65-66 Standard Master Cylinder Casting date

[Hector G.]

There's an article in the recently published Restorer, about rebuilding a 66 master cylinder, written by Ed Vignone. I spoke to Ed a couple of nights ago and compared notes on the cylinder's casting date. Does anyone know how to decode the casting date. My thinking is that it is based on the Julian Calendar. My 66 was built in March 1966 and has a date code of 284. Ed's, also with a built date of March 1966 has a date code of 362. Any thoughts? For your information, per Ed, the first photo in the article is incorrectly married with the caption. As you might have noticed, the date code on the photographed cylinder is 131, whereas the capiton refers to a date code of "362".

[Joe L.]

Re: 65-66 Standard Master Cylinder Casting date

Hector-----

The date coding system that you described is common on Delco-manufactured cast iron brake parts, including calipers, wheel cylinders, master cylinders, and other parts. Most of these parts were cast at the old Danville, IL GM ductile iron foundry and machined/assembled at Delco plants in Dayton, OH.

As far as I've been able to tell, the coding is probably a Julian date coding system or some variation of a Julian date coding system. However, from what I've been able to determine, there is no year encoded, either as part of the 3 digits or any other place on the casting. Some later master cylinders have a stamped-in coding which does include the year. However, the raised numbers, IF they are a Julian date, include no reference to year. Without a reference to year, the rest of the date code, assuming that's what it is, is pretty meaningless. I suppose that one could say that the 3 digits have to indicate a day of the year within 180 days of the car's build date. So, under NCRS and NCCB guidelines that means that 1/2 of the parts ever manufactured of the correct casting number would be correct for any given car.

In any event, it's all moot since I don't think that these dates, IF that's what they are, are judged.

[Hector G.]

Re: 65-66 Standard Master Cylinder Casting date

Thanks Joe. I just received the message.