Brake System 201: 2-Piece Rotors, Fluid and Lines

Brake System 201: 2-Piece Rotors, Fluid and Lines

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By Richard Fong

Upgrading brake pads and rotors can make considerable improvements to a vehicle’s braking system, especially since the factory equipment is generally adequate for an everyday street application but not always ideal for high-performance driving. However, there are a few other variables that can further enhance the performance of a factory brake system before making the jump to aftermarket calipers and larger rotors. Now that you’ve been familiarized with some of the first and most straightforward brake-system upgrades in our Brake Systems 101: Pads and Rotors, it’s time to look at the next modifications in line to optimize the factory brake system. Two-piece rotors, performance fluids and braided brake lines can further improve your factory brake system for greater performance on both the street and the track.

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Room to Expand

A smoothly-operating vehicle typically indicates that all is well and functioning properly. When an ABS-like vibration feeds back through the brake pedal, it can be disconcerting to some and annoying to others. It’s certainly an indication of something amiss that requires attention. That vibration could simply be caused by uneven pad material built up on the surface of the rotor, for which a proper brake service (new pads, resurfaced or replaced rotors, brake fluid flush) would remedy. However, in the case of performance and heavy utility applications, the damage to the rotors could be more severe.

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Dissipating Heat

A vast majority of brake rotors on the market are manufactured as a single piece of iron for cost and durability. As the friction surface for the pads, rotors are subjected to extreme heating and cooling cycles. Since the center or “hat” of the rotor bolts to the wheel hub, it is sandwiched between the hub and the mounting pad of the wheel. This limits the rotor’s ability to expand and contract freely when subjected to extreme braking conditions (as would be the case on a racetrack or during an aggressive mountain drive) and could lead to warped rotors. A viable solution would be to upgrade to a 2-piece rotor solution. In this application, a billet aluminum hat is fastened by way of “floating” hardware to a rotor, which permits the rotor to expand, contract and dissipate heat without being restricted by the hat. A 2-piece solution also permits the use of exotic and lightweight rotor materials as well, like a carbon-ceramic matrix.  An added benefit to having a billet aluminum hat and/or lighter rotors is reduced unsprung weight. This weight reduction helps to sharpen and lighten steering response which further lends to improved handling.

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Boiling Point

A recurring theme in brake systems is that heat is the enemy. For the most part, this is true, the exception being specialized brake pad compounds formulated to function optimally at higher temperatures (racing brake pads). Aside from this instance, heat that is generated by the friction between the rotors and the pad material eventually transfers to the calipers and then the brake fluid. Modern brake systems are hydraulic, which means that they rely on incompressible hydraulic fluid (in this instance, brake fluid) to actuate the pistons against the pads when the brake pedal is depressed. The Department of Transportation (DOT) has established standards to indicate a fluid’s capabilities. DOT 3 brake fluid is the most common fluid used in automobiles. The name denotes the fluid’s heat capacity and performance capability as required by the DOT. Street vehicles rarely exceed the capabilities of DOT 3 fluid under normal driving conditions. When brake fluid heats to the point of boiling, pockets of air form in the brake lines. These compressible voids translate into a spongy brake pedal and an unresponsive brake system with dramatically reduced stopping ability. If you’ve upgraded your pads and rotors and have not upgraded the brake fluid, this could be the cause of poor braking performance. The solution is to upgrade your brake fluid. Under performance conditions such as on a track or a road requiring significant and frequent brake input, upgrading to DOT 4, DOT 5 or DOT 5.1 brake fluid will help to maintain the responsiveness and effectiveness of the brake’s hydraulic system.

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DOT Standards

Typical factory brake fluid is engineered to function within a prescribed temperature range optimized for the majority of driving conditions that the manufacturer expects a vehicle to encounter. This covers a broad spectrum of conditions ranging from freezing to triple-digit ambient temperatures. While these requirements cover a seemingly broad range of temperatures, the brake fluid must endure far more extreme temperatures. DOT 3 fluid is the most common fluid type employed by automakers with some requiring DOT4 fluid (in the case of higher performance or heavy duty applications). DOT 3, 4 and 5.1 are polyethylene glycol based fluids while DOT 5 is silicone based. The hygroscopic traits (propensity to absorb moisture from the atmosphere) of the DOT 3, 4 and 5.1 fluids could render the fluids less effective over time. Regular flushing of the brake system mitigates this effect. The silicone-based DOT 5 fluid tends to cost more but benefits from its hydrophobic properties.

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Fluid Grade               Dry Boiling Point                  Wet Boiling Point

DOT 3                         401 F                                     284 F

DOT 4                         446 F                                     311 F

DOT 5                         500 F                                     356 F

DOT 5.1                     500 F                                     356 F

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Containing the Pressure

Another component of a factory brake system that could benefit from improvement is the brake line. The stock brake lines are often high-pressure rubber hoses designed to be flexible throughout the full range of travel for your suspension. However, during high performance braking, these factory lines tend to expand under extreme pressure, resulting in reduced responsiveness and braking performance along with a spongy brake pedal. To improve the responsiveness of the brake system hydraulics, swapping out the factory brake lines with performance brake lines is an essential upgrade. Performance brake lines (like those offered by Goodridge) feature a PTFE liner (inner hose) that is shrouded by a flexible sheathing (stainless steel or even exotic materials like Kevlar) that protect the liner and prevent expansion. This keeps the fluids moving toward the calipers, for more responsive braking under all driving conditions.

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Maxed Out

Now that you’ve learned about the basics of brake systems, you can maximize the stopping performance of your vehicle. Slowing and stopping are paramount for safety as well as performance, regardless of your application. From streetcars and track cars to tow and utility vehicles, a good braking system is a must. If you’re pushing your vehicle beyond these bolt-on solutions, you could be a candidate for a big brake upgrade, which will be covered in the next two installments of STILLEN University. Stay on track!

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Do you have more questions about what would be right for your application? Reach out to us at 866-250-5542, at sales@stillen.com or by live chat on our website stillen.com to help you select the product that best suits your needs.

In our next installment of STILLEN University, we’re going to explore big brake system upgrades in greater detail. Check back with us soon!

If you would like to shop for upgraded 2-piece rotors, brake lines, or brake fluid: