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Catastrophic RacingBrake 2-piece rotor failure on track
03-28-2014, 08:21 PM
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Catastrophic RacingBrake 2-piece rotor failure on track My posting about the rotor failure I had got barrock69's "V2 Caliper on a V1 How To" thread off track, so I figured I would start a new thread to discuss my problem. I've asked itsslow98 to move the relevant posts from barrock69's thread into this one, but it occurs to me that they were all made earlier than this post, so moving them here might put everything in the wrong chronological order. We'll see...
Anyway, last weekend I was at Summit Point with the Audi club for an HPDE. Front brakes are the 6-piston V2 Brembo calipers + Hawk DTC70s + Racing Brake 2-piece rotors. Rear brakes are stock calipers and rotors w/DTC60s. This was only the 4th day on track with these $$$$ rotors; more specifically, the failure occurred 8 minutes into only the 9th session with these rotors (each session being 20-25min long). All of those sessions were run at VIR and Summit Point, both of which are clockwise tracks with very few high-g left turns; the majority of the high-g corners are right turns, including the kink just before the braking zone where the rotor failed.
In the 2nd session on Saturday I came down through "the chute" (turn 4) and hit the brakes for turn 5. I got a moment of braking, then heard a POP! and the car jerked to the left. I let off the brakes and went straight off into the grass, managing to bring the car to a stop before reaching the track around turn 7/8. (I probably could've stopped a little quicker, but I wasn't sure what had broken - something with the brakes, a control arm, ??? - so I was wary of giving too much input that might make the car do something unpredictable.) The second picture on this site shows the chute and turn 5 - my off track excursion was basically coming right at the camera in that second pic.
The flagger waved me back onto the track, and I limped it through the last couple turns and into the pits. I didn't feel anything wrong with the steering or suspension, so I figured it was something brake related. When I got back to the pits this is what I found:
RacingBrake uses "center mount" hats, so the mounting tabs alternate from each rotor face. All of them failed, but as you can see in that third pic, one of the tabs (about the 7 o'clock position) looks to have been a different failure mode - it took some of the rotor with it. Some of the mounting fasteners are missing, and all of the rest that remain are sheared off (so I'm assuming the ones that are missing just fell out after they sheared). The hat is actually almost completely intact - only one of the fastener holes tore out. However, the holes that are empty are definitely oval'd. I don't know if that happened before or during the failure of the rotor.
In the past week I've done as much investigating as I can to try to find a cause of the failure.
- I've checked the hub/wheel bearing and it's solid. There's no play at all when I do the "normal" wheel bearing check (jacked up that corner, attempt to rock tire at 12 and 6 o'clock), and there's no abnormal noises when driving.
- I don't see any signs of bad material (inclusions or large grains) at any of the fracture locations on the rotor. I'm not a material science expert by any stretch of the imagination, but I do have some clue of what I'm looking for. I'm also not a very good photographer, but here are a couple somewhat close-up shots:
- I thoroughly inspected the caliper and don't see any signs of rotor-to-caliper contact - at least, not anything that would have happened prior to the rotor failure. (There's one spot where the rotor clearly rubbed once it had broken free of the hat.) The reason I looked for that is based on experience in the Mustang world. Back in the early '00s, folks started upgrading from the Cobra PBR 2-piston sliding calipers to the Brembo 4-piston fixed calipers from the 2000 Cobra R. A number of people had rotors fail on track, with the center hat of the 1-piece rotor fracturing away from the outer ring. Eventually it was determined that hub flex was causing excessive side loading as the rotor was pushing against the fixed caliper, which of course didn't move like the old 2-piston sliders did. Anyway, I saw no signs of that occurring here. Definitely some signs of shrapnel causing some cosmetic damage here and there.
- The pads were wearing normally, with maybe a little fore-aft taper and no top-to-bottom taper. That's an indication to me that there doesn't seem to be excessive hub flex. After the rotor failure, I installed my street rotors (which are the OEM V2 co-cast rotors, modified to fit the V1 hubs) and I continued to use the pads for the rest of the weekend. After another 4 sessions they were pretty much done, so I tossed them when I put my street pads and wheels/tires back on at the end of the event.
- I disassembled the driver side rotor so I could see if there was anything that might indicate why the passenger side rotor failed.
No, your eyes aren't deceiving you - all of the lock nuts are D-shaped, and there appear to be small cracks on a couple of them on the part that has been flattened.
Only 4 of the 10 nuts (which extend through the hat into the slotted holes in the rotor mounting tabs) came out of the hat easily. A couple came out very easily, and the other 2 I had to put pretty good pressure on with my thumb to get them to pop loose. The holes in the hat for those 4 all look good - no elongation like on the damaged hat. The other 6 nuts would probably pop loose if I gave them a quick tap with a hammer, but they're cocked slightly or otherwise bound up in the holes in the rotor hat. They all came free from the rotor ring pretty easily, so no binding there.
The mounting tabs on the rotor ring are ~6.5mm thick, but the nuts only extend ~2.5mm into the holes. That seems suboptimal to me, and doesn't jive with what RacingBrake shows on their website. The diagram on this page shows the nuts extending through nearly the full thickness of the rotor mounting tab. On my rotors, the nuts only extend about 2.5mm into the rotor, which means all the forces are concentrated on a pretty small portion of the nut. As a result, you get this - a little video look at one of the fasteners.
I've exchanged emails with RacingBrake - mostly from me to them. After not hearing anything for a few days, today I prompted them and they offered me a moderate discount on a new rotor assembly. They have yet to offer any comment on why they think the rotor failed, nor express any interest in having me send them the rotor so they can do their own post mortem on it. No comment on the deformed lock nuts on the "good" rotor, either.
I'm certainly not putting another one of these rotors on the car without having some answers to address my concerns.
Anyway, last weekend I was at Summit Point with the Audi club for an HPDE. Front brakes are the 6-piston V2 Brembo calipers + Hawk DTC70s + Racing Brake 2-piece rotors. Rear brakes are stock calipers and rotors w/DTC60s. This was only the 4th day on track with these $$$$ rotors; more specifically, the failure occurred 8 minutes into only the 9th session with these rotors (each session being 20-25min long). All of those sessions were run at VIR and Summit Point, both of which are clockwise tracks with very few high-g left turns; the majority of the high-g corners are right turns, including the kink just before the braking zone where the rotor failed.
In the 2nd session on Saturday I came down through "the chute" (turn 4) and hit the brakes for turn 5. I got a moment of braking, then heard a POP! and the car jerked to the left. I let off the brakes and went straight off into the grass, managing to bring the car to a stop before reaching the track around turn 7/8. (I probably could've stopped a little quicker, but I wasn't sure what had broken - something with the brakes, a control arm, ??? - so I was wary of giving too much input that might make the car do something unpredictable.) The second picture on this site shows the chute and turn 5 - my off track excursion was basically coming right at the camera in that second pic.
The flagger waved me back onto the track, and I limped it through the last couple turns and into the pits. I didn't feel anything wrong with the steering or suspension, so I figured it was something brake related. When I got back to the pits this is what I found:
RacingBrake uses "center mount" hats, so the mounting tabs alternate from each rotor face. All of them failed, but as you can see in that third pic, one of the tabs (about the 7 o'clock position) looks to have been a different failure mode - it took some of the rotor with it. Some of the mounting fasteners are missing, and all of the rest that remain are sheared off (so I'm assuming the ones that are missing just fell out after they sheared). The hat is actually almost completely intact - only one of the fastener holes tore out. However, the holes that are empty are definitely oval'd. I don't know if that happened before or during the failure of the rotor.
In the past week I've done as much investigating as I can to try to find a cause of the failure.
- I've checked the hub/wheel bearing and it's solid. There's no play at all when I do the "normal" wheel bearing check (jacked up that corner, attempt to rock tire at 12 and 6 o'clock), and there's no abnormal noises when driving.
- I don't see any signs of bad material (inclusions or large grains) at any of the fracture locations on the rotor. I'm not a material science expert by any stretch of the imagination, but I do have some clue of what I'm looking for. I'm also not a very good photographer, but here are a couple somewhat close-up shots:
- I thoroughly inspected the caliper and don't see any signs of rotor-to-caliper contact - at least, not anything that would have happened prior to the rotor failure. (There's one spot where the rotor clearly rubbed once it had broken free of the hat.) The reason I looked for that is based on experience in the Mustang world. Back in the early '00s, folks started upgrading from the Cobra PBR 2-piston sliding calipers to the Brembo 4-piston fixed calipers from the 2000 Cobra R. A number of people had rotors fail on track, with the center hat of the 1-piece rotor fracturing away from the outer ring. Eventually it was determined that hub flex was causing excessive side loading as the rotor was pushing against the fixed caliper, which of course didn't move like the old 2-piston sliders did. Anyway, I saw no signs of that occurring here. Definitely some signs of shrapnel causing some cosmetic damage here and there.
- The pads were wearing normally, with maybe a little fore-aft taper and no top-to-bottom taper. That's an indication to me that there doesn't seem to be excessive hub flex. After the rotor failure, I installed my street rotors (which are the OEM V2 co-cast rotors, modified to fit the V1 hubs) and I continued to use the pads for the rest of the weekend. After another 4 sessions they were pretty much done, so I tossed them when I put my street pads and wheels/tires back on at the end of the event.
- I disassembled the driver side rotor so I could see if there was anything that might indicate why the passenger side rotor failed.
No, your eyes aren't deceiving you - all of the lock nuts are D-shaped, and there appear to be small cracks on a couple of them on the part that has been flattened.
Only 4 of the 10 nuts (which extend through the hat into the slotted holes in the rotor mounting tabs) came out of the hat easily. A couple came out very easily, and the other 2 I had to put pretty good pressure on with my thumb to get them to pop loose. The holes in the hat for those 4 all look good - no elongation like on the damaged hat. The other 6 nuts would probably pop loose if I gave them a quick tap with a hammer, but they're cocked slightly or otherwise bound up in the holes in the rotor hat. They all came free from the rotor ring pretty easily, so no binding there.
The mounting tabs on the rotor ring are ~6.5mm thick, but the nuts only extend ~2.5mm into the holes. That seems suboptimal to me, and doesn't jive with what RacingBrake shows on their website. The diagram on this page shows the nuts extending through nearly the full thickness of the rotor mounting tab. On my rotors, the nuts only extend about 2.5mm into the rotor, which means all the forces are concentrated on a pretty small portion of the nut. As a result, you get this - a little video look at one of the fasteners.
I've exchanged emails with RacingBrake - mostly from me to them. After not hearing anything for a few days, today I prompted them and they offered me a moderate discount on a new rotor assembly. They have yet to offer any comment on why they think the rotor failed, nor express any interest in having me send them the rotor so they can do their own post mortem on it. No comment on the deformed lock nuts on the "good" rotor, either.
I'm certainly not putting another one of these rotors on the car without having some answers to address my concerns. 
03-28-2014, 08:25 PM
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WARNING: Turn down the volume before you start the clip below! The battery in the mic was dying (which I didn't know until I got back to the hotel that evening), and when that happens the mic feeds a ton of noise into the video recorder. Very frustrating, as I wanted to hear how things sounded beforehand and at the instant it failed.
Since I imagine nobody will go to Youtube to read what I wrote there, here's the video description:
Since I imagine nobody will go to Youtube to read what I wrote there, here's the video description:
Originally Posted by Me
First off, I apologize for the horrible audio - the mic's battery was dying and unfortunately I didn't know that until the end of the day when I got back to the hotel and reviewed what I had recorded.
This clip is from a Potomac-Chesapeake Chapter Audi Club HPDE @ Summit Point in late March 2014. During the 2nd session on the first day of the event, my right front aftermarket 2-piece brake rotor failed, which resulted in me going off at turn 5.
In real-time there was an audible "POP!" when the rotor went, and I was really hoping to be able to hear that on the video. Alas, the audio is hosed up so you can't hear anything at the instant it happens.
The "BRAKE" indication is, as far as I know, simply based on the g-sensor built into the ChaseCam DVR. You can see braking effort drops immediately when the rotor fails, and then goes to zero as the car jerked to the left and I took my foot off the pedal.
This clip is from a Potomac-Chesapeake Chapter Audi Club HPDE @ Summit Point in late March 2014. During the 2nd session on the first day of the event, my right front aftermarket 2-piece brake rotor failed, which resulted in me going off at turn 5.
In real-time there was an audible "POP!" when the rotor went, and I was really hoping to be able to hear that on the video. Alas, the audio is hosed up so you can't hear anything at the instant it happens.
The "BRAKE" indication is, as far as I know, simply based on the g-sensor built into the ChaseCam DVR. You can see braking effort drops immediately when the rotor fails, and then goes to zero as the car jerked to the left and I took my foot off the pedal.
Last edited by AAIIIC; 03-28-2014 at 08:31 PM.
03-28-2014, 08:59 PM
#4
For ***** and giggles, since Racing Brake is giving you the cold shoulder, give StopTech a call and see if they would offer an opinion on the failure. Sure, they're a competitor and as such would have something to gain with an unfavorable review, but you might get some interesting professional opinions after submitting all of your autopsy photos.
03-28-2014, 10:34 PM
#5
Thank you for actually posting an in depth discussion of the failure with pictures, sucks that it failed, but it is nice to see in detail what you can see.
I think you on on the right path with the cracked lock nuts. Looks like the deformed thread may have given out allowing the screws to slowly loosen allowing the rotor to bang around on the hat, when the holes got too large it allowed a large shock event under braking which sheared the mounting tabs. (possibly weakened from previous shock events, but the failure surface looks like one continuous failure, I don't see a lot on the edges that looks like a crack started then propagated.)
I think you on on the right path with the cracked lock nuts. Looks like the deformed thread may have given out allowing the screws to slowly loosen allowing the rotor to bang around on the hat, when the holes got too large it allowed a large shock event under braking which sheared the mounting tabs. (possibly weakened from previous shock events, but the failure surface looks like one continuous failure, I don't see a lot on the edges that looks like a crack started then propagated.)
03-29-2014, 04:13 PM
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I've stayed away from the RB's based on similar feedback from another NASA member. Different application but same outcome. Although I haven't had any better luck with my Colemans. Going to run the Girodisc's this season.
Glad it didn't turn out worse...
Glad it didn't turn out worse...
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03-29-2014, 06:09 PM
#8
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For ***** and giggles, since Racing Brake is giving you the cold shoulder, give StopTech a call and see if they would offer an opinion on the failure. Sure, they're a competitor and as such would have something to gain with an unfavorable review, but you might get some interesting professional opinions after submitting all of your autopsy photos.
No doubt! It chose to let go at probably the best option of the few hard braking points at Summit. A jerk to the left at 130mph going into turn 1 would've been a helluva lot more interesting to deal with!
04-01-2014, 09:22 AM
#11
I believe due to the excessive amount of heat of the rotor it was unable to expand therefore the tongues of the rotor were the first to give, if you look at the bolt configurations there's almost 0 tolerance for movement not much like the brembos which have oval holes where the bolts have at least 2-3 mm worth of expansion
04-01-2014, 09:23 AM
#12
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That is crazy dude. 2 things, #1 glad no one was hurt, #2 glad it wasn't on the street somewhere. I had a brake line pop on me one day while driving. I got real lucky there was an open lane for me to evade through. Smashed the parking brake to the floor and popped the trans into L.
So has racingbrake still not gotten back to you? I honestly like OEM rotors the best. Even on tracks. They may not shed heat better than nice aftermarket ones but as with all OEM equipment, they are tough.
So has racingbrake still not gotten back to you? I honestly like OEM rotors the best. Even on tracks. They may not shed heat better than nice aftermarket ones but as with all OEM equipment, they are tough.
04-02-2014, 08:24 AM
#15
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I don't think so, because RB uses that "center mount" hat that puts it more towards the middle of the rotor's thickness. Everyone else uses hats mounted to one face of the ring, so the hat offsets would be quite a bit different.
04-02-2014, 01:12 PM
#16
I might know a guy a Brembo from my chrysler days, i'll shoot him this email and see what they might have to say.
Like i said before, im glad you were ok. if this happened at the Glenn you might not have been able to write this thread.
Like i said before, im glad you were ok. if this happened at the Glenn you might not have been able to write this thread.
04-02-2014, 05:05 PM
#17
FYI--Banski Motorsports and I are exploring the possibility of building a bracket and hat to adapt 380mm rotors and the Audi RS6 Brembo 8-piston caliper ($590 each) to the CTS-V.
04-03-2014, 12:58 AM
#19
Fuzzy,
I just downgraded from that caliper. If you want i can send you my caliper brackets for the front.
They are a little crude but will fit 355mm discs. You can probaby use the original design to come up with a better one pc idea vs my three pc unit. The guy i bought it from swore it would fit perfectly, but i was 19mm short on height...
Let me know
I just downgraded from that caliper. If you want i can send you my caliper brackets for the front.
They are a little crude but will fit 355mm discs. You can probaby use the original design to come up with a better one pc idea vs my three pc unit. The guy i bought it from swore it would fit perfectly, but i was 19mm short on height...
Let me know
04-03-2014, 05:46 AM
#20
Fuzzy,
I just downgraded from that caliper. If you want i can send you my caliper brackets for the front.
They are a little crude but will fit 355mm discs. You can probaby use the original design to come up with a better one pc idea vs my three pc unit. The guy i bought it from swore it would fit perfectly, but i was 19mm short on height...
Let me know
I just downgraded from that caliper. If you want i can send you my caliper brackets for the front.
They are a little crude but will fit 355mm discs. You can probaby use the original design to come up with a better one pc idea vs my three pc unit. The guy i bought it from swore it would fit perfectly, but i was 19mm short on height...
Let me know