drum brake master cylinder date stamp format

[mtull]

I'm trying to understand how to read the assembly date on drum brake master cylinders.  I've seen mention of a 3 digit day of year followed by a single digit referencing the year. The first image is from a thread on this site and appears to have a 5 digit number: 12988?  The second image is from a master cylinder with AANF cast on the bottom and appears to also have a 5 digit number: 2968x?  The last digit looks like a '4'?

If I understand correctly, a 1969 10,000 day calendar defines 2968 as September 12, 1969 however that doesn't take into account the last digit?  I could also read it as the 296th day of 1968; October 22, 1968.

Any education help appreciated.
Thank you

[Cuda Cody]

Almost looks like a 1?  It was common to put the number of the shift that did the work.  For example, a number 1 or 2 would just indicate that it was the 1st or 2nd shift working that day that did the work on the part.

[mtull]

Almost looks like a 1

Could easily be a 1.  The last digit in the first image looks like an 8.  How many shifts per day?  Head scratcher for sure

Thank you for your input @Cuda Cody

[JH27N0B]

I studied master cylinders some years back and documented the info for Mopar master cylinders.  I never completely sorted out the '67 through 70 drum brake master cylinders.  They were used across almost all platforms at the time for drum brakes, unlike disc that had different master cylinders for different platforms.  And maybe due to how many they needed, they may actually have been built at multiple plants to supply the large demand and there were no doubt nuances between procedures at the different plants.
There are 3 different casting numbers and numbers stamped in them for internal use and for the date code are found in different locations.  The one you show is in the nose but I've seen numbers stamped in the side of the casting on other examples.
The date codes on the disc MCs were rather straightforward to figure out. Like 9 123 would be the 123rd day of '69.  But the system on some other master cylinders like these drums seem to be in a different format I don't completely follow.
I don't recall off hand on drum masters, but on disc there were also casting date codes cast into the body.  They used a removable plate in the mold so you see the outline of screw heads by those date codes.  Dan 6bblgt studied those and figured them out, offhand I think they were month and year. That doesn't tell you when it was manufactured, but at least tells when the casting was made, so it was typically not very long before the part was machined and assembled at the plant, which at the time was a Bendix plant as they made all the master cylinders for Chrysler.

[mtull]

They used a removable plate in the mold so you see the outline of screw

Thank you for you're post packed full of good info.  The removable plate detail was an interesting tidbit.  Regarding your statement: "I never completely sorted out the '67 through 70 drum brake master cylinders", did any of the one's you reviewed have a four digit date stamp (ddd y)? Thanks for your response!

[JH27N0B]

I'll have to look at some drum brake master cylinders I have at home, to see if they have the plate feature with the casting dates like I have seen on the disc brake MCs.  I have a couple drum brake master cylinders with the date code info stamped in the side, that seem to fit the format I see on disc brake ones.  The both started in 6's, so that brings a question was that '66 or '76. If '76 they would have been made as service parts. Those 2 are also E coated black so that brings another question to the mysteries with these.  Were all E coated, were just some, was it only for a brief time?
Noel Automotives YouTube channel recently featured some interesting videos documenting a survivor '70 Challenger R/T and the drum brake master cylinder on that car has its casting E coated black.
The disc brake master cylinders of that era, were black too, but they were clearly painted black.  Some Bendix MCs for other of the big 3 carmakers I've see were E coated, not painted.

[mtull]

I watched/enjoyed the video's he did on that car.   It's a sharp car IMO. I'm grateful for what he shared and wouldn't have complained if the video's were longer. 

Thank you @JH27N0B for helping me get my head around this topic.
 

[JH27N0B]

I looked at the ones I have.  2 I believe are NOS and have casting number 2225601.  Both E coated black.  One has what I believe is the date code and it's stamped 7 192 and the screwed in plate in the casting mold reads 146 in the casting.  The other is 6 342 and the number on the screwed in plate is 254.
The last one is rebuilt and has AANF as its casting number.  It has 346 stamped in nose and no numbers on screwed in casting plates on it.