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 Guide to Brakes

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donyong
Member


Number of posts : 308
Vehicle Type : Lancer GT 2.0
Registration date : 2008-07-18

PostSubject: Guide to Brakes   Thu Oct 29, 2009 10:05 am

Why are flexible brake hoses used in the first place? From the factory, nearly every production passenger car has short, flexible hoses that run from the fixed, hard metal brake tubes to the calipers (or wheel cylinders as the case may be). These flexible hoses are necessary because the wheel ends are free to move relative to the body of the vehicle. Inflexible tubes would not allow for the articulation of the wheel ends without subsequent failure.

What are OEM hoses made from? Typically, OEM hoses contain a compliant polymeric inner hose to transmit brake fluid pressure from the brake tubes to the caliper. While the polymeric tube itself does a good job of withstanding attack from the brake fluid, it must be protected from the outside world and is consequently wrapped (overmolded) with a thick, rubber coating. Hollow fasteners at one or both ends of the hose provide a direct flow path and a leak-free connection system.

So how are Stainless Steel lines different? Stainless Steel lines (they are actually hoses, but we'll use the common term “lines� from this point forward in this FAQ) are similar to OEM hoses in function, but differ greatly in execution. Unlike OEM hoses, SS lines incorporate a low-compliance Teflon inner hose. In addition, instead of covering the Teflon with overmolded rubber a woven braid of Stainless Steel strands is placed over the hose for protection. As with an OEM hose, the ends are terminated with hollow fasteners to allow for the leak-free passage of brake fluid.

So why is that better than the OEM rubber design? Stainless Steel lines provide a number of benefits as compared to their OEM rubber overmolded counterparts.

1. The SS braid provides superior protection from flying roadway debris.
2. The SS braid and Teflon hose reduce expansion during pressurization.
3. They provide the race car look.

I understand the protection benefit, but can you explain the reduced expansion benefit? Any time that an object is subjected to internal pressure, it expands. The amount of expansion will be proportional to the amount of pressure present and the rigidity of the holding structure. In the case of brake hoses, we are subjecting Teflon to internal pressures as high as 3000PSI. Because the Teflon is relatively flexible (which makes it ideal for the job in one regard), it will expand under these conditions. This expansion creates additional fluid volume in the hydraulic circuit which is felt by the driver as a soft or mushy pedal.

Rubber overmolding does little to reduce expansion under pressure, as rubber is also a relatively flexible material. A woven braid of Stainless Steel, however, can greatly increase the rigidity of the hose under pressure while still allowing adequate flexibility for wheel end movement. In many cases, this reduced expansion can be felt by the driver as a firmer or more responsive brake pedal.

In addition, the reduced compliance will result in a faster transient response of the brake system. In other words, the time from the driver hitting the brake pedal until deceleration is generated will be decreased by a small amount. The benefit will vary based on each individual application, but in general overall deceleration can be attained more quickly, resulting in slightly shorter stopping distances.

What impacts will SS lines have on my vehicle's P-T (pressure vs. torque) relationship? None. Because brake lines and hoses do not affect the torque generated at the wheel end, the P-T relationship remains unchanged when SS lines are installed. Only changes to a vehicle's caliper, rotor, or brake pad coefficient of friction will impact the P-T relationship.

Well then, will SS lines impact my vehicle's P-V (pressure vs. volume) relationship? Absolutely. Because SS lines are much less compliant than their OEM counterparts, the P-V relationship will be reduced to some degree (less volume will be required at a given pressure). This is exactly the reason that a car equipped with SS lines has a firmer brake pedal.

However, because the P-T relationship remains unchanged with SS lines, the impact to ABS, TCS, and other brake control systems is typically negligible. Our own BBK kit testing indicates that most ABS, TCS, and other brake control systems are robust to the small changes affected by the addition of SS lines. On the other hand, testing at StopTech (and at major OEMs as well) has shown that while decreases in the P-V relationship typically are invisible to SS lines, increases in the P-V relationship are not (as would be found with an inappropriately-sized BBK).

In summary, because SS lines and a properly sized and balanced BBK only serve to reduce the P-V relationship, we have time and time again demonstrated appropriate system integration with these products. Our in-house testing allows us to make this statement for every platform we service.

Will I feel a difference on my car if I install SS lines? The amount of perceived difference will vary by each car's individual design, age, and usage. Those cars with a significant amount of flexible OEM line or those that have seen years or use and aging will typically display a more dramatic improvement in pedal feel than new cars with shorter lines.

What is the difference between lines that are “DOT compliant� and “DOT approved�? The United States Department of Transportation (DOT) has established numerous standards for automotive components and subsystems. The regulation for brake hoses happens to be FMVSS106. In this document, anything and everything pertaining to automotive brake hoses has been laid out in gory detail – at least, those things important to the federal government.

If a manufacturer claims their SS lines are “DOT compliant�, it means that their SS lines have passed all FMVSS106 requirements, and they have submitted the test data to the government for official certification. This does not mean they are acceptable for use on your car, but it does mean they pass the government minimum standards.

Another term you may hear in this context is “DOT approved.� However, the DOT is not in the business of actually approving or disproving compliance – they don't typically run any tests on aftermarket components themselves. Under these circumstances, one can only surmise that these manufacturers are trying to state that their lines are actually “DOT compliant�, but it never hurts to ask before you buy.

So, do I need to use only DOT compliant SS lines on my car? Not necessarily. The DOT requirements must be met in full for official government approval, so even if a SS line passes every performance test but is labeled with the wrong type of tag (or something equally trivial) it would fail certification. While this might mean something to an auto manufacturer or assembly plant, it is meaningless to the performance enthusiast.

All the DOT compliance means is that the lines have passed a minimum set of government standards which may or may not be important to you. Does this mean that DOT compliant lines are the best for your car? Not necessarily, but the certification should indicate that the manufacturer understands the product and is trying to hold itself to a certain standard.

Why do some SS lines have a clear plastic covering? Under certain conditions, dirt and other abrasive contaminants can find their way between the SS braid and the Teflon inner hose. Over time these contaminants can be ground into the Teflon line to the point that a leak can develop. Naturally, a leak in the brake system is never a good thing.

Some manufacturers have taken the extra step to cover the SS braid with a polymeric coating to prevent contaminants from working their way into the Teflon liner. While this coating is not necessary for short-term longevity, hoses without the coating should be inspected and replaced on a more frequent basis.

Why do some SS lines have plastic molded over the end fittings? Some SS line manufacturers have adopted the practice of molding a semi-rigid polymer over the fittings at either or both ends of the line. These features act as a strain relief for the SS braid where the fitting is secured to the line. In some cases, lines without these features can fail certain dynamic portions of FMVSS106, as the SS braid can wear itself into the Teflon line where it is secured to the end fitting.

Do I need to take any special precautions when installing my SS lines? In general, no. The most important thing to note is that the routing of the SS line should match either the original stock routing or the instructions included for a new routing (if applicable). Because the SS braid will eventually wear through just about anything (once the protective outer layer is worn away), be sure that there is adequate clearance to all other moving parts under conditions of full wheel travel and full steering.

It should also be mentioned that after installation care should be taken to examine your SS line routing to ensure that the line is not stressed when the wheels are turned to full lock. This is best done with the wheel hanging at full droop to amplify any routing concerns. Of course the line should never come in direct contact with any part of the tire, but the line should not be pulled radially with respect to the overmolded end fittings either.

Q: Why would I want slotted or cross drilled rotors?
A: To help hot gases escape from the rotor.

When the brakes are applied the brake pads rub against the rotor to provide friction. This severe friction is what makes you stop. This friction also comes with a severe amount of heat. The more you apply the brakes the more heat is involved. This heat if allowed to build far enough creates hot air (gas) which prevents the pad from actually contacting the rotor. The result is what's known as brake fade. The brakes will have a soft spongy feeling and will temporarily lose their braking efficiency. Slots or drilled holes into the rotors allow the gases to escape away from the rotor, into the air. This significantly reduces the chances of brake fade.

Q: So which is better, slots or cross drilled?
A: Each one has it's advantages and disadvantages. For the typical application slots are more useful.

Slots are "valleys" that are carved into the rotor surface, usually in a pattern that agrees with the direction that the rotor turns. The slots are lower than the brake disc surface and allow a place for the gases to collect and make their way out from the rotor. Slots allow more brake surface to be used. In a typical setup slots are preferred because a street rotor will need as much braking surface as possible to help stop. If more cooling is desired, more slots can be added.

Cross drilled rotors have been drilled through sideways. This allows any heat to escape into the inner (open) area of the rotor. From there, the air can make it's way out to the edge of the rotor and dissipate. Some argue that these "holes" in the rotor cause the rotor to lose it's integrity or strength. Many an owner have seen their rotors crack in between holes due to the heat coupled with low rotor strength. You might wonder why race cars have these. Well, in extreme situations, the cross drilled rotors can be provided with a cold air source (brake cooler ducts) to help cool them down. These ducts force cold outside air into the rotor and make their way through these holes/vents to significantly cool the rotor.

Q: I have heard of cryo treatment, what is this?
A: Rotors are frozen to subzero temperatures then re-heated slowly to help stress relieve the part and make it ultra hard.

Whether it's slots, drills, or stock rotors you can't go wrong with this treatment. This will extend the life of your rotors beyond any expectation. This can also help to prevent cracking on cross drilled rotors. This process has been around for years and used on race cars around the world.

Q: Why would I want stainless steel brake lines?
A: Rubber brake lines can expand, which is not a good thing.

When braking force is applied, there is extreme pressure within the brake lines. Most of this pressure is transmitted to the brake caliper to help stop the disc from turning. There is however some swelling of the rubber brake lines due to their flexibility. This means you are not getting the full braking effect. By changing the lines to stainless braided, you can reclaim this force. The braided lines are capable of holding many times more pressure than any rubber line without expanding. Since this "extra" pressure is not lost, it must be applied to the only device than can accept pressure, which is the calipers. The result is the feeling of stronger brakes, without upgrading the brake system. Another benefit is the long life span of stainless lines that do not crack or fade.

http://www.alltrac.net/tuning/brakefaq.html
http://forums.delphiforums.com/Vivio/messages?msg=614.1

Pad and Rotor Bed-In Theory, Definitions and Procedures

When a system has both new rotors and pads, there are two different objectives for bedding-in a performance brake system: heating up the brake rotors and pads in a prescribed manner, so as to transfer pad material evenly onto the rotors; and maturing the pad material, so that resins which are used to bind and form it are ‘cooked' out of the pad.

The first objective is achieved by performing a series of stops, so that the brake rotor and pad material are heated steadily to a temperature that promotes the transfer of pad material onto the brake rotor friction surface. There is one pitfall in this process, however, which must be avoided. The rotor and, therefore, the vehicle should not be brought to a complete stop, with the brakes still applied, as this risks the non-uniform transfer of pad material onto the friction surface.

The second objective of the bedding-in process is achieved by performing another set of stops, in order to mature the pad itself. This ensures that resins which are used to bind and form the pad material are ‘cooked' out of the pad, at the point where the pad meets the rotor's friction surface.

The bed-in process is not complete until both sets of stops have been performed.

Bedding-in Street Performance Pads

For a typical performance brake system using street-performance pads, a series of ten partial braking events, from 60mph down to 10mph, will typically raise the temperature of the brake components sufficiently to be considered one bed-in set. Each of the ten partial braking events should achieve moderate-to-high deceleration (about 80 to 90% of the deceleration required to lock up the brakes and/or to engage the ABS), and they should be made one after the other, without allowing the brakes to cool in between.

Depending on the make-up of the pad material, the brake friction will seem to gain slightly in performance, and will then lose or fade somewhat by around the fifth stop (also about the time that a friction smell will be detectable in the passenger compartment). This does not indicate that the brakes are bedded-in. This phenomenon is known as a green fade, as it is characteristic of immature or ‘green' pads, in which the resins still need to be driven out of the pad material, at the point where the pads meet the rotors. In this circumstance, the upper temperature limit of the friction material will not yet have been reached.

As when bedding-in any set of brakes, care should be taken regarding the longer stopping distance necessary with incompletely bedded pads. This first set of stops in the bed-in process is only complete when all ten stops have been performed - not before. The system should then be allowed to cool, by driving the vehicle at the highest safe speed for the circumstances, without bringing it to a complete stop with the brakes still applied. After cooling the vehicle, a second set of ten partial braking events should be performed, followed by another cooling exercise. In some situations, a third set is beneficial, but two are normally sufficient.
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