When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Right after I had my Tarrett caliper studs installed with some new PFC11 pads, a ridge developed in the middle of my front AP rotors. It happened on both sides of the front rotors - no issues with the back rotors. The shop had no idea how the two events could be correlated, but I saw another GT3 at the track and he had the exact same thing happen after having his caliper studs installed. I've attached some photos. The ridge is very noticeable and can easily be felt when you run your finger across the disk. I've run with the ridge for 12 track days now, but I'm starting to worry a bit as the rotor gets to the latter stages of its life. Has anyone else seen this?
I also included a photo that shows my destroyed dust boots. I'm going to do a Racing Brake caliper rebuild since I'll be taking the caliper apart anyway to see what might be going on. Has anyone else installed their rebuild kit? I'll also get some thickness measurements then to see how much life is left and how deep the ridge is.
rm21,
That ridge in the disc is completely normal with the AP Racing J Hook disc. I don't believe it has anything to do with the studs. It is a function of the J Hook slot design. We see it all the time on across all applications, and it doesn't in any way impact performance.
Here's why it happens: If you notice where that ridge forms on the disc face, it's at the termination of the J Hook slots. The pad material that gets scraped off the pad with each rotation fills up the slots. If you think about the direction the disc is spinning, the 'back' of the J hook (the arced part) is leading into the pad. That pad material then exits at the tapered ends of the slots (see the red arrows in the image below). In the spot where that groove is, you're getting pad material exiting from both ends of adjacent slots. In other words, at that spot in the center of the disc face, you have pad material exiting the 'top' of the J from the slot closest to the hub, and the 'bottom' of the J on the adjacent slot closest to the OD of the disc. As that pad material exits the slots, it rides along under the pad squeezing the disc, and digs a little groove into the disc face.
The timing of you're noticing the groove could be purely coincidental, or it could be that your new pad material is more prone to build up or more abrasive than the old material when it's trapped in that spot.
We've sold thousands and thousands, and thousands of J Hook discs at all level of motorsport, and to my knowledge we've never had a premature failure or performance problem in any way related to this groove forming. That includes winning the NASCAR Sprint Cup championship 8 out of the past 9 years, winning Le Mans 8 times since the year 2000 on the factory Corvettes, and a host of other championships. The groove looks a little funky, but that's about it...nothing at all to worry about.
If at any time you have any other questions, always feel free to ask us. That's why we're here.
Thanks again for using our discs, and we hope they're getting the job done for you!
ps The discs look great and like they still have quite a bit of life left in them..just a little bit of typical heat checking.
__________________
'09 Carrera 2S, '08 Boxster LE (orange), '91 Acura NSX, Tesla Model 3 Performance, Fiesta ST
Jeff Ritter
Mgr. High Performance Division, Essex Parts Services Essex Designed AP Racing Radi-CAL Competition Brake Kits & 2-piece J Hook Discs Ferodo Racing Brake Pads Spiegler Stainless Steel Brake Lines
704-824-6030 jeff.ritter@essexparts.com
Last edited by JRitt@essex; 12-21-2015 at 11:49 AM.
Reason: added image
rm21,
That ridge in the disc is completely normal with the AP Racing J Hook disc. I don't believe it has anything to do with the studs. It is a function of the J Hook slot design. We see it all the time on across all applications, and it doesn't in any way impact performance.
Here's why it happens: If you notice where that ridge forms on the disc face, it's at the termination of the J Hook slots. The pad material that gets scraped off the pad with each rotation fills up the slots. If you think about the direction the disc is spinning, the 'back' of the J hook (the arced part) is leading into the pad. That pad material then exits at the tapered ends of the slots (see the red arrows in the image below). In the spot where that groove is, you're getting pad material exiting from both ends of adjacent slots. In other words, at that spot in the center of the disc face, you have pad material exiting the 'top' of the J from the slot closest to the hub, and the 'bottom' of the J on the adjacent slot closest to the OD of the disc. As that pad material exits the slots, it rides along under the pad squeezing the disc, and digs a little groove into the disc face.
The timing of you're noticing the groove could be purely coincidental, or it could be that your new pad material is more prone to build up or more abrasive than the old material when it's trapped in that spot.
We've sold thousands and thousands, and thousands of J Hook discs at all level of motorsport, and to my knowledge we've never had a premature failure or performance problem in any way related to this groove forming. That includes winning the NASCAR Sprint Cup championship 8 out of the past 9 years, winning Le Mans 8 times since the year 2000 on the factory Corvettes, and a host of other championships. The groove looks a little funky, but that's about it...nothing at all to worry about.
If at any time you have any other questions, always feel free to ask us. That's why we're here.
Thanks again for using our discs, and we hope they're getting the job done for you!
ps The discs look great and like they still have quite a bit of life left in them..just a little bit of typical heat checking.
Good to know!
Not to hijack the thread, but is there a....for lack of a better description, whirring harmonic that the hooks create as overall speed increases?
I don't know how to describe it, but since I had mine installed last week, I have noticed this noise as I drive by cars, curbs, freeway separation walls...as soon as I even tap on the brakes, it goes away. I have no vibration, braking is smooth.
The folks who installed them say that it's perfectly normal. I was fine with that, but as long as we have your attention, I figured I would ask!
Not to hijack the thread, but is there a....for lack of a better description, whirring harmonic that the hooks create as overall speed increases?
I don't know how to describe it, but since I had mine installed last week, I have noticed this noise as I drive by cars, curbs, freeway separation walls...as soon as I even tap on the brakes, it goes away. I have no vibration, braking is smooth.
The folks who installed them say that it's perfectly normal. I was fine with that, but as long as we have your attention, I figured I would ask!
Yes sir...whirring noises are completely normal. Any type of slot or drill is going to typically make some type of noise. The goal with a slot or drill hole is to create a leading edge for the pad to bite. The J Hook definitely tends to whir a bit more than a straight slot. The upside with the J Hooks are even heat distribution from the disc ID to OD, as well as a reduction in cool spots around the disc (which can happen with straight slots that have a big gap between them). When they heat up, that heat is spread very nicely throughout the disc. Long-term that reduces cracking due to temperature gradients, while evening out the pad deposits across the disc face.
Yes sir...whirring noises are completely normal. Any type of slot or drill is going to typically make some type of noise. The goal with a slot or drill hole is to create a leading edge for the pad to bite. The J Hook definitely tends to whir a bit more than a straight slot. The upside with the J Hooks are even heat distribution from the disc ID to OD, as well as a reduction in cool spots around the disc (which can happen with straight slots that have a big gap between them). When they heat up, that heat is spread very nicely throughout the disc. Long-term that reduces cracking due to temperature gradients, while evening out the pad deposits across the disc face.
This "uniform everything" (pad deposits, temp, wear, etc.) doesn't seem consistent with your earlier post about the J-hook concentrating debris / material in those groove regions, no?
This "uniform everything" (pad deposits, temp, wear, etc.) doesn't seem consistent with your earlier post about the J-hook concentrating debris / material in those groove regions, no?
The pad material has to go somewhere unfortunately. If you perforate the disc (drill holes or slots that go completely through the disc face), you create stress risers that lead to cracking...just like we see on the OEM discs around the drill holes. If you have a straight slot, the pad material evacuates at the outer disc edge and wears a groove out there, and you have substantial gaps/cooler spots between and around those slots. There is no perfect design, but the AP J Hook has proven time and again to be the best solution. Having a small cosmetic downside isn't a major trade-off for the performance benefits that are gained.
In addition to working with the top teams in motorsport over the past 30 years, we've also proven the design on our in-house brake dyno. We've run just about every brand and type of disc under the sun, as well as every type of simulation imaginable on the J Hook design. The J Hook consistently comes out on top.
In addition to the countless professional championships under this disc design's belt, there are plenty of people running these exact discs on this forum (hopefully they can chime in with their experience). We released our front 991 discs in spring of this year. To my knowledge nobody has found our discs to be shorter in life span or in any way less durable than a competitor's product. In all cases I'm aware of, our disc outlasted the competition by a considerable margin. You can also Check out blog for reviews of our discs and big brake kits (which use the same disc). There are lots of examples in which the user doubled or tripled their disc life (or more), lowered overall system temps, eliminated brake fade, improved pedal feel, reduced pad wear, or some combination of all of the above.
There is no perfect brake disc design that operates best in all conditions. They all differ in some way...weight, internal vane shape, slot design, metallurgy, noise, aesthetics, hat attachment mechanism, wall thickness, number of vanes, air gap, overall material composition (PCCB), etc. All of those factors come together in a disc to offer a certain level of performance and longevity, and they're all considered when a new disc is designed. The J Hook design is the culmination of AP Racing's 50+ years in brake system design at the elite level of racing. We believe it provides the array of traits & benefits that are most important to our customers. A mountain of positive feedback from Jeff Gordon to John Smith fortunately confirms that we're doing a solid job of exactly that.
The pad material has to go somewhere unfortunately. If you perforate the disc (drill holes or slots that go completely through the disc face), you create stress risers that lead to cracking...just like we see on the OEM discs around the drill holes. If you have a straight slot, the pad material evacuates at the outer disc edge and wears a groove out there, and you have substantial gaps/cooler spots between and around those slots. There is no perfect design, but the AP J Hook has proven time and again to be the best solution. Having a small cosmetic downside isn't a major trade-off for the performance benefits that are gained.
In addition to working with the top teams in motorsport over the past 30 years, we've also proven the design on our in-house brake dyno. We've run just about every brand and type of disc under the sun, as well as every type of simulation imaginable on the J Hook design. The J Hook consistently comes out on top.
In addition to the countless professional championships under this disc design's belt, there are plenty of people running these exact discs on this forum (hopefully they can chime in with their experience). We released our front 991 discs in spring of this year. To my knowledge nobody has found our discs to be shorter in life span or in any way less durable than a competitor's product. In all cases I'm aware of, our disc outlasted the competition by a considerable margin. You can also Check out blog for reviews of our discs and big brake kits (which use the same disc). There are lots of examples in which the user doubled or tripled their disc life (or more), lowered overall system temps, eliminated brake fade, improved pedal feel, reduced pad wear, or some combination of all of the above.
There is no perfect brake disc design that operates best in all conditions. They all differ in some way...weight, internal vane shape, slot design, metallurgy, noise, aesthetics, hat attachment mechanism, wall thickness, number of vanes, air gap, overall material composition (PCCB), etc. All of those factors come together in a disc to offer a certain level of performance and longevity, and they're all considered when a new disc is designed. The J Hook design is the culmination of AP Racing's 50+ years in brake system design at the elite level of racing. We believe it provides the array of traits & benefits that are most important to our customers. A mountain of positive feedback from Jeff Gordon to John Smith fortunately confirms that we're doing a solid job of exactly that.
Jeff,
Thanks for your excellent explanation.
Merry Xmas
I have the AP rotors front and rear on the GT3, with Ferodo DS 1.11 pads. There's some grooving, but it varies between rotors.
When I put in the rear AP rotors, it apparently threw off the parking brake sensor due to the rotor being a bit thicker than OEM. Has anyone else experienced this? My shop said it won't affect engagement and disengagement of the parking brake, but I find it annoying and a bit disconcerting to continue seeing parking brake warnings.
I also have the Racing Brake pistons front and rear, since my OEM ceramic pucks were failing and Porsche doesn't offer a rebuild kit. So far, they're working fine, and I'm not seeing evidence of pedal softening, etc., but I haven't done many track days with them yet. The piston material is about 10x lower thermal conductivity than the OEM pistons, but taking out the ceramic pucks increases heat transfer, so I'm not sure how the net overall heat transfer compares.
I have the same ridge on my rotors. No issues.
As far as longevity, there are 20 days on the front rotors and they look like they have plenty left in them. I believe some have reported 20 days on oem rotors, but I cannot report what my own experience has been because the oem rotors were swapped out before they were done.
Lap times on these rotors at the following tracks:
Laguna seca: 1:37-38
Thunderhill over the top: 1:57-58
Sonoma raceway: 1:47
Manifold, what was the appearance/concern over the pucks that pushed you to replace with rb pistons?
Manifold, what was the appearance/concern over the pucks that pushed you to replace with rb pistons?
They were cracking and starting to disintegrate. Initial response from Porsche was that it wasn't covered under warranty because the pads weren't OEM and they were presuming that I didn't do proper cool down laps (which is BS). Rather than fighting it, I decided to just replace the pistons with something which will hopefully prove more reliable and durable for track use.
They were cracking and starting to disintegrate. Initial response from Porsche was that it wasn't covered under warranty because the pads weren't OEM and they were presuming that I didn't do proper cool down laps (which is BS). Rather than fighting it, I decided to just replace the pistons with something which will hopefully prove more reliable and durable for track use.
When I put in the rear AP rotors, it apparently threw off the parking brake sensor due to the rotor being a bit thicker than OEM. Has anyone else experienced this? My shop said it won't affect engagement and disengagement of the parking brake, but I find it annoying and a bit disconcerting to continue seeing parking brake warnings.
I haven't had any problems with the parking brake yet. That being said, I'm only two-ish weeks into the rotors, and I don't use the pb very often at all. Houston is flat!
I haven't had any problems with the parking brake yet. That being said, I'm only two-ish weeks into the rotors, and I don't use the pb very often at all. Houston is flat!
12-21-2015, 08:30 AM
Ridge in middle of AP rotors
