DivinDriver

'03 touring Z, stock brakes, Nissan OEM pads. 82k miles. Eagle F1's all around, stock size.

A couple of months ago, I started feeling a vibration when braking from above 45mph. It's more noticable when braking downhill, which would normally point to front brakes. It's not real specific to the steering wheel: can be noticed from the passenger seat as well. Not violent, and seems to be higher frequency than wheel-rotation rate. It doesn't seem to be related to the ABS system (I'm familar with how the ABS feels; SoCal freeway driving being what it is).

Brakes had been replaced all around 4 months prior to symptoms, and rotors were turned true.

I knew my original struts were pretty much used up (ride had gotten harsh), and that I was likely due for an alignment, although tire wear was quite even. I installed Tokico Blues last weekend, and had the alignment done yesterday by a reliable dealer who understands the FSBs on Z alignments. The vibration is lessened, but is still noticable.

I've checked rotor runout with a dial indicator a couple times, trying to sort this out; it's less than 0.001 on all four wheels, well within tolerance. No measurable axial play, so I can't see it being bearings.

I've searched around the fourms and can't seem to find anything matching exactly.

I'm starting to run out of ideas at to what to check. Anyone had similar problems and know of a resolution? Suggestions?

Chebosto

iTrader: (43)

hows your tire balance? is the wheel fitted properly back on with lug nuts torqued properly?

did you check the brake pad surface, and if the pad or piston is getting stuck, causing uneven braking pressure?

check play in wheel hub flex.

one way to remove ABS from the question is to unplug the light grey connector wire in the brake compartment, that is going into the aluminum box which is the abs controller. this will disable traction control, abs, and vdc..

if the rotors are fine, and the pads are ok and moving freely.. maybe the wheel is bent, bad tire, or needs a high speed balance?

DivinDriver

That gives some things to look into, thanks.

I'd thought about tire balance, but every time I've had a balance problem in the past (other cars), it's been noticeable not just during braking, but also constant speed. Wouldn't a wheel problem show the same behavior?

When not braking, the car is butter-smooth up considerably past 90.

I always use my torque wrench on my lug nuts. Star pattern, three times around, finger/middle-tight/final. (I'm kind of a detail freak)

Good ideas, though; I'll look at the pads and calipers again, maybe tooth the rotors up a bit by hand in case I'm getting pad deposits I can't see.

Pedal's still plenty firm, but it probably wouldn't hurt to give 'em a bleed just for drill.

DavesZ#3

iTrader: (26)

How do the brakes feel at low speeds? Have you checked rotors or pad surfaces to make sure there's nothing contaminating them?

I'm having a similar problem with mine lately. Replaced pads and rotors about 8 months ago. About 2 months ago, I started noticing pulsing when stopping from high speeds. Also notice it when slowing from 25-30mph with light brake pedal pressure. I haven't tested runout yet but I'd be pissed if 8 month old rotors were warped already.

DivinDriver

At lower speeds, it's not noticable at all.

I haven't seen any obvious contamination, but I'm going to pull everything down again & check it out.

StopTechErik

Try rebedding the pads, could be an issue of light uneven pad deposits or a lack of consistent pad transfer layer causing a stick-slip scenario.

http://www.stoptech.com/tech_info/wp_bedinstock.shtml

DivinDriver

Thanks, Erik; It's certainly worth a shot, & simpler than tearing down. I'm generally pretty careful about my initial bed-ins. Tricky bit is finding a place near the house where it can get done properly without becoming a traffic hazard.

Question: Would a symptom of uneven deposition be the problem worsening with extended drive times?

StopTechErik

I wouldnt expect a longer drive to make the symptoms unless on shorter drives you werent getting the pads to a temperature where they were working in an adherent state.

As far as bedding in goes, I would recommend going to an industrial area after hours to do the process. If you cant do all 10 stops in succession, find a spot where you can do 2-3 stops and then make a u-turn and repeat until you have finished the process.

DivinDriver

I ended up combining both ideas; I pulled the rotors, gave them a light abrasion with medium-grit "red pad" until showing clear metal, then reinstalled them, checked runout, cleaned up and regreased the brake hardware, and took it out on the dairy roads to bed
them down.

On about the 7th decel, I smelled them starting to stink. I finished the cycle out, adding two additional decels until the fade went away, then cooled them for a couple miles.

Symptoms seem all but gone; I think one more bedding-in cycle will turn the trick.

Thanks for the advice!

Boozt

Sorry if this a thread hijack.....BUT, UNPLUGING THE LIGHT GREY WIRE IS ALL THAT IS NEEDED TO BYPASS ABS AND VDC????? I've been asking for an easy way to do this for a looooooonnnnnggg time, and now it seems it's this simple. WOW (if it really works) and thanks

DivinDriver

Thread back from the dead...

Rebedding seemed to clear up this problem for a few days, then it started to recur. Has gotten severe enough to be disturbing while driving, and I'm running out of things to check.

Question; is this possibly a problem with the LSD? Does anyone on-forum know technical details of the LSDs? My thinking is that if it is a 1.5-way or 2-way LSD, I could be seeing unequal application causing rapid transfer fluctuations. But I can't find any detailed spec on the LSD, and even the FSM doesn't go int oa lot of specifics about it. It simply points out that it is a viscous LSD.

Suggestions?

DavesZ#3

iTrader: (26)

Think about it - if rebedding temporarily solve the problem, then it shouldn't have anything to do with the LSD or anything else for that matter.

In theory, if both sides weren't braking at the same rate, then yes there would be some slippage through the diff, but I'm not sure why you would feel it as a high speed vibration.

Did you notice the problem return after you washed your car or drove it though the rain?

Chad68

iTrader: (1)

last time I drove my car I noticed vibrations when braking at higher speeds. faster the speed the more noticable it is.

It only vibrates when I brake.

Slowing form about 90 is interseting. Braking around town isn't really noticable. Doesn't fell like the car is going to go out of control or anything drastic but it's definatlly not right. Seems like in my case it's from the right front or the front in general.


When I brake and take my hands off the wheel at say 55, the car does not pull to the left or right, that I recall. I think it's maybe pad deposits. The car sits sometimes for months at a time and of course the rotors can get that thin coating of rust on them. Don't know if that has much to do with it in my case. The last time or 2nd to last time I drove it, before I noticed this issue, I pushed the car pretty hard through back roads for about 15-20 minutes or so and was hard on the brakes.

The car has the original stock non Brembo brakes and rotors with 27,000 miles on them.

DivinDriver

Yeah, I'm just kind of puzzled why after several years of no problems, now I have this recurring problem. Nothing changed, so why did something change?


I have no prev. experience with LSD rears - - I know that the clutch type can be prone to chatter, and I know that some types of LSD's operate under decel. I had this thought that if I was getting oscillatory engagement/disengagement (like an uneven engagement that was cycling), it would show up as a vibration... but yes, there's no good reason why it whould show up on a straight-line decel, since the tire speeds are damn-near identical.

No, it hasn't been relaed to any discernable condition. It came, I got it to go away for a short span, then it came back and has progressively gotten slowly worse.

I'm thinking hard-spot on a disk, at this point. But I can't explain why it:

1) appears only above a given speed, and
2) lessens as braking pressure increases.

Warped rotors, in my experience, will do 1) but not 2). Seems like pad deposit shake likewise shouldn't lessen under harder braking.

Only braking decel will cause it, though (downshifting doesn't), so it seems to me that it must be in the braking system, even though I can't find it.

Been a very long time since a car problem stumped me, but I'm going nuts on this one.

DivinDriver

Replaced the front rotors; problem went away.

Rotors still mic and dial-guage out within tolerance.

Puzzled, but glad the issue is gone.

AVmagneticZ

iTrader: (4)

i have this problem to i baught a set of oem brembos used. used oem rotors that i got machined and i noticed sometimes well most of the times that i can remember at higher speeds braking is not good and i never really thought much of it but it is annoying. at slow speeds i dont feel a thing. its only id say 50 + mph. so you think its the rotors? i dont know how the pads n stuff were set i took it to my trusty mechanic who knows what hes doing he took the car out set them or whatever.

also i was braking hard at about 65mph and at one point because i had to stop really fast the brakes actually gave way. for a spliut second...scared the **** outta me..could this be cause of the uneven rotors? but doesnt machining them make them like new again?

350ZMPH

iTrader: (12)

I have the same problem with my rotoras BBK....and I dont kow what to do....I replaced them with new rotors and pads and problem still there...