Everything you wanted to know about braking upgrades –
Why do I need a big brake upgrade?
Modern stock brake systems, for the most part, work well for a single 60-0 or 80-0 stop, and average daily street driving. The typical performance enthusiast will quickly push the stock brake system beyond its capabilities. Driving style and other performance modifications such as increased horsepower, tire and suspension upgrades quickly add up to overpowering stock brakes. A big brake kit will provide increased heat capacity, which means substantially more resistance to brake fade and caliper distortion with multiple stops from high speed. A firmer pedal due to stronger and stiffer components, as well as better modulation characteristics under threshold braking are also typical with a properly balanced brake upgrade.
Why is the pad and rotor break-in procedure so important?
PROPER BREAK-IN OF ROTORS AND PADS IS CRITICAL. Not properly doing so can cause permanent damage to rotors and adversely effect overall brake performance. Pads and rotors interact with each other to provide efficient brake performance. The break-in or bed-in procedure is done to condition the pad/rotor interface. Depending on the pad used, more or less pad material is uniformly transferred onto the disc as a thin film. The resins and bonding agents in some pads need to be heat cycled to work properly as well. By not properly bedding in pads, uneven pad material deposits can occur that may cause a vibration. Improper wear characteristics may also show up on either the pads, or rotors, or both. Always follow the recommended break-in procedure for any pads, rotors or brake systems.
What kind of brake fluid should I use?
As with brake pads, there are several choices of quality brake fluids available. Generally a DOT 4 fluid is sufficient for street use, any quality name brand or OE brake fluid will be sufficient. If running on an open track, you might want to step up to a racing brake fluid with higher dry and wet boiling points. I recommend Motul 600 due to its higher boiling point and almost universal compatibility with OE brake systems. Though priced quite a bit higher, Castrol SRF brake fluid is recognized as the best available brake fluid for professional racing due to its patented and unique chemical composition. The SRF fluid will need to be more frequently changed as well and is not recommended for the typical street/occasional track day user.
A bigger pad means better braking, right?
A bigger pad of the same compound in the same location as a smaller pad will not yield shorter stopping distances. The amount of pressure applied, pad friction coefficient, and the diameter on the rotor at which that pressure is applied, determine the torque reaction, or stopping force. A bigger pad does not apply more pressure, only the same pressure over a bigger area. Where the size of the pad matters is in terms of heat capacity and wear rate. A larger pad will absorb more initial heat (less thermal shock), and have better wear characteristics (longer pad life).
What are differential bores?
Differential piston bores are used to control brake pad taper. As incandescent material and debris from the leading edge of the pad is trapped between the pad and rotor, it tends to float the trailing edge of the pad off the rotor. A larger piston at the trailing edge of the pad provides more pressure to compensate for this debris buildup and keep the pad flat against the rotor.
Won't bigger caliper pistons stop better?
A bigger set of caliper pistons will provide more clamping pressure on that axle, but could have a negative effect on total brake performance. If the pistons are too large for the application there will be excessive pedal travel and an adverse change in front to rear balance resulting in extended stopping distances. Also, clamping forces can easily become so strong that pre-mature lock-up will occur making brake modulation difficult.
Which is better, slotted or drilled rotors?
For most performance applications slotted is the preferred choice. Slotting helps wipe away debris from between the pad and rotor as well as increasing the "bite" characteristics of the pad. A drilled rotor provides the same type of benefit, but is more susceptible to cracking under severe usage. Many people prefer the look of a drilled rotor and for street and occasional light duty track use they will work fine. For more severe applications, I recommend slotted rotors.
How do I retract the caliper pistons to change pads?
As brake pads wear, the caliper pistons extend from the body of the caliper but only retract a few thousandths of an inch so the pads stay close to the rotor face. When installing new pads, the pistons need to be pushed back into the caliper body. This can be done in several ways and does not necessarily require special tools. With any method of pad retraction, be careful not to nick the face of the aluminum piston where it contacts the backing plate of the pad. First off, the rotor is typically loose on the hub with the wheel removed. By rocking the rotor back and forth it will push back the pistons enough to make removing the used pads easier. This is especially true if rotor wear is such that there is a raised ridge on the outer edge of the rotor face keeping the pad from easily coming out the top of the caliper. Our most convenient method to fully retract the pistons is to use the used pads being removed from the caliper as a lever. Remove one pad from the caliper while leaving the other used pad in place. Turn the pad 90 degrees and re-insert half way it into the caliper lengthwise with the pad face still toward the rotor. Using the outer edge of the rotor against the center of the pad, use the pad as a lever to press both pistons in at the same time. Retract both pistons at the same time, or the one not being pushed in will extend further. Push the pads in as far as possible, remove the used pad and install the new pad. Repeat on the other side of the caliper. In retracting the first pair of pistons, the opposite pair of pistons where the other used pad is may extend, pressing the pad against the rotor. Rock the rotor again to move the pad away again. You can also use alternate tools to push in the pistons. I have also used the plastic coated handles on a pair of pliers or channel locks, which allow me to press both pistons at the same time and not nick the piston face. There are special tools available to retract the pistons, however unless you are a professional crew person making a hot swap in the middle of a race, it is likely not necessary. If you have trouble retracting the pistons, you can crack open one of the bleed screws with a hose leading to a tray or bottle and it will ease the resistance. You will need to bleed the system if you open the bleed screw. Also, keep an eye on the brake fluid level in the master cylinder reservoir. If the system was bled and topped off when the pads were worn, you might push enough fluid back through the system to overflow the master cylinder.
What do you mean by "uneven pad deposition?"
Virtually all modern brake pads are what are referred to as an Adherent type of pad. The pad is designed to transfer a layer of pad material onto the rotor. When a sufficient and EVEN layer of pad material is adhered to the rotor face, the pad material on the rotor, interacting with the similar material on the pad, creates the most efficient friction mechanism. These like materials, breaking against each other on a molecular level are what really stops the car well. To emphasize, there is supposed to be a layer of material pad material on the rotor. The problems occur if the pads are not properly bedded-in (an even layer of pad material on the rotor) and run aggressively, OR if the pads are overheated. The pad transfer occurs most efficiently at the pads optimal operating temperature. That means a higher temperature pad needs to be hotter to properly transfer material. If you have a high performance pad and never run it hot enough to get a proper layer of material onto the rotor, it will never be properly bedded-in. Thus, even after 1000 miles of "normal" street driving, when you blast your favorite canyon and heat the brakes, you can get uneven deposits on the rotor causing a vibration. The other common scenario is over-heating the pads even if they are properly bedded-in. In this case, the pad material starts to break down and smear onto the rotor face, again causing the UN-EVEN deposits. The other problem that occurs is if the system is really hot and you come to a complete stop and leave your foot on the brake pedal. In this instance, we get what is called "pad imprinting" where a small layer of material breaks off the surface of the pad and literally can be seen as an imprint of the pad on the rotor face. This can occur no matter the state of bed-in. All these scenarios leave very small, uneven layers (we call it TV, Thickness Variation) of material on the rotor. We're talking a few 10/1000's of an inch, like a TV of 0.0003". It starts out almost imperceptibly, but as the pads start to skip over the high spots, more material is deposited on those areas, ever increasing the vibration until it becomes quite noticeable, even days after the event that started it occurred. The best way to avoid these problems is proper bed-in of the system initially, and using the proper pads for your exact driving conditions. If you are planning on swapping pads for a track day, you need to re-bed the system before the event (or dedicate the first track session to bed-in). Remember, you have that layer of street pad material adhered to the rotor face, and if you don't remove and replace it with the track pad material, it is going to degrade from the heat and... yep, cause uneven pad deposits. Same goes when you put the street pads back in, you need to re-bed them for optimal street performance.
My car judders when I apply the brakes, what can I do to fix it?
Turning the rotors will take care of it, but you will be shortening the life of the rotor and decreasing its ability to absorb and control heat, as there will be less mass in the rotor after turning. Also, turning a 2-piece rotor that uses floating attachment hardware between the rotor and hat can be tricky. We have had very good success running an aggressive track pad at lower temperatures on the street in order to scrub off the rotor surface. We have found the Hawk Blue 9012 race pad to be very effective. At lower temperatures it is very ABRASIVE, not becoming ADHERENT until it reaches it's optimal operating temperature. If it is used with a few firm stops at a time, not getting too hot (we want to remove material, not transfer more), it will often remove the source of vibration. A WARNING: Do not leave an abrasive pad in the caliper longer than necessary to solve the problem. We have had rotors destroyed in under a week by leaving the abrasive track pads in on the street
Originally Posted by ~The_Duke~
