would be helpful to have someone video your car from a low angle when it happens... i'm still going on the theory that it kicks in when one tire picks up enough to cause significant differential wheel spin rates (as it would on ice)... the conditions you describe sound consistent with this theory... thoughts?

I believe this to be a plausable cause. Mine only kicked in at the end of the braking distances. The car would be able to stop from 60-0 in approximately 50ft and then it would just ice mode to a 75-90ft stopping distance. That would also go to explain why on some surfaces the car would be fine but others it would ice mode hmmm... I think you on to something Travis!

Another observation that I forgot to mention. My instructor did not seem all that concerned with the problem. The first time I experienced "ice mode" I was scared that he was going to direct me to pit and end my day. But he didn’t.

The second time it happened he told me to pit and had a marshal eyeball the brakes. The marshal took a look and said that the brakes were definitely hot but otherwise fine.

After that session he solo’d me.

So whatever he perceived in the passenger seat must have felt like simple driver error and not a mechanical issue. I imagine he thought it was simple brake lock up even though there was no tire squeal.

Take this for what it’s worth, I am not sure if it adds anything to the story...

I can reproduce it on a nice smooth sticky surface with the only factor being temperature. Once the brakes are thoroughly heat soaked ice mode is induced under heavy braking, and this is with totally respectable peak rotor temperatures. I can also prevent ice-mode from occurring by artificially cooling the brakes to prevent the heat soak.

All of my testing has been done on hot and heavy auto-x conditions. It typically takes 20-30 minutes of build up under those conditions to reach a point that ice-mode kicks in for the braking zones.

There are other conditions that activate the ice-mode as well such as sudden bumps, sand, marbles etc, but the heat related one has me beat. What's interesting is that during one of these ice-mode events, at the very end of braking once the car gets below about 15-20mph you suddenly get full braking back again. Totally bizarre.

trying to connect the theories... possible that as your brakes overheat, you're getting fade on inside front wheel and that wheel is therefore braking at a slower rate than the rest?

I don't think the overall temperatures are high enough to induce pad fade but it is a theory I will investigate.

One thing that doesn't add up with that theory is that the brakes fully return after the car slows down to a slow speed the ABS computer apparently "exits" its ice-mode. There is also no pull or anything else that would indicate more braking for on one side or the other.

There is however a large temperature differential front to rear, so it is possible that the ratio of front braking force vs rear braking force exceeds the ABS computer parameters causing the event.

I will also confirm that after an ice mode event the brakes come back at 100% efficiency. If it was purely heat related I would expect some residual loss of braking following an ice mode event.

Also, I can confirm that during ice mode I never felt like the rear end was going to come around on me. Rather, the car just tracked straight ahead. This leads me to believe that whatever our ABS is doing is to create a heavily front biased brake condition. This of course would create a easily controlled straight slide (for anyone who does not know, too much rear brake bias creates a dangerous situation under braking whereby the rear of the car slides out much like a power slide under heavy acceleration).

Also, this "ice mode" problem is not limited to the 370Z. Google the term ice mode and brakes and you will be amazed at how many cars have the exact same problem.

My theory is that this is a result of ABS technology advancing faster than real world practicality. I imagine there is some algorithmic equation in our cars brain that decides it is better to allow the car to track in a straight line at a controllable 25% braking than to lock one wheel up or flip the car around.

I guess its time to adjust our driving style folks...

solutions on the table:

- stiffer suspension
- more brake cooling
- switch ABS computers
- less aggressive compounds
- adjust driving style

Miss any ?

I only have two autox on the car so far, but ice mode was only apparent during complete panic stop when I have to do a complete stop at the finish line. It was never a real issue when I was running. I have a stock car with 265 and 285 tires

I have experienced ice mode in my 350, C6, RX-8, you just get used to it.

I only have two autox on the car so far, but ice mode was only apparent during complete panic stop when I have to do a complete stop at the finish line. It was never a real issue when I was running. I have a stock car with 265 and 285 tires

I have experienced ice mode in my 350, C6, RX-8, you just get used to it.

This is where it seems to get a little different between us.

I can brake as hard as I want for about 3 runs. After that I get ice-mode under firm straight line braking every time. It doesn't matter how gently I roll on to the brake either. The brakes are hot but not cooked, and the pads have twice the operating temperature range of stock (Mintex Extreme) but are not an aggressive compound at all. The brakes have a 15-minute cool down between runs.

The front ABS actuators pulse away like crazy as if there is lock up yet there is none. I have tried altering the brake bias to the front and to the rear by using a more aggressive pad on one axle at a time. This had no benefit.

Yes, stiffer suspension all around will prevent the weight transfer, and this is on the cards anyway, but the fact that it only happens to me when the brakes are warm makes me think there is something else at play here. Either the ABS computer is getting bad input from one of the wheel speed sensors due to heat expansion or something else in the ABS is acting up when the brake fluid temperatures rise.

chris, we need to construct tests for these theories... to rule out (or in) the heat theory, we need to measure temperature on the calipers and rotors and conduct trials... not sure how to test temp of the fluid though

I could measure the temperature of the hard brake line at certain points. In theory after a 10 minute sit the line that wraps the fluid should be close in temperature due to conductive heat transfer.

Okay for caliper temps I can use the temperature stickers and probably a portable laser thermometer (should read high enough). I will get some paint for the rotors and will see if 1400F is enough for the pyrometer, the 1800F unit is more expensive.

Ok picked up an Infrared thermometer from Grainger, it's good up to 1832F. If anything on my car gets that hot I expect spontaneous combustion!

Extech 42512: Dual Laser InfraRed Thermometer

http://www.extech.com/instruments/re...ages/42512.jpg

Cossie
I had 2 Rx8s and track them on a regular basis. Galiper would heat up, creating brake fade but the "Z ice mode" is different. I experienced it 2 times at the far end of a long braking zone where i needed extra braking, than "poof" no brakes at all... and the next corner was fine (which shouln'dt be the case if it was heat related). My theory does on ABS sensors recating funny when the rear will do not have enough road contact.
As said before, we may to adjust our driving styles accordingl until a solution is found...
Phil

After re-reading the Car and Driver article I am preparing a test to determine if it is boiling brake fluid that might be confusing the abs system.

On Friday I will be doing a track day at the Summit Point main circuit. Last time I ran Porterfield R4 full race compound with ATE super blue fluid and I experienced ice mode three times. I have made three changes to my brake system.

1. Castrol SRF brake fluid (at $80 per liter).
2. CarboTech XP10 pads up front and XP8 in the rear.
3. Home made brake cooling ducts from the fang inlets (however, they are not directly connected to the inside of the rotor).

I'll let you know how it goes on Saturday.

Looking forward to hearing your results.

That sounds good.

The expensive fluid won't lower temps as you know, but will have a higher b.p. So, you still may have an ABS sensor that gets excessively hot, and as you say, you will only be able to rule out fluid boiling as an individual cause.

Where are you pointing the air if not at the inside of the rotors? How far away is the outlet? Perhaps if you can point them towards the ABS sensor we can test the theory of sensor overheating as a cause.

The other one we need to test is differential wheel spin...

Suscribed

The ducts are pointing (as best I could) to directly under the brake caliper. I connected the end of the tubing to the lower part of the shock absorber. I would guess about 4 to 6 inches from the rotor. The main problem is the shape of our front spindle. It really blocks access to the inside of the rotor. In hindsight, I should have cut off the entire dust shield but I don't have a proper sheet metal shear (and I was getting tired).

I should have taken some pictures but I was not all that anxious to display my ghetto-cooling ducts. And it did take some cutting of the inside fender cover...


Keep in mind that I was retrofitting my fang ram air setup and this limited the length of my brake tubing.

So I finally experienced this at the last event. Last run on the day with a very hot and tired car. Noticed the ABS engage wayyy too early on the second to last corner then coming through the finish had almost no brakes, very strange feeling.

Car has all stock brake components with Hoosier A6's.

^ Sounds like fade? Maybe you glazed the pad?

Sorry to go offtopic folks, but I want to get in on the fun too. Where are you all buying your Carbotech pads at?

Forged gave me a pretty reasonable price.

Same thing happens to me. I thought it was fade at first, but the ABS ends up pulsing the front brakes, not the rear. If the fronts were overheated you would expect the rear brakes to be doing all the work and locking up as a result.

Something is f-d up in the ABS program (of which heat is an apparent factor). I'll know more this weekend after taking some measurements.

ABS systems are supposed to activate when the speed sensor at each corner notices the tire slowing down faster than it is physically possible for the entire car to slow down. When it reaches a threshold, it releases brake pressure to that corner until it senses some acceleration back from that tire, immediately after it lets it decel again until it reaches the threshold and the process starts all over.
I don't think our system is malfunctioning, in fact I think its working too well. It just thinks its going to loose traction immediately after it reapplies pressure. I think the parameters of the ABS system are simply too conservative to be taken on the track, problem is that if they were what we wanted, then we would have inexperienced drivers (read: the same idiots who crash when they turn vdc off) crashing in the rain all the time.

So put yourself in the shoes of the mfg, they would obviously rather a bunch of us enthusiasts bitch that we can't use our cars on the track that well, than people crashing and dying.
It happens to GT3's and Exiges all the same. The only thing we all really have in common is that the ABS system needs to be there to keep people in one piece and needs to undergo rigorous testing to meet standards.

At the same time, I realize that if the system were working properly, it should detect a point in which the tire deceleration can in fact keep up with the car's overall deceleration and stop the ABS system. If the ABS were programmed for big sticky tires such as the ones we have stock, that should minimize the intrusion of the system. It would allow for a more aggressive discrepancy between car decel and tire decel. I think thats too expensive though, to develop a customized ABS system specifically for this car and specifically for us track goers. They would rather probably use the same system as they do in the sentra, maxima and cube. Not to mention the problem again becomes; what happens when that same car is in the hands of soccermom late for practice in the rain?

The only way I can see us getting around this problem is turning abs off or having a system that is designed to allow more aggressive tire compounds. As someone already pointed out, that option is the BMW system that is $15,000.

I wish we had some sort of "Track" button that would switch us to a more aggressive ABS tune. I'm pretty sure Ferrari has such a system implemented within their manetino steering wheel system, but that's why they are $250k.

Anyone ever heard of a way to reprogram your ABS parameters?

In other words, I hope we find something punctual that is specifically causing the ABS to go and remain in icemode, but I have a feeling its just the system doing its job in what it is programed to think is a "complete panic stop". I can guarantee you all that the guys with GT3's out there, who have a little bit more resources than most of us do, (I said most, congrats if that doesn't include you) would have found a fix for this already if it were a hardware malfunction.

Just my .02 and on that note I will also add that I'll be looking for a punctual issue just like you guys. I'm just a little skeptical considering the facts.

EDIT: by this logic...folks with BBK's and stickier tires might be more prone to going into icemode. Maybe we need pads with less initial bite or less brake pressure. I'm just throwing ideas out there that might make someone put two and two together and say "Aha!". Not to mention it should happen less and less and not more and more as our crappy stock pads get hot and begin to fade, but that doesn't seem to be the case either.

Does anyone know what the BMW system replaces? Do they mention any components that hold up better to heat??

Yes I understand the difference between the ice mode and brake fade. At autox, there is no way you can generate enough heat or speed to fade the brakes. What I felt was clearly ice mode where the brakes would just pulsate and not stop. The C6 was notorious for thatThe RX-8 rarely got into ice mode compare to the Z and other cars.

Ice mode is normal as to prevent brakes from constantly locking in the snow

StopTech has a great white paper on BBK's and their potential impact on ABS.

StopTech : Balanced Brake Upgrades

The problems of a misapplication of a BBK described in the article would apply to the braking system across the board however. The issue raised here is after time on the track (heat buildup in the rotor, caliper, pad, fluid, etc.) the ABS system seems to kick in early. The parameters of the ABS system may be so tightly constrained that when brake fade (due to heat buildup) sets in there is an immediate overreaction. When combined with a misapplied BBK, the overreaction is exacerbated.

Possibly. Maybe. Dunno.

It's a possibility. But in this case it would be the stock BBK (small BBK?) that was misapplied. Has anyone with base brakes experienced ice-mode?

I will say that the AP Racing kit goes for a longer period before the heat related ice-mode failure kicks in. The most notable difference besides the calipers is that the rear rotor is much smaller in comparison to stock, reducing the rear bias the stock setup has just slightly.

Hopefully I can get some decent measurements this weekend and we will see just how much heat auto-x can actually generate. Our auto-x courses are roughly twice the standard length, but even still there shouldn't be any way the brakes can overheat in those conditions, but we will see.

I wish we could have real time monitoring of the brake temps. Maybe we could pinpoint a temperature that causes ABS failure.

Who's gonna do it?

http://www.advantagemotorsports.com/Sensors.htm

Last sensor is an IR electronic temp sensor with datalogging.

I would like to think that the ABS could be reprogrammed, but I'm 99% sure that Nissan we never do this unless a flaw can be easily reproduced under street driving conditions, and that the flaw leads to several serious accidents.

Pretty much the only hope of a cheap fix is to locate the source of the triggers and do as much as possible to alleviate them.

At some point Nissan might release a Nissan Motorsports ABS unit for race cars, but it will probably be sold with a moderate price tag and a large "for track use only" warning. The later isn't a real issue for experienced drivers.

This weekend I have an auto-x and will be taking careful temperature measurements of rotor, caliper and brake line both front and rear after every run using an infrared thermometer. This is about as close as we can get to realtime data. At the end of a run the brakes are at peak temperature and then you idle back to your hot pit at 5 mph giving the brakes no cooling on the way there.

Not exactly. Rotor size is not the only factor in determining brake bias as the caliper piston sizing has just as much to do with it. The AP Racing systems do not move the bias forward at all.

Chris

Let's see what Chris comes back with...

If more is needed and if the group is willing to pony up contributions, I would run this sensor (Brake Disc Temperature Sensor) connected to my traqmate and start collecting data... we might be able to get away with only 1 corner... cost a few hundred bucks

hmm...buy a toy for travis....I'll pitch in $30

subscribed

Simply by having 'ice mode' doesn't imply a misapplied ABS situation. My point was that by having a misapplied aftermarket BBK may be making the standard situation, which is expected, worse.

In my case it got better, but there are other BBK kits that didn't fair as well.

No it wasn't brake fade. The brakes were fine all day and the amount of pedal travel/effort required to stop the car never changed the ABS just started engaging well before it should have. What doesn't make sense to me is if it was a straight programing problem the ABS would go into ice-mode from the first stop. The fact that it also seems to be temperature related is very puzzling

Go directly to Carbotech - Carbo Tech, Inc.* - they have our pads in stock, can offer a pad bedding service so that you just install their pads and go (I haven't installed mine yet). They are very responsive with fast and reasonable shipping.