03Z33

iTrader: (49)

Sorry, I'm not too familiar with the wiring on the 05 Base Z... best thing would be to get the wiring diagram from the 05 Tech book and check out best place to disconnect.

THX723

iTrader: (3)

This sounds like a VDC issue not ABS or EBD.

As we all know cars equipped with VDC can't be completely disengaged. Toggling the VDC off swtich simply lowers the activation threshold. It'll still activate it self if the computer believes you are wayy out of shape (not hard w. R-tires or in a drift). Disconnecting the Yaw sensor (black box by the shifter) effectively renders the VDC system useless and is probably the best trick in the book ... all while still retainning ABS.

I've had this happen on occasion too at the track. No of those occured while I was on the brakes. It felt like the system was trying to counter the understeer ... and doing a very choppy job at it.

enZineer

This (above) is correct.

EBD has nothing to do with VDC. EBD controls only front/rear brake bias. Most systems will require at least two wheel speed sensors to be failed before EBD will shutdown. In this case, you will USUALLY see the red brake lamp on as well as the ABS warning lamp. I've seen some vehicles that do not light the red brake lamp for EBD failure -- there are goverment requirements for this lamp, depending on the longitudinal deceleration before impending rear wheel lockup.

EBD stands for Electronic Brake Distribution. It amounts to an electronic version of the old prop valve. EBD will dump pressure on the rear axle ONLY in order to prevent the rear axle from locking up prematurely. Both ABS and EBD should be a godsend on a race track (with an otherwise stock vehicle), as they attempt to maximize longitudinal friction during braking while not allowing wheel lock. The result is that you can get maximum decel during braking WHILE not losing the lateral force available at the tire. (50% or more slip at any wheel means that there is no longer lateral force at that wheel, which means that wheel is no longer helping you maintain a corner)

Now, for vehicles with modified brakes, different tires, or mismatched front/rear tires, is is very likely that none of the electronic brake systems mentioned will function properly -- in fact these modifications may DECREASE braking performance.

VDC and TCS

VDC will help to correct oversteer and understeer. In understeer it will reduce engine torque and may brake a rear axle wheel (right or left depending on turn direction) -- some systems brake more than one wheel during understeer. With the LSD in the Z, I'm not sure if the system is braking a rear wheel at all -- they may just reduce engine torque for understeer.

For oversteer, VDC will brake a front axle wheel to prevent the vehicle from spinning around.

TCS will reduce engine torque when the driver supplies too much torque to the rear axle, causing the rear axle to overspin.

Both VDC and TCS in the Z are tuned in order to help the average driver maintain control of his/her vehicle. It is possible that an experinced driver could get better times on a race track with VDC switched off.

Disconnecting the yaw rate sensor will cause VDC to shut down (and cause a warning lamp), and should not affect ABS or EBD.

John

iTrader: (17)

The "VDC" (yaw sensor) will brake the inside REAR wheel to prevent a spin. If it activated the front brakes, then the car would simply understeer or it would upset the balance of the car (if the front wheel had enough traction) and spin it.

enZineer

NO.

If the vehicle is OVERSTEERING, VDC will brake a front axle wheel.

In a left turn, if the vehicle oversteers (rear end is coming around), the driver should countersteer (turn steering wheel to the right). VDC will brake the front right wheel to prevent a spin.

PedalFaster

Per Nissan's website, in an oversteer situation the VDC will brake the outside front wheel.

John

iTrader: (17)

Think about it. If the front wheels have traction, and the VDC system is braking the front wheels, you're going to throw more weight over the front wheels, and will cause the rear to be even more unsettled.

Note to the Nissan illustration... it doesn't address the yaw sensor since it's a FWD car and I'm pretty sure (although I could be wrong) that Nissan's FWD cars don't have this incorporated into their VDC system. That illustration states "Increases responsiveness to severe braking conditions. Provides precise interaction with throttle and brakes simpler, quieter, smoother control." It does not address the oversteer issue (which is pretty difficult to achieve with a plowing FWD car.

I can assure you that the yaw sensor brakes the inside rear wheel (because that's what it does on Porsches, Corvetters, BMWs), and as proof to my statement you will read of premature rear pad wear if you leave the VDC on at the track.

Edit: "Drive should countersteer". Yes, you are correct. But 99.5% of drivers do not know this, hence the reason the car has VDC defaulted on.

Kolia

iTrader: (2)

I have some Nissan technical documents at home, I'll browse to see if I can find something to settle this discussion...

As for premature rear brake wear, I'd blame the ABLS for that (Active Brake Limited Slip) it is still ON when the VDC is turned OFF. Nobody talked about it in this topic but this guy will seriously heat up the rear brakes!

As a reminder, it applies brake pressure to a rear wheel that is about to spin (faster than the other wheel) when accelerating. So we end up in a situation where rear brakes heats up during braking AND part of the acceleration phase of a turn

John

iTrader: (17)

If it's still on, then why do I not have any problems with premature rear pad wear? At the track my VDC is always off, and I have never had that problem. Consequently, if you leave VDC on, then your rear brakes will go bye-bye.

enZineer

Only one front wheel will be braked in oversteer events. It's a moment balance. There is a yaw moment acting in the counterclockwise direction in a left turn. In order to counteract that moment, a force would need to be applied somewhere on the right side of the vehicle to apply the CLOCKWISE moment. It does not make sense to brake the rear axle in this case because you would lose the cornering force at that wheel.

Continental Teves ESC

Look at BOSCH's site, or Delphi's site, or TRW's site, and you'll find similar descriptions.

Bosch supplies the electronic brake system in the 350Z.

ESC (same as VDC) with FWD is no different than RWD or AWD. The front axle is still braked for oversteer events. TCS is there to reduce engine torque if the front axle is overspinning. The vehicle's understeer gradient will dictate whether or not the vehicle is inherently oversteering or understeering. There are FWD vehicles (such as the Ford Focus, which is available with ESC) that can easily be thrown into oversteer. It depends on the understeer gradient, which is different for every vehicle.

Again: The *only* time the inside rear wheel will be braked is during UNDERSTEER. The rear axle will not be braked during OVERSTEER.

This is true (I don't know about the 99.5% statistic), but the correction will be faster and more severe WITH countersteer. The control is based off of two things:

1. Driver's intention (as calculated from vehicle speed and steering wheel angle)
2. Actual vehicle behavior (as measured by the yaw sensor)

The delta between these two signals is determines the magnitude of the correction. If the driver countersteers, the delta between these two signals is huge, and thus a large pressure is required to get the vehicle pointing where the driver intends.

THX723

iTrader: (3)

Looks like enZineer's jumped the gun on me ... not sure I could have done a better job explaining it. Spoken like a fellow engineer.

The basis of all Active Differential Braking (i.e. VDC) is that of fundamental physics ... that is to generate opposing moment (torque) to counter the moments generated by the over/under-steering conditions.

During an oversteering condition, the front-end of the car is more or less the moment center. The effects of braking any of the rear tires will not have generate significant nor the correct moment to counter act the impending spin. The only way to induce such moment with the greatest efficiency is to brake the outside-front wheel. The Nissan illustration looks fine to me. And yes, the methodology would be virtually identical for a FWD car as well.

VDC is in fact the culprit for eating rear pads at the track. It is not the brake-LSD. The algorithm for VDC is simply not programmed to predict conditions one put the car through at the track ... nor would that be a good ideal for the average driver on the street. The result is an over-working VDC if left 'ON' at the track ... assuming the car driven at 8/10 or higher.

Cheers,

DavidM

Would anyone know which wire from the yaw-sensor to wire to switch in order to be able to switch in on/off? I looked for diagrams and the only ones I found show the yaw-sensor being connected through one plug. I pressume that this plug has a few wires in it, but I have not found any details. So does anyone know which wire to connect to a switch? Would anyone have diagram/details of what wires go into the yaw-sensor (and also what are their functions)?

Any help would be greatly appreciated.

DavidM

So is there noone who can provide me with more info in regards to the wireing that goes into the yaw sensor? Any help would be greatly appreciated as I would love to dive into this project this weekend.

"Would anyone know which wire from the yaw-sensor to wire to switch in order to be able to switch in on/off? I looked for diagrams and the only ones I found show the yaw-sensor being connected through one plug. I pressume that this plug has a few wires in it, but I have not found any details. So does anyone know which wire to connect to a switch? Would anyone have diagram/details of what wires go into the yaw-sensor (and also what are their functions)?"

enZineer

So is there noone who can provide me with more info in regards to the wireing that goes into the yaw sensor? Any help would be greatly appreciated as I would love to dive into this project this weekend.

I think most people don't want to touch this issue.

Two of the wires at the sensor likely supply power and ground. A multimeter will tell you which one is +12V.

03Z33

iTrader: (49)

It's actually a good idea for people that might still use the VDC at some point. I never plan on plugging the sensor back in, and am not good with electronics, so I can't help, but if you come up with a way to do it please share.

My version would most likely be to cut an access whole in the center console to make it easier to reach in and unplug the sensor each time hehehe........................just kidding

arizzee

iTrader: (28)

Try this.

Edit: jokes on me, image too large to upload. PM me your email address if you want the diagram of the yaw sensor pin out.

On the diagram, I don't see 12vdc wire. All yaw sensor wires go to VDC controller which supplies the ref. voltage/signal.

aki

not sure if this is related but it sure sounds like something that happened to me recently. I replaced the front tires (well Nissan did) at 21k miles. at 34k (?) miles I replaced the rears with stock size tires. I calculated that my front tires are 1/4 - 1/2 worn (haven't measured tread depth). rears are brand new but slightly taller than stock (Avon 555 AS). I have stock pads, originals.

Right after I had this done I had a hard brake need when a small truck pulled onto the highway from the shoulder without getting a running start. I was going about 65-ish in the slow lane, I was being passed, and the truck pulled in front of me with no warning - approx 100-120 feet in front and going walking pace. I braked as hard as I could and came within 5-10 feet of rear ending him.

I passed him after I got into second and traffic passing me cleared. At my exit (right bend) I braked firmly as normal - perhaps 70% pressure. My left front locked up and I found myself understeering as the left front brake kept chattering as the computer pulsed the brake. I straightened and turned less aggressively and it was okay. This has happened 5-6 times since. Each time I've been braking quite firmly from 80-95 mph as I approach a turn. I ease off the brakes as I enter the turn but the left front starts to lock/slide as I do so. straightening and re-turning works. Higher steering angles at slower speeds replicates this problem.

I've since caculated my tire diameters and differences. Stock the Touring has a .97344 ratio (front to rear). my worn front tire, with my new rears, lowers this ratio to about .9607. This combined with the outer tire turning faster in a turn could cause the car to think I'm starting to spin. Hence the left front brake going on. BTW this doesn't happen when turning left but I have very few occasions to turn left hard with any need to brake firmly.

I'm wondering if this is enough to set off the VDC - the combination of a smaller front tire with the brake/turn combination.

Regardless, I'm going to find the sensor and disable it.

THX723

iTrader: (3)

That is not enough to cause VDC to function abnormally. It is not uncommong to find new tires with a film of protective oil on the surface. It may take serveral miles to wear off and the compound to 'breaking in'. Are you still experiencing this?

aki

As far as I know, no. I have approx 1000 miles on the rear tires and still experience this. I relate the hard brake story because I've never braked so hard in the car ever and the first time I had the problem was right after this. I don't know if the two are related.

Also, if the rear tires were slipping under braking, wouldn't the ABS kick in? I start braking firmly while going in a straight line but it's when I turn the wheel right the left front wheel chatters so loud it sounds like it's about to fall off.

thx for any input
aki

THX723

iTrader: (3)

Just so we all heard you right ... you're saying you DO NOT normally have any issues otherwise. No surprise there. BTW ... are you mixing different brand/model tires front to rear?

Yes, ABS would kick in for any wheels that is or about to lock up. That is after all what ABS systems are suppose to do. It is possible to induce oversteer when attempting to turn during a panic stop. In that case, VDC would have kicked in to assist you in keep the car 'in control' by pulsing the inside-front wheel (to counter act the impending oversteer). Sounds to me like the system is working as it should.