Power Boosters: Power boosters were needed when disc brake systems were being used more and more on factory cars. The amount of boost created from the booster is directly related to the square inches of the booster and the inches of vacuum imputed from the engine. Since the disc brake calipers required a greater volume of fluid due to the size of the pistons and the clamping force (some times up to 6 tons), the master cylinder requires a bigger diameter bores to push the required volume of brake fluid. When you increase the bore size you reduce the output pressure of the master cylinder. In order to boost the pressure output of this larger bore master cylinder the factories installed a power booster. Power booster range in size from 7\" to 11\". Most street rods have floor mounted pedals so the master cylinders are generally located under the floor boards. This creates a room problem so the 7\" booster was incorporated to use with the 1\" and 1-1/8\" master cylinders. The biggest problem with using a power booster is it requires vacuum to operate and most hot rods have 3/4 race cams so there is little or no vacuum. If you are currently using a power booster and having problems stopping, take a vacuum gauge and check the inches of vacuum. To work properly it takes 16-18 inches of vacuum anything much less than this forget it.
In the past I have seen everything from remote vacuum canister to electric vacuum pumps to increase or store the vacuum. So what happens when the engine dies or you loose your 12 volt electricity? No brakes! Can\'t Stop! Funny you don\'t see power boosters on race cars. Yes, they use dual master cylinders.
To view the effect of inches of vacuum vs the size booster you have click on this hyperlink.
Brake Lines: Think of your brakes lines as the blood system in your body. Just like your body there are important things that need to be implemented when running your brake lines. Never run your brake lines near any source of heat, such as headers or exhaust pipes. Use steel brake lines as much as possible and keep the length of the flexible line as short as possible. In selecting brake lines always use thick wall tubing and steel braided teflon lined flex hose. The rigidity of the brake system is a must, you do not want any part of this to flex. Use 3/16\" brake lines on most applications, the small 3/16\" line will fit the need of 99 percent of the applications. Always double flare the steel lines, even if you are using AN type fittings. We first double flare the lines with a 45 degree, then flare it with a 37 degree flaring tool, when using AN type fittings.
It seems that the latest \"fad\" is to route your brake lines inside your boxed frame. I for one think the brake should be where you can get to them for service and inspection. How do you know if the lines are leaking, unless you buy tubing in 20 foot lengths the line inside your frame has a connection. Was the brake line mounted to the lower rail? Outside rails? or Inside rails? If you have to drill into your frame where is the brake lines? How was it mounted and where? Clamps? Was the clamps held down with machine screws? Will the machine screws work loose? Unless the brake lines were stainless, steel lines do rust, so how do you replace the brake lines? Simple is always the best, route your brake lines where you can service them.
Proportional Valves: Proportional valves are used to regulate the pressure in the line. The Wilwood valve shown here, has an adjustment range of 100 to 1,000 psi. It can decrease your line pressure up to 57 percent. It is generally used on the back brake to adjust the balance between the front and rear brakes.
Residual Valves: Residual valves are pressure valve use to retain pressure in the lines. The most common use is on a hotrod when there is a floor mounted brake pedal and master cylinder. Mounting the master cylinder (M/C) below the floor positions it below the calipers. Gravity will cause the fluid to flow away from the calipers. The residual valve will retain pressure within the lines. (i.e. 2 pounds residual valve will retain 2 pounds of pressure, 10 pound will retain 10 pounds.) Drum brake master cylinders have residual valve(s) built into the master cylinder. This is needed to maintain pressure against the cup seals in the wheel cylinders. If you are using a disc brake master cylinder or after market you will need to install a 10 pound residual valve for the drum brakes. Do not install a residual valve if your master cylinder already has one in it. This will cause the brakes to lock up after the second application to the brake pedal.
Always use the correct master cylinder for the application, because of the built in residual valves.
Brake Fluid: Brake fluid is the liquid that transmits the force through pressure for the brake pedal to the brake lines. Basically the brake fluid does not compress so it transmits this force (pressure) without lost.
One of the worse enemy of brake fluid is heat. If the brake fluid boils or there is a leak in your system there will be a lost of this incompressibility and your pedal travel will increase. Not all brake fluids are the same. Most brake fluid has ethylene glycol as it main ingredient. Ethylene glycol has lubricating capability for the rubber parts and has a high boiling point. Moisture is another enemy of brake fluids. All bake fluids will absorb moisture form the atmosphere, this moisture lowers the boiling point of the fluid drastically. This moisture also can effect the balance of the system casing corrosion. A perfect example of moisture getting your system is the early Corvette brakes where it was common to change the calipers or a regular basis due to contamination and corrosion.
Silicone brake fluid has a higher boiling point (around 700 degrees F.) than the ethylene glycol base fluids, but the major disadvantages is not \"hygroscopic\". Hygroscopic? \"Altered by the absorption of moisture\" What this means is since it is not a glycol based, when moisture enters the system it is not absorbed by the fluid. This results in beads of moisture moving through the brake line, collecting in the calipers. Since it is not uncommon to have temperatures in excess of 212 degrees F. (the boiling point of water), this collection of moisture will boil causing steam and vapor lock, this in turn will cause system failure. Silicone (DOT 5) is also highly compressible due to aeration and foaming under normal braking conditions.
If you are changing from a glycol base fluid to silicone or the other way around. The two types do not mix so your system should be completely purged, disassembled and dried out. When the two fluids are mixed you will get a gummy substance and it will really mess up your system.
We recommend using a good DOT 3 fluid. Wilwood makes a hi-temp fluid with a minimum dry-boiling point of 570 degrees F Dry-boiling point is measure in its virgin non-contaminated state. Wet-boiling point is the temperature a brake fluid will boil after it is fully saturated with moisture. DOT 3 fluids have a minimum wet boiling point of 284 degrees F.
Brake fluid should be changed periodically due to contamination. Never mix different DOT brake fluids. Under racing condition you would change these fluids like changing your oil.