Brake-System Basics

April 2007

Which is More Important-Going Fast or Stopping Quickly?

Text and Photography by Jim Smart

We place emphasis on going faster and making more power, but how often do we address safe and effective stopping? Not often enough. We don’t need to say this, but we will anyway-stopping is more important than all the horsepower and torque on the planet. Bling and speed aren’t worth a flip when your investment is all smashed up because you couldn’t stop in a safe distance.

Have you thought about your brakes lately?

Brakes just aren’t a priority in the “fun” department when it’s time to spend money on a classic Ford. We like speed equipment, and we like the bling that makes engine compartments, bodies, and interiors look sharp. Money wasted is the money you don’t spend on good brakes.

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Brakes tend to be a mystery for most of us because there are so many options available, and most of us are baffled as to how they work. What kind of braking system do you need? What type of friction material-organic, metallic, semimetallic, or carbon metallic? What size rotors? Slotted or cross-drilled? How many pistons in each caliper? Disc or drum? What about master-cylinder size and type? Power or manual brakes? Mineral-based or silicone brake fluid? Do you need a proportioning valve? Rubber or braided hoses? Man, it gets complicated.

To choose the right brakes, you need a basic understanding of braking systems. Hydraulic brakes date back to the beginning of the 20th century. They didn’t become standard equipment on Fords until the ’30s as power and speed increased respectively. Although this may sound like boring high-school physics, braking is nothing more than the absorption of kinetic energy (matter in motion), which is just a fancy term for friction bringing your Ford to a stop. Pads squeeze rotors and linings rub against drums, which turns linear motion (kinetic energy and friction) into heat.

The Necessity of Stopping

How well your Ford stops depends on its stopping capacity. Capacity comes from having enough hydraulics and plenty of friction. Power to apply pads to rotors and shoes to drums comes from having enough hydro-mechanical advantage-simply put, plenty of leverage under the dashboard coupled with just the right master-cylinder bore/piston size to brake comfortably. We don’t want too much braking or too little. We want brakes to become an extension of our minds, much as we would from engine, transmission, and handling performance.

Hydraulics

We could not have achieved the kind of stopping power we have today without hydraulics. It has been said you could move the world via the power of hydraulics-putting fluid to work under pressure. Hydraulics enable us to do what is physically impossible-steer big construction equipment, move heavy loads, vector huge jets about the sky, run elevators, lift cars, press parts together, pry components apart, and dozens of other uses. Hydraulic clutches use hydraulic pressure to release the clutch. That little bottle jack used to put your Ford on jackstands is the application of hydraulics. Turning a corner in your power-steering- equipped Ford or Merc is applied hydraulics. The examples are endless.

When you step on the brake pedal, you are applying physical energy to a master cylinder to generate hydraulic power. Pedal pressure becomes linear motion-like a doctor using a hypodermic needle to inject medication into your body. A hypodermic syringe is hydraulics-moving fluid under pressure- just like we do with a brake pedal. The master cylinder consists of a cylinder, a piston, and a rod; the rod is tied to a brake pedal. When you step on the brake pedal, you push a piston in a sealed cylinder full of fluid. Fluid travels through steel lines to your brakes.

On vehicles built prior to 1967, a single-reservoir master cylinder applied pressure to all four brakes. From 1967-up, it became federally mandated to have a dual-braking system- with a two-reservoir, separated-bore master cylinder that divides front and rear braking systems. A dual-braking system enables you to have some braking pressure should one of the systems fail.

Braking systems rarely complain, considering what we ask of them. Did you know you’re supposed to flush and bleed your brake system every one to two years? Doing so removes all air and moisture from the system. Air gives you a spongy pedal. Moisture boils during hard braking, creating air pockets, pedal hammering, and ineffective braking. Fluid cannot be compressed, which is why it is effective for hydraulics. A spongy pedal happens because air can be compressed. Solid brake fluid makes a pedal hard because fluid cannot be compressed. A hard pedal means solid fluid cohesion (contact) between your foot and all four brakes.

Air and moisture get into brake-system hydraulics through steel lines, master-cylinder castings, and reinforced rubber hoses because all of these components are porous. They soak up air and moisture from the atmosphere. If you live in a damp location, the problem becomes even worse. This is why regular, preventative brake maintenance is so important.

When moisture and air collect in brake lines, the result is corrosion, pitting, and eventually, line failure. Old, pitted brake lines must be replaced. You can fabricate them yourself with proper tools and procedure, or you can order a set of CNC-manufactured brake lines and parts. Classic Tube offers bolt-on kits, or if you have a Ford or Mercury that isn’t mainstream, the company will take your existing brake lines and custom fabricate a set from your lines. The choice is yours.

Brake Fluid

There are two basic types of brake fluid: mineral-based (DOT 3 and 4) and silicone (DOT 5). Mineral-based fluids seem to perform best because they help maintain a hard pedal. The downsides to mineral-based fluids are moisture absorption, contamination, and paint damage if spilled. Even the tiniest drop of mineral-based fluid will lift paint.

Synthetic, mineral-based brake fluid is DOT 4 spec, which can sometimes give the impression it is unique. However, synthetic, mineral-based brake fluid is more resistant to moisture and other contaminates. It also has a higher boiling point, which makes it more effective during hard braking.

Silicone brake fluid doesn’t absorb moisture. It stands up to the punishment of hard braking because it has a much higher boiling point. Silicone brake fluid doesn’t damage paint either. However, it is slippery, nasty stuff. It also yields a spongy pedal with even the best bleeding procedures. Silicone brake fluid takes getting used to because the pedal is spongy compared to mineral brake fluid. If you’re going to change over to silicone brake fluid, it is best to begin with all-new components and seals.

Synthetic, mineral-based brake fluid (DOT 4) can be mixed with mineral (DOT 3) fluids without consequence. We suggest going to synthetic DOT 4 brake fluid when flushing and bleeding the brake system.

Brake Types

Most classic Fords and Mercs came from the factory with four-wheel drum brakes. Fewer still were power assisted. This means braking effectiveness was less than adequate when our old Fords were new. As drum brakes go, Ford’s were among the worst, even when they were new. Chrysler and General Motors had better drum brakes than Ford.

As the name implies, drum brakes are shaped like a drum, with linings (shoes) positioned inside to stop drum rotation. When you step on the brake pedal, the master cylinder applies hydraulic pressure to the wheel cylinders. Wheel cylinders move shoes outward into the spinning drums. Friction material contacts the drums’ inside surface.

Drum-brake performance hinges on lining condition, drum surface, and proper hydraulic function. Glazed linings and mirrored drums are ineffective. They won’t stop your Ford. Overheated drum brakes won’t stop your Ford. Wet linings won’t stop your Ford. Are you beginning to understand why drumbrake condition is so important to safety? Drum brakes aren’t as tolerant as disc brakes. Overall, disc brakes do a better job.

Disc brakes are nothing new. They came along early in the 20th century. Fords didn’t get optional disc brakes until the mid-‘ 60s. Mustangs didn’t get power disc brakes until 1967.

Ford has tried different approaches to disc brakes through the years. Early on, a four-piston design from Kelsey-Hayes was utilized- and effective-because it applied even pressure on both sides of the rotor. Beginning in 1968, Ford went to a single-piston, floating-caliper design used throughout the ’70s and ’80s. The four-piston design’s main shortcoming was sticking pistons-a problem solved by Stainless Steel Brakes Corporation during the ’80s, making four-piston disc brakes more user-friendly.

Ford’s decision to use a floating, single-piston caliper design was rooted in economics and quieter operation. Single-piston, Granada/Maverick-style disc brakes have been popular because they are so plentiful-with cheap, rebuildable cores out there for a song. Enthusiasts have looked to salvage yards for single-piston cores, making it easier to have front disc brakes.

The downside to single-piston front disc brakes is performance. They don’t perform as well as the four-piston guys because there is a single pressure point, less fluid volume, and less pad. This is why Stainless Steel Brakes went to its own four-piston disc brake kit a few years ago. If you study the Force 10 disc brakes, an innovation from Stainless Steel Brakes, it’s a simple, lightweight, four- or six-piston design to get you stopped. Other companies, like Baer, Wilwood, and JMC Motorsports, have time-proven four- and six-piston designs born of the need for serious braking efficiency in high-performance street and racing applications.

Rear disc brakes are a personal choice rooted in the kind of braking performance you desire. Believe it or not, rear drum brakes are as effective as disc brakes under most driving conditions. Going to rear disc brakes reduces and eliminates fade during hard braking. The downside to rear disc brakes is poor parking-brake performance. They just don’t hold well with a Mustang/ Falcon/Maverick/Comet handbrake assembly activating them.

The master cylinder applies hydraulic pressure to the brakes. When you step on the brake pedal, you force fluid under pressure to each of the four brakes. Because fluid cannot be compressed, it becomes the perfect medium to convert foot power to brake power. This is a single-reservoir master cylinder common in Fords prior to 1967.

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This is a large, single-reservoir master cylinder for front disc-brake use. A larger reservoir is needed to accommodate the demand of front disc brakes. Shown here is a disc-brake master cylinder with power booster. It must have been installed with a shoehorn because ’65-’66 Mustangs were never factory-equipped with power front-disc brakes.

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Beginning in 1967, Ford went to a dual-braking system for improved safety. A dual-braking system isolates front and rear systems. This ensures some braking should one of the two systems fail. Tandem pistons on a common cylinder work two systems separated midshaft. Shown here is a disc-brake master cylinder. The larger rear reservoir is for front disc brakes. This is the rule with all dual-braking systems-rear reservoir for front brakes and front reservoir for rear brakes.

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In the interest of safety, it’s good practice to switch over to a dual-braking system. With most Fords, this conversion is simple and can be accomplished in a day. Conversion kits are available from Trans Am Racing, Master Power, and Stainless Steel Brakes, to name a few.

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Shown here is the brake-differential pressure-distribution block for dual-braking systems. Centered in the block is a sliding piston and light switch. If pressure is lost in one system, the piston is forced toward the disabled side by brake pressure, illuminating the “BRAKE” light on the instrument cluster. The light will go out when brakes are bled after the repair.

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Hoses and lines: What type?

There are two basic types of brake hose-rubber and braided. Reinforced rubber hoses are what you see from the factory. Braided hoses are super reinforced hoses with braided stainless steel outer linings. Because they are stronger and donít give as much as reinforced rubber hoses, they make your brake pedal even harder. Unless you are hell-bent to have original-equipment-style, reinforced rubber hoses, we suggest the use of stainless-braided brake hoses for best results.

When it comes to brake lines, you have two option-galvanized steel and stainless steel. Galvanized lines are your best choice when it comes to ease of installation and an original equipment look. They bend easily and are easy to seat when itís time to tighten everything. Flared line end should be mated square on the fitting to achieve proper seating and a leak-tight union.

What makes stainless tubing particularly challenging is its hardness itís not easy to bend or seat. Even under the best circumstances, with exceptional flaring and perfect fit, stainless tubing tends to leak. Seasoned car builders tell us to be patient with stainless tubing when it does leak, loosen and retighten it, and make sure flare is seated squarely in the fitting. Give it an extra twist for good measure. Often, a drop of brake fluid on the threads will aid in tightening the fitting by acting as a thread lubricant. Donít overtighten and then watch the fitting for leakage. Donít forget to bleed the brakes.

One area that is overlooked all too often is fitting integrity. Lines leak due to poor flare and damaged fittings-the microscopic stuff we rarely pay attention to. If either contract surface is damaged or nicked in any way, you will not achieve a good seal. The smallest nick in the wrong place will cause to leak regardless how tight you make it.

Original-equipment, reinforced rubber hoses are terrific for concours restorations and those who prefer original equipment. Braided hoses afford you a stiffer brake pedal and improved reliability. The also look sharp.

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Steel brake lines must always be double-flared to withstand high braking pressures. Double-wall flares are mandatory at every union. While stainless steel brake lines look terrific, they are challenging to bend, flair, and seat. Expect stainless steel brake lines to leak the first time around. Loosen and then seat them again until the leaking stops. This is caused by the hardness of stainless steel lines, which need to be loosened and seated several times in order to help them seat – and seal.

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Drum brake function is easy to understand. The wheel cylinder is a simple, two-way hydraulic actuator that pushes linings outward to contact and stop the rotating drum. The front shoe has more lining than the rear shoe for better performance and smooth operation. Shown here are typical Ford intermediate drum brakes with sell-adjustors. Not all old Fords have self-adjusting brakes.

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When we remove the brake drum, it’s easy to see how antiquated drum brakes are. Drum brakes are prone to lade when hot or wet. In fact, when they get wet, they won’t stop the car at all. Drum brakes make an effective support system in back because they complement front discs in daily operation. They also make better parking brakes than discs.

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For the best performance, brake drums should be turned on a brake lathe when it’s time for new shoes. This enables the shoes to “bed” properly during break-in for a higher friction factor. More friction equals better braking.

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Brake performance always hinges on having properly functioning hydraulics. Wheel cylinders should be inspected for leakage with every brake job. Roll back the seal lips and inspect the wheel cylinder for brake fluid. If it’s wet, replace or rebuild it.

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There are bonded brake linings and there are riveted brake linings (shown). We suggest riveted linings because rivets carry away heat better, which reduces lade. The bonding material used in bonded linings has been known to fail, causing the lining to slip, leading to brake lockup or failure.

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Self-adjusting drum brakes are terrific in theory but generally don’t work as advertised. The best you can do is check the adjustor, cable, and spring for proper operation. The adjustor turns the star-wheel adjustor when you back up and apply the brakes. If you want to adjust the brakes-just back up repeatedly while pumping the brakes. If the self-adjustor is working properly, it will move the star-wheel adjustor and tighten the brakes.

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This is Kelsey-Hayes’ original four-piston front disc-brake design common on Fords prior to 1968. The four-piston design puts solid, even pressure on both sides of the rotor. It also yields more friction surface area, hence better braking. These brakes suffered from corrosion and slicking piston problems. Stainless Steel Brakes solved this problem with stainless steel components during the ’80s. Today, Stainless Steel Brakes has four-piston kits for those who want performance as well as an original-equipment look.

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Baer is another major player in the high-performance aftermarket-brake business. Baer Claws, as they are known, are available in a variety of rotor sizes and caliper types to meet the need.

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Extreme braking performance comes from monster disc brakes from Wilwood. This is a huge, six-piston disc brake sporting a cross-drilled, slotted rotor for superior heat and gas dissipation.

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Stainless Steel Brakes makes a Kelsey-Hayes-design four-piston, front-disc brake kit for classic Mustangs and other Ford compacts and intermediates. They can be installed on any V-8 drum-brake spindle.

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From one extreme to another-this is JMC Motorsports’ four-piston front-disc-brake conversion kit for classic Mustang and other classic Fords. It’s a bolt-on kit that can be installed in an afternoon. Just make sure it will fit inside your wheels.

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Drum Brakes Done Right

Likely the biggest problems behind drum-brake performance issues are inattention to detail and being a cheapskate about your brakes. Drum brakes are high maintenance and temperamental. They demand the best components and your closest attention. Whenever you rebuild drum brakes, start clean with new, high-quality components including springs and hardware, riveted linings, wheel cylinders, and new or resurfaced drums.

When you go cheap with used components, youíre asking for trouble. Drum-brake components last for one, maybe two brake jobs. Springs lose their tension. Hard parts wear out. Wheel cylinders develop leaks. Drums become too large internally. Drums should be machine turned by qualified personnel at every brake job and replaced at every other relining. Even, though inside drum dimensions are within limits, drum brakes perform their best when shoes travel the shortest distance.

The bottom line with drum brakes is this ñ never cut corners. Use the best components, riveted linings, and new drums when itís time for an overhaul. When you donít turn drums, shoes canít bed like they need to. Whenever you push drums to their legal limit, brakes will not perform their best. They will also make unwanted noise because the shoe itself will rub the drum, causing and annoying squeal. Remember: one turning to a drum, then toss it.

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What Are Power Brakes?

There are two basic types of power-brake systems ñ vacuum assist and hydroboost. Vacuum assist is most common, employing a chamber divided by a spring-loaded diaphragm. The engineís intake-manifold vacuum creates negative pressure (suction) on one side ñ the side nearest the master cylinder. The diaphragm is drawn toward negative pressure, which helps the driver apply pressure to the master cylinderís piston rod. Intake manifold vacuum helps the driver do the braking, easing pedal effort.

Hydroboost power brakes work like power steering. When you touch the brake pedal, you open a control valve that applies pressure to the master cylinder, easing pedal effort. Hydroboost isnít at the mercy of faltering intake-manifold vacuum when you have a hot cam. As long as the engine is running, hydroboost gives you power-brake assistance. Hydroboost pressure comes off the power-steering pump-even if your Ford doesnít have power steering.

Hydroboost power-brake units can be sourced a variety of places, including Power Brake Service (www.powerbrakesonline.com. (800) 504-1060) and Hydratech Braking Systems (www.hydrabraking.com, (586) 427-6970). Hoses can be fabricated at a hydraulic or air-conditioning shop. Mustangs from 1996 to 2004 with SOHC and DOHC V-8s have hydroboost power brakes. So did some Lincolns and Mercurys. These are good sources for the units if you decide to fabricate your own setup. If you canít find one in a salvage yard, order one from your favorite auto-parts store, and be prepared to pay the core charge.

Vacuum-assisted power brakes donít do much for actual braking. They provide braking assistance and reduced pedal effort. Your engineís intake-manifold vacuum is the power boosterís source for negative pressure. If you have a radical camshaft profile and insufficient manifold vacuum, you need an electric vacuum pump. Another option is hydroboost power brakes when vacuum sources become nil.

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This exploded view of a ’65-’66 Mustang power-brake booster shows the diaphragm, return spring, bellows, and more. When you touch the brake pedal, intake-manifold vacuum takes over and assists braking effort. Assistance comes from one side of the diaphragm because we create suction (negative air pressure) while keeping normal atmospheric pressure on the other side.

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Brake-Bleeding Technique

Through the years, we have seen a lot of different approaches to brake bleeding. Most of us subscribe to the shade-tree approach of having a buddy work the pedal while we work the bleeders.

There are also tools that enable you to bleed brakes by yourself. One is a pneumatic-pressure bleeder that places air pressure on top of the master cylinderís brake fluid, pushing fluid and air out through bleeders. Another tool uses a hand-pump method, pushing fluid and air out through bleeders. Another tool uses a hand-pump method, pushing fluid and air back through the master cylinder. Both systems are quite affordable.

Bleeding the master cylinder can be done two ways ñ on the bench or in the car. Bench bleeding is preferred because it is the most foolproof method. On the bench, you can see whatís going on. Thereís less chance of jamming the piston and better odds of getting the air out. In the car, you need to pay close attention to pedal travel. Donít push the pedal to the floor. Slowly step on the pedal while watching air bubble traffic. One all bubbles have stopped, you have successfully bled the master cylinder.

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Pressure bleeders and bleeders that mechanically push fluid and air out of the system enable you to bleed brakes by yourself.

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Choosing a Brake Pad

After the business of hydraulics is done, we have to create friction in order to soak up kinetic energy and stop the vehicle. Choosing the right brake pad boils down to what you want from your brakes. No one wants brakes that are unpredictable. You want to be confident of your brakes and know their limitations. Few things are worse than learning those limitations when you’re out of control. What’s more, it isn’t just about stopping power, but driving comfort and noise levels as well. None of us wants noisy brakes on a daily basis because we didn’t choose the right pads.

Organic pads are typically what we find as original equipment in most classic Ford applications. Semimetallic brake pads, as their name implies, have a percentage of metal in the pad for improved performance and heat resistance. The more metal there is in the pad, the more effective it will be. However, with more metal comes more noise and brake dust.

In recent years, we have seen more exotic brake pads and shoes for high-performance use. Carbon-metallic and ceramic pads are used in racing applications. Don’t kid yourself-these materials are unacceptable for street use and will ruin brake rotors because they’re engineered for the primary purpose-racing. High-performance brake pads do best when hot during the extremes of racing. In street use, they never get hot enough to be really effective. In street use, they make a lot of noise and yield an extremely hard pedal.

With all of the issues surrounding ceramic and carbon-metallic in mind, it is important to choose the right brake pads and shoes for the street. Organic brake pads tend to be the most affordable material for street use. They are also the quietest because they absorb noise, vibration, and heat adequately in street use. They are not adequate for racing. Semimetallic pads do a better stopping job, but they are noisier.

We have seen our share of bonded pads and shoes and riveted pads and shoes. Riveted linings get rid of heat better than bonded. Heat is carried away via the rivets. Less heat is a factor in better braking. A good rule is to go with whatever Ford used. Most classic Fords and Mercs had riveted linings from the factory. Bonded linings didn’t come along until the ’70s. We’re convinced bonded linings are quieter. Ultimately, the choice is yours.

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Rear disc brakes are a personal choice rooted in the kind of braking performance you desire. Believe it or not, rear drum brakes are as effective as disc brakes under most driving conditions. Going to rear disc brakes reduces and eliminates fade during hard braking. The downside to rear disc brakes is poor parking-brake performance. They just don’t hold well with a Mustang/Faclcon/Maverick/Comet handbrake assembly activating them.

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Slotted rotors came along a few years ago as an alternative to cross-drilling. Slots carry away heat and gases, which puts more friction material in contact with rotors. The result is better braking performance. Performance also depends on the choice of friction material.