I've searched and can't find what I've been experiencing at the track this weekend.

Car: '09 R3
Brake Pads: Carbotech XP-12 Front, XP-10 Rear
SS brake lines
ATE Super Blue fluid - full flush and bleed
Stock tires
Brake pedal height has been adjusted to the highest point.

TSC/DSC is OFF (Button held for 8 sec., both lights on)

I'm instructing at Grattan raceway this weekend. It's the first time I've had the car on the track and it's running awesome except for an inconsistent brake pedal feel.

Sometimes the pedal is nice and firm with good feel. I am not getting into the ABS at all. It is in a good position for heel/toe downshifting.

Other times it gets a long pedal and drops below the throttle pedal. It never fails to stop though. Again, I am not getting into the ABS. The ABS is working fine, though because I can feel it kick in occasionally.

It is also not pad knock back. I make sure to pump the brakes a couple of times before hard brake zones just to be sure I have brakes. When I get to the brake zone, sometimes the pedal is firm, other times, not. Always slows down though.

I bled the brakes at the track and there was no air. Pad wear was fine.

So that is what is happening. Any ideas?

Thanks in advance!

Phil
www.PhilMatherRacing.com

 

did u bleed the Clutch side too ? on S1 they both shared the same reservoir

 

Some type of master cylinder problem perhaps? Never heard of 'inconsistent' or really I would call it 'intermittent' brake pedal feel before. Is there a pattern of right or left turn perhaps, as in a stretched or pulled/leaking brake line? How about a caliper slide pin that's REALLY bound up or a piston that cockeyed in the bore and dragging? Interested to hear the final call on this.

 

Be nice if you can somehow tap into the ABS diagnostic line & record brake pressure data. Then you will be able to help better isolate the problem.

If you know anyone with an autoenginuity, you can hook it up and have it record the data to a laptop while your on track. Too bad your not local to me!

 

Turns out it was the master cylinder. I pulled the master cylinder off the booster very slightly to check for leaks and some small amount of brake fluid came out. That is not supposed to happen. Off to the dealer tomorrow.

Yes, I did bleed the clutch as well when I did the brake lines.

Thanks for the input.

 

If you have air in the ABS it can act strange like that..I would pressure flush it and see if it happens again

 

I would guess you brake fluid geting close to the boiling point

 

Got my car back! 100x better in the braking department. If you're in need of service for a Mazda in SE MI, go to Brighton Mazda. Excellent customer service and they have an RX-8 specialist as well, Russel Gavin. And they confirmed my diagnosis of a bad master cylinder as well. The original dealer refused to even check without me paying, and then they did it wrong.

The original dealer (who will remain nameless since they did support my racing in the past), still denied me a refund for any diagnostic charges, but Mazda Customer Support did come through and are refunding my money.