Just got back from and HPDE event this weekend. Swapped in new pads/rotors all around (Hawk HT-10 fronts, HP+ rear, new Centric blanks). I bedded them in following procedure and they felt fine (besides ABS being a lot more obvious). My first session out yesterday, they were fine as I wasn't moving too fast, just getting the line down.

Every session after that, after a few laps, it would start to feel like I had warped rotors - not just in pluse - the whole car would vibrate when I was on the brakes (my instructor would feel it too). It would go away as soon as I slowed and started my cool down lap. Any ideas?

I did a visual inspection, and that didn't reveal anything - thought it might be the brakes getting over heated and putting deposits on the rotors when warm, then wearing off as I used the brakes on the slow down lap, but that didn't seem the case.

The rotors were discolored (purple/gold/etc) from heat near the hubs, but I figured that was normal. I am running a non-staggered set up, but don't think that is the issue. The car does have 106k miles on it, but is maintained very well and I just did a fluid flush two weeks ago.

If you've had a similar problem, id love to hear how you fixed it.

Thanks,

aCab

 

You may have used your e-brake between sessions or your foot was on the brakes at the end of the session while you were talking to your instructor.

Most likely cause if above was done would be uneven pad transfer.

 

all other times, my rotors don't feel warped though - driving home they were fine, cool down lap they were fine - nor warped feeling at all - even doing a few hard 80-0 stops on a road near my house they were fine too. Instructor and i were quite perplexed.

 

Normally, if your brake rotor was warped you'd feel the brake pulse all the time, not just when the brakes are hot.

I once had a strange brake vibration because I put one of the screws that hold the brake disks to the hub in the wrong hole in the disk--a non countersunk hole which caused the head of the screw to stick up so the wheel didn't fit flush to the brake disk. Take a close look at all of the wheel-to-brake disk area and make sure they are completely flush.

Also check all your brake caliper bolts, both the caliper mounting bolts and the brake pad access bolts--weird stuff happens when they start to loosen.

Don't give up until you find a problem because something is definitely wrong with your brakes.

 

Funny thing is I also was at the same track as you this weekend and had a very similar problem. When the brakes are cold I was getting a vibration from the rear but after I got them hot on the track it would go away. Also running a square setup. I was the white s2k.


Setup
Original rotors sanded with 400 grit, xp12/8, ATE super blue

 

is it coming from any particular end or corner of the car?

could it be an abs problem? most of the time u wont feel the abs but sometimes when you realy skid you will feel it vibrating.. that is not normal

 

My only guesss is pad material transfer which means you need pads with higher temperature capability.

I had the same thing happen on my Evo. During the session, I would get the pulsating pedal and the cool down with light braking would clean off the rotors.

 

I experienced this when I had an e36 BMW. It was warped rotors and 1 time I think it was what is suggest on this for ( uneven material transfer ) because it when away. I know what you are referring to. It was a very violent shutter.

 

It is most likely pad transfer issues. As the material heats up the amount of friction will change. If it is uneven the change in friction from each part of the rotor will change and get worse as the part that likes heat get hotter because it is working harder.

Sand the pads down and cut the rotors to test this out but check for loose bolts etc first.

Make sure to use brake cleaner as oil from the rotors can cause some bedding issues.

 

I have this same issue, would resurfacing fix this, or would it be a better idea to get new rotors. I ask because I hear resurfacing usually is only a short lived fix if the car is being tracked.