I like old topics...

I've browsed the extensive collection of VDC not OFF when OFF topics, and this one is closer to my latest finding.

I'll introduce a new player in all the electronic paraphernalia we have on our cars. One that has been around all the time but that we've never actually brought into perspective.

Brake Assist (BA). This system (or rather this function) monitors the timing between gas and brake application as well as brake pressure being applied to detect an emergency braking situation. When it does detect that, it will take over braking to apply the maximum safe braking force. I would assume that on VDC equipped cars, it will also read the steering angle and yaw sensors to keep the car on track.

That might be the VDC still On effect so many have been reporting.

It would also explain why in some corner, my brake pedal would stay down when I'm easing off the brake to go for the gas pedal, screwing up front end loading and turn-in...

I'm waiting for feedback from our dynamics department to confirm these interactions exists.

 

Sure its not a drive-by-wire software hick-up? I get that sometimes when I lightly left foot brake while on the gas in a corner. Throttle pickup hesitates for an instant. My guess is that the DBW software goes wiggy for an instant.

 

I might be brushing against the gas pedal, but the brake pedal definitely does weid things. In some instances, it stayed down while releasing it. I drive with OMP nomex shoes, very thin. And I can positively say that my sole wasn't in contact with the brake pedal for an instant.

I sometime get a suddenly hard pedal while loading the front end, followed by a dive as brake pressure increases. It really feels like I'm being shut out of the braking equation then.

I'll deactivate the yaw sensors for MidOhio in two weeks. If BA does indeed use the VDC to work, it should go to failsafe mode. I'll know more then.

edit: About LFB on the Z. I read that the ECU will cut power ~30% when both brake and gas pedal are depressed.

 

I'll add with a few of my observations. Keep in mind that I have the Enthusiast version, so no VDC. I always turn TCS off too.

1. My last spin was caused by what may be inadequate rear shock travel (I have since shortened my bumpstops). When my car started spinning, and I realized I had no chance of recovering from it, I put both feet in. During my spin, I'll let up on the brakes a bit in an attempt to point the car in the right direction, and I noticed my brake pedal stayed locked down with ABS/EBD still active. The brakes stayed locked down until the car came to a complete stop. I've noticed this same phenomenon when I spun out a year before.

2. Trail braking on higher radius sweepers feels good and the car rotates naturally. When the turns are sharper, ABS/EBD gets intrudes after initial rotation. On tighter turns, like T4 at Infineon, ABS/EBD activates about half way through my rotation, and it doesn't let me swing the rear around completely. It's almost as if I did have some yaw sensors, and it detected an 'intolerable' amount of rotation.

3. My left foot tap to the brakes will cause momentary throttle cut-off. Okay, this isn't the same topic of our discussion, but we've got the ecu taking control again.

4. The ecu, however, does nothing to intrude when you want to rotate via power drift. I know a my350z member who validated that to me.

 

I've got a base model, so no VDC, but I've found that the ABS and EBD systems will play nice if driven very smoothly.

 

I've only had one wierd experiance in a brake zone at VIR and I'm still not sure what happened.

I went into the brake zone hard getting ready to go down rollercoaster, ABS came on as usuall, but then it seemed like the car cut off competley!

I had no power steering or power brakes and the guages went off. I put the car in neutral while still going down hill and the car all of the sudden came back on!

I had no warning lights or anything and I went about my day and it hasnt happend since.

Anyone else experiance this?

I've had the car go into safe mode before when I put two off going in hot too a brake zone. The front tires locked up and I flat spotted a tire.

Also, I turn off VDC everytime and I dont pull and fuses or anything else extra.

 

sounds like your engine went dead

 

Interesting observations. For #2, note that even without a yaw sensor, it could derive law by looking at the differential (deceleration) in left vs. right wheel speeds. For example, if the right wheel is slowing down at a faster rate than the left wheel, it could think that either (1) the right wheel is starting to lock, or (2) you're yawing toward the right (clockwise). It could then look at the steering wheel angle to try and distinguish between (1) and (2) - if the wheel is straight, it's more likely (1), but if the wheel is turned to the right, then it may just realize that the right wheel has a smaller radius than the left. Note that these ideas are all just possibilities, I'm not saying it actually does this.

In the Best Motoring video that someone mentioned, when they're describing the 350Z's braking behavior with VDC off, they describe it as "brake-like LSD". I have definitely noticed the outside wheel "chattering" during a hard brake into a turn at the track (and on the street, for that matter).

 

Okay well, after much frustration at MidOhio yesterday, I pulled the Yaw sensor...

OMG, I had doubts about BA quicking in, but I had no idea how much that system was interfering!!!

Nearly spun braking for 7 down the back straight. I usually just floored the brakes and waited. Not anymore, the car came alive with plenty of tail wiggling! Much more fun!

Droped my time 3.5 seconds after getting used to it. Trailbraking was nearly impossible before, now its a blast. The car rotates very well under braking...

Any advance level driver should pull that sensor OFF!

 

Softer/smaller FSB. Should also help a little with the understeer.
Why different sized tires?

 

Had you noticed the topic was started a little while ago (2004)?

What's FSB ?

 

Ah crap, no.

front sway.

 

Front sway bar? Trust me, the car was plenty tail happy when I wanted it to be and rotation wasn't the issue. The trail braking and ensuing "plow-skid" was.

 

Or buy a base model 350Z...

 

Lol,

Yeah, a new base with the HR engine...

 

From what I read, you were looking for less understeer post-apex, and less of the extreme weight transfer to the outside front....

 

The skid was induced by the car's braking system playing with brake force distribution. Swaybars would have a limited effect on that.

 

Welcome to the club!
I remember we discussed this last year or so... and you were not convinced back then.
So are you going to implement the famous center console switch now?

I am glad that you found out. I went through a lot of effort to install a switch myself in the ashtray, but never really was sure whether it was worth it.

The other day on the track a G35 owner came by and asked me if I know any good shops that could look at his messed up ABS. He said his ABS is kicking in as soon as he brakes into turns, and it is driving him crazy and he thinks it's broken. And it only kicks-in on one wheel/side....
I sure knew what to tell him

 

whyyyyy????????

 

You okay dude ?