If you are tracking with your VDC, you have more to be concerned about than just ice mode

Note sure what you are implying here...

but even when you push the VDC button to turn it off ... VDC/Brake Control are still functioning but on a diminished level.

VDC no, ABLS and EBD yes. Computer doesn't apply the brakes for you with the VDC off. If you do use it, it would distribute the braking force accordingly.

In a 350Z, even with VGC in the off position, EBD is still working, so if you are in a drifting condition...it will apply one or more brakes in an attempt to straighten out the car...however not sure about the 370Z.

Both my 350Zs had this issue (2004 & 2006), and was completely resolved by removing the Yaw sensor that drives all the VDC related computing.

Note: I have not tracked my 370Z, so I can't verify that condition exists in that model. We need some 370Z TT or W2W racers to speak up here.

you need to layoff the fast and furious bible or do some racing 101 classes. braking in the middle of a turn is like eating beans before an anal scene

?????

Note sure this is going anywhere, dropping out of this thread

I think Laze1 was implying that the car would brake its self without applying the brakes to try and pull the car out of a drift. I don't know but I can drift my Z from side to side and the computer doesnt try and stop me

See #83.

No the car would only brake itself if you leave the VDC on or you light up the inner rear. (it would apply brakes to control that at least)

:icon18:

I read Mike's blog post and wanted to comment a little bit on the ice-mode as I had it on track for the first time this weekend (normally I just get it at auto-x). I was out in an open track session after the time trials, was running on the RE-11 street tires and had been out for 10 laps or so, the brakes were good and hot but not overheating. The suspension was dialed in fairly soft as the time trial ran under damp conditions and I had forgot to change the shock settings before going out.

Heading into the braking zone to turn 11 at NHMS is a gentle left with light to moderate acceleration followed by a pretty much straight braking zone but can be a little bit bumpy. As soon as I jumped on the brakes the pedal went hard and I only had about 50% braking force. I just rode it out as there was plenty of extra track and run off and I did manage to slow down enough in a straight line to eventually turn into the corner.

As it only happened the one time it is hard to say definitively what the issue is, but based on that experience and that of Travis's I'm thinking it is related to having a low traction situation in the rear and the ABS system's poor modulation. As the weight was transferring forward under braking the rear went light and the ABS system was unable to release enough pressure to the rear to unlock the wheel so instead it appears to release pressure to the entire braking system. It is also possible that I momentarily locked a front wheel by jumping onto the brakes too suddenly before the weight had transferred.

At this point the only factor I think heat plays in this is that the brake pads are performing better under the moderate heat and have a higher coefficient of friction. Similarly an aggressive bite pad can trigger the same condition with a much lower heat especially on a less grippy tire.

The other heat condition that seems to trigger an ice-mode like feeling is pad fade. If you get the pads outside of there operating range then their friction falls away, sometimes dramatically (especially the stock pads) and the rear brake is forced to do more of the braking causing rear lock up and poor braking performance. But with the proper track pads this shouldn't be an issue.

I was using the AP Racing rotor paint and caliper temperature stickers, the paint all turned white indicating rotor temperatures in excess of 1130F and the calipers peaked at just a hair under 500 degrees. There was some significant pedal fade on the slow in lap but not under racing conditions. Was running AP Racing 600 fluid. Rear brakes rotors reached 1050F and calipers were only 360F.

I didn't think as much into it as you did, but I did a track day and autox in the same week. At Lime Rock, I didn't get into ice mode as the XP8s have much less bite. On top of the better pad, I ran mostly in the rain and the pavement at the track is only two years old. Three days later I did an autox in a lot that is over 40 years ago, I was hitting ice mode on and off at the start and end of the run (70 second) with the same XP8. As soon as I switched to the stock pads, problem went away. While there might be other factors contributing to ice mode, I personally believe rough pavement is a big one for me.

It's not the pavement itself but rather the friction co-efficient, obviously (or not) older pavement has a much smaller contact patch with the tire due to more of the binding media getting eaten away, therefor less friction. Basically once the pad to rotor friction far exceeds the tire to pavement friction then there is problems.

For what it is worth I had ice-mode with the stock brakes and stock pads and RE-11 tires during auto-x, but only once the brakes got hot and on longer 90 second courses after about the 4th consecutive run. I'm guess that the bite of the pad just kept increasing due to the increasing heat.

Yes it certainly can be the decrease of friction level on the old pavement, but the uneven surface on some of the older lots or corners (turn 1 at VIR) can have a field day with the ice mode

Yes, bumps and pavement transitions certainly seem to be an issue as well.

Question:

On an empty road turn off the engine, pump the brakes gently several times until there's no servo and the pedal gets rock hard. (Yup, if you can't think how to do this professionally, without killing some-one, you'd better not try!)

Do you now have "ice-mode" and have to push madly for any effect?

If so then ABS action is probably "beating" the vac servo (which on a 370 is a bit different anyhow).

Cure? Maybe a big vac tank or a diesel vac pump (diesels have no manifold vac)

Just a thought, Fritz

A very interesting thought too! A temporary vacuum tank setup could be installed to test your very interesting theory. Let's hope some of the racers on the forum give it a try and post the results.

The more I think about it you could really be onto something. It's worth doing just to make sure that it ISN'T a lack of vacuum assist.

I don't believe the ABS system is active with the car turned off (I could be mistaken) so I'm not sure what this would prove.

He's only trying to simulate ice mode in a non-track environment.

The essence of the matter is his speculation that ice mode is not a software problem but a power brake assist problem. What he's saying is that heavy braking on rough surfaces requires such aggressive ABS action that the vacuum assist for the power brakes becomes depleted with a resultant loss of braking power. This would explain the reduced braking power and rock hard brake pedal because these are the same symptoms that occur when the vacuum assist is depleted or fails.

If he's right the fix could be as simple as adding a supplemental vacuum canister to increase the volume of the available vacuum assist to meet these high demand situations. His theory is very insightful and virtually DEMANDS investigation to see if it has merit. All I know is that if my track days were being compromised by Ice Mode I'd install a vacuum gauge to monitor the available vacuum in my power brakes and I'd be looking into adding a remote vacuum canister/tank.

I think it has been pretty clearly documented on this forum and others that the Bosch computer is the source...

well, ABS Ice Mode finally got me... - Rennlist Discussion Forums

... all about liability management for bosch / nissan... easier for them to be conservative and kick-in an aggressive ABS system and explain that in the EVENTUALITY of lawsuits than it is to say they 'tuned the ABS in order to keep race cars out of barriers/walls when they are ripping through bumpy transitions under intense braking'

I think we are going to have to just learn to live with it and practice trying to "reset" the icemode (release, re-apply, and again if needed)... or replace the computer with a $10K race ABS computer

I am a skeptic... still, I'd welcome your experiment, Fritz/Guard Dad, and would be happy to be proven wrong and have you find a simple fix.. to confirm, perhaps there is a variable on the canbus we can pick up that will allow us to monitor vacuum pressure?

travisjb, the link was great. Did you notice that one of the posters cited similar problems in the Lotus community? According to that post the problem was solved by increasing the capacity of the vacuum tank and replacing the the check valve. There was a difference of opinion as to if it really was a vacuum problem but I find it to be an interesting theory nonetheless.

Now I don't track my car but I do enjoy tracking down the answers to this sort of problem. Let's face it, spooky brakes are no fun on the road or the track, so I'm interested in this issue just the same as I'm interested in the boiling brake fluid/brake cooling issues that concern many members of the Z community. For me, a bulletproof set of brakes is a requirement on the street just as it is on the track . It could be the computer, in fact it probably is the computer, but I do believe an investigation of the vacuum issue is warranted and easily done and that's why I am advocating for an investigation of the possibility of this being the cause. Hey, if it's not a vacuum issue, well that's one less thing to worry about.

I've heard of the vacuum problem and experienced it in other cars but this isn't it. The ice mode is very easy to reproduce on the stock braking system and it doesn't require full throttle and zero vacuum to get there.

Easiest method to reproduce it is to heat the brakes up with several 60-10 braking attempts, then let the brakes sit and heat soak for about 5-10 minutes. Attempt some more 60-10 on a slightly less than perfect surface, small bumps, few grains of loose sand, downhill incline, or anything else that can take grip away from the rear (in particular) and it will raise it's ugly head. It doesn't seem to happen as often with the AP Racing brakes for whatever reason (less rear bias perhaps). Stiffer suspension also seems to help ward it off. Smoother application of the brake pedal also helps prevent it by preventing BA (Brake Assist) from intervening. BA responds to any sudden pedal application and amplifies the braking force typically resulting in a full ABS application. Setting the car up so that you don't really need ABS also helps. Definitely an evil computer at work here.

We can always try to run different pads to get different bias.

I have experimented with everything from different pads, different tire setups, different calipers and rotors. All setups eventually resulted in Ice mode.

I haven't run with abs fuse for months. Really forces me to think about brake force I apply which is very fun in a retro kind of way. I can run at turns much faster just knowing I will stop now. When I feared Ice mode I started braking early which was a real drag. I'm fairly experienced driver and I almost drove right off track twice with ice mode on the car. Fortunately I was on wide turns and just made huge arc to scrub off speed. Also experienced it at AX a few times.

I like the vacuum discussion. Has anyone tried playing with this idea yet?

I wonder what Mazda does as I never had ice mode in my MX5 or my MazdaSpeed 6

Guard dad, of 7/10/-2011 evaluated my post correctly, and added to it...thanks....especially re the Lotus bit.

To continue:
There was a time (when BMW tried to call ABS by its own designation "ALS")
At about that time ABS was strictly not for competition as it could not keep up.
The ABS pump in full flight should work madly and could outpace the then servo which on Audi and (maybe BMW) was all done for brakes and steering by a single pump, but on most cars was the usual servo set-up.

Just how much should a manufacturer do for you (us!) who wish to simulate emergency stops, one after the other, along with possible VDC use ? Why should the public (us too) pay for you or us to "go off-road" madly.

I'd guess it'd be OK for the car to do the job for two full blooded emergency stops, with VDC in between.

So folk should pay for more than that just to satisfy you (us!) madmen in an autocross/race ?

To race we all accept what's needed, from oil coolers to brake scoops and special fluids. We balance brakes by selecting the coeff of friction between front and rear pads: that's if we cannot get, or are not allowed, twin master cylinders!

I can hardly believe that ABS is compulsory in any competition event. "Allowed" maybe or "in operational condition" (to avoid folk junking the pieces). The exact terms of the regs need stating (here?)....and I'd be happy to interpret them (!) and hopefully find a solution within the regs.
Plainly one does not want or need ABS and VDC, and especially BA, interfering with driver inputs in any sporting event...and "ice mode" is just broody dangerous.

To quote ChriSSlicks "Setting the car up so that you don't really need ABS also helps" (He hasn't actually dumped it so it is still getting used).

And, for myself, I could do without BA on the road .... how can I dump that?

Fritz

I would love to permanently ditch BA but I don't think it is possible.

It's not like we are asking for race caliber ABS systems here, just asking for an ABS system that isn't out to kill the vehicle's occupants. The ABS computer in the 350Z/G35 never had these serious issues, the braking was 100% reliable.

ABS might have been fine, but the hose wasn't very good.... YouTube - ‪0507 350z Pocono North Big Spin No Brakes‬‏

Wow, that was scary. Yes, replacing the stock hoses is always a good idea. I typically replace them every couple of years thereafter on cars that see track duty.

I hadn't experienced it before my last couple events, but I'm currently running XP-12s and stoptech trophys front and rear and have been running my AD-08s instead of R compounds due to a spin and cording a tire. I have gotten ice mode once or twice, but mostly on the street tires, I was trying to threshold brake anyways and stay completely out of ABS because I've got way too much pad for the street tires.

Back on R compounds for next week though! First time getting to use the new brakes and R compounds, woo hoo!!!

Yeah I learned my lesson. The 370 with sport is a little bit better as the line going to the caliper is metal. The 350 had the rubber hose with the metal ends.

I still contend the Car and Driver crash was not a brake fade issue. It was more likely ice mode with somone who had never expereinced this Ice mode issue to extent it happens with 370Z.

C&D wrote it off as car just needing differnt pads. I suspect the car would have been just as bad with upgraded Nismo pads.

I have driven a lot of cars with ABS on the track and the system in 370Z is the worst by far I have ever expereinced. The system releases far too aggressively and doesnt recover quickly enough.

I truly worry about inexpereinced drivers expereincing this issue as they could easily panic and end up hurting themselves and others.

I thought that at first as well, but they also said the pads wore down to the backing plates and the pedal went to the floor indicating they boiled the fluid (due to having no pad material to insulate the caliper).

i am with chris. you got to be a complete newbie to not know the difference between ice mode and pad fade. ice mode isnt new, they have been around many cars.

Is anyone contemplating trying to experiment with the vacuum idea?

No, I have plenty of vacuum. I double tap the brake pedal after long straights to make sure of it, gives enough time for vacuum to build off throttle and gives you a nice firm pedal. The ABS system in our cars doesn't require any vacuum, lack of vacuum just results in extra pedal travel and effort.

ChrisSlicks wrote:

No, I have plenty of vacuum. I double tap the brake pedal after long straights to make sure of it, gives enough time for vacuum to build off throttle and gives you a nice firm pedal. The ABS system in our cars doesn't require any vacuum, lack of vacuum just results in extra pedal travel and effort.


I Think you've got that up-side-down or typos, ChrisSlicks. ... for example a lack of vac "just results in extra pedal travel ...etc". Nope, it results in less travel and absolutely huge driver effort (over-servo'd on our cars, like a truck almost!)

Recommended reading:
Any paper on Brake Assist (ABS related) from Bosch or Teves or M-B or BMW or ? (same thing on Germanic cars) most or all of which have an "accumulator" (of pressure).

Now read the Japanese equiv by Masahiro Hara et al. Hard to find, but just Google "9%-S2-P-17" or "98-S2-P-17". It is not hard to understand.

(And is this BA nonsense eating up Vac reserves.......? It certainly will if
you try to Heel and Toe in serious (competition) situations....on our cars the H&T will activate BA to make the idea a waste. Thank God for Sychro-Rev-Match ......

I'll wager that USA systems copy the Japan ideas....hence the problems ???
....Interested to see what Lotus do as they have a "Japanese" relationship".

Most if not all systems conceal the BA pressure sensitive switching inside the ABS unit. (and in the case of VW have had severe expense problems just out of warranties).
Nissan's BA pressure switching is hidden in that ABS unit too.

Sooner or later I'll find a means to dump this truly awful Brake Assist nonsense.

Afterthought: Winners these days usually left foot brake and pedal juggling must include not touching the brake pedal 'til it's actually used. That will guzzle up the Vac in quick time, especially as BA would be in continuous activation from a twitching foot !!!

Sooner or later, BA Bye Bye,

Fritz

Question. Has anyone on this forum experienced ice mode after installing brake cooling ducts?

yes

I need cooling ducts as my AP Racing rotors are starting to crack from heat fatigue, but that's besides the point. It can happen hot or cold, the ABS controller just can't keep up with the changing variables of weight transfer, pad fade and altering surfaces. The best combative solution I've found is to keep the car reasonably stiff (sorry stock guys), don't run a ridiculously aggressive bite pad (but must be high temperature), minimize revs on downshift to minimize engine braking (shift later), and move the brake bias forward slightly by running a slightly less aggressive rear compound compared to the front. If I follow that recipe I don't get ice mode.

I went from XP10 to XP8 on my stock car, I still get them, just not as bad

I can too if I don't follow the rest of the recipe.