Braking problem - malfunctioning ABS
 

Since I've got the car I've done 3 auto-x events. The first 2 events were on the stock brake pads, this last event I did with Hawk HP+ pads.

On all 3 events I had problems with the brakes where I was experiencing a type of "ice mode" where the ABS would activate seemingly prematurely. It seemed to be happening with both cold and hot brakes so temperature didn't seem to be a factor.

If I braked lightly there was reasonable braking force, if I braked harder the braking force would go away and I would "skate".

Has anyone else experienced anything like this? The only change I made to the car was tires, I installed Bridgestone RE-11's.

What exactly do you mean by "skate"?

Your wheels would lock up and you were unable to turn while under hard braking? Was the ABS not pumping the brakes for you after you locked up the wheels?
No sounds or ABS flashing lights?
I would for sure contact your dealer as the ABS is a safety feature that needs to be working at all times. You could have a faulty ABS sensor that needs to be replaced and this sort of thing would clearly be under warranty.

Haven't experienced that, once the pads bed to these rotors a bit more, I'll give it some really hard stops and see what happens.

I could turn just fine, it was like the ABS decided I was on a very loose surface (like sand) and started pulsing with no lock up. The result is that you get only about 50% braking (or less).

I just thought of something that could be the culprit and should be an easy fix if the dealer knows what they are doing. Because I changed the tires, the tire diameters are slightly different than stock (very close). The stock tires where slightly larger in the front (1.5%) but now they are slightly larger in the rear (1.0%). Recalibration may be able to fix this I hope.

BTW I was going to pull the ABS fuse to test, but it's on the same fuse module as the VVEL controller so I decided against that.

Um, ABS stands for Anti Lock Brakes. Sounds like ABS is doing it's job just fine to me. I have done VERY aggressive braking in the 370Z and the brakes feel great to me. I can get some chirping out of the front tires without locking them up completely which means the ABS is working perfectly.

MY ABS is also working great...

I'm pretty sure Chris knows what ABS stands for and what it does import111....

May have something to do with his ABS kinda "Sticking' when it has already done its job...

That "chirp" that you get is from a brief moment of lock-up (mere milliseconds). The point of ABS is to achieve maximum braking potential by riding the edge of lock-up. I'm not getting even close to the edge, there is no chirping, right now it feels like I have the drum brakes from a 1930's truck only with rock solid pedal feel.

The track conditions were very grippy so there has to be a reason for the malfunction. I hoping that it is something as simple as tire diameter confusing the readings the ABS computer is taking from the wheel speed sensors.

RCZ, what tires are you using, still stock?

Might be something got between the pad and rotor. That has happened to me a couple times in my last car (05 STi) during both canyon run and HPDE.

Still on the stockers. Going to pick up a set of wheels and r comps sooner or later though.... I don't see the point of upgrading tires for the street.

No, it was very consistently bad. I've had the wheels off and pads out twice to check, there is no sign of trouble. Pads are clean, rotors are smooth. At least the pads are easy to change which is nice.

Yeah I was mainly wondering if you had tried race compounds.

I had what you are describing happen to me with an S2000 on the track. I was using the Hawk HP Plus. It only did it one day. Never figured it out.

It was doing it with the stock pads as well as the Hawk pads, although it was worse with the Hawk pads.

This afternoon I switched the front pads back to stock and left the Hawk on the rear in an attempt to move the bias a little rearward. I did some 60-10 stops and everything felt good at first, very strong stops. But, once things got hot the problem returned. Do you think the stock brake fluid could be causing problems? I had plans to eventually change it out but I figured it could hold up to a few auto-x events.

If it was fluid, I would imagine that the pedal would not feel firm as you said it did in an earlier post. Sounds to me like the rotors might be messed up some how. Other 370Z's have had pretty deep grooves appear in the front rotors after hard driving. Hasn't happened to me yet, but it might be something to consider. Just trying to get as many ideas out there as I can think of.

I appreciate the brainstorming, it is really odd behavior.

Did some more testing today at lunch as the weather conditions were similar to the weekend, sunny and warm near 80. I mostly used the same roads repeatedly to rule out surface conditions.

The results were that the first few stops were great, like face through the windshield great. I did a couple of laps around the block between each stop to cool things down and even out the heat. After stop 5 things started to go downhill, gradually getting worse each stop. The pedal still feels solid, but something is happening to make the ABS think the surface is loose as you can feel it push back hard on the brake pedal as the fluid is pumped back the other way.

At this point I'm pretty convinced it is somehow heat related, but I'm just not sure how.

What you are describing is exactly what happened to me at Putnam Park in the S2000.

At Mid-Ohio with the 370 I ran the stock pads with Motul RBF 600. No brake fade but the laps were limited due oil temps issues.

I have seen some weird brake problems, very similar to what yo are seeing, that are from a tiny air bubble in the ABS system itself. I am told you have to bleed the brakes with the ABS cycled open. The ABS cycle is different for every car. The easist way is to have a dealership computer cycle it. Otherwise there should be some sequence of things you can do to cycle it open.

Thanks guys.

I'm taking it to the dealer in the morning, see if they can cycle the ABS controller and pop that bubble outta there.

I took it to the dealer this morning but the technician was unable to reproduce the problem, which isn't altogether surprising. He's going to talk to Nissan engineering to get their opinion but somehow I think I'm going to end up on my own.

I'm going to bleed the brakes with the car running and see where that gets me. I'm going with the ATE Blue fluid for now.

Without a computer hooked up that can talk to the ABS controller, you won't be able to properly bleed an air bubble out of the ABS. There are tools available that can do it for most cars, it's kinda like hooking up an OBD-II code reader (same socket), but the tool talks via CAN to the ABS computer and can instruct the ABS to purge itself, etc. This tool: Actron® does it for ~1996-2005 domestics, but probably doesn't cover our car. Or you can just have the dealer do it.

Yeah, I was afraid of that. Unfortunately I think I'm going to have a hard time convincing them to bleed the brakes even if I offer to pay for it. They're acting all suspicious now, the service writer walked around the whole car checking it out, looking for what I don't know ... signs of abuse maybe? I drive my car hard but I don't abuse it.

Ice mode, happens to the C6 a lot too

Yeah this happened to all of us who track the car hard, even with upgraded rotors and pads I remember someone went into ice mode.

I think Travis no longer goes into ice mode...because he has AP Racing 6pots....

simple fix i guess haha

As the temperature of the fluid increases, the pressure will increase while applying the brake. (although it will not always translate to higher braking power)

One possibility, is that the hot fluid and high pressure is triggering your emergency brake assist system. Maybe a little far fetched but wanted to throw it out. Most brake assist systems trigger based on the speed at which you hit the brake but could it also be somehow linked indirectly to brake fluid pressure? Also, the ABS sensor also detects brake pressure which could be thrown off by the high temp.

As RCZ mentions, with my AP Racing BBK I am not getting any of this... and I definitely had it before - I remember 'icing' my way towards a wall at Phoenix Intl Raceway !!! not something that is easy to forget... can someone verify where they abs sensors are located ? I suspect with the stock setup there is heat being transferred to the sensors which is throwing off the ABS computer... with my setup, heat is dissipated much more efficiently... yes $$ to upgrade... but sh1t- why take chances on brakes! here's a thread on the apr kit http://www.the370z.com/brakes-suspen...installed.html

I still not only have not had this issue...but quite the opposite. The hotter my brakes get the better they stop me. Other people have ridden in my car and driven it and they agree that the stock brakes on my 370Z are insane and stop hard as hell.

they are good brakes, until they overheat. come on up for the september nasa event at PIR and i'll show you exactly how it works

I have experienced the "Ice Mode" before too... Its a creepy feeling especially on the street when you need to drop 30+mph to make the turn LOL. I learned to let off and re-engage the brakes and it goes away. But dont worry I will have Alliance 8 Pots 15" 2 piece rotors real soon! I cant wait for the slam your face into the windshield braking... The sport brakes are good but these Alliance brakes are going to be the Sh1ts! I will post up pics and reviews when they are finished and come in. I am starting with 8 piston front and after those are done they are going to make my 6 piston rears!!!

has anyone measured any temps to see at what point this happens? i'm going to an auto-x this sunday and will try to get some readings. but at a typical auto-x, the brake temps may not go up enough to cause the problem. will see.....

I'm going to revive this old thread... new information

So, despite adding a massive AP Racing BBK and taking hundreds of pounds of my car, I'm still getting the icing issue on occasion. Happened to me today at Firebird Intl Raceway. I was going towards a carousel and braking hard to get set up at the correct speed and on the right line. I had just passed another car and had to make a big transition that upset the car's balance... then bam - icing set in and I began a slow terrible grinding towards the outer part of the track and straight-line braked (but not nearly as fast as I would have liked!)... nearly ended up 4x4'ing. It was total ABS lock up, but as has been previously described it was v inefficient with slow pulsing like riding on ice.

It didn't happen for the rest of the day.

It was NOT an overheat issue b/c it was early during a session.

As it turns out, there was a fellow at the track today who happens to be a test driver for a certain car mfgr that we know and love. Please don't ask me to elaborate. He says that the 370z and the 350z before it have had this issue. What happens has nothing to do with overheating. The ABS computer is kicking in icing mode when it senses any one wheel turning at a substantially different rate than the others. Confirmed it is a different mode than normal ABS when limits are exceeded.

We discussed potential solutions. His belief is that there is NOTHING that can be done except to get an increasingly stiff suspension that is less likely to result in 1-wheel up or other conditions that allow wheels to spin at differing rates.

Not sure where to go from here, but figured I'd share these thoughts.

So, anyone else have 'ice mode' recently? Anyone thinking about how to fix?

You've gone so hardcore that Nissan should just retain you as a consultant and use you for Z product development.

That's very interesting and yet not very surprising when I stop to think about it. Actually I think we've all suspected it had something to do with the ABS programming. Why doesn't every vehicle have this problem though ? I would figure that every vehicle had the same ABS standard programming. Also could it be as easy as fix as a reflash ?

All vehicles do have the problem, it's just a matter if you have reproduced the circumstances to induce it. We got excited when we noticed the stock pads were so bad but I knew something else was still going on.

I totally agree with the diagnosis by Travis at this point as those are similar circumstances to where I've encountered the ice mode myself. The two major times I have encountered it was hitting the brakes after going over a sharp crest, and after hitting a crack in the pavement. Prior to that I had pad fade which was confusing the diagnosis.

so now that we have the diagnosis... what do we do about it? ideas:

1. as binks points out, maybe there is some way to change the ABS computer to either get rid of the mode all together or 'widen the parameters' that cause this mode to kick in... I would have no idea where to start with this solution

2. fool the sensors into recording less wheel spin value difference... this is playing with fire, could cause more probs than it solves

3. disable ABS all together... again, not good for all but the most hardcore... I wouldn't do this

4. *much* stiffer suspension... band aid... prob requires 800 lb/in springs

others ?

Stillen might have to use their Nissan contacts for this one. There might be a race program or alternate ABS computer.

Possible, but would require an inline computer to receive the values, translate and retransmit to the ABS computer.

Actually probably the best solution for now but is going to require us to learn proper threshold braking techniques.

Also has the detriment of possibly reducing corner grip if taken too far.

Here's another idea... softer anti-sway bars! Very stiff anti-sway bars are going to cause the inside wheel to lift and 'overspin'. When this happens on the rear axle WHILE BRAKING, that's precisely when our problem seems to occur. Compounded by the fact that the rear end is light... Inside rear corner picks up, inside wheel spins faster than outside, ABS reacts to the extreme wheel speed difference by assuming the car is spinning on ice and it uses a VERY AGGRESSIVE slow speed ABS that is locked in until the car reaches nearly a complete stop.

So now I'm contemplating using the softest setting on the rear sway. It will cause more understeer, which I will have to manage some other way. Like perhaps with a square tire setup (275 widths all the way around).

Just a working theory.

I'm very curious to know if anyone has had this problem with the stock sway bars. I'll have to go back and check notes from early last year before I got my sways.

I second this!:iagree:

This is probably why C&D introduced their Nismo to a concrete wall...

I have a fully stock suspension and have upgraded my brakes with Motul RBF600 fluid and Carbotech XP10/8 pads. I'll be at Gingerman in three weeks and will report back if I get ice'd. Haven't had it happen before though, even on a wet track with stock pads and fluid (not that pads and fluid really have anything to do with it).

Personally, I'd be happy to kill my ABS and threshold brake. I find it very intuitive and would be a nice flashback to driving my landrover defender in the snow.

Had forgotten about the C&D incident until you mentioned it... you must be right - ABS icing.

If there had been a wall nearby yesterday my car would have been toast. If I remember correctly, the car resisted my steering inputs when it went into icing mode, which made the whole process tremendously difficult and frankly dangerous. I wonder if Nissan intended for the car to stop responding to driver steering inputs in this mode? If they did so deliberately, I think they have a serious liability that will eventually catch up with them and unfortunately some poor driver(s).

Re threshold braking, it is only a solution for a select few drivers. I've driven karts and formula cars like this but for a TT car that I'm pushing to the absolute limit, I like the idea of having ABS to fall back upon. I'd much prefer a real fix to this issue vs disabling.

Heavily following this, and bringing it up the ladder tomorrow.. as we also plan on heavily tracking our S/C'd 370Z, and will undoubtedly run into this as well.

Thanks for the collaboration of information, and I will happily post our findings as we get with Nissan and lean on our resources as well.

You guys are awesome in your documentation, and a complete benefit to this community.. repping like crazy on this thread..