Q: I was hoping to get some advice. Thirty years ago I started to replace leaking brake calipers with ones that had been reworked with stainless steel inserts. Due to a job relocation and family duties I am only now getting around to it. I am concerned that the rubber seals might have deteriorated over these past 30 years and it might be better to just purchase new calipers. I also would like to replace the single-reservoir master cylinder with a dual-reservoir master cylinder from a brake safety standpoint. Any comments?
The car has not been operated these past 30 years. I had not planned for this so no long-term storage preparations were done. The car was running great with no problems at the time of the move and has been in my basement garage, protected all these years. I’m running a Holley 4150 four-barrel and plan on sending it to Holley for refurbishment. I expected to find rust upon inspection of the gas tank; however, it appears that the gas tank has a coating inside. I would like some pointers on what preparations I need to undertake to get it back on the road. Any advice or comments would be greatly appreciated.
A: Roy, braking safety is always a concern when driving a vintage Corvette on today’s highways so for that reason I would have the brake calipers rebuilt or replaced. I would also inspect the steel brake lines for rust and replace all the rubber brake hoses.
With a single-reservoir master cylinder, a sudden loss of brake fluid such as from a rusty or rotten brake hose could lead to all of the brake fluid leaking out, which would cause you to have no brakes at all. So, if you are not concerned about originality, replacing the master cylinder with a dual-reservoir component is a great idea.
Several aftermarket companies offer kits that contain all the components necessary to make the swap from a single to a dual master cylinder. For example, Zip Products offers a brake conversion kit for 1963-’66 Corvettes (PN DB-503) for around $300. For the 1956-’62 Corvette crowd, Zip Products offers part number DB-520 for around $530.
The brake conversion kit should include a 1967-style Corvette master cylinder, new steel brake lines that run from the master cylinder to the front distribution block, a steel brake line that runs to the rear distribution block, the necessary distribution blocks, proportioning valve and the mounting bracket for the proportioning valve.
Generally, if you purchase the conversion as a kit, the installation is straightforward and requires only a basic mechanical knowledge and hand tools. The only additional items you will need are the brake fluid and a master cylinder bench bleeding kit.
One thing to remember when removing the original front-to-rear steel brake line is that it is mounted on top of the framerail and is difficult to remove. Installing the new steel brake line using the same route as the factory brake line is nearly impossible. Unless you want to lift the body off the frame to install this brake line I would suggest you find an alternate route.
Bleeding the brake master cylinder before installation is important. Bleeding the master cylinder prior to installation removes any trapped air in the master cylinder that would otherwise be introduced into the brake fluid, causing a soft brake pedal.
Bleeding The Master Cylinder
You will need fittings and tubes to route the fluid from the exit ports back into the reservoir. If the master cylinder bleeding tools do not come with the master cylinder you can purchase small sections of steel brake line from your parts house. Attach one end of the line to the master cylinder exit port. Attach vacuum hose to the opposite end of the line and route it back into the reservoir on top of the master cylinder.
Secure the master cylinder in a bench vice and use a screwdriver to depress the plunger slow and steady until you generate air bubbles. Once you purge all the air out you can install the master cylinder. Take care not to get any brake fluid onto the car’s finish as this could discolor the paint.
Bleeding The Brake System
Now it’s time to bleed the rest of the brake system. To start this process, I use four old water bottles with the tops cut off. I also like to form a hanger assembly for the bottles out of a small piece of wire. Fill the bottles up with about two inches of brake fluid. You will need a piece of rubber hose to run from the brake bleeder screw to nearly the bottom of each water bottle. This process can be done with one bottle; you will just need to move the bottle from wheel to wheel.
When bleeding the brakes, start with the wheel nearest the master cylinder then the wheel next nearest the master cylinder and so on until all four corners have been bled and there is no evidence of air or discolored fluid in the system.
Some Corvette calipers are composed of two halves. So, when bleeding an individual caliper, it is important to bleed the caliper half closest to the incoming brake hose (the inner half of the brake caliper) connection first. If you bleed the outer half of the brake caliper first it is possible for you to re-introduce air back into the outer caliper-half.
Gravity Bleeding Method
Remove the master cylinder lid, attach the rubber hose to the bleeder screws, open the bleeders one at a time in the order described above and allow the brake fluid to flow by means of gravity until the brake fluid runs clear and bubble free. This is a slow process so don’t be in a hurry. Just open the bleeder and walk away. Check the master cylinder periodically to make sure it doesn’t run dry.
If after approximately five minutes no fluid is flowing out of the bleeder screw you may need to slowly pump the brake pedal with the bleeder screw open. Install the master cylinder lid, slowly push the brake pedal about half way down then slowly let the brake pedal come back to the top. Do this three or four times; that should get the brake fluid flowing. Gravity bleeding is basically the exact same thing as pressure bleeding except the pressure is much lower.
Brake Pedal Pressure Bleeding Method
Another method of bleeding the brakes is to use brake pedal pressure. This process requires two people. One person’s job is to open and close the brake bleeder screw and the other person’s job is to press the brake pedal. First, open the brake bleeder screw and slowly depress the brake pedal. Close the bleeder before helper’s foot reaches the floor. Release the brake pedal and allow it to return to the top. Repeat this process until the brake fluid runs clear and bubble free into your bottle.
There is a reason I do not care for this method of bleeding the brakes. The proportioning valve’s function is when a brake line or caliper leaks hydraulic pressure the valve’s internal piston slides to one side, activating the dash brake light and closing off the opposite fluid circuit. When this happens, the closed-off half of the valve will allow little or no fluid through that circuit.
On a properly functioning proportioning valve, if it slides to one side it will re-center itself during the brake bleeding process using simple brake pedal pressure. It is possible for a poorly functioning proportioning valve to slide to one side and stick. If you cannot re-center it manually you may need to replace the valve.
There are a few other methods to bleed the brake system, but they require specialized tools that professional technicians use for bleeding the brakes. These methods include the vacuum pump method that pulls the air and old brake fluid out of the system and the pressure pump method that pushes the air and old brake fluid out of the system.
It’s important to continue the brake bleeding process until the brake fluid runs clear. This is to remove all the old brake fluid that may be in the system. Most brake fluids absorb water and must be changed regularly to keep the system from decaying from the inside out.
Roy, there are a lot of good choices for brake fluid today. One of my favorites is AMSOIL. Next time I will cover some other things you should look at for bringing your Corvette out of the garage and getting it back on the road. Vette