Soloontario

Finally got my wheel hub and EBCM issues sorted out (I think) but want to get the best brake balance for the car on the track. Even with the dreaded codes (C1225 at 2nd last event) gone and the brakes obviously working much better, I still feel that the antilocks are coming on a bit too soon. I am running stock brakes, quantum cooling ducts, Carbotech XP-10s up front and XP-8s out back. I drive with the nannies off.

I run a square setup with either 315 Nitto NT01s or Hankook RS3 285s (note that the Nittos are a small 315 and the Hankooks are big for 285s, not Hoosier big but big none the less).


I am used to having an F body with similar pads and had way too much rear bias which I had to get rid of by using much lower coefficient of friction rear pads and a proportioning valve to decrease rear brake line pressure.

I am assuming that the larger and grippier front tires, especially in a square set up, mean more wgt gets transferred to the front and that the front brakes should be able to take a pretty agressive pad. OTOH when the antilocks come on while on the track, I'm not really sure which wheels are triggering and no code history is recorded. And no, I don't just slam on the brakes. Having had enough time with wheel axle hop in an F body teachs you to really avoid that mistake and for that car, it was ALWAYS the rears which were locking.

Should I consider having an even weaker rear pad ( the answer in an F body) ? Frankly I'm not completely sure it is the rears that are triggering the antilocks too soon.

Bill Dearborn

Since you have an 04 your car has dynamic rear proportioning. That means the EBCM controls the rear brake bias and provides as much brake as the rear can handle although pad/tire compounds other than stock are not accounted for in the EBCM calibrations. If the fronts are tending to lock up and cause the EBCM to activate the ABS you should be able to feel it in the steering and the seat of the pants. It feels different than the rear. You could have a base brake issue that causes ABS to activate on just one wheel or if you haven't turned off Active Handling it could be activating to yaw the car in one direction or the other depending on which way you are turning the steering wheel. When the car is understeering (like when carrying some brake into a corner) the EBCM will modulate the rear brakes one at a time to yaw the car into the direction of the turn. In a right turn it will apply more brake to the right rear wheel to make the car yaw to the right and in a left turn it applies more brake to the left rear wheel to make the car yaw to the left. In an oversteer situation it will apply the outside front brake to keep the backend from swinging to the outside. Everything depends on the position of the steering wheel and the car's yaw response. If this is occurring under braking it would feel like the ABS is activating since your butt can't tell the difference between the two purposes of pulsing the brakes. Depending on what is happening it could modulate all 4 wheels within a few tenths of a second as the car swings between over and under steer in a turn. If you haven't turned AH all the way off do that first and see if the ABS like sensations continue.

Bill

Soloontario

Thanks for the comments Bill but I drive with all the nannies off. I have tried driving with the nannies on and as you say, it is quite intrusive.

I have to admit that if feels like it may be the fronts locking but certainly not always. I have new SKF race hubs, brake pad wear is remarkably good with not much taper, no sign of caliper spread and the slider pins work well. And as I said, I am not triggering any codes like I did before replacing the front hubs.

Now that the car is back on street tires and our race season is over, I'll have to try overdriving on the street and see if I can tell which end is locking.

As a note of interest to anyone reading this thread, what pads do you use front and rear? Do many folks run a stagger of coeffecients of friction front to back? Any different with a "square" set up vs stock?

moespeeds

I was driving with no ABS for a month or two and I ended up going with a more "grabby" compound (Wilwood Poly A) on the front, and something less sticky on the rear (Wilwood Poly H) to balance out the brake feel. It worked great, except that the Poly A tore up my cheap NAPA rotors in like a day. I fixed my ABS and went back to the thick H pads all around for longevity sake. I've since lost the ABS again, and although I've fixed it, I've decided to run with it off from now on since I like the way the car feels without it. Ultimately I'd like to go with a bias control but it's a hassle to install.