Master Cylinder application question

[John A.]

I have a master cylinder with the following markings:

Casting: 5480346 D1 with a date stamp of YA4059.

Can anyone enlighten me as to what this was used on?

Thanks

[Joe L.]

Re: Master Cylinder application question

John-----

This is a 1-1/8" bore master cylinder. It was initially used for 1967 applications with J-56 power brakes. After 1967 it was used for both J-50 and J-56 power brake applications at least through 1976.

This master cylinder casting was used for finished master cylinder applications with and without bleeder valves. 1967 to about 1973 versions have bleeders and about 1973 to 76 versions do not have bleeders.

I don't understand the "YA" coding for this master cylinder as indicated by the stamping. "YA" was a coding used for 1" bore master cylinders used mainly for power brakes (except 1967 when 1" bore master cylinder were used for J-50, too). The '346' was never produced with a 1" bore, as far as I know.

[Joe L.]

Correction

1" bore master cylinders were used primarily for MANUAL brake systems during the 68+ period.

[John A.]

Re: Correction

Thanks Joe,

... and the 4059... does that correspond to a month/day/year? I have a copy of "corvette by the numbers" but it does not cover MC's.....

Thanks again!

[Chuck S.]

Interesting...

Power brake MC casting number and standard brake MC "YA" stamp...either some MC "restoration" has occurred or some GM worker maybe made a beeg mistake.

If in a pinch, I wonder if GM could/would use PB MC castings for standard brake MCs? If it were me, I would have to mike the actual bore ID to solve the mystery.

[Joe L.]

Re: Correction

John-----

The date decodes to the 59th day of 1974. This casting was out of production by 1984, so it couldn't be 1984.

Does this master cylinder have bleeders and what is the actual bore size?

[John A.]

Re: Interesting...

... the casting has a 1" bore....

There is no machined surface or PG on the front of the casting...

....yes there are bleeders and it came configured with the equilizing valve mounted to a bracket... positioned on the left side of the casting.

Thanks

[Joe L.]

Re: Interesting...

John-----

Well, things get stranger and stranger. First, I've never seen a '346' master cylinder casting with a 1" bore. It's possible that this was a SERVICE unit and, perhaps, by 1974 they decided that they'd use this casting for all applications. The 1" bore IS consistent with the "YA" coding, so that part checks out ok.

I'm surpised that a 1974 edition of this master cylinder, PRODUCTION or SERVICE, had bleeder valves. It's possible, though, especially if this was a SERVICE unit.

Some "later editions" of these master cylinders lost the machined, semi-circular surface on the front of the casting. I think that the coding stamped with the date code into the brake line fitting machined surface replaced this. Earlier versions have the date code only on the brake line fitting surface and the application code is on the front surface.

The "valve" attached by the bracket that you describe could only indicate a 1967-68 usage. Those were the only 2 years that the brake distribution block and pressure differential sensing switch was attached to the master cylinder with a bracket. The block should be a steel block, if it's original 67-68. Some later 67-68 SERVICE blocks were brass.

So, this sounds like it's a 1974-era SERVICE master cylinder which was used for a 1967-68 Corvette application.

[John A.]

Re: Interesting...

I would have to agree with your evaluation! By the way, the "valve" is of steel construction.

Thanks for all your help!