During the 1960’s the automotive industry evolved quickly, and started setting standards that are still common in modern-day car manufacturing. Brakes were an area of concern as the horsepower wars began in the late ’50s, and continued to climb each and every year. The Corvette was among those high-horsepower machines, and Chevrolet introduced disc brakes in 1965. Corvettes with the power brake option in 1965 and 1966 were equipped with dual reservoir master cylinders, and by 1967 all Corvettes had the updated master cylinder design as standard equipment. The 1964 coupe that we’re wrenching on has a completely stock braking system, consisting of four-wheel drums and a single pot master cylinder. The plan is to swap the old-style master cylinder for a 1967 dual reservoir master cylinder, which is a much safer design.
Braking safety is always a concern when driving a vintage car on today’s highways. As a responsible driver, you likely keep a safe distance from traffic, but there are many situations where a panic stop can occur. In these situations, a rotten brake hose, a hairline crack in a hard brake line or even a leaking wheel cylinder can cause sudden loss of brake fluid. With a single pot master cylinder, all of the brake fluid will eventually make its way out of the reservoir, meaning you will have no braking power at all. This is obviously not ideal, so as a safety measure, we’re upgrading our braking system with a dual reservoir master cylinder, using a kit from Zip Products, Inc.
The kit we purchased (PN DB-503) contains all of the items necessary to make the swap from a single to a dual master cylinder and comes in right at $300. It includes a 1967 Corvette master cylinder, a new hard line to the front distribution block and a new hard line to the rear distribution block. Also included in the kit are the necessary distribution blocks, a 1967-style proportioning valve, and the mounting bracket for the proportioning valve. The only parts we had to buy in addition to the kit were the bench bleeding kit, the AMSOIL brake fluid and one adapter fitting, which we’ll explain in the captions.
The install took us a few evenings in the shop, and required basic hand tools. It’s important to note that removing the stock front-to-rear hard brake line is quite a task with the body mounted to the frame, as the line is mounted on top of the framerail. Installing a new line in the same route as the old one is nearly impossible, so we suggest an alternate route unless you like the idea of lifting the body off the frame for a simple brake line install … we didn’t think so. Other than routing the brake lines, the Zip Products dual master cylinder conversion kit was a simple bolt-on affair, and it gave our 1964 Corvette a little more braking power and a lot more safety.
01. Our 1964 Corvette uses a completely stock braking system, including drums on all four corners and this original-style single reservoir master cylinder.
02. The original hard line that runs from the master cylinder to the front distribution block can be disconnected and discarded. This line will not be used with the new kit.
03. Two 9/16-inch nuts hold the master cylinder in place. We remove the nuts and carefully slide the master cylinder away from the firewall.
04. As we slide the master cylinder away from the firewall we can access the dust cover and pushrod. We carefully peel off the rubber dust cover, as this piece will be reused.
05. OK, you caught us using the wrong tool for the job. Any time you’re dealing with brake lines, use a line wrench. Our 3/8-inch line wrench was missing, so luckily a regular open-end wrench did the job … barely. On stubborn fittings, Vise Grip pliers may be used.
06. The Zip Products Dual Master Cylinder Conversion Kit is simple and consists of a 1967 Corvette master cylinder, a 1967-’68 style proportioning valve and all of the necessary hard lines, fittings, blocks and brackets to make it work with a 1963-’66 Corvette.
07. It’s important to note that the 1967 Corvette master cylinder features a 1/2-inch thread front port and a 9/16-inch thread rear port. Luckily, the Zip conversion kit is complete with appropriately sizes lines and fittings.
08. Another quick note on the 1967 Corvette master cylinder is its 1-inch bore, which will offer a slightly stiffer pedal than the original 7/8-inch bore master cylinder. Also, see that this master cylinder has the deep hole for the pushrod, meaning it is designed for manual brake systems.
09. We found it beneficial to do a mock-up of the brake line and proportioning valve routing. The small hard lines are labeled front and rear, making it easy to figure out.
10. The only item that was not included in the kit was this fitting adapter, which reduces the size on the proportioning valve to fit the original style rear brake line fitting. You can pick these up at the local parts store, but bring the parts with you so you can confirm the size and flare type.
11. Bench bleeding the master cylinder is an important step. A bleeder kit is available from most parts stores and features plastic fittings that thread into the ports and clear lines that dump back into the reservoirs. Clamp the master cylinder firmly in a vise and use a large Phillips head screwdriver to slowly press the piston until the fluid is flowing smoothly with no bubbles.
12. We secured the original style lid to the master cylinder, and installed the master cylinder. Before sliding the master cylinder over the two studs, be sure to install the rubber dust boot and ensure proper fitment of the pushrod.
13. After tightening the two nuts that secure the master cylinder, we installed the front brake line. The kit includes a new line that runs from the proportioning valve to the front distribution block. The line fitment was nearly perfect, only requiring a slight tweak to make it line up.
14. The front-to-rear hard brake lines were fairly difficult to remove and install. Originally, these lines were mounted to the top of the framerail, making it tough to reach. Start by jacking up the car and securing it with jackstands. Then, the rocker panel molding can be removed.
15. Although it is tough to reach, we can now rip out the original line and carefully install the new line. Routing the new hard line in the same way the factory did it is extremely time consuming, so we made a few small changes in the routing to simplify the installation.
16. The Zip kit included a new front distribution block, which is held in place with the original bolt.
17. With the lines connected and fittings tightened, we filled up the reservoirs with AMSOIL DOT 3 brake fluid. Keep in mind that this stuff is very corrosive and will damage paint. According to the folks at Zip Products, this kit does not require the use of residual pressure valves, unless you are running disc brakes on the front and drums on the rear.
18. Now’s the time to grab a helper and bleed the brakes. We started with the two bleeders on the master cylinder, allowing any air to escape the system before we moved on to bleeding the four corners. Always start with the rears.
19. With the Zip Products Dual Master Cylinder Conversion Kit installed, the car stops well, and the dual reservoir setup gives us peace of mind that our braking system is safe. Add to that the period correct pieces included in the kit, and you have a great addition to improve any early C2.
20. AMSOIL makes a DOT 3 and a DOT 4 brake fluid. DOT 3 is ideal for street use but should you find yourself autocrossing or performing other forms of extreme driving with your Corvette you might want to consider going up the “performance tree” with DOT 4.