Calipers should be mounted in a near vertical position (or to manufacturers requirements) to allow proper bleeding of air from the system. When the car is moving forward, the rotor should always first pass the small caliper piston then the large piston. On front mount or leading calipers (mounted in front of the axle) the small piston is on top; on rear mount or trailing calipers (mounted behind the axle) the small piston is on the bottom. Consequently, with calipers that have two or more different size pistons, you can change a caliper from a front mount to a rear mount or vice-versa but you cannot make a RH caliper out of a LH or vise-versa. When mounted correctly the caliper bleed screws will be on top.
It is important that the caliper centerline be no more than .020" off the rotor centerline and that the faces of the pistons be parallel to the friction face of the rotor. All spindles used on racecars should be checked for caliper alignment. On racecars using racing calipers with aftermarket spindles, fabricated spindles, modified OE (Original Equipment) spindles or fabricated uprights the best approach to achieve correct caliper alignment is to machine the caliper mounting boss and / or tap the caliper stud holes after all welding and heat treating are done. On aftermarket racing spindles the alignment should be checked and corrected as necessary. This applies to lug mount caliper or radial mount calipers where the spindle has radial mount lugs fabricated in or uses a separate “caliper bracket” for the radial mount caliper. We cannot stress enough how important this step is to having excellent pedal feel and the best performance from all your brake system components.
If using radial mounted calipers, the caliper should be mounted so that the friction material on the pad is even with the rotor OD (Outer Diameter) and also have at least .080" clearance between the rotor outer circumference and the caliper bridge. Most installations will have clearance greater than .080” just to maintain the pad outer radius near the rotor outer radius. Radial mount calipers that are mounted to low and be adjusted with Pro-System shim kits PN # PSYSFCS & PSYSRCS. If using lug mount calipers and the pads overhang or under hang the rotor corrective action must be taken. Make sure the outer radius of the friction material is flush with the OD of the rotor and that there is the minimum .080” clearance between the caliper bridge and the OD of the rotor. That clearance is needed so the rotor OD does not rub on the bridge of the caliper. This also happens when smaller OD or larger OD rotors are used with calipers not designed for that diameter rotor.
Ideally the difference between pad outer radius and the rotor OD should be no more than .020" either way (pad over hanging the rotor when cold being preferred as the rotor will grow in diameter when hot). When initially fitting the caliper and rotor, check this dimension with several sets of pads as the pad friction may be displaced on the steel backing plate giving an erroneous reading.
In NASCAR the caliper and pad fit is constantly monitored as the wheel is the component with the greatest dimensional variance and teams avoid having the wheel rub the caliper.
Pads must come in and out of the caliper without using force. Clearance between the pad and abutment plates and between each pad and rotor must be a minimum of .020" when the pistons are fully retracted. Try to hit the .020” number as close as possible. Some brands of pads are better than other where fit is concerned.
Care must be taken to never over tighten the bleed screws. Over tightening will weaken the threads, increase the seat width and eventually cause problems. Follow manufacturer’s recommendations. Bleed screw torque will fall between 106 to 140 in./lbs for the typical M10x1 or 3/8-24 bleed screw.
Use copper washers when installing inlet fittings or banjo fittings in the calipers. Its good practice to only use copper washers once, replacing after each disassembly. Racing calipers typically don’t have ports with pipe threads.
For a long time in racing It has been accepted that two piece floating mount rotor assemblies have several advantages over the rigid one pieceor non-floating two piece designs. As the brake system temperature migrates into the hub the bearings can develop excess play. The expanding and contracting of the hub and bearings plus the flex of the spindle and other components results in the caliper centerline moving relative to the rotor centerline during braking. This is more prevalent in OE and lower priced aftermarket spindles and less prevalent in well fabricated or cast racing uprights. Floating rotors and hats are designed with axial movement to allow the rotor to seek an optimal path through the caliper. The design also allows the rotor to move radially allowing growth in diameter with less distortion during braking. Rigid mounted rotors will "cone" or “potato chip” at high breaking temperatures as a result of distortion. This can produce judder or pedal pulsation as the rotor distorts. In the best case the pulsation can be of high enough frequency that the driver does not feel it, however the actual stopping power is still reduced to some degree. In the worst case the pulsation becomes so bad that the car is hard to drive.
Higher quality cast or fabricated uprights and spindles with less flex can run less axial float, however radial float is still a critical component of good brake performance.
When installing rotor & hat assemblies check the float of the rotor after installation on the hub. A loss of float after all the lug nuts are tightened indicates that there is some interference in the mounting. This condition can cause several problems including rotor/wheel runout and brake drag or a long or mushy brake pedal. It is also possible with some aftermarket wheel studs for the knurl to protrude past the hub face after installation. This condition can also cause the hat to not seat flat against the hub resulting in a loss of float. Always check for this condition. The knurl will leave a witness mark on the stud hole inside of the hat. The solution is to remove the stud and turn the OD down in the problem area so that the hat fits flat against the hub. The short cut of chamfering the inside of the hat to clear the knurl is not a good solution as this process reduces the bearing surface of the hat on the stud and allows the problem to resurface if an un-chamfered hat is later installed.
Most of our rotors have directional vanes and directional groves. On heavy braking tracks, make sure that the rotors are installed in the correct direction of rotation to insure the best cooling efficiency. The directional vanes should run back from the inside to outside diameter. Directional or curved vanes give the rotor increased dimensional stability over straight vanes. The purpose of groves on the surface of the rotor is to facilitate a good even transfer layer of the friction material onto the rotor surface, to add more bite and to help clear away excess friction material from the face of the pads and interface of the pad and rotor – all essential to good braking in a race car.
- If using Timken style tapered roller bearings the use of a wheel bearing pre-load spacer kit will enhance braking performance & vehicle handling and increase wheel bearing & grease life. For NASCAR type front hubs, using the Pro-System preload spacer kit # PSY-9150-PL will minimize hub movement and improve overall braking performance and handling as well as increase the front wheel bearing and lubricant life. Typical preload for Timken type tapered roller bearings is Zero to .001” in a steel hub and up to .003” in an aluminum hub. This is true only for racing where excess heat migrates into the hub and bearings from braking.
- Check the rotor float after installation on the hub.
- Make sure that the hat is seated flat against the hub surface.
- Premature rotor cracks are usually caused by thermal shock.
- Hats and rotors should be cleaned with soap and water, "brake clean" spray or any good non-oily solvent.
- At the track, frequently check to insure that the wheels are rotating freely without any residual line pressure or pad drag and that there is no contact between the caliper and rotor or the caliper and wheel.
- Rotors and pads should be inspected after races and long practice/test runs.
- Heat checking on the surface of rotors at hard braking tracks or with heavy braking drivers is common. When the heat checks turn into cracks .200" long that have spread to the outside or inside edge and through the wall or cheek of the rotor they should be replaced before a long race or extended test run.
Rotors that have heavy groves formed on the surface from very high temperatures and/or show wear in thickness of more than .040" total when compared to a new rotor should also be replaced before a race.
- With the modern metallic pads in universal use today it is not necessary to de-glaze pads or rotors. Sanding or glass bead blasting the friction surface of either diminishes performance.
- Simply fit newly bedded rotors and pads when the pads are worn out or the rotors are worn and/or cracked.
BEDDING - Brake Dynamometers
Pro-System brake bedding insures that all our rotors and pads are ready to race and require no further break-in consideration beyond warming up on an initial out lap. We have two fully automated, computer controlled electric brake dynos that are used constantly for bedding, testing and development of brake parts. The fully automated bedding sequence uses the correct inertia and cycle time for the job to insure that you are getting the highest quality parts available and that they are the same time after time. Drivers and team personal have more than enough to be concerned with during a race weekend or a private test day. You do not have to waste valuable track time or money bedding brakes. To avoid thermal shock, with our bedded rotors as well as with any used rotor, they should be warmed up on the first lap. They do not have to be red hot, just warmed up and this will help prevent premature cracking. This is especially true in Road Racing and Circle Track at intermediate, speedway or light braking tracks.
CUSTOM BRAKE HATS
Don’t compromise your brake system by using a hat that is worn out or“doesn’t exactly have the right offset”. We have been manufacturing brake hats for 20 years and have made thousands that have been used by repeat customers in every major professional series plus by lots of grassroots and amateur racers. No matter the application –Grassroots to the highest Professional level - all of our hats are made to the same high standards using the same quality processes and materials. In this case there really is only one way to do it right and insure a good part. Please refer to the Hat section of this site to order your Brake Hats.
Cutoff Travel is the distance the master cylinder pushrod travels from off pedal until the point at which the master cylinder makes pressure and this is an important component in a properly set up pedal assembly; whether a single OEM style MC or a system that uses twin master cylinders with a balance bar. Most of the high quality racing master cylinders available today are set up to have a “cutoff travel” of .030” to .050”. Having a pair of master cylinders with equal cutoff travel makes for a better balance bar operating system. Another obvious reason for noting the cutoff travel dimension is that you must have some piston travel in the cylinder before pressure otherwise the fluid intake and return port might never open. This condition would normally show itself because you cannot bleed the brakes. However we have seen this condition in pedal assemblies where someone has installed a pedal return stop which is a very bad idea. In this case you can go on the track thinking everything is good only to discover that eventually your pedal drops and there is no hydraulic pressure to stop the car! The only exceptions are some OE applications that use a push rod that is not captured in the master cylinder. Those will need a pedal stop to keep the push rod from falling out of the master cylinder. In that case you have to make sure the pedal and pushrod have some free play before the piston moves - .between .030” and .050” is a good amount of free play to strive for.
Proper mounting of the master cylinders and pedal assembly are imperative to achieving optimal braking performance – this cannot be stressed enough. Drivers can exert a lot of force on the brake pedal and that force is multiplied by the brake pedal ratio. If any movement or flexing occurs within the mounting of the pedal assembly it will give negative feedback to the driver. The spongy pedal the driver feels as a result of any flex can be incorrectly blamed on the pads or other components in the brake system. Fix this problem once and it’s fixed for the life of the car!
Dual master cylinders allow you to have two independent hydraulic systems. The use of this set-up far outweighs a single unit. First and foremost is safety. In the event of a loss of front or rear brake the driver still has the other system available to stop the car. Dual Systems can prevent the car from slowly rolling, completely out of control, across the track and into oncoming traffic and also enable the driver to stop in the pits. Also, front to rear bias can be adjusted using different size cylinders and then fine tuned with the balance bar adjuster.
It is advisable to use one of the modern balance bar assemblies that eliminates the side to side slop and inefficacy of the old system using the spherical bearing. Pro-System designed and manufactures a line of very high quality affordable pedal assemblies and balance bars used extensively in professional racing for many years. We also carry the Tilton and Wildwood line of pedal assemblies.
In the older balance bar systems still in wide spread use today the spherical bearing on the balance bar should always be near the center of its tube or housing in the brake pedal. If, after balance is achieved, the bearing is more than 4 turns to one side or the other then it will be necessary to change master cylinder size to bring it back to near center. If the balance bar has 20 threads / inch 4 turns equals about .063” in master cylinder piston diameter or one size change up or down to re-center the bar. Make sure the master cylinder mounting places the pushrods parallel with and on centerline with the cylinder bores. Make sure there is some clearance between each clevis and the pedal housing. Either of the above, if set up improperly, can cause a binding or a shortened pedal stroke.
After initially setting the brake balance, be sure the balance bar is adjusted to be parallel to the firewall under braking pressure after balance is achieved (use approximate braking force for checking). Adjust the balance bar to be parallel by lengthening the shorter pushrod and shortening the longer pushrod equal amounts. Be sure to leave ample pushrod thread in the clevis for future adjustments, as adjustments may be necessary at the track if large bias changes are made.
SETTING BRAKE BIAS and PEDAL FEEL
Refer to the diagrams for how the pedal should look under pressure.
When setting brake bias and pedal feel, keep in mind that decreasing master cylinder diameter (or size) will yield more line pressure, more pedal travel and less pedal effort. The inverse is true when increasing master cylinder diameter. Initial bias should be set with approximately l00psi more front line pressure than rear. Ultimately the drivers' preference and feel will dictate the final setting but this is a good starting point.
Once a good brake balance is achieved at the track it is a good idea to take a line pressure reading front and rear for reference. This should also be done after a test or race if the driver indicates that the bias is correct. After a race inspect the pedal and balance bar assemblies, note their settings and how well the bar is centered and parallel to the firewall under the test pressure.
- It is recommended that you do not use a brake pedal return stop. Let the Master Cylinders determine the pedal position when off the brake pedal.
- The Pro-System brake gauge set (PN # PSY-BGKO1) allows the brake line pressures to be recorded accurately and quickly for reference by one person without requiring bleeding the brakes afterwards. These are reference numbers only and have nothing to do with clamping force against the rotor unless you factor in the caliper piston area.
- Use the gauges to keep a record of front and rear pressures for reference. Record pressures before disassembly and/or working on the system at the track. That way you will always be able to get back to "square one".
- The driver's style and preference is always a deciding factor in setting balance. With this system it is always possible to have the car set up to suite the driver.
- Pro-System offers a rebuild and testing service for the master cylinders to insure that they are working correctly and are to factory specifications.
Brake Pedal Ratio and Pedal Feel
The brake pedal ratio in your car should be known. Refer to the Pro-System pedal assemblies listed on this site and Tilton and Wilwood sites for pedal ratios of their respective pedal assemblies. You can apply more force with a 6:1 pedal ratio than you can with a 5:1 ratio but the pedal will be a little softer with the 6:1 pedal. You must consider master cylinder size, caliper piston area and pedal ratio all in the same context. It is proven that a harder pedal is easier to modulate than a pedal that is spongy or falling. Pedal firmness is a function of all three. A fourth and fifth variable in pedal feel, covered elsewhere on this page, are: 1. Pedal assembly mounting integrity and 2. Caliper alignment – both extremely important!
BRAKE FLUID RESERVOIRS
There are several high quality reservoirs on the market (Tilton being one that we like) and some teams fabricate their own. There are some ground rules if fabricating your own reservoir. First, the reservoir should hold the volume of fluid needed to provide fluid to the system when the pads are worn to the backing plate. Second, tall and skinny reservoirs are better than short and fat ones. This is easy to calculate. In a twin master cylinder system, the pad friction thickness is the travel and the total piston area of two calipers times the friction thickness is the minimum volume of fluid needed in the reservoir of a system where the calipers are blead and new pads installed. Some extra fluid capacity for safety should be added to the total. Since racing calipers come with many different piston diameters and fluid capacities there are typically no commercially available reservoirs sized for specific calipers. Therefore the commercially available reservoirs are typically oversized – information for the weight conscious car builders.
Aluminum is a popular material used in fabricating custom reservoirs. After finishing and checking for leaks, the newly fabricated aluminum reservoir should be anodized to prevent contaminating the brake fluid by exposure to bare aluminum.
Ideally the fluid should be 100% separated from the atmosphere by a bellows with the cap above the bellows having a vent hole. The bellows will extend or swell, pulling air through the vent hole in the cap, preventing a vacuum forming as the pads wear and the system requires more fluid.
If a commercially available reservoir is used make sure that its capacity is such that the fluid will be at or above minimum level mark after maximum pad and rotor wear have occurred (with fully extended pistons). Ideally it should have a bellows and a vent hole in the cap to completely separate the brake fluid from the atmosphere. It is important to avoid overfilling the reservoir. Initial heat build up at the start of a race can expand the fluid and cause pressure in the system until pad wear lowers the volume in the reservoir. Pay attention to the MAX and MIN lines on the reservoir for fluid levels. If no lines are present then add them.
- It is recommended that rigid metal lines with an ID of 3/16" or 4.75mm be used throughout the chassis because of their resistance to flex.
- AN-3 or AN-2 stainless steel braid Teflon should be used from the hard lines on the chassis out to the calipers and rear axle.
- AN-4 will increase displacement with the possibility of a spongy pedal feel. AN-4 is only good for the clutch line.
- Route all lines down hill from the master cylinders if possible and avoid loops that crate air pockets.
BRAKE FLUID and BLEEDING
As some racing brake fluids are not compatible with other brands, mixing fluids or changing brands without thoroughly flushing all lines and components in the car may cause problems. It is our recommendation for safety, simplicity and ease of maintenance that teams choose one fluid and use that brand exclusively.
- New or rebuilt calipers and master cylinders are difficult to bleed when empty and can consume a lot of expensive fluid in the process. Pressure or vacuum bleeding these components on the bench before installing on the car can make the job easier, quicker and more thorough.
- When bleeding a system with twin master cylinders, bleed one front and one rear caliper simultaneously in order to allow each master cylinder a full stroke.
- Start with the inside bleed screw and then go to the outside.
- Open the bleed screws and pump the pedal slowly waiting at least 2 seconds between strokes for the master cylinders to refill.
- Fast and hard pumping of the pedal should be avoided as air bubbles can be created through fluid cavitation inside the system.
- Vacuum, pressure, and gravity bleeding all work very well on the car or on the workbench.
- When bleeding is finished hold pressure on the system for 10 seconds while checking for leaks.
BRAKE COOLING & OVERHEATING
The very best cooling system design requires that the cross sectional area of the duct be maintained from the opening in the nose to the duct exit at the spindle or caliper and for the duct to be as short and straight as possible. In a NASCAR application this is near impossible to achieve with the compromises that must be made. However the closer the system is to that ideal, the better the system will cool and the smaller the opening in the nose can be for a given flow. During construction, the brake duct should be the priority over other fabrication in that area that could compromise the airflow or mounting. A simple brake cooling duct system is often the most effective.
It should be noted that in a NASCAR short track test situation with only one car on the track it’s easy for premature pad wear and/or rotor grooving to occur in a hard 40-lap test run on a 1/2 to 5/8 mile track. This can happen with the best cooling. Our experience has shown that the same wear rate rarely occurs during the race. You can destroy rotors and pads in 40 laps on a short track if you try. In these cases, an experienced based judgment call is needed between the driver and team regarding the premature wear.
Rotors operating constantly above 1200°F will grove and pad wear will greatly accelerate. If the red thermal paint is completely burning off the rotor more cooling is needed immediately to avoid a potential failure in the system. The maximum heat soaked temperature that a brake system will see in a race may take 100 laps to develop on a short track. On a road course it can develop in as little as 5 laps – depending on the track.
Increased wear on pads and rotors from overheating plus other temperature related problems could have another source. A driver that rides with his left foot on the brake pedal, and/or uses several brake applications through a turn to set the car, and/or pumps the brakes at the end of a straight can cause this. These drivers are not doing anything wrong but are instead using the brakes to make the car do what they want. The data acquisition system is the best tool for identifying this. Trying different size pedal return springs will sometimes solve the problem but all too often the solution is in providing a better cooling duct system.
An excellent way to enhance good ducting or to overcome less than perfect ducting is to feed it with a fan. We have brake fans designed specifically for this purpose. They have been successfully used for years and now are starting to be used more by Sports Car Teams. We have successfully put them into the front of Porsche 911's, Mustangs, Ferraris and many other cars. One advantage is that you do not need an opening in the front of the car for brake duct. You can pull the unwanted air from behind the nose of the car and force feed it into the brake duct. Or you can take excess air from in front of the radiator. On front or mid-engine cars the air can be pulled from the trunk.
The SRS800 fan is the 3rd generation fan produces by Suzuka Racing Services and benefits from lots of experience. When mounted in line in the ducting, the SRS800 does not restrict the air flow in cases where the air speed in the duct exceeds the fan speed or incases when the fan blade is not turning. Also they can benefit from screen over the inlet. This web site has complete data and information on this high performance fan.
These fans are much more robust and powerful than the cheep 12 volt fans that are typically sold for brake cooling. They have proven themselves for years in NASCAR Sprint Cup racing at Martinsville, Watkins Glenn and other tracks.
Rules for good brake ducting:
- Maintain the cross sectional area of the duct from the transition to hose at the front opening to the end where it connects to the brakes. Decreasing the cross sectional area will kill the flow due to the relative low pressures involved. This is very important and almost never adhered to. In any brake duct system the pressure is low – any decrease in cross sectional area will have a large effect on flow. If you doubt this, set up a test to demonstrate, using a fan, Magnehelic gauge with pitot tube and brake duct hose; you will see that lengthening, bending or flattening the hose only slightly will decrease flow.
- Make sure the duct it sealed and directs the air to the area you want. Just pointing the hose at the caliper or rotor won't do much good. It should have 1/8" and no more than 1/4" gaps around the end where it dumps onto the brake components. If this is not followed the air will take the path of least resistance around the component you are attempting to cool and escape without effecting the cooling.
- Keep the openings in the nose vertical and as close to the center of the car as possible to be in the area of highest pressure.
- Flow is decreased dramatically by even slightly crushing or bending the 3" flexible duct tubes. Added length also decreases flow.
- The brake cooling system should be under never ending development. It is much easier to find more air by pulling tape off a well-developed duct system than to be faced with redesigning an inadequate system at the track.
- Never believe that the duct system is as good as it can be.
- You can get more air by simply improving the delivery system to the caliper/rotor without increasing the opening in the nose.
- The high pressure in the radiator duct (in front of the radiator) is a low drag source for air to duct to the brakes. If this air can be used without raising engine temp - it is a good source.
- Pads that are constantly wearing with more than .040" of taper from top to bottom or .020" taper outside to inside indicate that there may be a mounting problem or cooling problem.
- Premature grooving of the rotor or accelerated pad wear in a race condition is a sign of inadequate cooling.
- The pyrometer can be a useful tool if consistency is used in recording temperatures. The same person should read the pyrometer each time, starting as soon as the car stops with the RF wheel and then going to the RR. The right front will be the hottest and will consequently cool initially at a faster rate than the right rear. It is important for the driver to use the same braking procedure exiting the track into the pits in order to have good data. The pyrometer can give unreliable data when used improperly.
- Temp stickers on the calipers are a good tool but must also be read fast when testing. If the car comes into the pits with extremely hot rotors, the heat will migrate into the caliper after the car stops. After a few seconds the sticker will give a reading reflecting the heat soaked temp and not the on-track temp. This is a useful tool to tell the highest temperature the caliper reached during a race and pit stops but only if read quickly after the car stops.
- The use of the 3 color rotor paint is a better tool to measure temperature. The paint colors change as follows: green 806°F - orange 1040°F and red 1130°F. The thermal paints reflect actual on track rotor temperature, as the temperature must remain at or above a level for a period of time for the color to go off. They will not change in the pits.
- Another good tool is the data acquisition system that most teams use in testing. Pro-System offers inexpensive thermocouples that are designed to run inside the pads near the rotor/pad interface and others that can be attached to the calipers. Also there are rubbing thermocouples that run on the rotor. They are fragile and must be handle carefully. The use of these devices is a good to record brake temperatures and is very useful in developing ducting. This system will show temps on the track and also the rate at which the temps migrate into other components. If the cooling system is verified to be adequate by using these tools during a hard test, the team can go to the race with confidence that they will not have brake-cooling problems.
- Many professional race teams have utilized Pro-System’s dynamometers to test various brake cooling systems. We have replicated there on-track recorded air flow and those test on our dyno have been useful in quickly recording accurate and reliable data in the development of brake ducting.