Rotor "wear"

[strengthrehab]

How do these look?

First 2 are rears, and the others are fronts.

Rears look like they overheated and smeared?

Affect braking performance?

I'm trying to nail down some inconsistent braking I've been experiencing for over a year.

I'm going to start changing things up, but want another set of eyes.



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[ArizonaBOSS]

The first couple pics look like a lot of material is deposited on the rotor itself. This may mean the rotor is getting too hot for your pad compound or a mismatch of pad compounds have been used on the same rotor. Could be worth replacing those two and starting fresh there with your preferred pad.

 

[strengthrehab]

The first couple pics look like a lot of material is deposited on the rotor itself. This may mean the rotor is getting too hot for your pad compound or a mismatch of pad compounds have been used on the same rotor. Could be worth replacing those two and starting fresh there with your preferred pad.

Would that contribute to decreased brake performance?

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[JAJ]

Think of it this way - if the brakes at one end of your car are giving up, the other end will take more load which can overwhelm the tires and put you into ABS at that end. If the the front is hitting ABS, the rear brakes are taking a break. If the rear is going ABS and your car just isn't slowing down, then the front is fading. But, if you're just having inconsistent braking without one end or the other going into ABS, then your brakes are balanced and the pads and rotors at both ends don't have the capacity to handle the heat and load you're asking for.

Your rotors in the pictures look like they've had a busy day, but they're not looking damaged or cracked. The heavy coating is from pads, suggesting the pads can't handle the heat, although that could be because the rotors are overheating. Regardless of why it's happening, you can attack the problem a couple of ways. First, you can just use pads that can handle higher temperatures. That might work, but often it doesn't because once they're working better, it lets you drive faster which hits them with more load so they just overheat again at a higher temperature. You can also upgrade to rotors with better ventilation structures and enhance the cooling air supply. The rotors won't get as hot and that'll keep the pads cooler. Or you can do both, which is what most people do.

 

[Stangra]

You might want try cleaning up those rotors and using different pads. If you do this, be sure to properly bed new pads after cleaning up the rotor surfaces:

Don't know why this guy didn't just remove the caliper instead of stacking rotors though, gotta do it anyway to get the rotors off.

 

[strengthrehab]

For clarification here is the rest of the story.

Starting back in August 2018, I began having issues with inconsistent brake performance. Back then, I experienced a hard pedal with decreased brake performance using R16/R12 pads and cooling ducts/hoses, etc. This has been an issue at least once per track day since. Over the course of this time, I've checked booster to rule out a vacuum issue, flushed brake fluid, bled the brakes to no avail. One of the issues I've noticed is I never experience ABS shudder in the pedal and highest braking G forces are 1.0-1.1g. For R16/R12, I'd figure it would be higher and ABS would be activated.

This past sunday, I was back at the track and the same thing happened again. This time, I had data to look at. At no time over this past weekend did I encounter ABS shudder in the pedal (the only way I know to identifiy ABS activation) and brake performance (measured via linear acceleration in Solo2 DL data) at no higher than 1.0g even with 989psi of brake pressure. Brakes were inconsistent between laps with g readings reaching a high of 0.85-0.89 sometimes with 400psi of pressure and sometimes with 700psi of pressure.

At one point, I reached a max of 989psi of pressure, with a corresponding 0.86g braking and the pedal was hard, but the car was slowing. Then all of a sudden, I heard a bang and felt like wheel hop (I have a 2016 GT PP) and the car almost spun. Looking at data, specifically at wheel speed, at that point. the R rear wheel speed vs L rear wheel speed was off by about 10 mph for a full second then it resumed to within 1 mph difference between the two as was typical for every other point on the track.

Here is that incident:
Data trace: https://photos.app.goo.gl/1pp5Sa5garLeCVuPA
Video:

Setup:
Stock GTPP calipers
R16/R12 pads
OEM rotors
brake cooling using 3" hose and Full Tilt Boogie Racing backing plates
Castrol SRF fluid.

simple brake booster checks have been performed with no indication of problem
No vacuum leak

I can send data to anyone who would like to help, but I'm at a loss. I know the rotors need cleaned up which I will do. I am also going to pull my pads to see if there is glazing present.

 

[TMSBOSS]

The difference in the rear braking makes me wonder if this is a "Nanny Issue". Is the traction control pulling or adding brake downstream of your pressure readings?

 

[strengthrehab]

The difference in the rear braking makes me wonder if this is a "Nanny Issue". Is the traction control pulling or adding brake downstream of your pressure readings?

I don't have my data with me, but I don't think so. I run the car in full nanny off mode or "sport" advancetrac mode, so it is possible at times.

My plan, nonetheless, is to clean up the rotors, check the pads, maybe replace the speed sensors, rebleed/flush fluid (cycling the ABS unit via ForScan). With some new information I've seen from testing brake cooling vs GTPP brake cooling, I may even try going back to stock deflectors and see if that helps with cooling the brakes just in case there is heat glazing happening. I wouldn't think so with R16 (high heat) pads, but never know I guess.

 

[JAJ]

It's rare to have more than one problem at the same time but this could be one of those times. The bang and side-step has the appearance of a stability control glitch - what was your AdvanceTrak setting when it happened? It could have also been a stuck caliper getting unstuck, but if you had a stuck caliper you'd see uneven wear on the rotor and pads and you haven't said that there's a problem like that with any of them.

The high-pressure-low-braking-effect problem still sounds like overheating to me.

 

[strengthrehab]

It's rare to have more than one problem at the same time but this could be one of those times. The bang and side-step has the appearance of a stability control glitch - what was your AdvanceTrak setting when it happened? It could have also been a stuck caliper getting unstuck, but if you had a stuck caliper you'd see uneven wear on the rotor and pads and you haven't said that there's a problem like that with any of them.

The high-pressure-low-braking-effect problem still sounds like overheating to me.

I was in advancetrac sport I think at that time. I wondered about the stuck caliper myself as that is the side with the "glazing" on the rotor. I haven't pulled the pads yet. I'm going to do that this weekend.