1967 Master Cylinder

[Donald H.]

Does anyone know of a way to tell if a 67 master cylinder is an original or one of the "correct" reproductions. As far as I know the correct reproductions (made by CSSB I believe) have all the features of an original. All the correct casting numbers, configuration of the casting, machined areas and the DC stamp.

The reason I ask is I'm trying to decide if one I have from a friend's car is worth rebuilding. I don't know what the current cost is to have one bored and sleeved but I suspect somewhere in the $125-$150 range. So, with having one sleeved, a rebuild kit and shipping the total is likely approaching $250. Worth it to me if it is an original.

The correct reproduction is $280 at CSSB and a little less at ZIP.

Thanks,
Don

[Mark F.]

call ken at lone star caliper and ask what his rebuild cost is

https://lonestarcaliper.com/

[Gary B.]

Don,

If you call Ken ask him if he’s switched to rubber O-rings that are DOT 5/Silicone compatible. Some of us have been waiting close to a year to get an answer to that question.

Gary

[Donald H.]

I did call Lone Star and the lady took my name and number. Let's see if I get a call back.

I am a little confused regarding dating and the 67 master cylinder casting 5455509. The 8th addition of the judging guide says "Stamping of Julian dates into the forward machined boss commenced after the 1967 model year..." However, I believe there is a Julian date casting just above the forward fuel line inlet. If the casting is a Julian date, then I assume all the reproductions would most likely have the same cast Julian date. I have seen two picture online and a picture from a friend of a know reproduction and they all appear to have the Julian date of 100. I have a spare original and the casting on it is 314. The one that I am not sure of has a casting of 19.

Here's a picture of my spare original unrestored one.

Don

[Patrick B.]

Don-The casting of the reproduction master cylinders look crude compared to an original. They are like things cast in India. Don’t use them if you want to use silicone brake fluid. That is not because of the rubber parts. The rubber parts are made by an actual brake part manufacturer out of some kind of EPDM, and they are not the problem. The problem is that the small passage from the reservoir to the piston bore is not like the originals. It is not countersunk and the tiny hole is much longer. As a result, silicone brake fluid won’t bench bleed because its higher viscosity interferes with its flow through the longer tiny hole.

The Julian date on a 67 cylinder is stamped in tiny numbers on the flat near the front brake line not cast in.

[Donald H.]

I got a call back from Brian (?) at Lone Star. He was able to confirm that the Master Cylinder I have is an original and that it was actually rebuilt by Lone Star. There are some numbers stamped into the end where it mounts to the firewall that are Lone Star numbers.

Regarding DOT 5, their position is still not to use it. In fact, they don't really like DOT 3/4 and prefer straight DOT 3. He basically said they are not engineers but they have done a lot of red-neck testing. I did not mention that I have DOT 5 in my 67 and have had for probably 6 or 7 years since I rebuilt the calipers and put in new brake lines. So far, I have not had any issues.

[Donald H.]

Don-The casting of the reproduction master cylinders look crude compared to an original. They are like things cast in India. Don’t use them if you want to use silicone brake fluid. That is not because of the rubber parts. The rubber parts are made by an actual brake part manufacturer out of some kind of EPDM, and they are not the problem. The problem is that the small passage from the reservoir to the piston bore is not like the originals. It is not countersunk and the tiny hole is much longer. As a result, silicone brake fluid won’t bench bleed because its higher viscosity interferes with its flow through the longer tiny hole.

The Julian date on a 67 cylinder is stamped in tiny numbers on the flat near the front brake line not cast in.

Thanks Pat. What I thought was a Julian date is actually a mold number per the Lone Star guy.

[Patrick B.]

I got a call back from Brian (?) at Lone Star. He was able to confirm that the Master Cylinder I have is an original and that it was actually rebuilt by Lone Star. There are some numbers stamped into the end where it mounts to the firewall that are Lone Star numbers.

Regarding DOT 5, their position is still not to use it. In fact, they don't really like DOT 3/4 and prefer straight DOT 3. He basically said they are not engineers but they have done a lot of red-neck testing. I did not mention that I have DOT 5 in my 67 and have had for probably 6 or 7 years since I rebuilt the calipers and put in new brake lines. So far, I have not had any issues.

I believe the only rubber used by Lone Star and the other Corvette suppliers that it not EPDM is the mystery rubber in the o-ring calipers. The o-ring caliper parts supplier is a machine shop not a large company that actually molds rubber brake seals and knows that EPDM is the industry standard material. Even the o-rings can go a long time in DOT-5 without a major problem. I recently disassembled o-ring calipers that had been used in DOT5 for 14 years. The o-rings were somewhat swollen but we’re not soft, torn or causing a leak. We have had long discussions here on the simplicity of obtaining EPDM o-rings to make the o-ring calipers compatible with DOT5.

[Joe L.]

Don-The casting of the reproduction master cylinders look crude compared to an original. They are like things cast in India. Don’t use them if you want to use silicone brake fluid. That is not because of the rubber parts. The rubber parts are made by an actual brake part manufacturer out of some kind of EPDM, and they are not the problem. The problem is that the small passage from the reservoir to the piston bore is not like the originals. It is not countersunk and the tiny hole is much longer. As a result, silicone brake fluid won’t bench bleed because its higher viscosity interferes with its flow through the longer tiny hole.

The Julian date on a 67 cylinder is stamped in tiny numbers on the flat near the front brake line not cast in.

Patrick-----


There is another "unseen" difference between originals and the reproduction master cylinders. The original master cylinders used on Corvettes from 1967 through at least 1972 were cast from ductile iron. The reproductions are cast from gray iron. Both materials are suitable for master cylinders but I still prefer the stronger ductile iron whether the extra strength has any practical benefit, or not. The difference in the type of cast iron may also be the reason that the reproduction master cylinders have a "rougher" appearance.

[Mark F.]

Don,

Here's a brief read on what Patrick and Joe are talking about...

https://www.urick.net/blog/ductile-iron-vs-cast-iron-whats-the-difference

Ductile parts in heavy duty trucks:

https://www.urick.net/industries/heavy-duty-truck

[Donald H.]

Thanks,

Don