brake

Helpful Hints for your Stopping Needs

You have played around with your car or trucks brakes, now you have to get your race car to stop..Here is a small section that I am dealing with first hand. I bought new master cylinders and new brake cylinders and plumbed new lines to them. With balance bar hooked up and bled the lines..I thought I was ready to roll, or stop, so I thought. Interesting notes.

Always match your braking components with your needs.

If you race asphalt you will need to use a 1" bore master cylinder on the front and at least 3/4" to 7/8" bore master cylinder for the rear.

If you Race on dirt, the cylinders you will need to use are the opposite to the asphalt application. Front will use a 3/4" to 7/8" bore Master and the rear use 1" bore master cylinder.

To offset the amount of heat build up in the calipers and to get the maximum stopping power, the cylinders are offset in size to aid the driver. Also depending upon the type of caliper you use will dictate the size master cylinder you use. A 4 cup (piston) caliper will require more fluid flow to the caliper from the master cylinder than a caliper with only one cup

Most race cars use or should be built with the use of dual master cylinders. A twin master cylinder(one made with a division of cylinder to accomadate both front and back brakes) will not push the amount of fluid needed in a racing application. The use of dual cylinders aids the driver when applying the brakes. All cars built within the last thirty years rely on a booster to aid the driver when applying the binders. Low vacumn on a racing motor makes this type of cylinder impossible to use.

Never use a drum brake master cylinder on disk brakes. This master cylinder cannot flow the amount of fluid that disk brakes need and also has a residual valve that equals 10 lbs of force to keep the pressure offset to the springs on brake shoes found in drum brakes. This master cylinder can be altered to use with disk brakes but is the opinion of this racer/builder to AVOID THE USE OF THESE TYPE CYLINDERS PERIOD.

Mounting your Master cylinders.

Always mount your master cylinder(s) higher then the brake calipers and lines. This prevents fluid flow back to the master cylinder from the brake calipers. Most all cylinders come with what is called a residual valve built in to keep the fluid from flowing back to the master cylinder, this valve also keeps the cups in the calipers tight to the brake pads and prevents gaps on the braking surface. In rare cases where the cylinder has to located lower then the lines or brake cylinders you will need to add a 2 lb residual valve. If you are using a disk / drum combination. You will need to put a 10 lb residual valve on the drum brake side of the system to offset the springs of the drum brakes.

In cases where you have to mount the master cylinder lower than the brake calipers or brake lines, invest in a 2 lb residual valve to be placed in line to the brakes and brake lines that are higher than the master cylinder. If you do not add this residual valve inline you will find that the fluid will flow back to the master cylinder from the calipers and lines that are higher than the master cylinder, one way to tell if you have flow back is that the system is bled of all air, press the brake pedal, with the brake pedal depressed have someone turn the tires on the side that you want to test. you should have equal pressure on both sides on the front or back. If one side locks up and the other side has a small amount of brake applied chances are the right side will lock. This is a sign of flow back. It will take longer for the furthest tire to lose pressure and fluid in the line then the closest tire. Does it take a few pumps to build up pressure in the system? If you have to pump your brakes 3 or so times before the pedal has adequate pressure on it and feels firm, let off the pedal and press down one more time..Chances are that if the pedal goes to the floor you have fluid flow back to the master cylinder

Residual Valve

A device used to keep a small amount of fluid pressure in a brake line to combat fluid flow back to the master cylinder when the brakes are released. As you have read in the previous paragraphs. Two residual valves are on the market. The first is a 2lb residual valve, used mainly to keep the flow of fluid from flowing back to the master cylinder from the calipers and brake lines in applications that have the lines and or calipers higher than the master cylinder. The second residual valve is a 10 lb valve used when the application is calling for or use of drum brakes. This valve is set to 10 lbs to offset the spring pressure of the springs mounted to the brake shoes

choosing the right caliper

Always size up your braking needs to how the brakes are going to be used. If you are racing on a short dirt track, you might be able to get away with using single or dual calipers, providing that you are not running an exessive speed and braking hard. The caliper will not over heat and you will get plenty of braking power. Using a single cup caliper will only apply braking force on one side of the rotor and does not provide maximum braking or wear to components.

If you are racing on a longer dirt track you will want to use a 4 piston caliper for maximum stopping power, the dual cups in the caliper per pad apply equal pressure on the rotor for maximum performance.

On asphalt race tracks I only recommend the use of 4 cup calipers on all corners of the car. Usually hard braking is involved in cornering going deep in the turn before applied, and you do not want components over heating and warping rotors.

Rotors

Always size your rotor for your application. rotor thickness plays a key role in how your car is going to stop and how it can dissapate heat. Life of the rotor also is a factor when buying a thicker rotor. Rotor diameter can vary according to the caliper and mounting you use. Rotors also come cross drilled to aid in cooling, beware that the drilled holes can gather dirt and dibris and stop their cooling properties, always clean and inspect the rotors after every race.

Brake Line

Only use Stainless steel brake lines for your primary lines running from the master cylinder(s). There are teflon lines out there that will also do the job of stainless lines, but with a race car in all its conditions, meaning if you drive over debris, heat, or what ever can cause abrasion or cutting the teflon line, will find you with no brakes. Always use a rubber cover over the line in areas where the brake line is secured to the chassis. This will stop vibration and keep abrasion to a minimum.

Remember that the larger the brake line the more flex that line will encur as pressure is pushed through it. A larger brake line will have its walls bulge when 1000-2000 psi is pushed through it. I always recommend the use of 3/16" steel line.

Use a full braided line where crossing from the frame to the wheel. Some flex lines come with teflon lining which is perfered over the use of neoprene. Neoprene lines do not stand up as well as the teflon braided line and failure will occur when you least want ti to.

Brake pads

Brake pads are at the bottom of the line for me.. I will go out and buy a non matallic pad to put on the rotors. The non metallic pads are rotor friendly and with the little braking action I apply they last as long as metallic pads. There are a variety of manufacturers of brake pads designed to fit the racers needs.. Do your research before you purchase the $20 pads from your local parts store.

Bias

Certain classes of racing allow the use of a bias bar. This adjustment is used in the cockpit of the race car to tune the brakes from front to back allowing the driver to adjust how much braking force is going to the front or rear axle in relation to the other axle. This device is used inbetween the brake pedal and the master cylinder. Turning the adjustment will move a roller bearing from one side of the housing to the other offsetting the pedal pressure to one of the two master cylinders. Causing more pressure to go to the front or rear brakes while taking pressure from the opposite end of the car.

one other type of valve is used to do the same as the bias bar in cases where the driver cannot adjust the bias between front and back brakes. This valve is called a proportion valve, Two different types are available. One is used with a knob restricting the flow of fluid through it and the other is controled by a lever that restricts flow. Both of these valves are usually mounted outside the cockpit out of reach of the driver.

Remember your life is at stake so take braking seriously. Race hard and have fun. Racing is a dangerous sport, the above is only a reference and used to help make racing your car safer and fun. Please take care while on the race track.