Optical TDI

iTrader: (2)

Here's my brake set up: Motul 600 fluid, Carbotech XP8 pads at all 4 corners with stock rotors, calipers, and lines.

Brake fade did occur at the end of the long straight. 115 mph down to about 55 mph (I wasn't looking at my exit speed, so the 55 is a guess based on RPMs in 3rd gear).

I thought this set-up would be fine because I used a very similar set-up in my 2007 GTI last year using the same XP8 compound. However I used ATE fluid (similar properties as the Motul 600)and I had stainless braided lines.

I had no fade with the GTI and it has slightly smaller rotors, but a few mm thicker I believe. Plus the GTI is about 250 lbs. heavier and I was hitting 120 mph vs. 115 mph in the RX8 at the end of the long straight.

This doesn't make sense to me unless the lines could make a difference or perhaps the stock rotors and calipers on the GTI are better in some way.

On the RX8, I'm considering getting 2 piece stock sized rotors up front to use with stock calipers. Or 4 piston calipers with the stock rotors. Will either help my fade situation? Please provide any solid advice from experience. Thanks.

dannobre

iTrader: (3)

Don't know much about the pads...but the fluid if it's fresh and bled properly should be ace.

I have a lot of 130 mph to 45 type corners here...and had no fade problems ever

The stock system should be OK as well......

How bad was it....soft pedal...or half way to the floor??

You did have fresh fluid and a bleed right

Optical TDI

iTrader: (2)

Yes, fresh fluid (not new, but unopened container) and bled a few days prior to the event. The Carbotech XP8 are the first level of track pads that are not recommended for the street, so they should be fine. (200°F-1350°F+).

The pedal wasn't soft, but it went half way to the floor during braking, then the next brake zone it was fine. It was mostly slowing down from the 115 mph since that's the longest braking zone on the track. Towards the end of the 20 min. sessions, I ended up not going over 100 to help the situation.

olddragger

iTrader: (3)

Huh? I run the carbo techs xp8 for a couple years now(track only) and have 140+ down to approx 60-70 at road atlanta and roebling. NEVER had any brake fade whatsoever. oem rotors, ate fluid and ss lines and hoosiers.
maybe some air in your line you were not aware off?
olddragger

mwood

That was my first thought, also. The XP8 should have plenty of heat range for the described use and car. But, the fact that the braking goes away and then comes back sounds like pad fade...hmmm. Still, I'd agree that there's probably air in the system, somewhere, or some other bleeding/fluid related problem. The Motul 600 should be fine, as far as temp range.

How hard are you on brakes? I would suggest cooling is the next step, with some spindle mount ducts being needed. I don't think a brake system upgrade is needed.

ZoomZoomH

iTrader: (1)

did you bed in those xp8's per their instructions?

FRANCES

Just my thought as well. When I talked to the guys at carbotech they were very clear that this might happen and strongly recommended getting a different set of OEM rotors or turn them down and then re-bed for carbon brakes and not go back to stocks for the street.
A recommendation, I'm now running Cobalt XR2 front and XR5 rear, just as good as the hawk blues without the issues of corossive dust (thanks mwood, spin9k). they were great yesterday here in corpus at our TT, braking from 120 down to 50 with great modulation and no fade. Oh, 94 degrees, 78% humidity.

Razz1

I think your feeling the lack of SS lines.

At least that's part of the problem.

Cryogenically treating the rotors help alot.

FRANCES

I've only seen brake feel degrade but not brake fade from oem lines.
May still have air in lines, get a power pressure bleeder.

ZoomZoomH

iTrader: (1)

^I agree, does not sound like a brake line issue at all

air in line or glazed pads seem like the primary suspects

Optical TDI

iTrader: (2)

Thanks for the suggestions. I'm going to buy a pressure bleeder soon so my wife doesn't have to pump the brake pedal for me. Also, I may have gotten air in the master cylinder during my last bleed, but I kept on bleeding for awhile to be sure any air was gone.

I had the rotors turned to clean them up and bedded per instructions. At least the best I could do on the street. Carbotech recommends bedding on the track, but I needed to bed them prior to the recent track day.

dannobre

iTrader: (3)

The 05+ master cylinders don't have an bleeder like the 04's which I find strange....It's really easy to get air in MC when you change fluid if you aren't real careful

altiain

iTrader: (3)

Umm.... fail.

If the pedal travel is changing, that indicates fluid problems. I'm going to go with an air bubble trapped somewhere in one of the lines.

BTW, I run nearly the same setup (RBF600, XP8/Panther Plus), and I've never experienced pad or fluid issues, regardless of running OEM rotors and lines. I run R compounds at several tracks that tend to be abusive on brakes.

SouthFL

FWIW...

SolarYellow510

If you use a pressure bleeder, make sure it has a diaphragm to separate the air from the fluid. If you pressurize air that's in direct contact with fluid, it is absorbed, and makes your pedal go all to hell when the calipers get hot.

Having your wife pump the pedal for you is still the best way.

TheArchitect

For what it's worth, XP8s should absolutely be fine on track on a non-FI RX-8. One consideration you might keep in mind next time you head to the track with new or resurfaced rotors is that it's generally a good practice to make your first session an abbreviated bedding-in session. Generally I have seen the best results from going out for a few laps (3-5, depending on track and ambient temps) and getting the brakes good and hot, then come in and let it sit until the next session, with the second session being run as normal and always (for me anyway) resulting in solid and consistent braking.

True, it does suck to waste part of a session, but it's better (IMO) to compromise one session than getting glazing that hampers your fun on every session. I even saw a guy go off track several years ago due to glazing who hadn't properly bedded his brand new Brembo setup - tore up a pretty nice looking 330 on his second session out. Obviously that's more the worst-case scenario, but just pointing out that it can be hard to completely bed in on the street.

Also, FWIW (and it might not be much), I have run an awful lot of fluid through an awful lot of track events that was pumped in by a Motive PowerBleeder (very basic pressure bleeder, no separation of air and fluid), and I've witnessed no ill effects from it. YMMV, as they say, but just thought I'd present the other side of the story on the pressure bleeder thing. I can't definitively say that it doesn't affect the boiling point, but I can say that I've never experienced ill effects in either of the RX-8s I've owned running ATE fluid and P+ or XP8 pads over thousands track miles. Frankly, the RX-8 braking system is really top-notch and great for track days with just fluid and pads, and the XP8/ATE setup is exactly what I've been running for years with exactly zero issues.

One thing I'm not clear on is whether it was truly brake fade or whether it was increased pedal travel/soft pedal/pedal variability. As others have suggested, if it was a spongy pedal or the pedal dipped further to the floor than usual, that's a fluid-related issue; could have been air in the system, could have been boiled fluid (unlikely), or heck it could even have been a leaking caliper piston seal, which I had happen on an aftermarket BBK on my old 350Z which almost resulted in a hairy off-track excursion. If it was fade, it was probably glazing from not properly bedding in the brakes, not from having insufficient heat range in either the fluid or the pads. Maybe there could be another reason for it, but I'm coming up blank on what it would be.

Also, I should probably chime in that Carbotech makes very OEM-compatible pads. They do often recommend a separate set of rotors, and I'm sure that guarantees best results, but I've never had issues swapping between OEM pads and Bobcat/P+(AX6)/XP8/XP10 on any of my cars over the last ~6+ years of using their products. Definitely not bad to get the rotors cleaned up beforehand, but usually not entirely necessary unless you've been using some other aftermarket pad that they aren't compatible with.

TrackAddict

Sounds like lots of good advice. However even with proper bleeding, proper bedding, proper everything, if you dont use the brakes hard over short distances, you could overheat the fluid. Sounds like you have some experience. I often see novice drivers ride the brake pedal into the braking zones. The RX8 stock braking system is surprisingly good so maybe coming from another car you underestimated it?
My frame of reference is my own experience running HP+ (yeah I know I know but I have never had any issues), ATE fluid, and RA1s or Hoosiers in countless HPDEs and Time Trial events for the past 4 years in my RX8.

FRANCES

Motive Power bleeder will purge all air, you only need to follow the directions and have a syringe to get the excess fluid out.
www.motiveprocucts.com
Out!

darnellm

iTrader: (1)

I think you mean www.motiveproducts.com.
I tried to find the right setup for the rx-8 (3 tab 45 mm id of reservoir)
ended up with a GM application. Tested find at 10 psi without the fluid.
Heard the dreaded pop after I put fluid in it.
Anyone know what the right part no?