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Author Topic: What the hell is a disc brake system  (Read 4981 times)

Offline Indecisive

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What the hell is a disc brake system
« on: 03:16:04 AM / 11-Jun-04 »
[span style=\'color:red\']Posted by Magnum[/span]

There are several criteria which are vitally important when choosing, designing and working with a disc brake system: (1) Keep deflection down; (2) The use of hard linings to avoid flex from sponginess; (3) The use of small diameter flex lines; (4) The use of steel brake lines whenever possible; (5) Volume requirements of the caliper; (6) Available pedal ratio; (7) Master Cylinder size and design.

Calipers: There are two types of calipers floating or non-floating. Calipers are generally made from three common casting metals: magnesium, aluminum and cast iron. Calipers are made of different materials the most common are aluminum and cast iron. The material used in the calipers becomes important to help eliminate deflection, deflection results in a spongy pedal. The modulus of elasticity is very important to eliminate the deflection (flexing) of the caliper. The higher the modulus of elasticity number, the greater resistance to flex. Magnesium has a modulus of 6.5 million, aluminum has a modulus of 10 million, cast iron has a modulus of 14.5 million and steel has a modulus of 30 million.

The floating design was designed by the car manufacturers essentially to make the caliper less expensive to produce. It successfully applies the physics principle of \"for every action caused an opposite and equal reaction happens.\" With this in mind they eliminated the piston(s) on one side of the caliper. This floating caliper is not solidly mounted, but slides back and forth on bushings. When braking force is applied, the piston push the brake pad on the primary side and the reaction is the rotor being squeezed from the force of the pad primary side allowing the horseshoe shaped caliper to slide on the bushings so the secondary pads is used to squeeze the rotor. The caliper has to be very rigid retain low deflection or the principle will be lost. Cast iron and steel is used because of its\' modulus number of 14.5 million and 30 million respectfully. This also increases the \"sprung weight\" and it retains the heat longer. The big advantage to the full floating design (single piston) is if the rotor has a slight run out (wobble), the floating feature will compensate without creating any instability. The other advantage is the single piston design is easier to bleed. The disadvantages are it heavier, retains heat, requires approximately 100 pounds of pressure more to \"slide\" the caliper and requires more volume of brake fluid due to the diameter of the piston. Floating designed calipers also come with 2 pistons, that are on the same side.

Non-floating calipers (i.e. 2, 4 or 6 piston) require a fixed mounting bracket. Most race applications use this type of caliper, because they are generally are made of aluminum which displaces the heat faster and requires both less pressure and less volume to operate. The floating design allows all the piston to be applied at the same pressure, because the pressure is equalized when pressure is applied, thereby allowing the rotor to be squeezed by opposing forces (piston on each side). Aluminum will displace heat 1.5 to 3 times faster than the cast iron or steel calipers. This is important when the rotors heat up to 1100 to 1200 degrees in a race car. Don\'t forget brake fluid has a boiling point of 550 to 700 degrees F. We have come a long way for the old 1965 Corvette design calipers, current non-floating calipers are easily rebuilt and even have thermo barrier type pistons that reducing the transfer of heat from the rotors.

OEM (floating) vs 4 piston (non-floating): Most of the brake kit currently being sold is single piston OEM type caliper. In order for the caliper to squeeze the rotor it has to use a floating design, otherwise it would only apply pressure from one side to the rotor. Because of this design you loose approximately 100 psi. 4 piston caliper squeeze from both sides and are fixed (don\'t float), so they (4 piston) do not require as much pressure. The single piston calipers also requires more volume to work. The area of a 2-3/4\" single piston caliper is 5.93 si VS the area of two (2) pistons on a 4 piston design of 3.53 square inches. (you only multiply by 2 piston to get the area because the other 2 piston are being apply at the same time to squeeze the rotor, unlike the one piston design) anyway 5.93 si VS 3.53 big difference. Does the volume effect the braking? Yes, it has a great effect on the master cylinder volume that is required for all 4 wheels. This will mean you will have to use a larger diameter master cylinder to meet the requirements of the calipers. The larger the master cylinder is the lower the pressure output.

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Offline Indecisive

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What the hell is a disc brake system
« Reply #1 on: 03:16:53 AM / 11-Jun-04 »
Rotors: Rotors come in various designs, but basically there is a vented rotors and solid rotors. Rotors can be a one piece design with the hat or hub incorporated in the casting or the two piece design where the rotor is separate from the hat or hub. In this case the bigger the rotor the better. The bigger the diameter means it takes that much longer before the pad is in the same area during the rotation of the rotor. This size also gives a mechanical leverage \"advantage\" when you increase the diameter of the rotor with the same calipers and master cylinder.

A good example of upgrading would be if you have a Mustang/Pinto 9\" rotor and upgrade to a 11\" rotor. Not only does it allow more surface for cooling, it give a significant mechanical advantage. This results in less pressure and brake force by the caliper to stop your vehicle.

On vented rotors the fins should be far enough apart to allow air to flow between the fins, but close enough together so it allows enough support for the rotor walls. There can be as much as six tons of force being applied during braking and you do not want any deflection. Some vented rotors have curved fins to allow better flow of air and maximizing the transfer of heat. Don\'t forget these rotors can get up to 1,200 degrees F. so anything you can do to assist the transfer of heat is a plus. If you have ever watched a NASCAR short track race with the camera on the rotors, you will know how hot they get.

Solid rotors should never be used on a car weighing over 2,800 pounds. These were designed for light duty and never used on a vehicle where heavy braking is needed. These rotors serve a specific need and work very good under limited conditions.



Your better designed brake systems will have the rotor separate from the hat or hub. This allows the rotor to have a uniform temperature across the rotor (remember the NASCAR rotor?). By having this uniformity it minimizes the warping and cracking. Wilwood for an example uses an aluminum hub in the front which the rotors bolt to. This allows the hot rotor to cool at the same rate throughout the rotor, because it is made of different material and it is a separate part. The aluminum hub is also designed to displace heat and keep it away from the bearings (remember the modulus of elasticity number is 75 percent that of cast iron, meaning it will displace heat at a faster rate). Having a two piece design also prevents the storage of this heat compared to a one piece cast iron rotor. Calipers also benefit by having less heat transferred to them and it assists to keep the brake fluid under the boiling temperature.

Factories use a one piece design, incorporating the hub/hat with the rotor, this was done strictly for cost. Notice that the hub and rotor is cast as one piece. This does not allow for the uniform distribution of heat and it is high prone to warping and cracking due to the differences in temperature between the rotor and hub area. The one piece cast iron rotor will also retain heat longer, thereby transferring excessive heat to the calipers and brake fluid. The only advantage to the one piece design is initial cost. Did you really save any money?
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Offline Indecisive

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What the hell is a disc brake system
« Reply #2 on: 03:17:27 AM / 11-Jun-04 »
Master Cylinders: The basic design of master cylinders are single reservoirs or dual reservoirs. Before disc brakes all master cylinders had single reservoir. This was because you wanted to apply equal pressure to all 4 drum brakes. The proportioning between the front and rear brakes was regulated by the size of the wheel cylinders. Generally you ran bigger wheel cylinders in front, because it applied more pressure and if you need fine tuning you added a manual proportioning valve to the system. In the late 60\'s and 70\'s when disc brakes were being used more and more, there was a need to have a dual master cylinder, because the requirements were different when you ran disc brakes in front and drums in the rear. Remember the volume requirements of the OEM caliper? Well this high volume and more pressure required the factories to build the master cylinders so it was cheap to produce, have a large volume and met the requirements of both the disc and drum brakes. Notice the larger reservoir in the front portion of the disc/drum master cylinder and the small reservoir for the drum brakes.

OEM single master cylinders are generally for drum brake applications. They normally have a residual valve built into the master cylinder. This valve is needed so that the cup seals in the wheel cylinder has pressure against it preventing them from leaking. It also allows for a certain amount of pre-load on the mechanical parts. You can not use this master cylinder if you have disc brakes in front because of the residual valve. I have answered many questions regarding people that have installed brakes incorrectly by using a drum brake master cylinder.

If you experience a brake lock up after a few applications of the brake pedal, it is directly related to a residual valve retaining the brake fluid within the lines and not allowing the fluid to flow back to the master cylinder. The problem is either the wrong residual valve being used, a drum brake master cylinder being used on disc brake calipers, a inline residual valve plumbed in to the brake system with a built in residual valve in the master cylinder or a defective residual valve.

OEM tandem master cylinders will have a residual valve built in when there is a drum brake application. That is why it is important to buy the correct master cylinder based to application. Yes, you can remove the residual valve from the master cylinder, but often the reservoir is to small and it does not hold enough brake fluid for the disc brake application. So great care must be taking when using a modified master cylinder. OEM tandem master cylinders were designed to be cheap. Careful consideration should be made when selecting the master cylinder, because of the high volume of brake fluid required and pressure for the disc brake application. OEM tandem master cylinders do not produce the same volume as two side by side master cylinders. Remember the application is stacked one in front of each other so you have a limited travel and volume to work with.

For over 30 years race cars have used dual master cylinders, this is the use of two master cylinders that are side by side being applied at the same time. The mounting is generally done on the fire wall, but special applications have made it possible to mount these on the floor, under the dash and in a remote location. A balance bar is used to balance the force to each master cylinder. Think of a bar with a pivot point in the middle, when pressure is applied to the pivot point both ends move the same distance. Now think of the same bar with the pivot point move more to one side, when pressure is applied the shorter end will move before the long end. That is basically how the balance bar works. In a race car there would be a cable connected to one end of the balance bar, this cable would go to a knob in the drivers compartment, so he can make adjustments as the condition of his brakes and road condition changes. The balance bar also eliminatesthe need for a proportional valve. On certain applications a remote reservoir(s) are used, in these application it deletes the use of residual valves on disc brake applications. Master cylinders of this type do not have built in residual valves in them so if you have a drum brake application you will still need an inline ten pound residual valve, this is needed to retain pressure against the cups of the wheel cylinders.

There are major advantages to using dual master cylinders: (1) Smaller diameter master cylinders can be used to increase output pressure. The design allow the application of two master cylinders being applied at the same, thereby doubling the volume output. Because of this high pressure output you will not need a vacuum booster, besides if you are running any type of camshaft, chances are you do not have enough vacuum to run the booster anyway. (2) The balance bar eliminates the use of a proportional valve and give you the optional remote adjustment. (3) The remote fill applications deletes the need for residual valve normally used when the reservoirs are lower than the calipers
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Offline Indecisive

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What the hell is a disc brake system
« Reply #3 on: 03:18:21 AM / 11-Jun-04 »
Formula for Master Cylinder Pressure

I have been asked hundreds of times how do you determine the pressures output of the master cylinder. The following information will help you determine the proper size master cylinder:

To figure how much pressure your master cylinder is putting out:
C = pedal ratio
D = pounds of pressure apply by your foot
E = area of you master cylinder
F = pounds of pressure out of the master cylinder
C X D /(divided by) E = F

Example: If you have a 1\" master cylinder the area equals 1/2\" x 1/2\" x 3.14 = 0.785 Square Inches. So, 100 pounds (of applied foot pressure) X 6 (pedal ratio) divided by 0.785 = 764 pounds of pressure.
If you have a 1-1/8\" master cylinder, 100 psi X 6 (pedal ratio) divided by 0.9935 = 604 pounds of pressure.

Here is some info on master cylinder with \"constant\" of 6 to 1 pedal ratio and 100 psi being applied.
3/4\" master cylinder = 1359 psi
13/16\" master cylinder = 1158 psi
7/8\" master cylinder = 998 psi
15/16\" master cylinder = 870 psi
1\" master cylinder = 764 psi
1-1/8\" master cylinder = 603 psi

DO NOT Try to use a OEM master cylinder smaller than 1\" without figuring out the volume requirement. It is like choosing between jump off a cliff or a plane, how do you want to die? Remember you can not do anything after you run out of brake fluid, but you can still press on the brake pedal harder.
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Offline Indecisive

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What the hell is a disc brake system
« Reply #4 on: 03:19:00 AM / 11-Jun-04 »
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.
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Offline Alex Frost

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What the hell is a disc brake system
« Reply #5 on: 09:42:51 PM / 31-Jul-04 »
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.
 
This is a very important point, I\'m glad you mentioned it...you do not want this gummy mess to happen in your car, now fortunately with the S12 they all came with DOT fluid, but on older models, this is a big point...
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