slipstream444

Sure they can and I did. Like I posted before - my office moves a lot faster than that and I have to measure stopping distance on the fly (literally).

alexf20c

Why don't you two take it to PM?

jbotstein:
Jonathan, I would NOT remove the ABS fuse. Especially if the problem you're trying to fix is premature engagement. ABS is there for a reason - humans can't pump the brake pedal ten times a second. The concept of ABS is to preserve as much traction between the tire and road surface as possible. As soon as the ABS reads a wheel speed sensor(s) to be out of range (more than ~15% variance) due to wheel lockup, it will pulse the hydraulic pressure to the affected wheel(s). In doing so, it allows the tire to regain traction. (Coefficient of static friction is greater than that of sliding friction.) The ABS will pulse the brakes until it is happy with the wheel speed sensor signals - when the vehicle has come to a stop or wheel lockup and braking effort are back down to "normal."

ABS is something all cars should come with from the factory, but it is a very expensive option. A replacement ABS unit can cost up to $4500. It will save your ass dozens of times, especially in the rain or in a panic stop. Unless you're "trained" to do otherwise, most people will not pump their brakes without ABS. Your instinct is to hit that brake pedal as hard as you can, and to not let off. If your tires are already locked up, that's the worse thing you can do. You lose all steering and pretty much all braking. ABS, however, allows you to stand on the brake pedal. It does all the pumping for you, and allows you to maintain control of the vehicle. Even during an anti-lock event, you will still have control of the vehicle (roughly).








ANYWAY...

What makes you think your ABS is engaging prematurely? Just because you feel the vibration in the brake pedal does not mean that the brakes themselves are being pulsed. If the tires are not locking up, then there is no variation in wheel speed and thus, you will NOT have an anti-lock event.

The problem may be in the ABS unit. There is an accumulator which stores fluid/pressure during an anti-lock event. Because your brake pedal is fully depressed, the fluid must have a place to go every time the ABS unit releases the pressure to the affected wheel(s). It cannot go back to the master cylinder so it is routed to the accumulator. Pressures start at 800psi, and are normally in the 1800-2300psi range. If the pressure drops below the minimum allowed, the ABS pump will prime itself. When it does, you will probably feel a vibration in your brake pedal - just like in an anti-lock event.

You may have noticed one morning, after the car has been parked overnight, that as soon as you start the car and apply the brake, that the brake pedal will vibrate. It'll scare you for a second, until you realize what it is: The ABS is priming itself.

With that said, I'm willing to bet that what you're feeling in the brake pedal is simply the ABS unit priming itself. During hard braking, you lose a lot of line pressure. Check your brake fluid level. If it's full, you may want to bleed the entire brake system, including the ABS. You'll probably need a scanner to open the secondary valves in the ABS unit to allow a complete bleed.

RACER

How Brakes Work
by Karim Nice

Hydraulic Systems
The basic idea behind any hydraulic system is very simple: Force applied at one point is transmitted to another point using an incompressible fluid, almost always an oil of some sort. Most brake systems also multiply the force in the process. Here you can see the simplest possible hydraulic system:

Simple hydraulic system
In the figure above, two pistons (shown in red) are fit into two glass cylinders filled with oil (shown in light blue) and connected to one another with an oil-filled pipe. If you apply a downward force to one piston (the left one, in this drawing), then the force is transmitted to the second piston through the oil in the pipe. Since oil is incompressible, the efficiency is very good -- almost all of the applied force appears at the second piston. The great thing about hydraulic systems is that the pipe connecting the two cylinders can be any length and shape, allowing it to snake through all sorts of things separating the two pistons. The pipe can also fork, so that one master cylinder can drive more than one slave cylinder if desired, as shown in here:

Master cylinder with two slaves
The other neat thing about a hydraulic system is that it makes force multiplication (or division) fairly easy. If you have read How a Block and Tackle Works or How Gear Ratios Work, then you know that trading force for distance is very common in mechanical systems. In a hydraulic system, all you have to do is change the size of one piston and cylinder relative to the other, as shown here:




Hydraulic multiplication
To determine the multiplication factor in the figure above, start by looking at the size of the pistons. Assume that the piston on the left is 2 inches (5.08 cm) in diameter (1-inch / 2.54 cm radius), while the piston on the right is 6 inches (15.24 cm) in diameter (3-inch / 7.62 cm radius). The area of the two pistons is Pi * r2. The area of the left piston is therefore 3.14, while the area of the piston on the right is 28.26. The piston on the right is nine times larger than the piston on the left. This means that any force applied to the left-hand piston will come out nine times greater on the right-hand piston. So, if you apply a 100-pound downward force to the left piston, a 900-pound upward force will appear on the right. The only catch is that you will have to depress the left piston 9 inches (22.86 cm) to raise the right piston 1 inch (2.54 cm).

If you reversed this scenario, the left piston was 6 inches and the right piston was 2 inches, you applied a 100 pound force one inch down to the left piston, the right piston would move 9 inches. You have the same force, but the left piston only moved one inch instead of 9 inches.

The article confirms this fact.

[QUOTE=slipstream444,Oct 8 2004, 12:34 AM]Aren

alexf20c

If it takes 2 minutes between each 120-0mph max braking effort for the Pinnacle brakes to cool, and operate consistently, I would not consider them "true racing calipers and rotors."

alexf20c

You drive an S2000.

But when the S2000 is the closest thing to a racecar you have driven, of course you will think it has the best feeling brakes. Compared to my shifter karts and my Baby Grand, an S2000's brakes (Pinnacle or not) are absolutely numb.

RACER

How many miles are on these tires? Once the tires wear down, you lose grip, which in turn increases your braking distances. As far as removing the ABS fuse, I will not advise you one way or another, but a few peeps seem to think that they can shorten their braking distance on a closed race course. (dry) I believe it may be possible to threshold brake on a dry surface on a closed course better without ABS than with ABS. I definitely believe that ABS is the best for adverse conditions such as rain or dirt, sand ect. by far. I run my car hard sometimes and I never know what kind of adverse condition lies in front of me, so I wont be pulling my ABS fuse.

There is a possibility that if you replaced your S-02's that it would be much harder to engage ABS.

btw, alex gave a good explanation of how the ABS works

slipstream444

The 2 Minutes was not to cool Alex ... that's how long it took me to go from a dead stop after the first run to measuring, confirming and then going back out to the course and starting all over again. It was not deliberate ... just a result of the test being done by only two folks ... more of a manpower issue than anything else.
I have driven some grass roots race cars and the Pinnacle system is the closest thing you're going to find short of a true race car - for the S2000 at least. Talk to the folks who track the S on a regular basis with these brakes ... you'll get some interesting info.

Cheers

slipstream444

Okay "Racer", here is your quote. The size of the piston DOES dictate the overall clamping force. You are wrong.

I gave you (and everyone else that has had to labor through this thread) the website to read, not copy and paste. The fact is you can't put a spin on the facts in an attempt to magically become correct. You are wrong ... period. Once again ... larger pistons = greater clamping force ... end of story. Pedal feel is not controlled by the piston size alone and is subjective.

My point has been made ...

slipstream444

Just as you would, I reply to quotes with attacks Alex.

I made a simple point: smaller piston area means less clamping force ... Mr. Racer came out and stated (incorrectly) that piston size only determines "feel" and did not determine clamping force.
If you drive race cars and/or have a strong grasp of the physics involved (and I'm sure you do), you would agree that his statement (involving clamping force) was false on its face. I make no statement about "feel" other than it's subjective.

The intention here was not to hijack the thread (but it unfortunately came to that), but to explore all of the possibilities involving the ABS problems in the original post, including a possible problem with his aftermarket calipers.
I made the point that his Willwood 4-puck brakes actually create less clamping force (due to less total piston area relative to stock calipers) and shouldn't cause his ABS to cycle unless there was excessive caliper flex or loose brackets (when looking at the calipers alone as the possible problem). I also addressed what components in his braking system and/or suspension/tires may be causing the problems.
When there was crap flung my direction, I slung it right back, just as you should.

Sorry folks have had to tolerate this ... but it's not the first time we've seen it and it probably won't be the last.

davepk

Here we go again

Been there done that with those brakes. And i wouldn't recommend them to anyone who is serious about tracking their S2K. They couldn't handle the heat i threw at them and there were nothing but problems from day one.