threewinmag

My friend is at the track right now (Friday) and this is the first DE weekend of the season. He's got a 99 frc that has t1 bars, has been lowered on the stock screws and is running z06 wheels sizes and Kumho v710's. He is still running stock calipers and uses Super Blue fluid.

This morning he replaced the front rotors and is using new Wilwood pads (which is a normal setup for the car). He getting some heavy vibration after about two laps on the track (just when things start to heat up.) We're currently thinking maybe rear rotor warpage or maybe a front wheel bearing that is failing under load.

anybody have any other suggestions to look at?

AU N EGL

No such thing as rotor wappage. WHat may feel like a wapped rotor is uneven brake pad materail on the rotor from improper on no bedding of rotors and pads. But dont think that is the problem

Besides that a few things come to mind about that vibration:

Is the vibration under braking or over 80 mph?

if under braking then look at
1. cracket rotor
2. bent caliper brackets causing unven braking.

if not under braking but normal driving:

a tire is flat spotted
loose wheel
bad bearing ( when were the bearing last changed on the car ?)
alingment is off
( did he realign the car after putting on the T1 bars ??)
did he realign the car after lowering ?? ))

How low did he put the car?? if lowered more then 1" from stock could be a suppension problem. Vetts should not be lowered more then 1" if that much when your tracking the car.

What specifilty is going on when the vibration occures ???

Falcon

I have exactly the same problem when I haven't bedded the pads enough. It has felt so bad while braking real aggressively that I thought the front end was coming out of the car. It finally settled out after a session, but it was a problem at first. It was with WW "H" pads. If he can ride it out, it may clear up like mine did. Otherwise, I'd recommend another set of front rotors (used, preferrably) and try that.

I'm assuming it wasn't vibrating previously.

Good luck.

varkwso

My experience:

* bedding on pad
* cracked rotor(s) - rare for me
* bad tires (try swapping them out to troubleshoot)
* funky track surface....

94ZR1#444

I've had what seems ito me is alot of experience with HEAVY vibration when braking. The steering wheel would shaking violently when braking hard and nto so hard braking. I tried everything when it started, rotating other people's tire/wheels (Thanks Falcon) on my car, still did it. One day it got so bad that I changed the rotors and the problem immediately went away. I'd have to agree with previous posts that it was a due to correct bedding which led to a buildup on the rotors. If the rotors are new, keep them and have a thousanth or so shaved off just to clean them up. I haven't ahd the problem since.

threewinmag

thanks, fellas, for all the advise. I think I'm going to agree with the poorly bedded brakes. they are new WW H's and new rotors. He's buying a new set in the morning and basically start over with the process.

We talked with a mechanic and he didn't think it was a bearing either because there was no sound from the wheel during regular driving. Sessions are over for the day. We'll see how it goes tomorrow morning. I'll let you all know if it goes away.

Ag-z06

I had the same problem on my Z06 with Wilwood H pads, front and rear. I replaced rotors and still had the problem. Swapped out front and rear tie rod ends - problem gone.

larryfs

I had the same thing. final solution was rear rotors.

threewinmag

I think the problem was properly diagnosed as poorly bedded pads. As the weekend progressed the vibration calmed considerably. There is still a slight vibration but he thinks it might be an unbalanced tire. So, thanks for all the replies.