is a 3 digit embossed number formed during casting and located on the outboard side near the rear. While the 1966 NCRS Judging Guide does specify the location, it does not specify the number of digits. A supplier of reproduction master cylinders told me the Julian dating is a 4 digit number, which I questioned. He emailed me a file with what appears to be a copy of a portion of a GM drawing depicting the Top View of the master cylinder. There is a note pointing to the face of the front brake line port stating, "STAMP (4) .06 HIGH FOR LAST DIGIT OF YEAR FOLLOWED BY (3) DIGITS REPRESENTING CHRONOLOGICAL DAY OF YEAR MANUFACTURED." This note is marked as Revision M. The title block of the drawing is not shown, so there is no way to know the date of the revision or even if the revision is legitimate.

Can anyone out there shed any light on this?

I believe that some C3 master Cylinders were stamped that way. The Vendor needs to check the date on their drawing.

[Gary B.]

[James W.]

Re: 65-66 Power Brake Master Cylinder Julian Dating

Unfortunately, I took these pictures a few years ago and can't read the date code from the pictures either. I'll have to look at it in person tonight.

James

[Bill M.]

Re: 65-66 Power Brake Master Cylinder Julian Dating

100_3524.jpg

Here is the 3-digit date on my '65 master. It is 247 (in case it is hard to read).