Cracked yet another rear rotor

[dquarasr2]

I cracked a rear rotor back in June at Homestead. It had radial cracks starting about halfway up the pad area out toward the edge of the rotor, but not all the way through to the outer edge. I replaced it.

While at 1st Class Automotive for other service, Oster noticed that there seemed to have been uneven wear of the rotors. It appeared as though the pads contact the rotors more strongly at near the rotor hub than they do near the outer edge. He lubricated the pins.

At Sebring two weeks ago I apparently cracked the other side. This one is cracked in two places, again, radially. This again goes from the middle of the pad contact area radially out to the edge of the rotor. These splits, however, do go all the way to the edge.

I am surmising that the uneven wear and resultant disparity in temperature is causing the cracks (hotter near the hub). I have had inconsistent braking performance nearly each time I have tracked the car.

Other pertinent info: All four calipers were rebuilt in early 2006. I always use fresh Motul 600. Stainless steel lines. OEM calipers and Tire Rack's Brembo OEM replacement solid rotors. Cobalt GT Sport pads. Kumho V700 Victoracer DOT R-compound tires. Car has 83,000 miles.

I'm actually thinking of retiring the car as a track dog and going back to tracking my '94 Miata; it seems to take the abuse much better.

Ideas?

Thanks in advance.

 

[docjohn]

I would just switch back to oem rotors or those from racing brake.You seem to be doing the right thing in keeping them lubed.I never had problems with my rear oem rotors.

 

[DocL]

Doug, I've encountered the same problems with the brakes when I track my NSX. It makes no difference what kind of pad or rotor I use, the rotors usually warp or crack on me also. I can tell you that I like to brake late and hard, so maybe that has something to do with my situation. What is your style of braking?

 

[Hugh]

Brembo OEM replacement solid rotors.

When are people going to learn that Brembo consumer products are junk? Get a set of Power Slot rotors and your problems will go away. Carbotech pads wouldn't hurt either.

 

[dquarasr2]

When are people going to learn that Brembo consumer products are junk? Get a set of Power Slot rotors and your problems will go away. Carbotech pads wouldn't hurt either.

I shied away from slotted rotors originally since when I purchased the car it had slotted rotors (although I don't know what brand; I'll ask the original owner when I see him tomorrow) and they cracked in multiple places. I had thought it was a function of them being slotted since they cracked radially starting from the slots.

I haven't tried Power Slots. I was trying to keep the costs down by buying the Brembo OEM-style rotors since the Power Slots were more than twice the price. But I'm spending that much anyway replacing them, so I'll give them a try.

Any reason I shouldn't get just rears and keep the OK solid fronts?

I won't buy from Carbotech again. 'Nuff said. The Cobalt Spec Miata pads are comparable to the Hawk Black I was using on that car, and the way I use them. I like the Cobalt GT Sport for the NSX since they perform well on the street as well as on the track. I don't think my problems relate at all to the pads.

Thanks for the tip on the Power Slots.

 

[dquarasr2]

Doug, I've encountered the same problems with the brakes when I track my NSX. It makes no difference what kind of pad or rotor I use, the rotors usually warp or crack on me also. I can tell you that I like to brake late and hard, so maybe that has something to do with my situation. What is your style of braking?

I used to ease into the brakes trying to transfer weight gradually, but I was counseled that that ends up heating the brakes more than hitting them fairly hard early in the braking zone. Sure enough, I got better performance and less fade when I braked hard early. Either way, though, I've cracked the rotors.

 

[Hugh]

These are Power Slots (which are made by Bradi) shipped in a non branded box. They're only $320 for a set of 4. That's twice the cost of Brembos?

http://www.daliracing.com/v666-5/catalog/index_browse_part.cfm?focus=365

 

[2slow2speed]

Just curious what is the worst case speed differential for the NSX at the tracks that you've been tracking the car at?, from the brake markers all the way to the point that you released the brakes. How is your heel and toe technique?

I tracked my NA2 NSX with the OEM brakes and never had any problems with the rear rotors cracking, even at a track like Laguna Seca that is brutal on the brakes that would easily cause spider cracks on the OEM rotors after 1 track day. From the 60+ track events with the OEM brakes I never had to replace the rear rotors on the NSX because of radial cracks.

The rear rotors on the NA2's are supposed to be a little bit larger than those on the NA1 but I doubt that would make that much of a difference. Worst case you might be able to get the bigger NA2 brackets or the kit from Racing brake to go with the NA2 sized rotors.

 

[dquarasr2]

These are Power Slots (which are made by Bradi) shipped in a non branded box. They're only $320 for a set of 4. That's twice the cost of Brembos?

http://www.daliracing.com/v666-5/catalog/index_browse_part.cfm?focus=365

I need to retract what I said. The Brembo slotted were more than double the Brembo OEM.

The $320 for all four is actually slightly cheaper than the Brembo OEM from Tire Rack. Hmmm. So, you say these are the ticket, eh?

 

[dquarasr2]

Just curious what is the worst case speed differential for the NSX at the tracks that you've been tracking the car at?, from the brake markers all the way to the point that you released the brakes. How is your heel and toe technique?

Thanks.

Lessee. (Disclaimer: numbers might not be exact, just approximations from memory.)

Sebring turn 3 110-50, "safety pin" T7 is about 115 to about 30 MPH. T10 about like T3, T13 about 95/100 to 50; back straight 130 scrub to 90 then turn in let the speed bleed off to 70-75. Other turns inconsequential with respect to braking.

So, at Sebring the biggest differential is the safety pin, about 85 MPH.

At Homestead there are only a couple of places that require similar braking, 110-115 range to 40-50.

Heel-toe isn't a problem for me.

 

[john@johnhudakracing]

Ideas?

Brake ducts.

 

[scorp965]

These are Power Slots (which are made by Bradi) shipped in a non branded box. They're only $320 for a set of 4. That's twice the cost of Brembos?

http://www.daliracing.com/v666-5/catalog/index_browse_part.cfm?focus=365

fwiw, I installed these dali rotors when I first bought my nsx, but, a year later, the rotors were gone and the pads were 40% remaining - this is roughly 16k miles of use, and the rotors had worn to an incredible degree, perhaps due to an inferior metal used in the rotor's construction. This was the first time I had gone through rotors faster than pads, but I would stay away from this product.

I just purchased a 4-corner set of the project mu SCR-Pro rotors:

and will make a thread once I have had an opportunity to install them and get an idea as to their performance and longevity.

 

[NSXLuvr]

Another vote for brake ducts. Cheap and easy mod that will help tremendously. Based on your list I think the rotors are the weak link. Somehow, I have never had the issue(but mine's a NA2). I would go with OEM or RB rotors. Otherwise you have to step up to the Porsche Big reds or Brembo's.

I doubt that GT sports are the issue.

 

[nsxnut]

Another vote for brake ducts. Cheap and easy mod that will help tremendously. Based on your list I think the rotors are the weak link. Somehow, I have never had the issue(but mine's a NA2). I would go with OEM or RB rotors. Otherwise you have to step up to the Porsche Big reds or Brembo's.

I doubt that GT sports are the issue.

I have brake ducts on the front but not on the rear.
I have the oem rocker pannels. How do you install ducts on the rear?

Thanks in advance.
Later,
Don

 

[Hugh]

I'm still trying to figure out why the rears are having problems. It's the fronts that take a huge chunk of the load during hard braking.

 

[Hugh]

fwiw, I installed these dali rotors when I first bought my nsx, but, a year later, the rotors were gone and the pads were 40% remaining - this is roughly 16k miles of use, and the rotors had worn to an incredible degree

That's bizarre. My first set of Dali/Power Slots lasted over 100K miles and 2 sets of Bobcats and at that point they were just at the service limit.

 

[nsxnut]

From Dal Motorsports
http://www.dalmotorsports.com/cars.asp


Another subject is Brake pads… The track is no place of OE brake pads. There are a lot of aftermarket pads that are better suited for autocross or tracking. DAL uses Cobalt Friction blue front with Hawk blue rear. The Cobalt’s are a better on the rotors than some aftermarket pads. Speaking of rotors- we can crack the familiar aftermarket rears in one race… don’t even think of using them in the front. Use OE, or even better a two part rotor like Stoptech with curved cooling veins. When you go to a race setup, investigate other rotor manufacturers with the same bolt patterns. I know a famous racer who doesn’t use his *Free* Brembo rotors (About $300 each), he pays near $800 each for Alcon rotors. Material, design, and treating are very important in a super brake system. Brakeman rotors are an in-between to Brembo and Alcon leaning closer to Alcon, and are at near Brembo prices. If allowed, carbon rotors are even better. Fluid- I use Motul if I don’t have heat issues and Castrol if I do. DAL uses ATE Super Blue Racing Fluid. Brake ducts are important in the front (Usually can’t get enough heat in the rear). You want to point the air in the center of the rotor, to be drawn out with the veins. Not an easy task, until you have a race car and can remove some things in the way, and add an under-tray for protection. Back to the ABS system- In a race car that allows ABS, unfortunately you must use it to be the most competitive (even if you need to add weight)! As mentioned earlier they are expensive $10,000 and up, but are unbelievable. When programmed right with good brakes, you can use both feet on the brake pedal as hard as you can, and slow before a turn as good as if you were trying. And if it rains, competitors won’t understand why you and the other ABS cars are lapping them. *Recent information: I’m looking at brake modulation test sheets from Tex Racing (They do more then 50% of the Winston cup cars). Their brake dyno runs from 125 to 80 mph consecutively and records speed, brake torque, air pressure, hydraulic pressure, and rotor temperature. The Lighter and less expensive Brake Man F4 caliper out performed the $2000 each Brembo GT monoblock caliper (Previously the industry standard for best) The F4 ran 30 degrees cooler, required 100lbs less line pressure (On average), made a flatter torque curve, and most important had a much more consistent torque vs. line pressure between runs.(this means less caliper flex)

Brembo monoblock

 

[dquarasr2]

That's bizarre. My first set of Dali/Power Slots lasted over 100K miles and 2 sets of Bobcats and at that point they were just at the service limit.

Hugh, how much tracking did this include?

 

[CL65 Captain]

My one piece RB slotted (fronts) developed spider cracks after 4 track days. I installed 2" cooling ducts front and rear and replaced the fronts with two piece slotted RB and so far have had no problems. I think the key is the cooling ducts... the rotors just have a hard time with the kind of heat that is developed on the track.

 

[NSXLuvr]

I did a search and don't see anything on rear cooling ducts for stock cars. I have seen it on race cars but not on a stock NSX so I don't know if that is possible. Therefore I suspect your rotors are the weak link. Some of us have tracked for years and don't have issues with cracked rotors. I have no problems with my OEM rotors with Motul 600, Carbotech P+'s.

Link with some good info.http://nsxprime.com/forums/showthread.php?t=63057&highlight=Rear+Brake+Cooling+Ducts

 

[CL65 Captain]

I will post some pics tomorrow of my cooling ducts front and rear. Prior to the ducts my rear brakes were always running 75-100 deg hotter than the fronts. Now they are about the same as the fronts. Even though the natural bias for braking is the front, we have a tremendous amount of weight sitting over the rear 40/60.

I am still running the RB one piece in the rear and no problems. Switched to RB 2 piece in the front because the 1 piece spidered.

 

[L8apex32]

Here is a +1 to you having a problem unique to your rear brakes. I have countless track events on my 1992 and never had any rear brake problems. In contrast, I've had terrible front brake problems, from cracks to pads disintegrating, etc.

Plus, you notice uneven rear rotor wear. So, the question should be, why are your rear rotors wearing unevenly? Are your pads also wearing unevenly?

 

[Ponyboy]

Wow, never had a problem with the rear rotors and I'm fairly hard on the brakes at the track. I use the PowerSlots, bought through TireRack (more likely to actually get the product you buy), for the rears and have about 20 track events on them. No ducts in the rear.

This is a longshot but what kind of wheels are you using? I ask b/c some wheels inhibit air circulation to the rear rotors thus affect rotor temp.

 

[dquarasr2]

l8apex32, that's what is perplexing. The pads seem to be wearing evenly. And all four calipers were rebuilt in early 2006 (although I didn't do them myself so I don't know for sure how well that was done. B4 anyone asks, no it's no vendor that has been discussed here on Prime.)

When I replace the rotor I will do some disassembly and see if the root cause presents itself.

ponyboy, yes, Tire Rack is great. That's where I've been getting tires for years (and they sponsor SCCA Autocross Nationals) and in fact where I got the OEM Brembo rotors for the NSX. I've been tracking '91 15/16 OEM wheels and on the street use '94 16/17 OEM seven-spokes.

I'm wondering if it just makes sense to replace the rear calipers with brand new ones (not rebuilt). But then that begs the question: if I'm going to do that, why not take the big plunge and do BBK and go for wheels, too? It's only money!:biggrin:

 

[Ponyboy]

Right, you could always go with a big brake kit though that brings upon it's own series of headaches (cost, fitment, wheel fitment, rubbing, etc). But you won't worry about your brakes ever again. And for some, that alone is worth the price of admission.

I'd seriously consider the NA2 Racing Brake option, 2 piece front and rear, maketed by ScienceofSpeed as an alternative. Maybe cryo reat them or get the interiors coated with ceramic. Maybe pick up a set of the 02+ 17/17s and you're golden...until your skill level catches up with your equipment again.