corydlent

Hello All,

I am seeking insight from the track-oriented 350z community on a issue I am having.
I spent an entire year with the VDC/ABS system disengaged (due to faulty wheel speed sensors).
Recently I fixed this and I did my first track event with the VDC off but with the ABS lights off (I am assuming functioning normally).
This is when I noticed something odd about the ABS.

When trailing the brakes on corner entry, the ABS starts to engage, the pedal pulls away from my foot as it actuates.
I run CarboTech XP10's in the front so even mild actuation really upsets my car on entry.
The actuation is premature and I feel it is unnecessary for the braking system to be doing this.
At the point in the turn it does this, I am transitioning off the brakes, so brake pressure is light.

To make matters even more interesting, at some point mid-session, the car does something even stranger.
It looses all power for about 2-3 seconds and that's when the slip light becomes continuously illuminated.
The light goes off with the car sitting until the next session (usually 40 min or so).
I always turn the VDC off whenever I drive on track so it was off for all of the above and it did this consistently in every session of the day.

I would greatly appreciate any information from other 350z drivers who have experienced this and how they fixed it.
I would like to keep my ABS if possible, but if the only solution is to disable it, then that's what I'll do.

Thank you in advance.

dkmura

iTrader: (64)

From your description, it sounds like you're confusing ABS with VDC actuation. Keep in mind that the VDC off setting NEVER truly turns off even if the button is pushed. Parts of it remain active. You need to physically disconnect VDC to fully disable it when racing, otherwise you'll still get limp mode at some point on track. I've never had VDC on since we built these Zs to SCCA Touring car specs.

And while I use a different brand of brake pad than CarboTech, my XR2 racing compound's strong torque usually activates ABS as soon as I reach my braking point. This might not be true when threshold braking isn't used, but most times I can feel ABS pulsing even if I'm trail braking into a slow corner. Don't disable ABS, learn to use it IMO.

corydlent

Thank you for the reply dkmura I really appreciate it.

It makes sense that it would be the VDC since the actuation felt substantially slower than what I was expecting it would be.

I definitely want to keep the ABS, but I do not want the VDC active at all. I will do some research to see if there is a way to keep one and delete the other.

Thanks again!

JMII

I've read this from multiple people but nobody ever explains the "parts of it remain active" thing. What parts are we talking about here? Is it a traction or a yaw thing? How much safety margin is still "on" when the system is off? So is off really like having the VDC at 10% (for example)?

I really wish the Z was more like brother's Golf R, it has two levels for the nanny: one allows the car to slide a little (maybe 50%) but the other is truly O-F-F (0% help).

dkmura

iTrader: (64)

I'm no engineer, but in my experience, VDC "off" still utilizes both individual brake caliper actuation at a later point (50%? 70%?) of yaw angle development. If a spin is prevented, VDC can also cut power to prevent any further overcorrection. I have no idea about the software programming, but Nissan clearly developed it to keep unsuspecting Z pilots out of the woods and ditches of the world. Keep in mind this software was developed almost TWO decades ago and is not nearly as sophisticated as current stability systems.

guitman32

iTrader: (15)

A good description from the manual:

"The VDC system uses a Brake Limited Slip
Differential (LSD) system to improve vehicle
traction. The brake LSD system works when one
of the driving wheels is spinning on a slippery

5-22 Starting and driving

surface. The brake LSD system brakes the spinning
wheel to distribute the driving power to the
other driving wheel.

If the vehicle is operated with the vehicle dynamic
control system turned off, all VDC and
TCS functions will be turned off. The brake LSD
system and ABS will still operate with the VDC
system off. If the brake LSD system or the ABS
is activated, the slip indicator light will blink and
you may hear a clunk noise and/or feel a pulsation
in the brake pedal. This is normal.

While the VDC system is operating, you may feel
a pulsation in the brake pedal and hear a noise or
vibration from under the hood. This is normal and
indicates that the VDC system is working properly"

MicVelo

I find this quite interesting... normally, brake LSD systems don't actually distribute the power to opposite/non-spinning wheel. And maybe it's just a semantics issue with the manual's description. I would tend to think that better wording would be "It cuts power to the spinning wheel and therefore the result has the effect of equalizing side-to-side forces because the power remains constant to the non-spinning wheel due to the VLSD."

Overthought, and totally "who cares?", I know. Laff....

Either way, I still marvel at how far we've come in terms of vehicle electronics in a relatively short time. My Datsuns have NOTHING electronic in them vis a vis my 350Z. And as dkmura said, even the Z33 system itself is "OLD" now.

And then there's the cars of the Orwell work, "1984". They're called "anything built after 1996, notably Tesla."

Heck, even in 2001 when I got my original Benz E55, I was sitting in the driveway of my house trying to figure something out on the new car... then the damn thing started talking to me! Apparently from 3,000 miles away in New Jersey! Whoa.... I think that was when the expression "WTF" came about. Hahahahahaha.

JMII

Interesting... thanks! This seems to indicate the car will still use the brakes in attempt to prevent a slide/spin but will NOT engage the dreaded throttle dumping nanny. My experience with the VDC is it works... a little too well. If you spin the tires or have aggressive yaw the computer kills the power. I know it also activates the brakes because of how quickly the car snaps into alignment. Because just killing the power wouldn't correct the car's yaw. Twice I've dropped a gear in a turn (3rd to 2nd) which induced a slide - then the slip light went nuts and the car corrected itself. I've also the slip light blink away while powering out of a turn, or after an aggressive up shift (2nd to 3rd), in those cases it did the throttle dump (aka limp) deal. To me this second situation is more like TCS (traction control) behavior because it effects BOTH rear wheels. Guess we need a skid pad test to really learn what is happening

guitman32

iTrader: (15)

I agree, VDC can become a liability if you are pushing the car, especially in the wet. It is not smooth by any means.

With the button off, the pulsing of the "Brake LSD System" lol is definitely there as the ABS actuates at a given corner. Aside from when the system goes haywire (which it does sometimes), it has been pretty workable for me...since I do generally think that if it is activating it is a sign you need to be smoother or change something. Usually comes in when you are really on limit aggressively trail braking or in a decreasing radius sweeper and have carried slightly too much speed. By my estimation it is probably primarily wheel speed dependent, the same feeling as when in ABS in the wet and the pedal pulsates.

If someone wanted some hard data best get a SOLO DL or similar that can log the wheel speed sensors via OBD and analyze if/when it happens again.

JMII

Agreed. On the track I only go into ABS when trail braking. SLIP only occurs if I do something obviously wrong like too much power (or too much RPM) or an abrupt direction change that throws off the balance of the car. If I am smooth the VDC never kicks in. This is why I leave it ON even at the track. Most people seem to think they can drive better then a computer not me... I just your average Joe, that happens to instruct at HPDE events.

I just wish the VDC wasn't so aggressive in dumping the throttle. Its a very odd sensation to push on the gas and watch RPMs drop. The car just dies, thus the reference to limp mode. The other scary part is once the car regains traction because then it hooks up and launches forward. When I first started track driving I was amazed at how responsive and fast 3rd gear was - then I realized I was just losing traction in 2nd gear as the VDC was limiting my acceleration. As I got smoother on throttle application this problem went away. Clearly if the tires are spinning your going nowhere fast , thus the slip light is a good teacher in how to be smooth

dkmura

iTrader: (64)

Interesting discussion and I agree that VDC continues to be useful on a street car with all-season or high performance tires. But there are limits and they become apparent on a D2D 350Z racecar. There VDC becomes an impediment to putting down quick laps no matter how smooth you are! Using R-compound tires seems to overwhelm VDC and the quick transitions at many tracks can sometimes leave you hanging. After a lot of experimentation, most Z racers simply end up disconnecting VDC, while still retaining ABS (although some don't even like that either).

JMII

Makes sense. I haven't moved up to R-compound yet. Track driving runs the gamut from using your daily driver twice a year all the way up to dedicated race car in an enclosed trailer. I am somewhere in the middle.