Braking Problem

P

puhahacj

Member
Hi Guys,

I just encountered a huge brake problem today on my way back to work during lunch time. On the big turn off the 105 W, Nash exit, the Fx35 slip lights started flashing and then the brake system felt whacked out. There was a constant electric buzz noise coming from the engine, and the brakes would pulsate and felt no pressure. As soon as the car went straight again, the slip lights went off, buzz noise gone, and brakes back to normal. This is killing my mind since the turn was at a slow 35 mph, dunno why the hell slip lights went on.

Checklist:
- tires properly inflated
- warm weather
- brake fluid at max line
- brake pads 70% life
- bled brakes with pressure bleeder 3 weeks ago.
 
maybe something slick on the ground?... don't take much to detect slip, especially in a turn where the wheels are already at slightly different speeds anyway & closer to the threshold of a slip condition to begin with...

don't think I'd be too concerned if it was a one time event...
 
from what your describing I wouldn't suspect that at all.

didn't even have to be an oily or even a wet spot, a bit of sand or gravel even coulda caused this..., wet leaves, even a few twigs,,, anything that allowed a wheel to slip slightly...
 
That's crazy......super safe, a little annoying too. Do you keep the VDC on or turn it off?

---------- Post added at 03:16 PM ---------- Previous post was at 03:06 PM ----------

actually......do you think it could be do to an uneven balance of "grip"? I had the rear 2 tires replaced 1 month ago with some grippy Nitto 420s tires, and front 2 are still the old RSAs.

Do you think the imbalance of grip can throw off the vdc slip light??

---------- Post added at 03:19 PM ---------- Previous post was at 03:16 PM ----------

This is the exact same problem! http://x.infinitihelp.com/forum/showthread.php/vdc-traction-control-new-tires-3990.html?t=3990
 
ah, some pretty important information you left out:wub:


ok, simple explanation, or as simple as I can try to explain anyway



the computer is monitoring the exact speed of each wheel

your wheels only all turn at the exact same speed when your going perfectly straight, when you turn or drive through a curve all 4 wheels are traveling at slightly different speeds, the inner wheels will be following a smaller radius & be turning slightly slower, so the computer has to have a certain window of tolerance to variations in speed or it would sense a slip any time you turned....

ok, so now your traveling down the road straight at a given speed, using a fictitious # as a reference, lets say each wheel gives back a value of 100, 100-100-100-100. now, you enter a curve, so maybe your seeing 105, 106, 96,95... within this window of tolerance, no problem alls fine....

now the turn gets even sharper, so were seeing 108,109,94,93... still within the window, but approaching the limits, lets just say for illustration again, that the widest acceptable gap is a spread of say 20, so if the fastest wheel reports a value of 110 & the slowest reports 90, that's the limit... under normal circumstances you wouldn't be able to hit these threasholds without wheel slip, alls fine & the system works as it should...


now, you go & replace just 2 tires, if there the same brand but just 2 of them are worn, then the new tires will be slightly larger than the old, a few 32's of an inch maybe, but enough that maybe straight is not 100,100,100,100 anymore, now maybe its 100,96,96,100, so just with this simple tire swap you have just caused it o be slightly closer to the limit threashold than it should be, still won't be a problem, but, at the limits, this small difference can be the difference between in tolerance or out of tolerance..

now you go & compound this by using 2 tires from a different manufacturer, all tires are not the same, just because you see the same "size" on the sidewall, don't mean there exactly the same... think of tire size as a reference more than an absolute, different brands or different tread patterns even within the same brand can vary pretty significantly.

so now your at 100,93,93,100 when going straight, when your pushing the same curve that before was within tolerance, now you can be out of tolerance because of this size issue, so what used to be within that window of ok can now be outside of that window, bang, slip detected...

guys have had a lot of issues with this very thing in the G's & Z's when they go with staggered setups, they after find that it is much easier to kick off the vdc, many just say that they turn the vdc off every time they drive... it's because of this difference in wheel diameter... simple answer for you is replace the 2 other tires, until you do it will be much easier for you to hit times that the system will think there is a slip, even if there is not... you are always closer to being out of tolerance the way it is now...
 
TURBO.......you just cleared my f'ing mind. So that electronic buzz noise is normal when the vdc kicks in? The VDC also controls the abs system that caused the weird braking?

That is some good info. Thank you. I thought it had to do with rear grip and thought putting the old tires on the rear and new in the front would solve the problem.

So no matter what, this slip is gonna stay until I replace those tires, or at least rotate the new to the front and over some time with wear, the problem should be fixed.

Damn slip light.
 
the noise is normal, it's doing what it's supposed to do.

rotating won't help, waiting for them to wear won't help cause they'll all wear together but the difference will remain.

awd you should def have all 4 tires the same unless you really research diameters & rotations per mile & properly match a set....

you really should replace the other 2 & be expecting issues until you do... the issues shouldn't be too great, just annoyances like what happened to you in that turn...

long term usage like this has the potential of causing damage to the awd system, awd especially it's important to maintain the same exact diameter all around...
 
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You're right Turbo......thanks for the advice. Gotta find two more tires now.

I really appreciate you writing up that info.......thank you thank you.

IS love
 
your welcome bro, just trying to help you understand what's really the problem, rather than a one sentence response that would still leave questions & doubt & still being unsure...

now you can stop worrying & at least be comfortable by knowing what's going on with your fx :tongue:
 
Great info John! I replaced my front two tires a few months ago but with the same brand and size of course. I have had no issues thankfully with slip or vdc coming on inadvertantly. I will be replacing the rear e in the summer.
 
again, much IS respect......

I have the 2wd, and the front 2 are pretty worn, I'd say around 8,000 miles left on those, so there is a difference in drive feel in terms of that cushion comfort.

Nitto tires are f'ing neato.......love em'.....

UPDATE:

Just rotated the tires.......with the new tires in the front, it seems this slip problem doesn't happen anymore.....weird!
 
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Bringing this thread back from the dead.

This exact thing just happened to me. Replaced my 2 rear tires with Hankooks 265/40/22. They were absolutely shot, almost crashed during the last rain...that's how I found out how bad they were. They used to be 285/35/22... My fronts are still in good shape, so didn't replace those yet. But after installing new tires on the rear, the very first sweeping turn I take, the exact same occurance as the original post. Your brakes go wacky. Slip light starts flashing, buzzing under dash, and you feel like your brakes don't work.

Never had this happen before, so search found his thread...... Thanks Turbo.. you confirmed my suspicions. Going to put new tires in front and see how that works till I can get new matching fronts.
 
If you want to repeat this effect, hit full throttle on a moderately wet surface from a full stop and you can witness your car's computer go crazy to stop you from killing yourself.
 
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