High Speed Braking shudder
 

I'm getting a shudder at very high speeds on the track, especially when initially engaging the pedal at speeds over 100 mph. It tends to go away the harder I press on the pedal.

Is it possible that I have a warped rotor? Or perhaps I just have some brake pad deposits on the rotors and they need to be cleaned off? Some agressive bedding and 2 track days haven't seemed to correct the issue.

I did several tracks days using OEM pads and a couple using Hawk HP+ pads so now I've done 10 track days on the original rotors with no turning in between.


My next event is this weekend, but I may not get my new rotors in time. I'll need some good braking because it is at Road America, one of the faster tracks in the country.

I have some Carbotech Panther XP8s. The plan is to use them for a few days on the street, bed them in and see if I can clean off the rotors and get rid of the deposits. Does that sound like it may work?

Any other solutions other than having the rotors turned/replaced?

How often are track guys replacing the rotors?

Sounds like it could be unneven pad transfer deposits. As I understand it, when the unevenness is minor, you can basically wipe it "clean" by hard braking at speed (which is what it sounds like you've been trying to do.) However, if the unevenness is worse, then hard braking can have the opposite effect, because when the pad touches the "ridge" of elevated pad material on the rotor, a small amount of pad is scraped off and stays there, which builds up the edge a bit more. This continues in a downward spiral.

Another possibility is that the pad transfer of the HP+ never happened properly because of the pre-existing OEM pad transfer layer. I've heard Carbotechs are particularly sensitive to this, but I haven't heard anything about Hawks specifically.

In both the above cases, a shallow machining of the rotor will take care of it. I especially recommend this prior to installing your XP8s.

The idea of using the XP8s as an abrasive cleaner of the discs might work. However, I don't think the XP8s are nearly as abrasive as, say, a Hawk Blue, which apparently is VERY effective at cleaning (and eventually destroying) your rotor at cold temperatures.

You could be experiencing this

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

agree with Marc, the Carbotech will likely keep it from happening on the softer OE rotor at the expense of wear, but they have been reported to create the problem on wear-resistant rotors like RacingBrake, which now only recommends Hawk pads for their racing rotors as a result

Thanks guys, I'll put on the Carbotechs and see what happens. The new rotors have been ordered (Thanks Rosenthal Mazda). If the Carbotechs don't get rid of the shudder, I'll replace the rotors and have the old ones turned and keep them as a backup.

FYI: Another possibility could be over-torquing of the wheels. Too much torque can distort the rotor and cause it to wear unevenly.

Also, if you plan on changing your rotors your self, expect a PITA getting the front ones off. I tried an impact screw driver to loosen the philips head screws that hold them to the hubs, but that didn't work. I tried a torch, and that didn't work. I eventually just drilled them out with a 1/2" bit first, then a 1/4" bit and chiseled out what was left. I didn't put screws back on.

Also, I got slotted rotors from www.rx7store.net that were slotted from brembo blanks. they worked great and were FAR cheaper than OEM rotors. You might wanna check them out :boink:

^ which rotors did you get? I'm assuming the FD ones?

Are you saying "FD", as in the 3rd gen RX7? I don't think so...
Jason has RX-8 rotors on the site. At the bottom of the left hand column there's a tab to click on rx8 performance parts. A couple more clicks, and you're there :)

http://www.rx7store.net/product_p/sl...etrotorrx8.htm

So I just swapped out four pads and put Carbotech in front and OEMs in back. I went out to bed the brakes in and didn't hit triple digit speeds but I did hit 90 or so with no shudder.

Also when removing the Hawk HP+ pads, I noticed a little chunk missing out of one of the front pads. Perhaps this was causing the shudder that I was feeling.

I'll know more this weekend when I hit the long straights at Road America.

Which carbotechs did you get? KC <3 Carbotech. :)

Carbotech Panther XP8s for the front and OEMs for the rear. I ordered them from driven performance equipment (www.dpeweb.com). Great customer service and some great information on their website.

I just got my sways from DPE. They were great.

I ate up my OEM rear pads in 1 weekend at the Glen. I'd suggest either bringing extra pads, or get a set up upgraded pads in back, as well.

my OEM rears got toasted pretty quickly at RA to the point that I couldn't finish my 2nd and 3rd session the second day. I will def. be bringing another set of both front and rear pads to my next event

which pads were you using?

.

My bad, I misunderstood and thought you fried the OEM rotors.

Suggestion - if you have brake pad deposits on your rotors try to get a set of hawk blues from someone to use for a short while. Twenty minutes of regular driving with them will clean off any deposits.

If you turn your rotors, please don't use on track...

When you are ready for a good race pad try Colbalt VR's front with Hawk HP10 rear. I use them with NASA HPDE group 4 and TT group.

Jay Goldfarb

Why shouldnt you use the rotors on track after you had them turned?

To take out the warping you are getting close or past min. thickness. Also, I come from German cars and they never recommend turning rotors. I believe it is just cheap insurance and my life is worth a hell of a lot more than the cost of a set of rotors. I just throw out a set of slotted Stoptech rotors that had spider cracks all over the service. None were full cracks, but when you push hard at the track, to err on the side of safety is always best. You don't want to see what happens if a rotor cracks and brakes off under heavy braking.

Jay

Whatever the brake issue was it is gone now. I put on the Carbotechs and had no issues heading into the braking zones at 120+ at Road America last weekend with the local bimmer club.

I bought some new OEM rotors from Rosenthal as a precaution so I'll take them with me to the track in case I ever need to swap them out. The box is pretty heavy to lug around!

So far my stock rotors show no signs of stress cracks after 12 track days.