First time on Circuit
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SoundGuyDave
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Oh, I will freely admit that, my % estimates were based on having DOZENS of students with S197s, though. Also, if you check your owners' manual, I believe (don't know for sure, though!) Ford is still recommending a 12-month service interval on brake fluid.
Honestly, I wouldn't be paranoid about it, but buying a $6.00 bottle of DOT3 is really cheap insurance versus sitting out half of a $400 track day because you boiled your fluid...
Honestly, I wouldn't be paranoid about it, but buying a $6.00 bottle of DOT3 is really cheap insurance versus sitting out half of a $400 track day because you boiled your fluid...
I would highly agree with you there
SoundGuyDave
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And the answer is: It depends... The RBF600 has a dry boiling point in excess of 600*F, a significant "improvement" over the stock fluid's DBP of around 415*F. A hard-tracked Mustang, unless running on FRESH pads (insulator), can easily exceed the stock fluid's boiling point, particularly over longer runs, or frequent shorter runs. In that sense, it's a HUGE improvement.
Following Heinlein's TANSTAAFL principle (bonus points for identifying the reference), the trade-off to that performance is its more aggresively hygroscopic nature. Simply put, to keep it from boiling, the chemicals used absorb water even more readily.
If you track your car hard, then you will see benefit to the Motul (or similar, like ATE) fluid. If you don't want the maintenance, then go with Castrol XRF. AT $70 per liter, it's a touch on the pricy side, but that gives you the best of all cases: Less hygroscopic, higher boiling point. Just add money. If you're not tracking your car hard, then don't even worry about it. Simply put, unless you're driving in a patently unsafe manner, you won't generate those kinds of brake temps on the street to justify the higher DBP of the racing fluids.
Following Heinlein's TANSTAAFL principle (bonus points for identifying the reference), the trade-off to that performance is its more aggresively hygroscopic nature. Simply put, to keep it from boiling, the chemicals used absorb water even more readily.
If you track your car hard, then you will see benefit to the Motul (or similar, like ATE) fluid. If you don't want the maintenance, then go with Castrol XRF. AT $70 per liter, it's a touch on the pricy side, but that gives you the best of all cases: Less hygroscopic, higher boiling point. Just add money. If you're not tracking your car hard, then don't even worry about it. Simply put, unless you're driving in a patently unsafe manner, you won't generate those kinds of brake temps on the street to justify the higher DBP of the racing fluids.
sheizasosay
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I think I just found my brake fluid of choice. BTW I found it for $60 on Amazon http://www.amazon.com/Castrol-SRF-Brake-Fluid/dp/B000JL760C
DUFUS
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I had considered the Castrol uber-fluid, but figured you'd have to do a total flush (and be exacting about it) to make sure you wouldn't be at the mercy of any remaining/legacy stuff, whatever you had been using before. So, we're not just talking about 1 liter, more like 3, correct? And even then, though it may not boil, it would still be subject to contamination as any other fluid. So periodic bleeding might still be necessary maintenance. Granted, it would be less often. But I don't think you can "set it, and forget it". It's Castrol, not Popeil.
OkieSnuffBox
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Track use will always = regular bleeding.
I can't imagine needing 3 liters to flush the system. However, this is why so many guys use ATE fluid (myself included), same fluid, two different colors, very easy to identify once you've flushed out the old stuff. (You alternate colors with each flush).
If you guys don't want the maintenance that comes with tracking a car, then don't track the car.
I can't imagine needing 3 liters to flush the system. However, this is why so many guys use ATE fluid (myself included), same fluid, two different colors, very easy to identify once you've flushed out the old stuff. (You alternate colors with each flush).
If you guys don't want the maintenance that comes with tracking a car, then don't track the car.
DUFUS
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Yeah, I was thinking of needing three .5 liter bottles. So ~1.5 of the Castrol stuff for a flush.
Using ATE just turned everything green for me.
Regardless, maintenance was my point. If you're flushing, or even bleeding regularly with "typical" hi-temp fluid (thus making wet boiling figures less relevant), then SRF seems to be overkill. Or an over-expense at least, since you should be maintaining it similarly.
SoundGuyDave
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Bleed at the track? YES.
How often: End of day (multiple day event, or at home afterwords), for preventive purposes; as required if you get a spongy pedal. Note that the thinner your pads get, the less insulation they provide, and the more heat gets transfered to the fluid.
Replace (flush) twice annually. Beginning of season, and 5-6mos later. Here in the Midwest, we only run April through October, and I flush mine the week before the first event, while doing pre-season prep, and end-September/beginning-October. If you notice you're getting a spongy pedal more frequently, that's a good clue that it's time. I think the SRF will extend those periods, possibly to annually, but I don't know that the price difference makes it worthwhile long-term. You spend a little less time on maintenance, but at triple the fluid cost.
How often: End of day (multiple day event, or at home afterwords), for preventive purposes; as required if you get a spongy pedal. Note that the thinner your pads get, the less insulation they provide, and the more heat gets transfered to the fluid.
Replace (flush) twice annually. Beginning of season, and 5-6mos later. Here in the Midwest, we only run April through October, and I flush mine the week before the first event, while doing pre-season prep, and end-September/beginning-October. If you notice you're getting a spongy pedal more frequently, that's a good clue that it's time. I think the SRF will extend those periods, possibly to annually, but I don't know that the price difference makes it worthwhile long-term. You spend a little less time on maintenance, but at triple the fluid cost.
I find bleeding at the track unnecessary unless you are also doing a pad change. As Dave said, when the pads get real thin, they heat the fluid a lot more, and almost always end up with a slightly squishy pedal at the same time I need new pads.
I just bleed before each track weekend, ATE seems to work fine on this car but is not my first choice, as I had trouble with it on my previous '97 Cobra. But it was the only thing available on short notice so I've used it pretty regularly now without issue, I also like that it's less hydroscopic than other 'race' fluids. Only using the Super Blue, and don't have any trouble with getting a full flush, just run the reservoir nearly empty, top off, and bleed back to the MIN line... Everything should be out then.
Cheers.
I just bleed before each track weekend, ATE seems to work fine on this car but is not my first choice, as I had trouble with it on my previous '97 Cobra. But it was the only thing available on short notice so I've used it pretty regularly now without issue, I also like that it's less hydroscopic than other 'race' fluids. Only using the Super Blue, and don't have any trouble with getting a full flush, just run the reservoir nearly empty, top off, and bleed back to the MIN line... Everything should be out then.
Cheers.
SoundGuyDave
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Okay, let's take a BIG step back here, and get a little brake system operational theory on the table. If I sound like I'm talking down, I don't intend it, but I don't know your background, so I'm starting from square one... The description is targeted at the standard braking package, the PBR-style 2-piston caliper, but is essentially the same for the 4-pot Brembos.
The disc braking system operates under hydraulic pressure, initiated by a lever (brake pedal) acting on a piston (master cylinder) that compresses the fluid in the front and rear circuits independently. These two circuits then feed the ABS controller, and under normal conditions, is simply split into four lines, one to each corner of the car. The pressurized fluid then forces two pistons (in the caliper) outward, thus forcing the inboard pad against the brake rotor. Since the caliper itself is mounted on two slide-pins, this will simultaneously shift the caliper body itself towards the inside of the car, pressing the outboard pad against the brake rotor as well. These two pads, clamped against the brake rotor, convert rotational energy (wheel turning) into heat, via the process of friction. The larger the differential in wheel speed from start to finish of the braking event, the more heat is generated. The more inertia in the system (rotational weight as well as vehicle weight), the more heat is generated. The rotor itself acts as a heat-sink, absorbing the bulk of the heat, then dissipating it as a radiator into the ambient air, or forced air if brake ducts are used. HOWEVER, some portion of the heat generated will also be absorbed into the brake pads, as well. While the pad acts as a pretty good insulator from the heat, inevitably, some of the heat (even from just radiant transmission from the rotor) will get to the pistons, and caliper housing, and thus be transmitted into the brake fluid itself.
Now, under "normal" operating conditions (street driving), there is more than enough heat-sink capacity in the rotors to handle the heat generated, and even under panic-stop conditions, the braking system is able to support one or two 80mph-to-zero braking events in close succession with little bad result. However, the way we brake on a road course is not even CLOSE to the "normal" operating conditions the design engineers envisioned, and the accountants approved. As a result, we will, unless changes are made (brake mods!), exceed the thermal capacity of one or more components in the braking system, and when we do, the result is generically called "brake fade," as you no longer have the stopping power you once did: the brakes are fading away.
There are two prinicpal types of fade: pad-related and fluid-related.
Pad fade: Since the interface between the pad and the rotor is the point of friction that makes the whole shooting match work, it also stands to reason that this will also be the point of highest temperature, as well. IF the temp at the interface exceeds the thermal capacity of the pad material, the original pad will begin to melt, losing it's "grain," and thus the bulk of it's ability to create friction. Symptoms will be a nice, high, hard brake pedal (normal, in other words), but the car just doesn't want to stop. You have to use inordinate amounts of pedal pressure just to start to slow, and there is essentially NO "bite" to the brakes at all. Fix: replace the pads with ones designed to operate at a higher temprature range. Don't go overboard, though, since "hardcore" race pads also have a MINIMUM operating temp, below which they are far less efficient.
Fluid fade: If sufficient heat is transmitted into the fluid (though the pistons and caliper body), you may exceed the boiling point of the fluid. Fluids are non-compressible, however gasses ARE compressible, and as a result, you have less pressure acting on the pistons due to loss to the generated gas. As mentioned earlier, brake fluid is aggressively hygroscopic; it pulls moisture out of the air, like a sponge in a bathtub. The more moisture content in the fluid, the lower the boiling point. Motul RBF600 has a dry boiling point over 600*F, but when contaminated with water this plummets to just a tick over 400*F. Before you think that 400*F is still pretty high, I see rotor temps well over 1000*F on a regular basis on hard-braking tracks! Symptoms of boiled fluid are a brake pedal that has a "mushy" or "spongy" feel, and tends to sink quite a bit lower than normal prior to actually biting. Frequently called a "soft" or "low" pedal as well. Fix: discard your pads if more than 50% worn, to maintain sufficient insulation from the rotor; add forced-air ducts to the center of the rotors to help bleed off heat; if the fluid is contaminated, flush with fresh fluid, if it's not contaminated, then you need to use a higher-temp fluid.
A few other rambling musings:
"Big Brake Kits" AKA BBKs, do not actually let you brake any better, since the determining factor is tire grip, and the stock brakes do a fine job at putting the car into ABS. What BBKs WILL let you do, is let you brake more often before the thermal capacity of the rotors is reached, due to the increased mass of the larger diameter. Additionally, the pads on BBKs are usually quite a bit larger (surface area) and thicker than the stock pads, creating that much more insulation between the pad/rotor interface and the fluid itself.
Stainless steel brake lines are both "bling" and necessary. The will reduce the amount of energy lost due to expanding the lines under pressure, but honestly, it's fairly minimal, and only noticeable at the ragged bleeding edge. What they WILL do, and do VERY well, is provide much better protection against track debris, like small stones and bits of rubber traveling at very high speeds.
Slotted, drilled, dimpled, scalloped, etc. rotors are, in my opinion, pure bling, and have no place on a track car. Slots were orignally introduced to allow organic (asbestos) brake pads the ability to off-gas without creating a gas layer between the pad and rotor, thus allowing consistent braking even at higher temps. We haven't used asbestos in brake pads in probably 30 years, and the modern binding agents don't off-gas like asbestos did, so there's no need for slots. The other factor is that ALL of the "modified" rotors have one thing in common: reduced mass. This is not only not good, it's actually BAD, since we know that the thermal capacity of the brake system is hugely dependent on the rotor capacity, which is directly related to MASS. More mass in the rotor, more thermal capacity. No point in throwing any of it away.
Other factors that affect brake heat generation: 1) driving style: "limousine stops" create more net heat than the classic "threshold braking technique" will. Get those stops done hard, and fast. Get in and out of the brakes, and you'll make everything last longer than if you gradually drag the car down. 2) Vehicle weight: It only makes sense that a 3800lb Mustang will take more energy to stop than a 3300lb Mustang, all other things being equal. 3) Tires: You WILL go through more brakes on Hoosiers than you will on a street tire. Not due to braking grip, but because you'll be carrying more speed going into the braking zone.
All brake fluid "ages-out," by absorbing moisture, and with the exception of the SRF, they all absorb at about the same rate. Stock fluid, in a daily driver that never sees the track still needs to be flushed annually to maintain a sufficient thermal capacity for multiple panic-stops. Upgrading to a racing fluid will not buy you anything there, at all. However, under track conditions, we are operating MUCH closer to the fluid's limit, and a relatively small contamination can result in boiled fluid, thus leading to the more frequent service interval. I have no personal experience with SRF (what I use works for me, no need to change), but there is a good deal of anecdotal evidence that it is much less hygroscopic, thus extending the usable life. You will have to work out the cost/benefit analysis for your own situation, factoring in time spent doing bleeds and flushes, versus the lightening of your wallet for the fluid, but there will be a point where SRF either makes sense or doesn't.
If you're going to track your car, you will need to decide "how much is enough" in terms of braking ability, and the resultant heat generated. Yes, you can just throw a set of StopTech competition 6-pot calipers at the car, along with multiple 4" ducts with inline blowers, and SRF fluid at the car, but if you only go out once a year, it's all just a waste of money. I found by switching from the stock PRB setup to the GT500 Brembo setup, the additional cost of pads and rotors was MORE than offset by the reduced change interval. To the point where the calipers themselves were paid for in the first season. Granted, I do over 30 track days a year, so your break-even-point could well be different.
Hope this helps!
The disc braking system operates under hydraulic pressure, initiated by a lever (brake pedal) acting on a piston (master cylinder) that compresses the fluid in the front and rear circuits independently. These two circuits then feed the ABS controller, and under normal conditions, is simply split into four lines, one to each corner of the car. The pressurized fluid then forces two pistons (in the caliper) outward, thus forcing the inboard pad against the brake rotor. Since the caliper itself is mounted on two slide-pins, this will simultaneously shift the caliper body itself towards the inside of the car, pressing the outboard pad against the brake rotor as well. These two pads, clamped against the brake rotor, convert rotational energy (wheel turning) into heat, via the process of friction. The larger the differential in wheel speed from start to finish of the braking event, the more heat is generated. The more inertia in the system (rotational weight as well as vehicle weight), the more heat is generated. The rotor itself acts as a heat-sink, absorbing the bulk of the heat, then dissipating it as a radiator into the ambient air, or forced air if brake ducts are used. HOWEVER, some portion of the heat generated will also be absorbed into the brake pads, as well. While the pad acts as a pretty good insulator from the heat, inevitably, some of the heat (even from just radiant transmission from the rotor) will get to the pistons, and caliper housing, and thus be transmitted into the brake fluid itself.
Now, under "normal" operating conditions (street driving), there is more than enough heat-sink capacity in the rotors to handle the heat generated, and even under panic-stop conditions, the braking system is able to support one or two 80mph-to-zero braking events in close succession with little bad result. However, the way we brake on a road course is not even CLOSE to the "normal" operating conditions the design engineers envisioned, and the accountants approved. As a result, we will, unless changes are made (brake mods!), exceed the thermal capacity of one or more components in the braking system, and when we do, the result is generically called "brake fade," as you no longer have the stopping power you once did: the brakes are fading away.
There are two prinicpal types of fade: pad-related and fluid-related.
Pad fade: Since the interface between the pad and the rotor is the point of friction that makes the whole shooting match work, it also stands to reason that this will also be the point of highest temperature, as well. IF the temp at the interface exceeds the thermal capacity of the pad material, the original pad will begin to melt, losing it's "grain," and thus the bulk of it's ability to create friction. Symptoms will be a nice, high, hard brake pedal (normal, in other words), but the car just doesn't want to stop. You have to use inordinate amounts of pedal pressure just to start to slow, and there is essentially NO "bite" to the brakes at all. Fix: replace the pads with ones designed to operate at a higher temprature range. Don't go overboard, though, since "hardcore" race pads also have a MINIMUM operating temp, below which they are far less efficient.
Fluid fade: If sufficient heat is transmitted into the fluid (though the pistons and caliper body), you may exceed the boiling point of the fluid. Fluids are non-compressible, however gasses ARE compressible, and as a result, you have less pressure acting on the pistons due to loss to the generated gas. As mentioned earlier, brake fluid is aggressively hygroscopic; it pulls moisture out of the air, like a sponge in a bathtub. The more moisture content in the fluid, the lower the boiling point. Motul RBF600 has a dry boiling point over 600*F, but when contaminated with water this plummets to just a tick over 400*F. Before you think that 400*F is still pretty high, I see rotor temps well over 1000*F on a regular basis on hard-braking tracks! Symptoms of boiled fluid are a brake pedal that has a "mushy" or "spongy" feel, and tends to sink quite a bit lower than normal prior to actually biting. Frequently called a "soft" or "low" pedal as well. Fix: discard your pads if more than 50% worn, to maintain sufficient insulation from the rotor; add forced-air ducts to the center of the rotors to help bleed off heat; if the fluid is contaminated, flush with fresh fluid, if it's not contaminated, then you need to use a higher-temp fluid.
A few other rambling musings:
"Big Brake Kits" AKA BBKs, do not actually let you brake any better, since the determining factor is tire grip, and the stock brakes do a fine job at putting the car into ABS. What BBKs WILL let you do, is let you brake more often before the thermal capacity of the rotors is reached, due to the increased mass of the larger diameter. Additionally, the pads on BBKs are usually quite a bit larger (surface area) and thicker than the stock pads, creating that much more insulation between the pad/rotor interface and the fluid itself.
Stainless steel brake lines are both "bling" and necessary. The will reduce the amount of energy lost due to expanding the lines under pressure, but honestly, it's fairly minimal, and only noticeable at the ragged bleeding edge. What they WILL do, and do VERY well, is provide much better protection against track debris, like small stones and bits of rubber traveling at very high speeds.
Slotted, drilled, dimpled, scalloped, etc. rotors are, in my opinion, pure bling, and have no place on a track car. Slots were orignally introduced to allow organic (asbestos) brake pads the ability to off-gas without creating a gas layer between the pad and rotor, thus allowing consistent braking even at higher temps. We haven't used asbestos in brake pads in probably 30 years, and the modern binding agents don't off-gas like asbestos did, so there's no need for slots. The other factor is that ALL of the "modified" rotors have one thing in common: reduced mass. This is not only not good, it's actually BAD, since we know that the thermal capacity of the brake system is hugely dependent on the rotor capacity, which is directly related to MASS. More mass in the rotor, more thermal capacity. No point in throwing any of it away.
Other factors that affect brake heat generation: 1) driving style: "limousine stops" create more net heat than the classic "threshold braking technique" will. Get those stops done hard, and fast. Get in and out of the brakes, and you'll make everything last longer than if you gradually drag the car down. 2) Vehicle weight: It only makes sense that a 3800lb Mustang will take more energy to stop than a 3300lb Mustang, all other things being equal. 3) Tires: You WILL go through more brakes on Hoosiers than you will on a street tire. Not due to braking grip, but because you'll be carrying more speed going into the braking zone.
All brake fluid "ages-out," by absorbing moisture, and with the exception of the SRF, they all absorb at about the same rate. Stock fluid, in a daily driver that never sees the track still needs to be flushed annually to maintain a sufficient thermal capacity for multiple panic-stops. Upgrading to a racing fluid will not buy you anything there, at all. However, under track conditions, we are operating MUCH closer to the fluid's limit, and a relatively small contamination can result in boiled fluid, thus leading to the more frequent service interval. I have no personal experience with SRF (what I use works for me, no need to change), but there is a good deal of anecdotal evidence that it is much less hygroscopic, thus extending the usable life. You will have to work out the cost/benefit analysis for your own situation, factoring in time spent doing bleeds and flushes, versus the lightening of your wallet for the fluid, but there will be a point where SRF either makes sense or doesn't.
If you're going to track your car, you will need to decide "how much is enough" in terms of braking ability, and the resultant heat generated. Yes, you can just throw a set of StopTech competition 6-pot calipers at the car, along with multiple 4" ducts with inline blowers, and SRF fluid at the car, but if you only go out once a year, it's all just a waste of money. I found by switching from the stock PRB setup to the GT500 Brembo setup, the additional cost of pads and rotors was MORE than offset by the reduced change interval. To the point where the calipers themselves were paid for in the first season. Granted, I do over 30 track days a year, so your break-even-point could well be different.
Hope this helps!
OkieSnuffBox
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Great post, just wanted to add.........another plus of aftermarket BBK's is the feel that comes from the fixed caliper vs the floating caliper. At least in my experience.
SoundGuyDave
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Agreed, just getting the stiction of the slide-pins out of the equation is a plus. Even pad wear for the win!
claudermilk
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Excellent post, Dave. I knew most of it, but the way you outlined things made a couple of concepts click.
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