Braking problem - malfunctioning ABS

ChrisSlicks

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.

Namir

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.

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Minicobra1

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.

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ChrisSlicks

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.

import111

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.

RCZ

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...

ChrisSlicks

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?

import111

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.

RCZ

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.

ChrisSlicks

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.

ChrisSlicks

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

alan93rsa

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.

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ChrisSlicks

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.

import111

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.

ChrisSlicks

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.