I put this in RRAX because it may relate more to track users than brakes in general. Is there any relationship between pad wear and pedal feel? I have noticed a slightly less firm feel in the pedal as my track pads wear. Not sure if that is the cause. The normal firm feel returns with change to street pads. The feel stays if I leave the track pads on even when cool and in street operation. I do not notice it when the pads are new and thick. Brakes are NSX fronts and RSX rears. I leave the pads in the rear on, so, no change there. Also, as expected, little wear on rears. Pads are Cobalt Friction XR2 in front and XR5 rear. Also noticed with last pads, XR3 F and XR5 R. I did not really think about the relationship until it started happening again, so did not try to make the link last time. I vaguely remember similar with HP+ front and rear. Steel lines, new fluid and no pedal change with fluid flush, ATE blue. Pedal is firm, normal, with street pads. The track pads work fine, but feel progressively less firm in the last 1/3 wear. No MC leaks noted and it is normal with street pads. Seems like the hydraulics would account for the piston extension. Any good explanation or look elsewhere to explain the feel?

 

Don't know anything about pad brands. But perhaps the track pads are made to be changed out before worn all the way through? You could try contacting the manufacturer and asking them. I would've said they were overheating but you've used them on the streets. Is there any difference in the thickness of the track pads vs the street pads when new? If they are just a little bit slimmer you could feel a difference because your having to push the pedal down more to get contact with the pad.

But again these are just the things that come to mind reading your problem, I doubt I've nailed it on the head. Hopefully it will get you or someone who knows more about this stuff thinking along the right track.

 

Thanks for the reply. Yes, I have asked about wear, and I am plenty thick for recommended wear. Track and street pads are about the same thickness new. Not pedal travel, but firmness/feel. Do not think that I am over heating, XR2's have pretty good high temp, and they still work, just feel less firm.

 

What do your rotors look like?
Are they glazed???

 

The rotors look fine. Fastbrakes plain HD 11." Again, they feel fine when I switch pads to street. I am really trying to find the problem, and realize that pedal feel and pad use, and piston extension, may not really be linked. I guess that is the question.

 

Could it just be the extra movement in the hydraulic system? As the pad wears, the caliper piston has a greater distance to travel, meaning more fluid is pushed around. Your MC reservoir probably looks a little low. I have this same "issue" with my car, but it seems to be related solely to the fluid level. New pads = back to old pedal stiffness. Topping it off would probably work, but then you'd be overfilled with new pads.

 

I was thinking something similar to Stinky - I assume you flushed or at least bled the brakes when you installed your hi-perf pads. Have you flushed the brake lines with fresh fluid since? The heat generated by pads with a higher CoF can wreak havoc on brake fluid.

 

I mentioned piston travel associated with pad wear, but it seems that hydraulics would account for this. Fluid in the reservoir moves to fill lines and calipers and new space as pistons move out. As long as the reservoir is above minimum, or not getting air, then the fluid should compensate, at least my understanding. Yes the level changes with pads, back up a little with street pads. I wonder if pistons extended have the different feel than when pushed most of the way in with new pads???

 

Yes a couple times per season, and the feel seems fine with change back to newer, albeit street, pads. Actually changed fluid just before the last track outing. I also do a cool down lap around the pits after "the cool down lap" and drop rotor temps from about 550 after track cool down to about 350 after second cool down, before parking and letting any heat soak in.

 

Could the link be caliper piston travel vs pedal feel, though I am not sure why?

 

One last thought...if as the pads become thinner the pedal feels softer, then one would deduce it is because the pads have to travel further before coming in contact with the rotor. But the caliper should only retract enough to allow the pads to clear the rotor...no more. So it sounds like the caliper pistons are retracting more than they need to thus allowing the pads to back further away from the rotor. Are the rotors warped? Wheel bearings tight? Is there anything that would result in the pads being pushed further than necessary to just clear the rotor?

 

It is pedal feel, not travel. I do not believe that the pistons are backing off, and as noted, I think that the hydraulics compensate. Could the fact that the piston is out further, beginning and end, with no more motion or travel, give a different feel?. Anyone notice better feel, not travel, with new street pad as they changed out old, of course allowing for several stops to bed? New bearing this winter, and rotors feel fine and stop fine, pedal just slightly less firm.

 

I'm not positive, but I don't think the principles of a hydraulic system account for variability like you describe. Rather, they would allow the system to continue functioning at all, as opposed to not functioning at all. I could REALLY be wrong with that though.

 

I hope that you are correct. I chased the problem last time toward the end of pads and was convinced it was MC. The old had 200k miles and may have been failing, but, the old track pads did not feel better with the new MC. With new pads good firm feel again, and now less so. I am trying to understand a normal cycle vs prevent or fix a problem.

 

Your pads are tapered, it explains all the symptoms. I had stock calipers\rotors, and even with XP-10's they would taper by the end of the pad. Mine tapered to the point that the pedal didn't do anything until you got halfway down, but since you have the legend calipers its probably to a lesser extent. Put the pad on a flat surface and measure the height on either end, I bet they'll be different.

 

NSX, which supposedly have the correct large and small piston order. There are a few thousands taper, with calipers, but I suspect that this is normal even with one piston. The leading edge to the rotor gets hit harder. That said, taper may help explain it. It seems that taper may cause the piston to back off sl more from the thin end, as the fat end of the pad has to clear. So, sl more travel on the pedal to get the pad down, but different feel?? Do street pads feel sl less firm toward the end, then to feel firm with change to new, or does pedal travel change?

 

I took off a set of pads that were worn concave. Gave the brakes a spongy feel, kinda like air in the system.

 

I was wondering this exact same thing the past few days. After leaving the track on Sunday my brakes felt like crap, taking a lot of pedal travel to stop the car, even then not working very well. After a few miles they more or less seemed to fix themselves. This in on 7-8 event old Colalt GT-R Spec VR's. Pretty much gone. Once putting my street rotors/pads back on the pedal travel is definitely reduced, and has a firmer feel. I think the pad tapering may have something to do with it. I'm guessing it doesn't take much of a taper to create a noticeable difference in pedal feel.

 

There's a lot of missinformation being thrown around here and people really dont understand the hydraulic concept with the piston travel/pad wear and fluid displacement.

As the pad wears, the piston follows that wear rate and stays in contact with the pad and the pad with the disc. This is effectively done so by the fluid displacement. The pad is ALWAYS in slight contact with the disc (unless you have knockback but thats a totally different issue) So that being said, pad wear never increases pedal travel.

Now back to the topic, given that the pedal is firm again with steet pads, it means its not an hydraulic/seal/caliper pins/etc problem and the only issue I can think of is the compressibility of the pads has increased as the friction material burnished over the different thermal cycles.

Toss those cobalts and get something else decent.

 

Eh? You're saying the PAD is compressing? Like, getting soft?

 

Yep. Different pads have different rates of compressibility too.

Glazing a pad can also give you some weird pedal feel.

 

I really hate the word "never" when talking about car setup.

What several of us have been suggesting is that either the pads are being knocked back or that the pad surface has worn unevenly and is no longer parallel to the backing plate resulting in the pads not coming in even contact with the rotor as soon as it does with nice, new, even, thick brake pads. I think that is more likely than the friction material decomposing in the heat and becoming more sponge-like (that really seams like something even the lamest of brake pad manufacturer would take into consideration).

 

Was not aware that Cobalt pads were not decent. Pads do develop taper, most at micrometer level but visible, but I thought that the piston pushing the pad would seat the pad, even if it sat slightly uneven on the piston. How does it continue to wear the thin end? In fact, 2 piston calipers try to address this with different size pistons. The greater surface of contact is the pad to rotor, vs pad to piston. They do not seem glazed, they work well on the track, just seem slightly less firm.

Stinky’s suggestion makes some sense: “I'm not positive, but I don't think the principles of a hydraulic system account for variability like you describe. Rather, they would allow the system to continue functioning at all, as opposed to not functioning at all."

Perhaps the feel is lost with piston out farther, pad taper, and other small factors. It is not really travel of the pedal. I have not gone through street pads and replaced old street pads with new. Is there a change in feel in changing an old street pad to a new street pad or like or similar CofF?

 

Cobalt Friction brake pads are among the best in the business.

 

Drive, please do note that I am not an engineer, and again, could be VERY wrong

As for Cobalt pads, I and many others have had much success with them. I would not call them perfect, but I would say they are a damned good compromise between performance, cost, and longevity.

Also FWIW, I recently dealt with glazed pads, and the symptoms were a little similar to what you describe.

I had no idea pads would compress to the point that you could feel it in the pedal, very interesting.