[smokewagon]

I was driving on an interstate (traction control OFF) at 70 mph in 6th gear. To pass, I downshifted to 5th and accelerated to 100 mph. When I eased off the gas, the rear end started to shake and vibrate as if I had 2 flat tires. I slowed down and pulled off the road to look at the rear tires. I turned off the engine and examined the rear end. The tires were OK. I found NO problem. I restarted the car and drove another hour under similar conditions without a recurrence of the problem. It seems to me the problem (ABS? Traction control?) was under computer control and when I restarted the engine, the computer was rebooted.

Has anybody out there experienced similar problems with the Z06?

 

[fcalmes]

Smokewagon,

Cool name!! /phpBB/images/smiles/icon_lol.gif Welcome to the Forum.

I haven't experienced that, hopefully c4c5specialist will step in here soon with some insite. If anyone can help you, he can.

 

[Ranger]

Smokewagon,

First thing I'd suspect is a concrete section of road with drainage grooving; that surface will create vibration and control issues induced by rapidly changing directionality impulses. I got a lot of that on I-80 in IL and OH during my post-delivery treck home to MD.

Catches ya by surprise. Feels like one or more flat tires. Doubt it's mechanical.

Ranger

 

[FUBU69]

Smokewagon, have it checked out by the daeler. Don't take any chances. FUBU69/LES BTW WELCOME! Terrific group of caring enthusiasts here!

 

[c4c5specialist]

HI there,
This is an intersting issue, and not something that I have heard of. If I may, I have some questions, how long had you been driving before this happened??
Did any lights come up on the DIC? Has the problem come back at all after that time?
Was it after extremely hard acceleration? I mean, did you have the traction control off??
Please let me know, c4c5

 

[smokewagon]

c4c5 specialist,

Thank you so much for your reply. To answer your questions:

I had been driving at normal highway speeds for about 1 hour before the incident occurred. I don't recall seeing any DIC lights. The traction control was OFF and the acceleration was pedal to metal (70-100 in 5th).

This incident, described in my original posting (2001-05-06 16:04) was actually the 2nd such occurrence of the problem. However, the 1st time it happened I was on city streets at 40 mph (can't remember if traction control was off or on) when the rear end vibration started. I pulled into a gas station, turned off the car and inspected it. No visible problems. When I restarted the car it was OK. It wasn't until the high speed incident that I became really concerned.

By the way, in BOTH instances, when I walked around and inspected the car I could smell brake odor. Almost as if I had been driving with the emergency brake on or the ABS system had been braking on it's own.

I took the car to the dealer and left it for 2 days. They ran diagnostics and drove the car 50 miles trying to duplicate the problem. They found no problems. Rather than leave the car with the dealer forever, waiting for the problem to reoccur, I am driving it and hoping to find someone such as you to provide me with a clue.

I'll certainly appreciate hearing your thoughts. Thanks again, smokewagon.

 

[c4c5specialist]

Hi there,
Ok, the first thing I need you to do is attempt a retrieval of codes.
Sit in the car, start it, hold the #4 button, while pushing the #1 4 times.
Have a pen handy, as they come quick, and only concern your self with PCM, and TCS.
Ignore the rest for now, ok??
Let me know what you have, xc4c5

 

[smokewagon]

c4c5 specialist,

Diagnostic intel follows:

10 PCM 1 Code P1631 H
28 TCS No Codes

Seriously, thanks so much for your continued help.
smokewagon

 

[c4c5specialist]

Hi there,
Ok, the p1631 is a ghost code for an incorrect password enable to the BCM.
You might have had a 'pull key, wait 10 secs' displayed on the DIC.
Otherwise, we know that there is no problem with either control module, so let continue.
Was the vibration ever occuring on turns, and did you at any time spin the tires??
This is our next course of action, as if the tires were spinning, occasionally, you may have a tire hop condition, if it is sever enough.
Fill me in, and we can continue, or if you like, my ICQ is 117320292, AOL at c4c5specialist, or yahoo at c4c5specialist_2000. These are all instant messengers, so we can talk real time.
Take care, and this is what I live for, c4c5
PS I like a challenge

 

[Ranger]

c4c5Specialsit, You're the man.

But the symptoms smokewagon described are provoked whenever a C5 is driven over a concrete road section with serious drainage grooves. The grooves seem to give the meaty C5 or Z06 tires conflicting directionality input that feels like severe vibration accompanied by a sense that a tire has gone flat.

This has happened to me a dozen or more times with the Z06. In each case the symptoms disappeared once blacktop returns.

Just more input.

Ranger

 

[c4c5specialist]

Ranger,
Very good point, as road surface conditions was not something that I have thought of, looking for the hard problem, ya know.
Anyway, you have an excellent thought, and it is something that should be considered, thanks for the head up, c4c5

 

[iwantone]

Could it be dragging brakes?

 

[smokewagon]

c4c5 specialist,

Good to hear from you.

Thanks for the real time offer. We may need to go that route eventually, but for now maintaining this public forum will certainly provide other Z06 owners the benefit of your insight and may even encourage someone to provide information beneficial to both of us.

In answer to your questions, there was no opportunity for me to detect vibration on any real turns. The vibration did continue as I exited the interstate onto a blacktop road, but I was never in an environment that would require hard turns at speed.

There was no driver generated tire spin on either occasion but it seems that this rear end may have a mind of its' own, so I can't be sure there was no tire spin. I'm not sure exactly what you are asking here.

Please read my reply to Ranger regarding his suggestion that bad road surfaces may have caused the problems.

Let's continue. Thanks. smokewagon

 

[smokewagon]

Ranger,

Your experience is helpful and your input is certainly appreciated. I have driven on roads with drainage grooves and other structural irregularities (dead armadillos, possums, etc.)and experienced the vibrations you are describing.

However, the situation we are confronting here is unique in several aspects:

1. The first time the problem occurred was on relatively smooth city streets (see my posting of 2001-05-07 11:56).

2. When the second (90 mph) incident occurred, I exited the interstate onto a smooth blacktop road before stopping to check the rear end. The vibration continued after I had exited the interstate while driving on the smooth blacktop, even at low speed.

3. I had often traveled this particular stretch of interstate highway before the incident and never experienced vibration problems.

4. Normal, even excessive, road vibration wouldn't account for the distinct brake odor that I noted after each incident.

5. Most curious to me is the fact that in both instances once I had turned the ignition off and restarted the car it was fine. Both times I continued to drive for an extended period after the incident without any recurrence of the problem.

Thanks again for your input,
smokewagon

 

[Ranger]

Smokewagon,

Your additional facts eliminate my theory from further consideration. Back over to c4c5Specialist. I'll be following the thead. Good luck.

Ranger

 

[c4c5specialist]

HI there,
Iwantone could possibly be on to something here, as it could be possible. Do a quick check and pull up the brake pedal, and see if it comes up any while you are driving?? If it moves up at all, this could also be an issue.
I am doing further research on this issue, and will repost later.
Smoke, you got me goingon this one, c4c5

 

[smokewagon]

c4c5 specialist,

Hey,

I am aware of the "sticky brake" problem that some Z06 owners have experienced. I too have noticed on a couple of occasions that my car wouldn't coast very well after applying the brakes. The problem hasn't YET been persistent enough for me to ask the dealer to replace the brake booster.

I cerainly haven't ruled out "sticky brakes" as a contributing factor to our current problem. But how do we make the leap from occasional "sticky brakes" to the sudden onset of severe rear end vibrations at 90mph?

On the other hand, it (sticky brakes) may be consistent with the problem disappearing after stopping the car and restarting the engine. Also, there was the strong brake odor each time.

This weekend, I'm going to return to the same stretch of interstate and attempt to duplicate the problem. Besides testing the brake pedal occasionally, is there anything specific you want me to do or to avoid doing during this exercise?

Thanks. smokewagon

 

[c4c5specialist]

HI there again,
Please make sure that tire pressures are set at 30 psi cold or 34 hot.
Then, make sure to note clutch engagement, if it is different at all from previous times.
Also, try this in a different gear, and see if it goes away.
Let us know how you make out, as every one of us is listening on this one, c4c5

 

[smokewagon]

c4c5 specialist,

Same road. Same driver. Same TC setting. Same acceleration pattern. Good news/bad news.

The good news is that this little yellow Vette is running great.

The bad news is that we don't have any additional data with which to analyze the problem. Perhaps this schiZ06phrenic car needs medical, instead of mechanical, attention.

I know of nothing to do now but wait for the problem to remanifest itself. If anything occurs to you, please let me know.

Thanks again for all your consideration. I owe you a case of some cold adult beverage.
smokewagon