67 509 Master Cylinder

[George D. 31849]

Is the 509 master cylinder for a 67 the same unit for both PB and non PB? Thanks...

[Donald O.]

Re: 67 509 Master Cylinder - YES *NM*

[John H.]

Re: 67 509 Master Cylinder - YES

There were several versions of the 5455509 used in GM cars, but the one stamped "DC" was used on all '67 Corvettes (except J56), power or manual; it had a "deep hole" rear piston, which is an unusual configuration for a power brake application.

[Joe R.]

Re: 67 509 Master Cylinder - YES

Gentlemen,

The casting number is the same for both power and non power but the casting is not machined the same. Non power DC MC's are machined to a 1 inch bore and the power MC's are machined to a 1 1/8" bore. It makes lot of difference when you are trying to stop. You don't want to put the wrong MC if you want to stop properly. The smaller bore of the non power MC creates more pressure and the larger bore of the power MC is helped by the power assist.

Regards,

JR

[Joe R.]

Re: 67 509 Master Cylinder - YES

Hi Joe:

I thought that in 1967, both the power and non-power MC bores were 1 inch, and that in later years the power MC bore was increased to 1 1/8 inch.

I don't know about the usage of the DC marking in years other than 1967, but it seems odd to me that GM would have two assemblies that were outwardly identical but had differing internal characteristics. Seems like this could lead to mix ups on the production floor if the internals were different.

[John H.]

Re: 67 509 Master Cylinder - YES

The A.I.M. shows the same finished part number for the master cylinder in both standard non-power(UPC 5) and in J50 Power Brakes (which is the 5455509 casting stamped "DC" with the "YA" bail tag described in the '67 JG), and the P&A30B also calls out the "DC"-stamped master cylinder for both manual and J50 usages, and shows it with a 1" bore. The other master cylinder (called out in the A.I.M., the JG, and the P&A30B as used only for J-56 H.D. Brakes) is the 5480346 casting, stamped "PG", shown in the P&A30B as the one having the 1-1/8" bore size. '67 was a very unique situation where both manual and J50 power brakes used exactly the same master cylinder, with the same bore size and "deep-hole" rear piston.

Manual brake master cylinders always have the "deep-hole" rear piston so the pedal pushrod won't fall out due to wear, bad pedal free play adjustment or loss of the pedal "up" bumper, and most master cylinders for power brake usage have a "shallow-hole" rear piston, as they're actuated by a "short" captured booster pushrod which can't fall out; the '67 J50 booster assembly includes a unique "long" booster pushrod to accommmodate the "DC" master cylinder's unusual "deep-hole" rear piston.

[Joe R.]

Re: 67 509 Master Cylinder - YES

Guys,

Better check that out again as my rebuild kits have 1" for non power brakes and 1 1/8" for power.

Maybe it changed in later years but they are labeled 67-82.

Regards,

JR

[Joe L.]

Re: 67 509 Master Cylinder - YES

JR-----

First of all, "DC" is a code for a finished master cylinder assembly; it's not something that applies to a casting only. It would not be possible for one master cylinder coded "DC" to have a 1" bore and another with the same code to have a 1-1/8" bore (or, any other size bore).

Second, if you search for a 1,000 years I don't think that you'll find a '509' master cylinder that was originally manufactured with a 1-1/8" bore. In fact, I don't think that you'll find one that someone later converted to a 1-1/8" bore. That's because the '509' casting was designed for a 1" bore only; it will not accomodate a 1-1/8" bore.

[Peter L.]

Re: 67 509 Master Cylinder

George - Here's what the August 1968 Chevrolet Parts and Accessories Catalog lists.

67 Corvette (exc H. D. Brake),
68 Corvette (exc P. B.) ............... (1" dia. cyl.) (stamped DC)

67 Corvette w/ H.D. Brake,
68 Corvette w/ P.B. .................... (1-1/8" dia. cyl)

so it appears that the 1" dia. cyl. is for all 67s exc w/ H.D. Brakes. Pete

[Michael H.]

Re: 67 509 Master Cylinder - YES

Joe,

Agree. I just looked this up in a 69 printing and it lists the cyl's as follows.

67 (exc H.D. Brakes)
68 (exc Power Brakes)....................5458833

67 w/H.D. Brakes
68 w/Power Brakes
69 w/H.D. Brakes.........................5469399

67 with and without power brakes would be the 1" dia cyl and 67 with HD brakes would be the 1.125" dia cyl.