Take a look at this...
10-10-2008, 02:28 PM
#1
Le Mans Master
Thread Starter
Take a look at this...
OK, I have had an issue with vibration on my C6Z while under HARD braking (not noticeable on the street). I recently installed new rotors, but did not bed one of them in properly, which lead me to beleive it could be warped (basically uneven pad material). It is hard to tell which side the vibration it's coming from. So, I replaced the right front rotor after the vibration started, and it did not cure the problem.
Last night, I replaced my left front rotor and while trying to get the rotor off the hub, it was locked in place slightly off center on the studs. It's hard to explain and I should have taken a picture, but even with the little play the holes have mounted on the studs, you could see the rotor was slighty (I'm talking 2mm) off center. You could see where the rotor was very tight on some studs and with slight spacing on others, almost like it "twisted" on the studs?!?
Here is the kicker. I literally had to take a large hammer and bang the rotor with tremendous force to get the thing off the studs. I had to hit the rotor about 10 times SO hard, even with a rag, I damaged the rotor from any possible future use just to get it off the hub.
Now, while I am looking through the suspension to do my monthly check up, I see THIS...
Here is the other side (normal).
So obviously this bushing is SHOT. Now my question, could the deformation of this bushing under extreme braking, alter the geometry of the control arm to cause the caliper/rotor to sit incorrectly and cause some kind of vibration or seize the rotor on the studs? With the stiff coil-overs, T1 bars, and oversized Hoosiers, I am putting cornering pressure that I have never seen in any other car I have ever ridden or instructed.
Basically, could the bushing be causing my problems, or do you think I just had a bad rotor? Either way I will find out on Thursday as I have my last track day at NJMP and then I can get the bushing replaced by the dealer.
Last night, I replaced my left front rotor and while trying to get the rotor off the hub, it was locked in place slightly off center on the studs. It's hard to explain and I should have taken a picture, but even with the little play the holes have mounted on the studs, you could see the rotor was slighty (I'm talking 2mm) off center. You could see where the rotor was very tight on some studs and with slight spacing on others, almost like it "twisted" on the studs?!?
Here is the kicker. I literally had to take a large hammer and bang the rotor with tremendous force to get the thing off the studs. I had to hit the rotor about 10 times SO hard, even with a rag, I damaged the rotor from any possible future use just to get it off the hub.
Now, while I am looking through the suspension to do my monthly check up, I see THIS...
Here is the other side (normal).
So obviously this bushing is SHOT. Now my question, could the deformation of this bushing under extreme braking, alter the geometry of the control arm to cause the caliper/rotor to sit incorrectly and cause some kind of vibration or seize the rotor on the studs? With the stiff coil-overs, T1 bars, and oversized Hoosiers, I am putting cornering pressure that I have never seen in any other car I have ever ridden or instructed.
Basically, could the bushing be causing my problems, or do you think I just had a bad rotor? Either way I will find out on Thursday as I have my last track day at NJMP and then I can get the bushing replaced by the dealer.
10-10-2008, 03:11 PM
#2
Are you sure this wasn't caused by the rotor not being seated properly when you first installed it? The reason I ask is because it seems that it would be hard for the rotor to shift that much without breaking studs...unless it actually deformed the rotor.
10-10-2008, 03:27 PM
#3
Le Mans Master
Thread Starter
The only thing I can think is that I installed the rotor at the track when the brakes were hot recently from a session. But would a cold rotor on a hot hub not seat properly somehow?
10-10-2008, 04:03 PM
#4
I don't think the heat should have anything to do with it...the clearances are tight...but not THAT tight. I've seen rotors get put on in the way you described above, but usually it gets caught because it becomes very difficult to then get the calipers back on.
And sorry if my tone somehow sounded like I thought you didn't know how to put a rotor on properly...not what I meant at all.
I doubt that the suspension bushing could cause the rotor issue, but I would bet that it could be the other way around. If you had a sever enough vibration under braking it can put a load on the suspension in a way it was not designed to take, thus unseating it from the bushing.
And sorry if my tone somehow sounded like I thought you didn't know how to put a rotor on properly...not what I meant at all.
I doubt that the suspension bushing could cause the rotor issue, but I would bet that it could be the other way around. If you had a sever enough vibration under braking it can put a load on the suspension in a way it was not designed to take, thus unseating it from the bushing.
10-10-2008, 04:08 PM
#5
Melting Slicks
Member Since: Jun 2002
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The rotors are hub-centeric and as such not centered by the studs but rather by the hub. The stud holes are cut a little bigger than the studs and, based on brand, can move until they contact the studs.
My guess is that you had two issues. Mounting a cold rotor on a hot hub may have caused the rotor to not seat properly giving you some run-out which would make it vibrate under braking. The temperature difference may have caused the two metal surfaces to "bond" together also.
The bushing looks like the old C5 bushing problem of pushing out due to the use of sticky tires and aggressive cornering. The C5 bushings were upgraded by 2004 to reduce this problem. Either replace the bushing or upgrade to poly bushings to avoid this in the future.
My guess is that you had two issues. Mounting a cold rotor on a hot hub may have caused the rotor to not seat properly giving you some run-out which would make it vibrate under braking. The temperature difference may have caused the two metal surfaces to "bond" together also.
The bushing looks like the old C5 bushing problem of pushing out due to the use of sticky tires and aggressive cornering. The C5 bushings were upgraded by 2004 to reduce this problem. Either replace the bushing or upgrade to poly bushings to avoid this in the future.
10-10-2008, 04:55 PM
#6
Le Mans Master
Thread Starter
I don't think the heat should have anything to do with it...the clearances are tight...but not THAT tight. I've seen rotors get put on in the way you described above, but usually it gets caught because it becomes very difficult to then get the calipers back on.
And sorry if my tone somehow sounded like I thought you didn't know how to put a rotor on properly...not what I meant at all.
I doubt that the suspension bushing could cause the rotor issue, but I would bet that it could be the other way around. If you had a sever enough vibration under braking it can put a load on the suspension in a way it was not designed to take, thus unseating it from the bushing.
And sorry if my tone somehow sounded like I thought you didn't know how to put a rotor on properly...not what I meant at all.
I doubt that the suspension bushing could cause the rotor issue, but I would bet that it could be the other way around. If you had a sever enough vibration under braking it can put a load on the suspension in a way it was not designed to take, thus unseating it from the bushing.
I am really on the fence about the heat vs cold thing. I have replaced crack rotors in between sessions at track days several times and never had something like this happen. I guess anything is possible.
I also really gave both wheels a good back and forth jerk to see if there was any play due to bearing failure and none at all. The test drive after the new rotor didn't show any vibration, but it only rears it's ugly head under threshold braking that you can not replicate at street speeds.
10-10-2008, 05:10 PM
#7
Former Vendor
There is also a tapper on the hub, which the rotor needs to go over. It's just a little radius but can get in the way.
Having a bushing like that will cause a vibration. Bolt your wheel back on and give it a couple pushes around. I'm willing to bet that the bushing gives a little.
Randy
Having a bushing like that will cause a vibration. Bolt your wheel back on and give it a couple pushes around. I'm willing to bet that the bushing gives a little.
Randy
10-10-2008, 05:26 PM
#8
Le Mans Master
Thread Starter
There is also a tapper on the hub, which the rotor needs to go over. It's just a little radius but can get in the way.
Having a bushing like that will cause a vibration. Bolt your wheel back on and give it a couple pushes around. I'm willing to bet that the bushing gives a little.
Randy
Having a bushing like that will cause a vibration. Bolt your wheel back on and give it a couple pushes around. I'm willing to bet that the bushing gives a little.
Randy
The bushings on the C6Z are just so soft, even compared to the ones that came on my C5Z. Since they put stiffer springs and sways on the C6Z, it seems like they soften the bushings as a compromise. It would explain the floating sensation I got with the car.
We'll I got one last event then I will be tearing it down...
10-10-2008, 08:24 PM
#10
Safety Car
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St. Jude Donor '08
Matt,
A while back, maybe even more than a year ago, Aaron Pfadt started a thread about the bushings in the C6 Z06 being destroyed by some hard driving at the track.
Might want to try and find that post, or better yet drop him a pm. He might be able to give you some insight. IIRC he thought it might be cause by the hard braking.
Tim
A while back, maybe even more than a year ago, Aaron Pfadt started a thread about the bushings in the C6 Z06 being destroyed by some hard driving at the track.
Might want to try and find that post, or better yet drop him a pm. He might be able to give you some insight. IIRC he thought it might be cause by the hard braking.
Tim
10-11-2008, 01:37 PM
#12
Burning Brakes
I would investigate why the rotor was so hard to remove. Either the rotor was manufactured incorrectly or you have bent or otherwise damaged studs. It is highly unlikely rotor temps had anything to do with the problem. Will the suspect rotor easily fit on the other side of the car? Will other rotors easily fit on the suspect hub? You may want to consider changing out the studs since they may have been over stressed.
My car has similar suspension modifications, StopTech BBK and Hoosier R6 tires. I had the Pfadt poly bushings installed since the stock parts were slowly working their way out similar to your photos. All is now good!
Dean
My car has similar suspension modifications, StopTech BBK and Hoosier R6 tires. I had the Pfadt poly bushings installed since the stock parts were slowly working their way out similar to your photos. All is now good!
Dean
10-11-2008, 01:57 PM
#13
Melting Slicks
It's kinda hard to "install" a rotor incorrectly. unless there was some dirt between the rotor and the hub, but even then. The wheel against the rotor and hub makes a pretty solid mounting. I can't see anyone messing that up.
I once had a vib from a rear rotor, that shook the whole car to pieces.
I keep on looking at the front brakes, the front suspension, etc, for like 3 events.
Then finally I changed the rear rotors, and problem solved.
I once had a vib from a rear rotor, that shook the whole car to pieces.
I keep on looking at the front brakes, the front suspension, etc, for like 3 events.
Then finally I changed the rear rotors, and problem solved.
10-17-2008, 11:13 AM
#14
Le Mans Master
Thread Starter
Just figured I would provide my results from this. The braking vibration WAS caused by the rotor. Once I got back out on the track with a new rotor, I had no vibration under braking. This is a GOOD reason why you need to bed your pads in properly even when at the track. So, that extra hot session cost me another $120, even on a new rotor.
Now that the braking vibration was gone, I am now able to discern the steering vibration in some of the turns caused by the bad bushing. It is ever so slight, but a definate sloppyness and vibration from that corner.
Now that my track season is over, transforming the car back into street mode begins:
Change out rims
Do a street allignment
change out the race seat
fix the bushings
Oh and clean all the crap off this car!
Now that the braking vibration was gone, I am now able to discern the steering vibration in some of the turns caused by the bad bushing. It is ever so slight, but a definate sloppyness and vibration from that corner.
Now that my track season is over, transforming the car back into street mode begins:
Change out rims
Do a street allignment
change out the race seat
fix the bushings
Oh and clean all the crap off this car!
10-17-2008, 01:44 PM
#18
Melting Slicks
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I have a similar condition with the upper control arm bushings in my C6Z. This situation is common on Zs that see track or autocross duty. Nothing to be alarmed about, except it throws your aligment off.
I plan to put plastic bushings (Delrin or whatever) on my car this winter. I know they tend to squeal, but they also give you less deflection and thus better cornering because of less misalignment under load.
See you at the track.
Frank Gonzalez
I plan to put plastic bushings (Delrin or whatever) on my car this winter. I know they tend to squeal, but they also give you less deflection and thus better cornering because of less misalignment under load.
See you at the track.
Frank Gonzalez
10-17-2008, 01:55 PM
#19
Le Mans Master
Thread Starter
I have a similar condition with the upper control arm bushings in my C6Z. This situation is common on Zs that see track or autocross duty. Nothing to be alarmed about, except it throws your aligment off.
I plan to put plastic bushings (Delrin or whatever) on my car this winter. I know they tend to squeal, but they also give you less deflection and thus better cornering because of less misalignment under load.
See you at the track.
Frank Gonzalez
I plan to put plastic bushings (Delrin or whatever) on my car this winter. I know they tend to squeal, but they also give you less deflection and thus better cornering because of less misalignment under load.
See you at the track.
Frank Gonzalez
10-17-2008, 04:50 PM
#20
Intermediate
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Anyway, hope you guys had fun yesterday! Even though I don't know what you were doing at the end of the day...did you take your grandma out for a ride?
And Mike -- sorry but I don't want you behind me when you're out for a sunday drive....not with your luck.
