Dean S. Oshiro

The Brake Article©

"Brake Article"© was written in 1994, before I started building our Zero Offset™ Brake Kits. After reading it you will know more than the next salesman you talk to. It has been read, down loaded, copied and counterfeited by many people. I am sure that it has saved someone's life. I have only changed some wordage from the original article.

© 1994 to 2015 Dean S. Oshiro

The Brake Article© by Dean S. Oshiro 1994-2015

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 or pins. 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 on the same side.

Non-floating (fixed) calipers (i.e. 2, 4, 6 or 8 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. Calipers made of aluminum are also not subject to corrosion and rust, like the Corvette calipers in the 60’s. The fixed 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.

Six Piston Calipers: When I first wrote this article there were no 6 piston calipers commonly used on street vehicles. You can thank computers for the fast advancement of c n c machined parts. Generally there are four (4) smaller pistons and two (2) larger pistons. The two small pistons are placed in the leading edge of the caliper. If you will calculate the "area" of the two small pistons they equal the "area" of the larger piston. Spreading the force over a greater brake pad area allows for even pad wear. Normally the leading edge of the pad would wear before the trailing edge, By design the 2 smaller pistons are located in the leading edge. You should be aware that just because it is a 6 piston caliper it does not mean that it is better than a 4 piston caliper. Combined piston area and the area of the brake pad is directly related to force and overall stopping power.

OEM (floating) vs 4 piston (non-floating): Most of the brake kits currently being sold is the 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 the 4 piston caliper does not require as much pressure. The single piston caliper also requires more volume to work. The area of a 2-3/4" single piston caliper is 5.93 sq inches VS the area of two (2) pistons on a 4 piston design of 4.80 square inches. (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) 5.93 s.i. VS 4.80 s.i. 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.

Brake Pads: Think of stopping a spinng wheel with two (2) fingers vs five (5) fingers. More area equals greater friction. It is also important to know that the greater the mass (volume) the more material there is to absorb heat, as heat will glaze the pads and cause brake failure. All of this should be taken into consideration when purchasing calipers.

i.e. a.) person living on a hill vs no hills; b.) Lincoln vs Honda (weight of vehicle); c.) street vs racing (driving demand)

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 (6) 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.

The width (how thick) of the rotors should be determined by the demand of the bracking system. Greater mass will retain more heat build up, which holds the temperature down. Glazing of your brake pads is from extreme heat and that is what causes brake failures.

Solid rotors: Should never be used on a car weighing over 1,500 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.

Vented rotors: Factories and cheaper brake kits use the 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 highly 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? You would never see a one (1) piece rotor on a race car.

Floating rotors: Floating are generally used on race car. Instead of having a bolt hole these rotors have t-slots and they require a t-nuts and harden bolts to secure the rotor to the hat. This is the optimum rotor design, because it allow the rotor to expand and contract independently from the hat/hub. We recommend this rotor to be used on extreme application.

Scallop Rotors: Scallop rotors were originally designed for sprint cars to the would have less rotating mass. Now we use them for different race applications and show cars. They are the coolest looking rotor we make.

Two Piece Rotors: 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. For an example aluminum hub or hat 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 or hat 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.

Here are some important things to know when purchasing vented rotors:
1. Try to get the maximum diameter rotor that will fit inside the diameter of your wheels;
2. Check the vanes for maximum venting. The vanes should have nice clean corners to allow the air to flow.
3. Anything over 1" thick, 12" diameter and all racing applications should be balanced. This is important if you plan to drive your car over 100 MPH.
4. The thickness of the rotors should be based on your a.) weight of the vehicle; b.) braking requirements; c.) type of rotor
5. Under extreme use order floating rotors "stress relived"
6. Order slotted only for race conditions. Drilled is nice for the street, but will crack for that weekend warrior.

It would take a lot of time to explain the relationship the rotor diameter has on the braking force. To make things as simple as I can it basically is the relation of the old rotor size vs the new rotor size.

Example: No change in tire size, going from a 11” rotor to 13” rotor. The effective radius of the 11” with a 2” pad would be 9” and the 13” rotor with the same pad width would be 11”. Or 11 ¸ 9 = 1.22 or 22% more efficient.

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 applies 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 reservior master cylinder (tandem 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. The earlier master cylinder had built in residual valves for the drum brake systems. 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 with built in residual valve(s) 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.

Most 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.

The size of the master cylinder reservoirs is directly related to the caliper piston sizes and the thickness of the pads. Standard master cylinders use a reservoir that is anywhere from 8 to 14 oz. The capacity of the reservoir is figured by the maximum use age of the caliper and the brake pads. Here is how you calculate the brake fluid requirement for your brake system.

I.E. Typical 4 piston fixed caliper system with 1.75" diameter piston in front and 1.38" diameter pistons in back have a volume requirement of 10.34 oz:

Front Calipers: 4 Piston Design 1.75" diameter pistons, uses 0.600" thick pads;
0.875" radius x 0.875" radius x 3.14 = 2.40 square inches per piston;
2.40 si x 4 piston caliper = 9.60 square inches per caliper;
9.60 si x 2 front calipers = 19.20 square inches;
19.20 si x 0.600" thick pads = 11.52 cubic inches front 2 calipers.

Rear Calipers: 4 Piston Design 1.38" diameter pistons, uses 0.600" thick pads
0.69" radius x 0.69" radius x 3.14 = 1.49 square inches per piston;
1.49 si x 4 piston caliper = 5.96 square inches per caliper;
5.96 si x 2 rear calipers = 11.92 square inches;
11.92 si x 0.600" thick pads = 7.15 cubic inches back 2 calipers.

11.52 cubic inches (front) + 7.15 cubic inches (back) = 18.67 cubic inches;
Conversion rate 1 oz = 1.8047 cubic inches
18.67 cubic inches ÷ 1.8047 = 10.34 oz. minimum brake fluid required for the reservoir.

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 or 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 is a cable connected to one end of the balance bar and a knob in the drivers compartment on the other end. This allows the driver to make adjustments as the condition of his brakes and road condition changes. The balance bar also eliminates the need for a proportional valve. On certain applications a remote reservoir(s) are used, in these applications 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 allows 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. 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 gives 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.

When calculating the output pressure of each master cylinder you can not say that applied pressure is “shared” equally between the two (2) master cylinders. If the two master cylinders did not have a balance bar between them and the application of force was always equally distributed this statement would be true. The balance bar allows the applied pressure to be distributed unequally.

Example:

6:1 ratio pedal assembly
¾" master cylinders
Applied force of 100 pounds with your foot

The formula shows that this combination produces 1359 psi, however if you apply the 100 pounds of force to both of them equally it will only produce 50 percent or 679.5 psi.

What the balance bar allows you to do is apply 65% of the force to the front and 35% to the rear so the actual output pressures would be 883 & 475 psi.

This is how you are able to obtain maximum braking with the same amount of applied force.

When you are using a tandem master cylinder (OEM type inline bore) the output pressure is equal in both ports and the only way to reduce the pressure to the rear braking system is through metering (distribution block, combination valve or engineering in the master cylinder) or proportional valve. This works fine when you have more than enough pressure with a power booster but when you are using a manual master cylinder this energy is “wasted”.

The easiest way to test this "wasted energy" is to apply 100 uniform pounds of pressure to a 6:1 pedal ratio and measure the pressure at the front calipers and the rear calipers with a pressure gauge. You will find that you will not have 763 psi you will have a reduced amount directly related to your proportioning or reduced pressure in the rear. If you reduce the pressure in the rear by 15% the out pressure in the front system will only have 648 psi at the gauge. The 648 psi is not taking into account "Friction Lost". Friction Lost is the amount of pressure lost from length of travel and the size of the piping.

The newer designed firewall mount is the optimum method to supply calipers with brake fluid and can be adapted to your car without replacing your stock pedals. The Bal-Bar™Assembly puts the balance bar on your stock pedal, the 4 way firewall brackets allow the mounting of two master cylinder in almost every model vehicle. The best thing it only takes about 16 square inches of space in the engine compartment. We have taken the 30 year old technology of dual master cylinders and applied it to your stock pedal. We used two 3/4 master cylinders with an out put pressure of 1359 psi each. The deletion of the power booster eliminates the need for vacuum.

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 calculating 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.

If you are upgrading you brake system check the following about your master cylinder:

1. Check your vacuum before you buy anything. If you do not have more than 17 inches of vac. You need to rethink what braking system will work. OEM disc will not work because the require a booster. Go back and read about calipers.
2. If you can use a booster the correct master cylinder used with a booster will generally have a dimple in the back of the bore. This dimple will mate to the flush mounted rod on the booster.
3. If don't have enough vacuum , use the dual master cylinders (side by side) set up or the smallest diameter master cylinder that will give you both pressure and volume.
4. On installation be sure to check for a small amount of free play so the master cylinder is not preloaded.

The easiest way to think of the master cylinder bore is to compare it to a garden hose. The smaller the bore the more pressure. Like putting your thumb over the end of the garden hose, small hole more pressure, but don't run out of water! Make sure you have enough brake fluid to service the calipers your are using in front. Floating vs Fixed.

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.

The dual diaphragm 7” has a total area of over 76 square inches about the same as a 10” single. This doubles the vacuum assist of the single diaphragm. I would recommend anyone using the older single diaphragm to update to this booster.

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 or take more than two pump on the brake pedal? No vacuum and no brakes!

The newest thing is to install a hydrostatic system driven by the power steering pump. This is an after market version of the systems often found in one (1) ton pick-ups. I had a 1 ton crew cab that was used to pull a 48 foot 5th wheel trailer with a gross weight of 21,000 pound. I once lost a serpentine belt descending off Mt Ashland (Oregon) on I-5. No brakes! I was luck enough to have 3 miles of straight highway. It is a good thing I had good trailer brakes or I might not be writing this article.

It basically boils down to the fact that there are all sorts of supplemental equipment to assist your lack of vacuum, but if you keep everything SIMPLE you will not need them. Someone once said, “keep it simple stupid”.

That is why race cars depend on manual master cylinders.

This is the formula to figure your output booster pressure.

Force in pounds = (Diaphragm area in square inches) x (manifold vacuum in inches Hg) x ½

Example: 7” single diaphragm booster with 17 inches of vacuum. 3.5” x 3.5” x 3.14 = 38.465 square inches x 17 inches of vacuum x 50% = 326.95 psi

Here is quick table for your reference;

Maximum Diaphragm Force in Pounds
Inches Hg
7 inch
9 inch
10 inch
15
289
477
589
16
308
509
628
17
327
541
668
18
346
573
707
19
366
604
746
20
385
636
785

Of course this it based on the booster being 100% efficient, a good rule of thumb would be 80 to 85 percent efficient.

Booster Master Cylinder Combinations: When ever possible you should always replace the existing booster with another one of similar size and design. Engineers designed the booster/master cylinder based on the weight, tire size, calipers, rotors, etc. However when you change anything on your vehicle it effects other parts that was engineered to be compatible with the part you changed.

When choosing a booster/master cylinder take all the factors into consideration.
1. Do I need a booster? Who will be driving the vehicle? How big is that person? The bigger the person the more applied force there is available to the brake pedal. It is much easier for a 250 pound person to apply 150-200 pounds of applied force to the brake pedal than a person weighing 110 pounds.
2. Location of the booster? Valve covers, shock towers, floor boards, clutch linkage are some restriction that will restrict the size of the booster. The last thing you want to do is remove your booster to take your chrome tall valve covers off.
3. Amount of vacuum? If possible measure the available vacuum. 18-20 inches no problem, 16 inches marginal, 12 inches or less forget it. Use the dual master cylinders setup.
4. You will need to calculate the combined pressure of the booster and master cylinder so the combined pressure is about 1,000 psi. Of course we would want to put the smallest bore master cylinder with the booster we have chosen. If if you choose too small of a bore, you will run out of brake fluid or you might have too much out put pressure causing your pedal to feel spongy or to sensitive.

Brake Lines (Hard 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 to a minimum. 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. In most applications the smaller 3/16" line will fit the need of 90% 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. Use .025 or .035 stainless lines and single flare at 37 degrees with AN fittings.

I can not say enough about having good tools for the job. Beg, borrow or buy a good set of Ridgid flaring and bending tools. After you have used a cheaper flaring tool you will know what I mean.

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.

Some day the Cool-Flow™System will be mandated on all vehicles over 3,500 pounds. This system is designed to recycle the brake fluid and reduce the temperatures of all brake components. This is a Patent-pending product that will soon be available for the public. (dso 5/2010)

DOT Approved: There is no such thing as DOT (Department of Transportation) approved brake kits. They do not certify or approve components. When a brake manufacturer or seller claims their product is "DOT approved", the claim is false.
The only components regulated by DOT are:
1. Brake hoses
2. Brake fluid
3. Tires
4. Exterior Lamps
(A manufacturer using the DOT symbol on the above products signifies that the manufacturer has "self certified" that the product meets FMVSS standards) New vehicles must comply with certain government standards. The controlling document for standards is the "Federal Motor Vehicle Safety Standard", or FMVSS. Brake performance is covered under FMVSS sections 105 and 135. Vehicle manufacturers certify, either through self-certification or independent certification, that their vehicles comply with the standards. Brake components, like many other vehicle components, are generally the way they are as a result of performance, cost, manufacturer preference, and sometimes, tradition! Materials, features (anti-rattle, anti-squeal, dust boots, fixed mount, sliding mount, piston count, etc.) and finish are not dictated by DOT

Always use DOT flexible brake lines. DOT approved lines have a surge band around the crimped fitting. This is important because it help prevent the fitting from working loose during the surging of the brake fluid. This is commonly over looked, just because they often come "free". Non-DOT approved lines should not go on a street driven car. As a shop or mechanic you can not afford to have someone sue you for your negligence.

Brake Pedals: The number one cause of a very hard brake pedal is pedal ratio. There isn't a day that goes by I solve someone's brake problem by tell him his pedal ratio is probably wrong in his street rod. To many times a product get copied by another person or manufacturer that does not understand the engineering of the product he is copying. I always say there are people that have good mechanical skills, there are engineers and then there is the person thinking of the all mighty dollar. We need a little of each in our industry, the engineer can not make the part, the welder should not engineer the part without knowing the why and what for and the copy cat should not make the part without having knowledge of the original design principle. Everything would be fine if things were copied exactly as the original, but sometime things get modified. I have seen a few pedals where someone have remade the upper length of the pedal shorter or the lower link longer. This changes the pedal ratio and it has a direct effect on the output pressure of the master cylinder. See formula for master cylinder output.

Formula for Pedal Ratio:

Pedal ratio is the ratio of leverage you brake pedal applies to the master cylinder. To determine the pedal ratio you need to measure the height of the pedal to the pivot point then divided the measurement of the pivot point to the lower arm that controls your rod to the master cylinder.

A = height of pedal
B = center to center measurement of the lower arm
C = pedal ratio
A divided by B equals C
Or example 9" divided by 1.5" equal 6 to 1 ratio.
Pedal Ratio Drawing Brake Article by Dean Oshiro


If you apply 100 pounds of pressure to the brake pedal, 100 pounds X (6 to 1) = 600 pounds of pressure. So, if the brake pedal has been modified from its' original design the pedal ratio is effected drastically. You can now see the pedal ratio is a "multiplier" of the pressure you apply with your foot, because this is the leverage that is applied to the master cylinder.

Now, take this same formula and substitute 2" instead of 1.5" you end up with a 4.5 to 1 ratio. Multiply 4.5 times the 100 pounds of applied pressure and you get 450 pounds instead of 600 pound. That half inch cost you 25 percent of your braking power. The same thing applies when you shorten the upper measurement.

Factory cars generally have two (2) pedal ratios , one for manual brakes and one for power brakes. You will find manual pedals with ratios from 5:1 to 6.5:1 and power pedals 4:1 to 5:1. A good example of this would be the 68 Mustang uses a longer brake pedal with a power booster. This pedal mounts about 2.5” above the manual pedal setup. The longer pedal reduces the pedal ratio. If you did not change the pedal your brakes would be to sensitive, because there would be to much pressure applied to quickly. GM cars have two holes on the pedal, when a power booster is used the brackets are at an angle so the rod will point to the lower hole. Installing the rod in the wrong hole will cause damage to the booster.

Proportional Valves: Proportional valves are used to regulate the pressure in the line. A proportional valve 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.

You NASCAR car fans can relate to over braking by the rear wheels. Remember the drivers on the short tracks that forgot to change the balance bar before ending the pits? Yes, they did spun out.

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.

You may need a residual valve on a firewall mounted master cylinder, if the location of the master cylinder is close to the level of the calipers or if you are having trouble bleeding your brake system. This will sometimes happen when you run small and large tires and your chassis is at an angle.

Distribution Blocks or Combination Valves: One of the biggest misconceptions is the distribution block or combination valve. Almost every factory car has one. This usually serves as a metering block to adjust the proportioning to the rear brakes, as a "T" fitting for your front left and right front brake lines and brake light warning switch. What people fail to understand is that each car is "engineering" for a specific distribution block based on weight, braking characteristics and tires. So generally most factory cars have different blocks.

Ask yourself this. How can one distribution block be engineered for all applications? So, we have this 23T with tiny tires in front and big tires in the back, we have a 57 Caddy and a 57 Chevy pick up. Do you really think the braking is the same for all three vehicles?

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. 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.

Sometime in the near future you will no longer have to worry about contamination of brake fluid. The Cool-Flow™ System will someday be mandated on all vehicles. This is our answer to reducing the temperature of the rotors and thereby control tire pressure in the middle of a race. The Cool-Flow™ System will revolutionize the way we thing about brake systems.

This was republished to update you on Brake Systems. There is two things that will never change physics and math. Nobody can redesign a brake system and change physics and math, you can not reinvent the wheel. If anyone can prove to you anything in this Brake Article© with a formula, then they are correct. Engineers have been reading this Brake Article© since 1994. I can always tell an engineer, they ask black and white questions. They want a black and white answer. I hope someday reading this might save someone's life.

The Brake Article© by Dean S. Oshiro

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