'14 AGM 1SS/1LE Track build [COTW 11/17/14]

[X25]

Originally Posted by Stephen12ZL1

http://my350z.com/forum/brakes-and-s...a-concern.html

Well, I was feeling better until I saw his rotors cracked in half the next time he went to track, but that was also 5 months later.

The pass criteria for thermal fatigue testing specifies that the rotor is allowed to have small thermal cracking up to 2/3 of the brake plate surface. The brake plate surface for the front rotor is 50 mm (1.96 in) radially which means cracks are permitted up to 33 mm (1.29 in) radially across the rotor brake face in length. This would be the pass criteria for the end of severe testing. To have a large safety margin, a rule of thumb - small thermal cracks are allowable and the rotor does not need to be replaced unless the cracks connect from hole to hole or the crack reaches the OD of the rotor.

Some of these cracks seem to be running the whole length, so I guess I indeed need to discard these : (

[Stephen12ZL1]

I got this info from Baer several months ago when asking them about this same condition. This was a TSB from GM regarding Corvette rotors.

Bulletin No.: 05-05-23-007

Date: August 03, 2005

INFORMATION

Subject:
Information on Visual Brake Rotor Surface Cracking

Models:
2005-2006 Chevrolet Corvette

with Heavy Duty Brakes (RPO J55)

Important: DO NOT replace OR resurface rotors for small surface cracks that are described below.

The pass criteria for thermal fatigue testing specifies that the rotor is allowed to have small thermal cracking up to 2/3 of the brake plate surface. The brake plate surface for the front rotor is 50 mm (1.96 in) radially which means cracks are permitted up to 33 mm (1.29 in) radially across the rotor brake face in length. This would be the pass criteria for the end of severe testing. To have a large safety margin, a rule of thumb - small thermal cracks are allowable and the rotor does not need to be replaced unless the cracks connect from hole to hole or the crack reaches the OD of the rotor.

[X25]

Originally Posted by Stephen12ZL1

after reading a few threads, the answer isn't clear. Some of the cracks are merely superficial and are of no concern. My ZL1 had cracks after a 2 day event and never caused any issues. I put a new set of rotors on the car and they had cracks after another event. So, it is a judgement call and GM says "superficial heat cracks are no reason to replace the rotor" according to a post in the first link above.

Were those cracks reaching to the outer diameter of the rotor? I think I should replace them since they reach the OD. I already have the spares. Considering this will be the first time changing them after this whole season and also end of last season, it's somewhat acceptable.

I had quite a bit of vibration at the brakes when they got hot during my last track day. I figured it was due to using ST47s without bedding them in, and the vibration disappeared next session. Perhaps the vibrations also contributed to the occurrence of these cracks; who knows.

[Stephen12ZL1]

were your vibrations due to your loose caliper condition that you described in earlier posts? If you have spares, you should probably just swap them out to be sure especially if they extend to the outer rim. I think the "superficial" cracks described in the GM bulletin are just the round/somewhat octagonal shapes that are definitely from heat and do not extend further into the metal. My cracks never appeared to extend like some of the pics in the links above.

[BaylorCamaro]

My OEM rotors on my ZL1 had surface cracks similar to yours. Did several more track events without an issue. But like you, I wasn't sure if they should be changed out or not. Eventually I changed my rotors to a new set of OEM ZL1 rotors. I think I could have done a little more on the original set but you never know. They looked like it was just surface cracks to me.

[White_SS/RS]

I have the same thing going on with my rotors. Ive kept using them and I haven't noticed them getting any worse over the last few track days. I have one more track day left this year and then I'm going to take them off and get a good look at them. You could have them Magnaflux checked and see if any cracking has made its way through the castings or to the edges.

[X25]

Originally Posted by Stephen12ZL1

were your vibrations due to your loose caliper condition that you described in earlier posts? If you have spares, you should probably just swap them out to be sure especially if they extend to the outer rim. I think the "superficial" cracks described in the GM bulletin are just the round/somewhat octagonal shapes that are definitely from heat and do not extend further into the metal. My cracks never appeared to extend like some of the pics in the links above.

OK it was very late when I posted, and I mixed up the cars; the vibrations were coming from the Miata; sorry for the confusion!!

Originally Posted by BaylorCamaro

My OEM rotors on my ZL1 had surface cracks similar to yours. Did several more track events without an issue. But like you, I wasn't sure if they should be changed out or not. Eventually I changed my rotors to a new set of OEM ZL1 rotors. I think I could have done a little more on the original set but you never know. They looked like it was just surface cracks to me.

Originally Posted by White_SS/RS

I have the same thing going on with my rotors. Ive kept using them and I haven't noticed them getting any worse over the last few track days. I have one more track day left this year and then I'm going to take them off and get a good look at them. You could have them Magnaflux checked and see if any cracking has made its way through the castings or to the edges.

Our rotors (and StopTech as well) are 32mm-thick, and I have a feeling that these small cracks cannot crack the whole rotor that easy. I will probably have one more track day before retiring the car (to test out MPSC2 + Eaton diff), and they should hold for one more day. I will definitely keep an eye on them.

Actually, I will take a look again tonight, and see if they ever cracked outside the pad area by the outer diameter. If not, I'll stick with them for one last track day.

[White_SS/RS]

Looking through images on google, it seems like serious cracking is easily identifiable. I'd just keep an eye on it. Have you been running brake cooling the whole time you've had these rotors?

[X25]

Originally Posted by White_SS/RS

Looking through images on google, it seems like serious cracking is easily identifiable. I'd just keep an eye on it. Have you been running brake cooling the whole time you've had these rotors?

Yes, I have, but keep in mind overcooling can also crack rotors if the rotors overheat and then cool all the way down at the straightway in every lap. Not that I think that's what happened here.

[White_SS/RS]

Originally Posted by X25

Yes, I have, but keep in mind overcooling can also crack rotors if the rotors overheat and then cool all the way down at the straightway in every lap. Not that I think that's what happened here.

I was just curious since Ive only had cooling ducts for the last few track days myself. I had cracking even before adding them.

[X25]

The season is coming to an end, yet all in a sudden I have quite a bit to do:

• Differential: I got the pumpkin back from the diff shop, and now it has Eaton diff in it! It is pretty straightforward to put it back in, but I want to do the Tick bleeder before doing so, while the shaft and transmission cooler lines are out of the way.
• Tick remote bleeder: I don't know how these people did it, but my hands just don't fit!
  • I ended up cheating: I lowered the engine by .25" (removing BMR motor mounts' spacer), and lowered the transmission about .5" (loosening its mount), after which I was able to put my fingers into the access hole much easier.
  • Anyway, the bleeder is finally on, but I'm having hard time making sure it's tight. I'll get the exact fit (7/16") flare nut crowfoot wrench tomorrow, since my metric 12mm is a bit too loose to feel for it through the hole by hand.
• Engine mounts: The BMR engine mounts' bushings lost their shape a bit in time, just like all the other aftermarket bushings I had. Better late than never, I'll put back my lovely, high quality 1LE motor mounts. As a bonus, I will no longer have the annoying vibrations; wooHoo! BMR's claim of not feeling they're there at all once they settle is completely wrong, but I know why they make their claim. These bushings are much softer at 90 degrees F. No wonder, since BMR is in Florida, it's all good there
• Rock guards: I've replaced the rock guards with the replacement ones sent by ZL1Addons. I think they're too small for the track duty, but they think they are adequate. Oh well. The top bolts were loose since they were self-tapping onto the plastic of the fender. I used small plastic bolt anchors, and they worked perfect! The rock guard is tight in its place:
  
• Left rear caliper: Since it was damaged due to falling caliper bolt, I will be replacing it once the differential is finished. I will also use the Nord-lock washers on the calipers. They are not going anywhere anymore. I also have new OEM bolts to use.
• Exhaust: My exhaust was one piece and I had to cut it to work on diff cooler, etc. I have clamps to use; here is hoping it works out. If not, the muffler shop is close : )
• Fluids: I've drained every oily fluid this car has during this surgery: brake (for clutch bleeder), transmission, differential, and engine oil. The car will have a 'fresh start' to the winter I'll use Redline 75W90-NS for diff, Mobil1 5W-30ESP for engine, Amsoil Signature ATF for transmission.
• Harness bar and new racing harness: I finally drove down close to Portland, and picked up his custom harness bar from EarlyApex. He is an engineer, and has designed it himself inspired by the B.K. bar. However, it is using better quality attachment points and joints. Looking forward to trying it at the track! I am also ditching the Schroth Rallye 3 ASM harness in favor of Schorth Profi II ASM, now that I have a proper harness bar (and tank plates).
  

BMR engine mount after 1 summer. Observe the compressed (squeezed) top red bushing. Perhaps they're better for street use. I'll put them up for sale if anyone would like. I'm sure BMR would replace the bushings with new ones; they do have good customer service.


Excuse the leaf mess; I had to leave the exhaust outside to increase space. It was quite hard to handle as one piece during the uninstall.


I have carefully examined the cracks, and they are all concentrated in the middle of the rotor, and are not heading to the edges. I think they will hold up just fine. I will probably replace them in spring time before the next season.


The OEM bleeder, and its replacement. It's mind boggling why Tremec would leave the bleeder like that. If they made it a little longer, and perhaps make it bende 90 degrees down with the bleeder valve at the tip, we would not need this mod.


I'll need this in 7/16" size. I put zip ties to the tools, OEM bleeder, etc. to make sure I don't drop them into to the transmission.


Here is the hole. The clutch looks pretty clean, in good condition; no leaks, etc.


With the new bleeder on

[Stephen12ZL1]

11mm=7/16" in every case I have tried. Maybe get the metric crows foot instead.

[Burt]

Yep, 11mm and 7/16 are basically the same, with the 11 being just a hair smaller. The 11 should do the trick

[X25]

Originally Posted by Stephen12ZL1

11mm=7/16" in every case I have tried. Maybe get the metric crows foot instead.

Originally Posted by Burt

Yep, 11mm and 7/16 are basically the same, with the 11 being just a hair smaller. The 11 should do the trick

11mm is 'skipped' in the metric crowfoot kit; how convenient! I'll stop by Harbor Freight and see what they have. I'll also see if they have flare nut type..