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It's easy enough to rule out ABS - just pull fuse #52. Its a 40amp fuse in the main fuse box, right side. A flat spotted tire or out of balance wheel can do this - but doubt thats the issue since you've tried two sets. If the feeling is coming thru the chassis more than the wheel then it wouldn't be the front rotors warped or pad-deposits - could be the rears. If its not hubs then - ball joints? suspension bushings?
Excellent, and now that you reminded me I looked it up in the owner's manual and what do you know, there's actual info in that thing!
I had Phoenix install their Delrin bushings last year along with the SKF hubs so probably not bushings. Ball joints looked OK but will be easier to inspect when I have the car on the lift at home instead of on the ground in the paddock.
When you checked the rear brakes did you check the back side of the rotors? I have seen C5s get a lot of corrosion on the back side of the rotors with pitting in the rotor surface that will feel and sound just like what is in the video.
For example these pictures taken the day I inspected the 03 Z06 I was purchasing.
Most issues people describe as "warped rotors" are actually pad deposit issues, that's why bedding in pads & rotors is so important.. which yes I did as well!!
You reminded me about a time I tried some PFC 01 pads at Mid-Ohio. I am used to using Cobalt Friction pads which don't require much (if any) bedding. I gave the PFCs a couple runs up and down the drive outside the Paddock to bed them as I didn't have time before heading to the track. It obviously wasn't enough as I developed a major shudder on braking after a couple sessions. Good brake performance just shook the hell out of the car. I was using plain rotors at the time and you could really see the chatter marks from the pad material on the rotors (wish I would have taken a picture).
I threw on a new set of Cobalts and everything was good as new. Just goes to show that some pads really need a good/careful bedding to work properly.
Yup, add me as one more track addict who has experienced "warped" rotors, only to discover it was due to uneven pad material deposits. I tried resurfacing, but no go, so new rotors fixed it right up............hope it's that simple for you!
Some good ideas posted already but you ought to check the A-arm dogbones and make sure they are tight to chassis. The aftermarket SS studs are bad to gall when tightened with air tools.
Symptom: Under braking there is WICKED, might even describe it as violent, hammering and shaking. The brakes are still very effective, pedal is firm. You can feel a slight vibration at first but once you build up heat it's like flipping a switch, by the end of 2nd lap or start of 3rd at NJMP Thunderbolt.
What I've done so far: I installed a "Sprint" kit from Essex so the car has brand new calipers, rotors (hats & rings), pads, brake lines and fresh fluid. Swapped tires & wheels.
If pictures are worth 1000 words maybe a video is worth 10,000?
Have identical (almost) issue with my 2010: wicked front end movement under braking, can get it every corner even when bedding new pads, new calipers front and rear (Wilwood), new rotors all around with no deposits, track pads F+ R, ~15 days on SKFs, feel is much more in chassis and similar to ABS but much stronger.
The differences: my ABS ACTIVE does go off, at least when bedding; too busy trying to stay on track to notice in a brake zone. Have had to use the runoff @ Big Bend at least 4 times this year because just couldn't get slowed down enough to make T1 without risking going into the grass halfway through. Chassis movement is not up and down but decidedly side-to-side. Oddly, the movement as I am trailing off from say 50% brake to 10 - 20%, is as large as the initial application - a violent snap to the left. The initial snap can go either way but is usually to the right. If I brake much earlier and easier, the movement is much less.
Instructor I hired for the Glen feels as if issue is either (1) too much toe out on bump steer and/or (2) brakes are biased to the rear. Rears do feel like they lock more than F's. Was 30* sideways ~ 3 car lengths before turn in for Bus Stop earlier this year. Caught it thankfully but never want to feel that again.
Check your rear rotors for uneven pad transfer. It is pretty obvious visually if this is the problem.
I had something like this a few years ago at Road America in my C5 Z06. Vibration got worse as brakes got worked until I had to pull in as the vibration was so violent that it was hard to hold on to wheel when braking. It seemed like a cracked front rotor.
My friend with C5 Z06 pulled in about the same time with what he thought was a cracked rotor. We could not find any cracks.
Background:
New front Chinese rotors in plastic bags installed the night before. Cleaned once with carb/brake cleaner to remove goo (rust preventative).
New Hawk DTC-70 pads on front with stock calipers. Drove from Chicago to Elkhart Lake with pads on and tried bedding on the way. Picked up vibration immediately under hard braking within a mile of my house. It seemed to go away as miles accumulated.
Both of us installed new front rotors and DTC-70 pads the night before.
After first session I could see uneven pad deposit on rotors & I used the end of my flat file to scape off pad build-up. It helped, but each session the vibration returned with a vengeance. We were advised by fellow track rats to just beat on the brakes and drive thru it. That did work kind of...
My opinion is that the rotors were not sufficiently clean and metal particles from Blanchard grinding were still on the surface. The DTC-70 pads moved the iron dust around and created high spots that caused uneven pad transfer layer.
I still run cheap blanks, but clean them with carb/brake cleaner until the paper towels are still white after wiping down. My friend goes one step further and washes the rotors with hot detergent. We have not had a problem since.
What little garage time I had this week went to my son's Grand Cherokee brakes! Tomorrow the C5 comes out of the trailer and onto the lift. Will replace rear rotors, inspect ball joints, wheel hubs, bushings and see if there are any wheel sensor codes in the computer. Test drive and will report!
I had the exact same issue earlier this year after installing new Wilwood front calipers. Tried and checked almost everything people have mentioned. I rebled the calipers, pulled the ABS fuse, and switched from Carbotech xp24 to Ferodo pads. The issue is now resolved and the ABS fuse is back in. I will try the Carbotech pads again next month and see what happens.
What little garage time I had this week went to my son's Grand Cherokee brakes! Tomorrow the C5 comes out of the trailer and onto the lift. Will replace rear rotors, inspect ball joints, wheel hubs, bushings and see if there are any wheel sensor codes in the computer. Test drive and will report!
Spent some time on the car yesterday. No codes in the computer, all the visual inspections (ball joints, tie rod ends, end links, bushings, etc) look good so I just swapped out rotors and pads on the rear. Best I could do was to try to get the brakes hot on the street with some hard stops (we're in a rural area with low traffic). I got into ABS a bunch of times and the brakes felt good every time. Never felt anything like what I'd experienced on track with it but I think the only way to be sure of all of this is going to be to take it out on track.
The rear pads were ready to be replaced, only about the thickness of the backer left (approx 1/8"-3mm). The rear rotors looked OK visually, just some heat checks in the center and to the hand they felt fine but I know that doesn't always tell the tale. Still can't get it to click in my brain that the heavy shudder was REAR brakes but I can't deny the results or the experiences of you guys, can only hang my head in shame a little for making a bad assumption!!
Fingers crossed that it truly is solved with the rear brakes replacement. Our next track event is 8/28 and I'll report back in after that. Thanks again to everybody, this place is an awesome resource.
I'd take a look at the rear toe links as well. These can go from OK to very bad, very quickly. Recently has a similar problem and couldn't figure it out until I found a scrape on the inner wheel which was the result of wheel to control arm contact during hard cornering. Also... Investigate the possibility of a cracked spindle. I had one in May at NJMP while coming through turn 12 and ended up in the pit wall at 122mph. The crack was invisible even after the wreck as it was at the bolt hole where the hubs bolt on. Go through the whole suspension. Don't wait to find out the problem on track.
If the problem was pad deposits it would have self corrected after a session of hard braking.
If the problem was pad deposits it would have self corrected after a session of hard braking.
In general, all good advice, but just note that my experience was a little different regarding pad deposits. I had "warped" rotors one day at Laguna, and decided to stick with it for three more sessions that day...it did not get better, nor worse, just major shimmy. Took rotors to local shop and confirmed rotors not warped. Tried to burnish deposits off and start over again, but that failed as well. Solved it by changing rotors and making sure I did a good job of bedding pads in with new rotors.
Well color me a bit embarrassed, but when you make an assumption these things happen. New rear rotors and the problem disappeared. Chalk it up to another lesson learned.
Thanks to all for the contributions, it was VERY helpful.
08-04-2015, 08:33 AM
