Howdy,

I was at VIR this past weekend (E36 M3, street tires, carbo XP8s) and noticed that under heavy braking like right before/at ABS, the car and steering wheel vibrated pretty badly. It felt more tight and harsh than like warped rotors, etc and it only happened when i was really on 'em. It seemed to get worse as the weekended went on.

The control arms/balljoints and tie rods are original parts at 125k so i'll be replacing them this winter. I'm guessing that this vibration is being caused be these parts. I have new (about 10k old) OE CABs. Could the OE bushings be at all to blame? I ask because w/ new control arms comes new bushings and i'd like to use OE unless theyve been found to be too soft and could cause this problem.

Thanks

Check the rotors for a "funny" appearance. A stuttered glazing would indicate problems with respect to rotors. I would suspect under heaving braking that the OEM parts would be causing this. OEM M3 bushings are VERY good and with 10k miles I would not be suspecting them at this point especially with the other "worn" parts present on the car.

Do you get the vibration on cold rotors, or does it only happen after hard use? If the problem only occurs after getting the rotors hot it could be heat warping on the front rotors.

Your control arms have 125K on them? I am going to point to those. In reality you should not replace the bushings only. Control arm and bushings are a single piece ;)

well control arms and balljoints are a single part. you can replace the CAB in the lollipop seperately. The only reason ive kept these control arms is because they keep passing tech and i can't feel/find any play in them. but yeh, definately due.

I'll give the rotors a good looking over tonight when i swap pads. they're euro rotors that are getting a bit old

Also check motor mounts. My brothers race car had this problem and we discovered a slight crack in his front subframe and the nut was loose underneath the car. We did a track side fix and all was well for the weekend.

Grab a large pair of channel locks (as in about 2' overall) and use then to squeeze each ball joint. Any motion in the ball joint indicates that it is worn and requires replacement.

Howdy,

I was at VIR this past weekend (E36 M3, street tires, carbo XP8s) and noticed that under heavy braking like right before/at ABS, the car and steering wheel vibrated pretty badly. It felt more tight and harsh than like warped rotors, etc and it only happened when i was really on 'em. It seemed to get worse as the weekended went on.

The control arms/balljoints and tie rods are original parts at 125k so i'll be replacing them this winter. I'm guessing that this vibration is being caused be these parts. I have new (about 10k old) OE CABs. Could the OE bushings be at all to blame? I ask because w/ new control arms comes new bushings and i'd like to use OE unless theyve been found to be too soft and could cause this problem.

Thanks

Are you sure it's just not pad deposits? I had the same problem when I was running Hawk HP+ on the track and it only happened under heavy braking. Then again, I'm not sure what type of compound the XP8s are.

Dat
Hook 'Em!

I was there this weekend also. Sporting my new driveway paintjob. Green yellow and silver. What group were you running?

As far as your car, control arms on regularly tracked cars are two year items. They do break on occasion so if you are going to track your car regularly they should be on the list for preemtory maintenence every two years.

It still could be pad deposits on the rotors. Check this from stop tech.

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


I run Carbotech pads also. 9s front and 8s rear this weekend. I like them because I can go back and forth to the track with them and still stop very well. They are not as good as Hawks(which I have also used) but they are easier for me to live with. But by the end of yesterday I was getting some shudder under braking as well. I think that the Carbotech's will leave some deposits on the rotors when they go out of their happy heat range. They then clean themselves gradually as they return to their happy heat range. It is just a theory but I have run Carbotech pads for a while and I have had this happen a couple of times. It seems to clear up with some regular driving before the next DE.

I would say if you are going to do this DE thing regularly that all rubber bits: bushings, mounts, etc., should be replaced on your 125k old car as preventative maintenence. Motor mounts, tranny mounts, RTABs, etc, should all be freshened for that added confidence factor and to help rule them out when trying to diagnose problems.

HTH

I had similiar issues at times w/ carbo's when they were less than 1/2 full......but it turned out to be a sticky/stubborn caliper pin/guide which became symptomatic only at 1/2 pad width.....

Replace those arms asap, the ball joints are worn and could totatally fail get you into serious trouble, joints are probably bad and bushings are weak.

+1 on the pad deposits, had the same problem but with different pads though. I have investigated this situation and if the pads you were running were for more for autocross/extreme street driving than that is your problem.

Specter, hey yeh i did see your car, it looked good. I went over and poked around it a bit checking out your roll bar since i have a sedan w/ fixed rear seats, too. Where did you get the bar? You werent around when i stopped by though.

I was in the Blue group. I was solo the last four sessions so i was having fun messing around by myself trying not to get ran over by the c6 z06 :eek:

My car has new RTABs w/ delrin shims and new CABs. tie rods and control arms are happening this winter for sure. I also recently rebuilt all four brake calipers. I guess my question really was asking if OE bushings surely would be ok and not cause this.

Do you think i really could have overheated the XP8s (front and rear) in that cool weather? Maybe i was being a noob and over braking. I was in ABS a lot. Also, how do XP8s wear compared to heavier duty pads? Are they at all softer and maybe more prone to tapered wear? I started getting a long springy pedal. I tried bleeding the brakes after the 1st session on Sunday but i found no air and the pedal remains the same through daily driving today. hrmm

http://www.stoptech.com/tech_info/img/warped_4.jpg

I did see some splotches on my rotor in sort of a ring around the center of the friction surface. hrmm

The Stoptech article is good, but not quite correct. While the writer might have never seen a set of warped rotors, I've got a set that is warped as proven by a dial indicator. Those rotors show about 0.005 runout at very low (less than 40F) or hot (more than 250F). In between at moderate temps (~70-120F) there was essentially zero (less than 0.001) runout. The surface color of the rotors is completely uniform, which implie that uneven pad deposits aren't to blame. And besides, if pad deposits were to blame the runout would not vary with rotor temperature.

At 125k on the ball joints I can't imagine those being anything *but* bad.

I've seen a failed ball joint on an autox vehicle. The damage wasn't pretty, and it would probably cost $1500+ in body and paint work alone. If it happened on a road course, I'd imagine it could be fatal.

I strongly suggest you have a qualified mechanic check it out immediately. A tech inspector could easily not detect a problem.

Mike

If you think about it the difference in air temp between a hot day say 95 degrees and a cold day say 40 is 55 degrees. A brake pad that has an operating temp range of 600-1200 degrees or so is not going to notice a 55 degree difference in air blowing over it. Brake temps depend on time between applications and amount of cooling air that flows around them. Our E36s have ducts in the bumper that vent air into the wheel wells which cools them better than nothing. But for extended track use they fall short of optimum. VIR is not that hard on brakes compared to say CMP but it does have two high speed straights followed by relativly slow corners. Add in some left foot braking to rotate the car and you are on the brakes quite a bit. You can overheat just about any pad if you do not keep brake health in the back of your mind while you run. Before ducting I could overheat Hawk HT-10s(1600 degree pad) at CMP if I was careless.

If you got into the ABS much then it is possible there is some air in the ABS pump. You have to cycle it while you bleed by jumping it's relay.

Roll bar is autopower from IO Port racing. Does the job. Price is right. If you want something that allows you to keep the rear seat back then this might not work. The rear downbars mount far enough in that there was no way without serious upholstery work that the seatback would go back into the car. I have seen some other bars though that mount far enough outboard that you can jam the seatback into the car. You can't just cut into it though because it has an outer wire that is in tension that holds the seat in it's form. If I had it to do over again I would find someone who does cages and have them weld in a bar. I think that if you are at the point of putting a bar in you are going to have it a while(no ten step program for track addiction that I know of). Might as well get a nice one. But it is easy to install.

i had front discs that wore unevenly at the raceway, causing vibration. on cold discs, i ran my fingers radially outward atop the braking surface and could feel it was no longer even/flat. i figured it wasn't due to deposits, and found out i had reversed left/right discs! my guess is that uneven wear was caused by uneven heat dissipation, as the vents were backward. luckily oe brembos cost only 150 a pair shipped.

Also if you are getting pad taper where one end of a pad is worn more than the other then you should look into the solid caliper guide pins. Everybody sells them.

About the roll bar. This is what I would have done given a second shot at it.

http://www.tcdesignfab.com/4door_e36rollbar.html

Weld in and more structurally sound. Plus if you ever need a full cage you just have the same guy weld on the front half.