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Old 03-10-2015, 11:03 AM   #1
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Exclamation Uneven wear with AP Racing Sprint BBK

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UPDATE: I've been meaning to update this thread. I just came off a year-long hiatus from track days with the BRZ a few weeks ago at Road Atlanta. I installed a new set of Cobalt XR2's along with the newly released Velox Motorsports brake cooling kit. I used a Beastronix 86Nanny PD to engage the pedal dance with the push of a button every session. My pads and rotors wore evenly all weekend and upon inspection the uneven wear, severe rotor heat checking, pad crumbling and glazing that I had last season are not present. So in conclusion I would attribute my issues to lack of pedal dance and/or proper brake cooling. I'm still very happy with my BBK!!
I've had my AP Sprint BBK installed since July 2013 and I've been noticing uneven wear on the pads and rotors since. The driver's side pads and rotors are wearing significantly faster than the passenger's side.

My car is tracked heavily and my first set of rotors have 8 track days on them and I believe they need to be replaced as of yesterday at Road Atlanta.

First set of CL RC6's that came with my kit lasted 5 full track days and the wear was uneven on the pads (driver's side more worn) and before the 5th track day I swapped the driver's side pads with the passenger's side and finished those off.

My second set of pads were Carbotech XP12's and I wasn't happy with those. They lasted 2.5 track days and they felt softer on the pedal since they aren't sintered and contain kevlar. Bite was great and they never faded, I just didn't like the feel compared to the sintered RC6's.

I removed the XP12's yesterday at Road Atlanta at lunch hour and installed fresh RC6's and finished my track day with much enjoyment aside from this perplexing uneven brake wear issue.

Here are the pics of my XP12's off the car and the rotors on the car. First is my driver's side rotor. The J Hooks are fading away and I can see cracks forming between the gaps in the hat. Deep groove around the outer edge of the rotor.



Driver's side XP12 pads. Note the bottom pad was on the inside.




Passenger's side rotor. J hooks still look okay and the grooves are less significant.



Passenger's side XP12 pads. They are worn significantly less and the slot in the middle is still visible.




Disclosures: I do not do the pedal dance prior to tracking my car; I do hold the button down to turn "everything" off. I instruct at every track day and I simply do not have time to fully warm up my car or remember/look up the sequence to do it. I am typically jumping out of my student's car and immediately into mine and taking 20 minute breaks every hour to rehydrate, use the restroom, track talk, etc. I am also running 911 GT3 brake air guides strapped to my control arms to direct air in the wheel wheels at speed to the inside face of the rotors to help keep rotor temperatures under control.


Help, advice and insight is much appreciated. I'm at my wits end.



@CSG Mike / @JRitt / @Racecomp Engineering / @Reaper / @buddy32
Please help me by tagging anyone else with the AP Sprint BBK
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Old 03-10-2015, 11:12 AM   #2
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Could it be as simple as a sticky pot on the driver side caliper?
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Old 03-10-2015, 11:22 AM   #3
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What would cause more wear on the driver's side? Could it be something as simple as increased weight from the driver or braking into left corners more than right corners or something like that?
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Old 03-10-2015, 11:25 AM   #4
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Could it be as simple as a sticky pot on the driver side caliper?
I'm able to push back all the pistons with the same (frustratingly significant) amount of effort when changing pads. No pistons seem sticky or more difficult to push back.


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What would cause more wear on the driver's side? Could it be something as simple as increased weight from the driver or braking into left corners more than right corners or something like that?
I don't know. I've run both clockwise and counter-clockwise tracks with the BBK. I threshold brake in a straight line and rarely trail brake. I am not engaging ABS into every corner.
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Old 03-10-2015, 11:44 AM   #5
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This is a good post. Thanks for sharing the info. It seems to me like there could be several causes of this uneven wear. I also think the next step in diagnosing the issue is to turn off all of the nannies. Without doing that, you really don't know how much the brakes are being applied at each corner.
I appreciate what you say about being rushed while at the track. I am sometimes in a similar situation. That said, to do the pedal dance takes almost no time. Therefore, you'll have a tough time convincing me you can't do it easily. The car does have to be warm, of course, which can take some time. Do you have a helper that can start it up 15 minutes before your session? If not, could you just let the car idle between sessions? I know it's wasted gas, but it doesn't burn much if it's just idling. And when you consider the cost and/or complexity of other methods of diagnosis, it still seems like a pretty good option IMO.
I'm looking forward to hearing what others have to say.
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Old 03-10-2015, 12:06 PM   #6
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I have a hard time believing this would be related to not doing the pedal dance. The chance of it always applying that much more force to the same wheel at every braking zone is essentially zero.

If the rears were wearing more than the fronts, I would blame VSC, but assymetrical wear left to right on the same axle sounds more like a hardware issue.

It also looks like they're wearing significantly more at one end of the pad than the other which makes me think it might be a crossover tube? Are they more worn at the front or the rear? How does the fluid flow through these calipers, crossover at both ends, or only at one end? Which end is the brake line attached to compared to the more worn end of the pads?

Another thought, could the caliper bracket be mis-aligned or bent at all? Can you feel more drag on that wheel with the car in the air
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Old 03-10-2015, 01:25 PM   #7
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I would start by pulling the scoops off for an event or two, see if those are feeding uneven amounts of air.
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Old 03-10-2015, 01:46 PM   #8
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With uneven wear like that my guess is it is a caliper issue. I doubt the GT3 air guides or not doing the pedal dance are the primary causes. Have you only done two pad install/swaps on the calipers? I would pull the pistons out of the calipers and give them a good look. The uneven wear like that on a multi piston caliper is most likely caused by one of the pistons providing more pressure. Perhaps there is an issue with the anti-knock back spring behind one of the pistons as well.
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Old 03-10-2015, 01:56 PM   #9
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The uneven wear like that on a multi piston caliper is most likely caused by one of the pistons providing more pressure.
Both pads from the driver's side are worn significantly more than both pads on the passenger side though. Would one piston of a four piston caliper cause both pads to wear down that much more?
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Old 03-10-2015, 01:58 PM   #10
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Have you only done two pad install/swaps on the calipers?

IIRC....

Carbotech 1521 street pads > CL RC6 > Carbotech 1521 street pads > CL RC6 > Carbotech 1521 street pads > Carbotech XP12 > CL RC6
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Old 03-10-2015, 02:00 PM   #11
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It is heat. What rear pads are you using? If you overwork the rear, it'll cause the front to work harder. The heat is also a function of how you use your brakes too.

This can be replicated on other brake kits as well. Wilwood is the worst. You'll end up just eating one pad up instead of a pair...lol.
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Old 03-10-2015, 02:31 PM   #12
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It is heat. What rear pads are you using? If you overwork the rear, it'll cause the front to work harder. The heat is also a function of how you use your brakes too.

This can be replicated on other brake kits as well. Wilwood is the worst. You'll end up just eating one pad up instead of a pair...lol.
I am currently using XP12 rear pads. On my first set of RC6 fronts I ran PMU Club Racers in the rear. I have been using the original rear rotors since I bought the car. It's finally time to replace them.
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Old 03-10-2015, 02:41 PM   #13
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Curious, because the topic of VSC came up, I am under the impression that VSC would alter brake pressure by use of the ABS system, individually per wheel. So if VSC were a culprit you should feel the telltale vibration from ABS activation.

Or, does it have the ability to modulate brake pressure more finitely at each wheel transparently, to the point that the driver might not even know it's happening?

Brakes are a dumb mechanism, they rely purely on physical force to do a thing. When brake pressure is applied, its in the same proportion, every time (unless VSC/ABS/etc). Braking in a straight line shouldn't cause any of these variables. If one side is getting hotter to the point that it's visibly expediting wear, I'd suspect something mechanical.

Could be a stuck piston that's not retracting properly, causing the pad to drag excessively. In the DS pad pic, I assume the left side of the pad is the leading edge (points toward rear of vehicle)? That would make sense as the pad wants to be drug out of the caliper by the rotor, that the leading edge can wear more, but not when the opposing pad (and both on passenger side) looks so even. I wonder what the back side of the rotor loos like... I'd check piston movement.
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Old 03-10-2015, 02:54 PM   #14
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The driver side pads look like one piston is not working correctly. Notice that one pad is worn evenly while the other has a clear diagonal wear pattern.
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