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The Hummer Knowledge Base
Date: Sun, 29 Jun 1997 13:56:12 -0700
Subject: HML: Brake info - Part 1
I have collected info about brakes from a number of sources on the net and emails sent to me. I don't have any idea where some of this came from, so I can't give proper credit where credit is due, sorry. Some of the info is for different vehicles, but the info is useful, read it anyway and you might learn something.
When we hear that high-pitched squeal coming from your brakes, it often causes them to turn and look at you as if you were scraping your fingernails across a blackboard. It's a sure sign that it's time to replace your truck's brakes. Replacing disc pads and drum shoes is a routine maintenance procedure, yet many truck enthusiasts don't see it as an integral part of their truck's overall performance. The better your braking system, the quicker you will stop, and the longer the interval will be between pad and shoe changes.
It stands to reason that if you want to improve your brakes' performance, you simply have to add a set of higher friction pads and shoes. This is true to an extent, but it is also something of a Catch-22. The more friction that is applied to your factory brake system, the more heat it creates. And excessive heat causes brake fade and shortens the life of your pads and rotors. Consequently, enthusiasts should take more care in choosing brake shoes and pads, rather than walking into the nearest auto parts store and purchasing whatever pads are on sale.
With the exception of some older vehicles, most sport trucks use disc brakes in front and large drum brakes in the rear. The discs are what do most of the stopping and they affect the overall performance of your truck. Manufacturers of disc pads and drum shoes have their own "formulas" for making friction materials. Many, how-ever, use common compounds that include traces of titanium, graphite, iron powder and organic fibers. Obviously some blends work better than others, but for the most part, the automotive industry has all but eliminated the use of asbestos. In fact, many OEM auto and truck manufacturers now use some form of semi-metallic compounds.
Carbon metallic blends have been the most successful at increasing stopping power with higher levels of heat dissipation. The carbon matrix acts as a heat absorbing material that essentially allows the pads and your brake rotors to run much cooler. Furthermore, carbon metallic pads are more durable and have a longer life span than conventional pads. Some manufacturers, especially in late-model GM and full size Ford trucks, already use carbon metallic pads as OEM parts.
Many consider the carbon-kevlar matrix pads to be the best pad compound available for street-driven cars and trucks. This mixture allows for much higher friction and improved stopping power, yet provides excellent heat dissipation and does not cause excessive wear to rotors or drums. Furthermore, the carbon-keviar matrix works well when the pads are cold and requires less pedal effort.
Whichever pads you choose for your next brake job, make sure they are made by a reputable company and that the front disc pads are bonded to the backing plate. With the exception of rear shoes, riveted front disc brake pads have been known to shear away under severe stopping pressure on heavier full-size trucks. For this reason, most pad manufacturers have discontinued their use. Also, take the time to break in new pads and rotors. Proper break-in procedures will extend brake life and performance.
10 Tips For Better Brake Performance
From countless hours of driving experience, testing various brake systems and advice from brake experts and manufacturers, we've compiled a list of tips for improving your truck's brake system.
Brakes are one of those things on a car that people think is really complicated. Actually they aren't really. Basically, you are just compressing some liquid against a piston which is squeezing a couple of pads against the rotor. It's just about as simple as that. Those of you with ABS have some neat stuff in between but essentially it all works the same.
In order to slow down we must generate heat. This is one of the few times that we LIKE friction. Friction is good. The more friction, the faster we can slow down, assuming the tires have some traction of course. There are two reasons why one would like to upgrade their brakes. One, you would like to be able to stop shorter and or faster. Two, you want to get rid of this annoying sinking pedal known as brake fade.
There are two kinds of brake fade. The first is pad fade. This is caused by the brake pads giving off gasses and fumes as they heat up. The gas prevents full contact between the rotor and the pad, something similar to hydroplaning. In order to get rid of this type of fade, cross-drilled rotors or slotted rotors are needed. The holes in the rotor give the gasses a place to go and also serves to evacuate water. Sometimes you might have noticed after hitting a puddle, the brakes are not as efficient. This is because the water first has to be boiled or thrown off the braking surface. In my limited experience you won't notice the difference between cross-drilled/slotted rotors and regular rotors on the street. The only time pad fade really comes into play is when they get really hot, like stopping from 100-0 mph. On the track you will notice the difference because you use the brakes more heavily. So unless you have a REALLY heavy foot and drive in the city only, don't waste your money on the rotors.
Fluid fade is the second type of brake fade. This is caused by repeated heavy braking which heats up the brake fluid in the calipers and cause it boil and then turn into a gas. A gas can be easily compressed which causes a sinking pedal and decreased braking power. The only way to get rid of fluid fade is to use a fluid with a higher boiling point and to avoid excess heat.
Then there is the brake pad which really takes the beating. The stock pads that come on our cars are semi-metallic up front and organic in the rear. These pads are usually softer than most performance pads and are used in order to satisfy certain government regulations on required pedal pressure. Organic used to composed of asbestos but I don't know what they're made of now. Semi-metallic pads have about 40-50% metal in them. Metallic pads carry about 70%. The more metal the pad has, the more friction it has. Because these pads have real metal in them sometimes they will squeal and make horrible noises if not installed right. Usually some nice gooey anti-squeal compound will take care of it. But sometimes they will still slightly squeal or grind. This is normal. However use your own judgment. If it squeals really bad, then check out your brakes. Almost all pads have a wear indicator which is just a piece of metal that scraps the rotor to make a horrific noise. This is to let you know that you are about to run out of brakes.
Then we have the exotic pads. These things can be made of metal, carbon, kevlar, ceramic and any combination thereof. Usually these are best used for the track because they require a warm-up time to become effective. In order words, the pads have to heat up before they reach peak efficiency. This is not "cool" when you want to stop for the red-light a block in front of you. However, many companies have several different formulations which may be able to allow you to run them on the street and track safely. Usually these pads dust a lot, squeal a little more than normal, and wear varies greatly. Sometimes they will last forever, and sometimes they will only last for one track event. It all depends on their formulation.
Date sent: Sun, 29 Jun 1997 13:56:05 -0700
Z Car Brake Systems and Modifications an excerpt from the ZCCW Newsletter Source: Steve Golik of the Smoky Mountain Z Car Club
The Datsun/Nissan Z/ZX car remains one of the most frequently owner-modified sports cars ever produced. Typically these modifications involve increasing the output of the engine or improving the handling of the car. Both basically have the same end result: making the car go faster. Often overlooked are the brakes. I am a firm believer in that a vehicle that is faster than stock should also be able to stop just as good as stock-if not better.
All brake systems use friction to stop the vehicle. The kinetic energy of the moving car is converted to another form of energy, mainly heat. Recall from basic physics that the kinetic energy of a moving object is proportional to the mass (or weight) of that object and the square of the speed of that object. When the speed is doubled, four times the kinetic energy is developed. However, moving automobiles also have rotating parts namely wheels, tires, axles, drive-lines and even brake rotors and drums. Strictly speaking, the additional kinetic energy stored in each of these rotating parts must also be absorbed in the brakes.
The brake system must perform the following tasks: It must be massive enough to absorb the heat produced by braking. It must capable of dissipating this heat.
Ideally a braking system should absorb most of the heat in its components and not at the tire/road surface interface. Think of a wheel that is locked during hard braking. All of the energy must be dissipated by the friction of the tire against the road surface.
As braking components absorb heat, the temperature of these parts increases. What determines the amount of temperature rise is the mass (or weight) of these components. Larger brake parts will have a smaller temperature rise than smaller components for the same amount of heat absorbed. This is why large road vehicles and race cars have large brake rotors and calipers (or drums). They have more kinetic energy to be absorbed as heat by the braking system. This is one of the reasons that high performance sports cars utilize large diameter wheels. Larger rotors and calipers can then be fitted more easily.
The maximum temperature of the brakes must be controlled to prevent the complete destruction of the brakes or structural failure of the mounting brackets. However, long before this will happen the brakes will fade or the brake fluid will boil. If the brake system is properly designed the only factor determining the stopping limit is the load on the tires and the adhesion between it and the road. The "60 to 0" stopping distance tests often featured in automotive literature are not a good relative measure of a braking system since this distance is mainly determined by the weight of a vehicle, the grip of the tires it is using, and the condition of the road surface. It can be, however, used for evaluating changes made to the braking system of a single vehicle.
A moving vehicle's inertia force acts at its center of gravity point. All the inertia forces on the individual parts of the car added together are the same as a single inertia force acting at its center of gravity. Since a car's center of gravity is above the road surface, the inertia force from braking tries to load the front tires and unload the rear tires. This effect is called weight transfer. Weight added to the front tires is subtracted from the rear tires. The total weight of the car does not change.
Because weight transfer loads the front tires, additional friction forces are developed by the front tires (before they skid). To counteract this force, the front brakes must produce more braking force than the rear brakes. This is why the front brakes on cars are typically larger than the rear brakes: they must dissipate more energy.
Greatest vehicle deceleration occurs when both front and rear tires reach their traction limit. Tires develop maximum grip just before they lock. A locked, skidding tire actually has less grip.
One complication affecting weight transfer is that it depends on the degree of braking. This dynamic loading/unloading of the tires will cause the rear wheels to lock before the front during hard braking. For maximum deceleration of a vehicle on a given surface, all wheels must be on the point of maximum grip. However, the point of wheel lock is determined by the tire load, adhesion between the tire and the road surface and the condition of the road surface. A way to cope with the changing conditions affecting wheel lock is to fit an anti-lock system to the vehicle.
Anti-lock brake systems work on the principle of measuring the deceleration of a sensed wheel and if it is above a certain value, that is, if the wheel is at the point of locking, the braking force to that wheel is reduced. The wheel then speeds up and then the braking force is re-applied and the cycle repeats. Anti-lock devices give improved stability during emergency braking and will help to give the shortest braking distance without loss of control over a wider range of road surface conditions.
The front brakes on all Z cars are disc brakes. Disc brakes have several advantages over drum brakes, primarily in regards to cooling. Disc brakes have increased resistance to fade because the friction surfaces are exposed to air. The rotors also have a larger swept area than a drum brake so there is more surface area. This allows more heat to be dissipated. The rotor expands with heat, moving closer to the pad surface, unlike drum brakes which when heated move away from the brake shoe. The piston seal automatically adjusts the pad-to-rotor clearance. Disc brakes do not have the servo action that drum brakes do so they are not as sensitive to changes in pad friction.
There are two types of disc calipers: 'fixed' and 'floating'. The fixed type was used on the 1970-78 and the 1990 and later Z cars. Fixed calipers have either two or four pistons that push on the pads. A fixed caliper is more rigid and usually has more mass so it can absorb more heat. Fixed calipers have more balanced pad wear than floating caliper designs.
The floating type caliper uses one or two pistons on the inboard side only. The hydraulic pressure forcing the piston and inboard pad towards the rotor also forces the piston housing in the opposite direction which forces the outboard pad against the rotor. There are advantages and disadvantages to using floating calipers. A floating caliper has the piston and fluid chamber inboard so it can be cooled by the air flow better so there is more margin for fluid boiling. There is also less potential to leak. Wheel packaging is better, especially for large offsets (front wheel drive vehicles).
Some disadvantages of floating calipers are pads that may wear at an angle because of the less rigid mounting and increased tendency for "squealing".
Rotors (or discs) come in two varieties: solid and vented. Vented rotors feature internal passages through which air can circulate, and are superior to solid discs in terms of heat dissipation. Vented rotors are also more massive and can absorb larger amounts of heat. Vented rotors are the optimal solution for front brakes.
The first generation Z car (1970-78) had drum brakes at rear, this being common practice on passenger cars built before 1980, as drum brakes do allow a relatively simple hand brake mechanism to be used. The arrangement used on the Z cars is referred to as a "leading-trailing" type of drum brake.
Because the friction surfaces are inside the drum, air circulation is poor so drum brakes suffer more from fade than disc brakes do. Drum brakes can be designed with some degree of 'self-actuation' or servo action which makes them nonlinear, and therefore more sensitive to changes to the friction coefficient of the brake shoe.
Drum brakes require adjustment of the shoe-to-drum surface distance as wear occurs. Fortunately, in Z cars, the rear drums brakes automatically adjust themselves whenever the parking brake in engaged.
Lining Materials (Pads and Shoes)
The coefficient of friction (u) between the lining material and the rotor (or drum) is defined as ratio of the force applied to the pad (or shoe) to the friction force developed. The higher the friction coefficient, the higher the friction force. Most pad materials range from u=.25 to u=.45. The force applied to the brake pad is simply the hydraulic line pressure times the area of the piston. So by changing the diameter of the piston the force can increased or decreased.
There are several types of friction material available: organic; semi-metallic; carbon-kevlar; and carbon-metallic. Organic are referred to as 'soft' pads, and the metallic are often called 'hard' pads.
The braking process is initiated and controlled through the master cylinder. The DOT (Department Of Transportation) stipulates that passenger cars must be equipped with two separate hydraulic circuits. This is satisfied by using a master cylinder designed as a tandem unit by using a 'floating piston'. If there is a leak in one of the circuits, there is extended pedal travel which alerts the driver to the problem.
All Z cars use a hydraulic system to operate the brakes. Pedal force is applied to the hydraulic fluid through the pistons in the master cylinder. This force creates pressure in the fluid. The fluid pressure is the force acting on the piston divided by the area of the piston. A smaller piston thus gives a higher pressure. However, fluid displacement is the area of the piston times the distance it moves. So if a smaller diameter master cylinder is used, greater movement is required at the pedal.
All the Z cars use a vacuum booster located behind the master cylinder to reduce the pedal effort. Disc brakes lack the self-energizing feature of drum brakes and need some power assist except on very small vehicles. Because intake manifold is highest when the driver lifts his foot off the throttle, vacuum in the booster is maximum when the brakes are applied. Since the extra force developed by the booster is proportional to the area of the diaphragm in the booster, a larger diameter booster will produce more force.
All the booster does is amplify the driver's foot pressure. It's gain should be kept low for a more precise and sensitive control of braking. Boosters reduce the response time of the braking system and they are rarely used on race cars.
As mentioned earlier, a moving vehicle undergoes weight transfer during braking. However, this weight shift is not a linear process. Its magnitude increases as a function of vehicle deceleration.
To counteract this, the braking force should be applied to each wheel in proportion to the weight (or load) on it and correct brake balance means that front-to-rear braking forces are proportioned so neither front nor rear wheels lock first. One way to accomplish this is to reduce the rear brake pressure relative to the front brake pressure.
A hydraulic brake system has a certain ratio between front and rear brake line pressures. If the master cylinder has equal sized pistons for the front and the rear (like a Z car), then equal pressures are developed when the brake pedal is pushed. If this is plotted on a graph, a straight line is produced. However, this is not what we want! We need to gradually reduce the ratio between front and rear hydraulic pressure as the degree of braking is increased to automatically account for weight transfer.
Brake fluid boiling point is a very good comparison for evaluating regular or "glycol" (glycol is actually short for polyglycolether) based fluids because it roughly represents the conditions under which glycol turns compressible. It is a very poor comparison for evaluating silicone based fluids because they turn compressible at a lower temperature than that at which they boil.
Glycol based brake fluid is hygroscopic, i.e., it absorbs water from the surrounding atmosphere, and it starts adsorbing water as soon as you put it into your car's brake system. The brake fluid reservoirs on top of the master cylinder are vented to the atmosphere. Moisture can also enter the brake system through the rubber seals and hoses through a 'diffusion' process.
As glycol brake fluid absorbs moisture the result is a lowering of the boiling point of the fluid and also a greater chance of corrosion of the brake system components. The boiling point of glycol brake fluid typically decreases about 100 degrees after 6 months, and another 25 to 50 degrees after another 6 months. The DOT ratings were supposed to simplify choosing a fluid, but they do not take into consideration the compressibility of a fluid, nor it's affinity to absorb water.
The big advantage of silicone fluid is that it doesn't absorb water so corrosion of brake system parts is greatly reduced or even eliminated. It also won't damage your paint if it gets spilled accidentally. However, not absorbing water can be a disadvantage because if there is water trapped in the system, it will settle out in the lowest points, causing rust or possibly freezing.
One of silicone fluid's supposed advantages is a higher dry boiling point. What is not generally publicized is that unlike glycol based fluids, silicone fluids become compressible independently of boiling, and at a lower temperature than they boil at. Thus, the higher dry boiling point is merely a technicality that doesn't actually offer much in practice. At elevated temperature, silicone fluid has four times the compressibility of glycol based fluids leading to increased pedal travel and a spongy pedal.
Brake modifications can be roughly divided into different areas 1. Increasing brake torque. 2. Reducing fade. 3. Miscellaneous items, such as reducing system deflections and adjusting brake balance.
Often, increasing brake torque will result in higher pad and rotor temperatures, so reducing fade is very important.
By examining some of the equations we can gain some insight into possibly improving the performance of a braking system. In a moving vehicle that is coasting (no power applied to the wheels) the wheels are turned by their contact with the road surface. This produces a twisting motion or torque on the axle: torque = Fv*ut*R...where Fv is the vertical force on the wheel, ut is the grip (coefficient of friction) of the tire, and R is the rolling radius of the tire. To counteract this torque the brake must produce a torque in the opposite direction. If the torque produced by the brake is larger than the result in the above equation, then the wheel locks. This is not what we want. What we want is have the brake torque equal to that produced by the motion of the rolling wheel. This will give us maximum deceleration.
The brake torque can be calculated by: brake torque = Ff*Re....where Ff is the friction force and Re is the effective brake radius. The friction force produced by the brake Ff is equal to the hydraulic pressure times the area of the brake piston times the coefficient of friction of the brake lining. The brake torque can be expressed as: brake torque = P*A*ul*Re....where P is the hydraulic pressure, A is the area of the piston, ul is the coefficient of friction of the brake lining, and Re is the effective brake radius.
Since the hydraulic pressure is a function of how hard we press down on the brake pedal, brake torque can be increased by pressing down harder on the pedal. However there are limits to which the hydraulic pressure can increase. Leaks and excessive deflections in brake lines and calipers will result from excessive pressures. What is desired is to have a large value of brake torque without having a large value of pressure. In other words, the remaining parameters in the equation must be increased.
The piston area could be increased by going to a caliper with a larger diameter piston, but what is usually done is to add more pistons. Going to a 4 piston caliper will increase brake torque. In addition, the pad area can also increase, which has further benefits. Increasing the effective brake radius means increasing the diameter of the rotor. This usually entails increasing the wheel diameter as well. The pad coefficient of friction can be increased by going to a different (soft) pad material. However, this may increase the possibility of pad fade.
Recall that braking is the transfer of the kinetic energy of a moving vehicle to heat energy. This heat build up will eventually result in a decrease of braking force. This is called fade. There are three types of fade: Pad fade; Fluid fade; and Mechanical fade.
Pad fade is when the friction coefficient of the pad drops as the pad/rotor interface temperature increases. The leading theory is that the pad begins to "out-gas" at high temperatures and this acts as a lubricant. Pad fade can be reduced by either using a pad that can handle the higher temperatures, a so called "hard" pad and/or reducing the rotor temperature rise. This can be accomplished with a more massive rotor, a rotor with more surface area, or a vented rotor. Vented rotors are hollow and have air channels which greatly increase the surface area that is exposed to the airflow. They are also more massive than a solid rotor of the same diameter. This means that they can absorb more heat. Using ducts to channel air to the rotor surface will also reduce it's temperature rise. One often overlooked cooling aid is changing to a wheel with a more open spoke design. Also, an aluminum wheel conducts heat better than a steel wheel and will help conduct heat away from the hub. Increasing the pad area will also reduce the pad temperature level. However, unless the piston area is likewise increased, the braking torque will decrease.
Fluid fade occurs when the brake fluid starts to boil and becomes compressible. You can distinguish between pad fade and fluid fade because when the fluid boils the brake pedal becomes soft or mushy. The brake fluid expands and can spill out the tops of the reservoirs. With pad fade the pedal feel remains hard, but the braking force decreases. The best way to reduce fluid fade is to use a fluid with a higher boiling point. Other less common methods are an air duct pointing at the caliper and the use of a poor heat conducting spacer (ceramic, for example) between the pad and the caliper piston.
The only example of mechanical fade that comes to mind is the classic one concerning the drum brake. When heated, the drum expands and moves away from the shoe, reducing the braking force.
Other Brake System Improvements
In addition to increasing brake torque and reducing fade, there are other objectives to be considered when brake improvements are sought. Reducing system deflections will reduce pedal travel, increase driver "feel" and improve the dynamic response of the brake system.
One source of deflection is the flexible rubber lines which connects the steel brake lines on the car's body to the brake components mounted on the wheel. The answer to this is to install stiffer hoses. Steel-braided Teflon-lined hoses are stiffer than the fiber-reinforced rubber hoses. They are usually smaller in diameter, and this fact also reduces hose swelling.
Other causes of deflection include fluid compression, firewall flexing behind the master cylinder, caliper deflection and brake pad compression. Surprisingly, on some brake systems the major cause of deflection is the compression of the pads!
Adding a brake balance adjustment will allow you to get the full benefit from any brake modification, as it will allow you some limited control over the point where the rear wheels will lock. An adjustable proportioning valves can perform this function.
Levels of Modifications
With all the above considerations in mind we can now start to discuss brake system improvements. In order of complexity and cost, modifying your Z car brakes can be divided into a "Three Stage" approach. One modification you should not do is to install a larger vacuum booster. This will only make it easier to lock up the wheels and almost guarantees that will happen in a panic stop.
The easiest way to upgrade your Z car braking system is to install a performance set of brake pads. Repco Metal Masters (they are actually semi-metallic) are the most popular choice for a street driven car. For a competition (or a very hard driven street car) use carbon-kevlar pads or carbon-metallic pads. Carbon kevlar pads from are available from Porterfield Enterprises (800-537-6842). Porterfield recommends the R4-S compound for the street. Carbon-metallic pads are available from Superior Friction (408-436-1101) or Dando's (800-918-6363). However, you should be forewarned that both these carbon compound pads work best when they are hot and have poor grip when cold! Installing them on the rear will reduce the effectiveness of the parking brake. Also, they throw off a lot more brake dust and are harder on rotors.
Changing the brake fluid to one that has a higher boiling point is next step. Although this subject is not without some controversy, the general guidelines are as follows:
For street cars: use a DOT 4 fluid. This will give you some margin even when the fluid has absorbed some moisture. Change it at least every two years. The Castrol LMA fluid seems to be available in most locations. If you can boil fresh Castrol LMA, then try ATE SL. This DOT 4 fluid is original equipment on a lot of European cars. You can find it at dealers. There is now available a DOT 5.1 fluid, Motul 5.1 which would be the best fluid for the street, but availability is limited.
For competition cars: Ignore the DOT ratings!! Use a the fluid with the highest DRY boiling point you can find or afford and change it often! Serious racers will change their brake fluid before every race. Ford Heavy Duty Fluid has an excellent boiling point (somewhere between 500 to 550 degrees), is readily available and is very cost effective. Other suitable fluids include AP 550 (550 degree boiling point), and Motul 300 or Wilwood 550 (both are 570 degrees). Motul 600, AP 600 and Castrol SRF all have a boiling point close to 600 degrees. The price of these fluids seems to increase exponentially with their boiling point.
Show cars, restorations or "garage queens": For cars that don't see much road use and will never see any serious driving, silicone fluid (DOT 5.0) works fine and is highly recommended.
There is a 4 piston caliper that will bolt on to the 1970-78 Z cars utilizing the stock solid rotor. This caliper was used on the 1979-85 Toyota four-wheel-drive truck. It requires some slight trimming of the backing plate (if you are going to retain this) and some re-bending of the 'S' shaped brake line. You can also obtain the R4-S carbon-kevlar pads for this caliper from Porterfield.
The Toyota 4 piston calipers have unequal diameter pistons. This is done to better equalize the temperatures across the surface of the brake pad. Normally the trailing edge of a brake pad runs hotter than the leading edge.
Because slightly more fluid displacement is required for the Toyota calipers, pedal travel is increased. To solve this, change the master cylinder to one from a 280ZX. This master cylinder has a larger bore diameter (15/16 inch vs. 7/8 inch). The reason that there is interchangeability between Nissan and Toyota is that a single company, Sumitomo, made the calipers for both Nissan and Toyota.
Another 4 piston caliper is available for the 1970-78 cars from Nissan Motorsports, but it has equal sized pistons and is a lot more expensive than the Toyota calipers.
Adding air ducts from an opening in an air dam is an effective way to cool the rotors. You can buy high temperature silicone duct hose from Racer Wholesale or Pegasus Racing, but it is fairly expensive. You can also make them out of 4 inch dryer duct hose or the black corrugated plastic irrigation pipe. Mount the ducts so that they are well supported with brackets. Point the duct at center of the rotor if you have a vented rotor. If you have a solid rotor, aim the duct so that BOTH sides of the rotor will receive some airflow. This will prevent rotor warping. Make sure the ducts can't come loose and jam the steering. You can also improve the cooling of the rotor by removing the sheet metal baking plates. These are installed mainly to keep water and debris off the rotor.
As mentioned above you can also install braided steel brake hoses. These are available from several vendors, including Motorsport Auto and Jim Cook Racing. On the 1970-78 Z cars, the rear drums can be painted with a thin layer of glossy black to reduce their temperature.
Replacing your stock rotors with cross drilled rotors: There are pros and cons about using cross drilled rotors. You will have to make your own decision about using these. You can actually reduce the rotors surface area if the holes are too large! Make sure the holes are no larger than 1/4 inch in diameter. Cross drilling rotors offers these advantages: 1) Increases the surface area of rotor, provided the drilled holes are not too large; 2) Reduces pad fade by giving the gases released from the pad someplace to go; 3) Clears any water from the rotor surface faster.
Disadvantages of Cross Drilling: 1) Rotor will tend to develop cracks at the drilled holes because of the machining process. Stress relieving or annealing after drilling will help. 2) The mass of the rotor is reduced. 3) A sudden rotor failure will be more dramatic. 4) The balance of the rotor may be affected if the hole pattern is not symmetrical.
Alternatives to cross drilling are dimpling and slotting. Dimples made with a 1/8 to 1/4 inch ball end mill in the surface of the rotor will give you some limited benefits of cross drilling but will reduce the crack formation. Slots cut across the rotor surface with a .060" ball end mill will help with pad fade and again will reduce the crack formation.
Adding an adjustable proportioning valve involves some degree of complexity, so it is considered a Stage III mod. Adjustable proportioning valves are available from several suppliers (Porterfield, JFZ, Tilton, Arizona Z, etc.). Catalogs which cater to the hot rod crowd are also a good source.
Replacing the rear drums of the 1970-78 Z cars with the 1979-81 280ZX rear calipers and rotors. This can be accomplished by either purchasing an entire kit from Jim Cook Racing (800-527-1440) for $780, or you can purchase only the brackets for $179. Another source for adapter brackets is Z-Quip [(770) 253-4356], price is $125. You must remove the rear stub axles to make this conversion. The proportioning valve must be replaced with the 280ZX one as well.
Arizona Z (602-844-9677) sells a front brake kit for the 1970-78 Z car which utilizes an aluminum 4 piston caliper and a 11.5 inch diameter, 1.25 inch thick vented rotor for $749. They also have a rear kit which features an aluminum 4 piston caliper and a 11.75 inch diameter, 0.81 inch thick vented rotor for $799.
Top-End Performance (818-764-6768) has similar kits for the 1970-78 Z cars using JFZ components. Their front 12 inch diameter vented rotor kit sells for $850, and they also have a 11.38 inch diameter front rotor kit for $750. For the rear they have a 12 inch diameter vented rotor kit for $850, or a 11.38 inch rotor kit for $775. They also sell a rear kit with solid rotors for $475.
Design Products (714-892-1513) also has kits for the 1970-78 Z cars using Wilwood components. Their front 12.18 inch diameter vented rotor kit goes for $865, and their 11.4 inch diameter vented rotor kit sells for $755. At the rear they offer a 11.4 inch diameter vented rotor kit for $795 or a 10 inch diameter solid rotor kit for $395.
Two notes on the last three brake kits mentioned: There are no provisions for a parking brake with the rear kits. Also, you must use 15 inch or larger wheels, but this is no guarantee that you will not have interference problems.
For the 1990 and later 300ZX's you can replace the brakes with the ones from the Skyline GTR. The vented front rotor is 295mm in diameter (stock is 280mm), 32mm thick (vs. 30mm) and is cross drilled. The vents are different from stock in that they have fins in the center that scoop air which is vented through the drilled holes to dissipate heat. The front caliper is also replaced, but uses the same size stock pads. These calipers are thicker than the stock ones and will just touch the stock wheels. However, a couple of swipes with a file on two or three of the raised letters of the calipers will eliminate the interference problem. You also have to remove the front backing plate behind the rotor by breaking it off its spotwelds. The rear rotors are also replaced by a drilled disk but you keep the stock caliper and pads. The Skyline GTR kit is available through Steve Millen (714-540-9154) for about $2000.
Steve Millen also sells a Brembo kit for about $2500. The kit only replaces the front brakes, and requires going to 17 inch wheels for clearance.
Several companies (Grip, Euro, Porterfield and Brembo) offer 'sport' rotors, which are OEM spec rotors that have been cross drilled.
On the 1990-91 cars you can add a set of plastic air deflectors. These deflectors route the oncoming air to the inside of the rim for better cooling.
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