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Are my X-Drilled rotors toast (small cracks)?

After a recent DE I was changing my brake pads back to street pads and found these cracks on my rotors. I have another DE in a couple of weeks.

Are the rotors done for?
Is this always going to happen to x-drilled rotors?
Did I do anything wrong that might have caused this.?

I put these rotors on about 18 months ago they have 14 DE days and about 9k street miles on them. Track pads are hawk Blues and I am on my second set. The holes are always clogged after a DE.

Thanks
Andrew


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Old 10-16-2005, 02:12 PM
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I'm not an expert (Bill Verburg is), but I understand that hairline cracks like these are not unusual, and as along as they don't extend to the edge of the rotor, are fine.
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Old 10-16-2005, 02:28 PM
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Worry when they get to be over 7mm long, or reach the edge of the rotor.
Old 10-16-2005, 02:36 PM
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Jack is correct the spec for factory rotors is ~7mm , connecting holes or to the edge. But those are not factory cast in holes in rotors designed for such. There is much less "meat" holding them together and so the factory spec is optimistic for them.


Yes, they will always do that, I would buy new undrilled ones and swap them in at my convenience and on my time table otherwise carry them around and watch those very carefully, be prepared to do a track side swap.

For street use I wouldn't be overly concerned, just observant.

They crack because they get too hot, Keep them cool to slow the cracking down, the cooler they run the less cracking

Part of keeping them cool is keeping them clean, blow the junk out of the air gap and holes
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Old 10-16-2005, 04:19 PM
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Quote:
Originally posted by Bill Verburg
Jack is correct the spec for factory rotors is ~7mm , connecting holes or to the edge. But those are not factory cast in holes in rotors designed for such. There is much less "meat" holding them together and so the factory spec is optimistic for them.


Yes, they will always do that, I would buy new undrilled ones and swap them in at my convenience and on my time table otherwise carry them around and watch those very carefully, be prepared to do a track side swap.

For street use I wouldn't be overly concerned, just observant.

They crack because they get too hot, Keep them cool to slow the cracking down, the cooler they run the less cracking

Part of keeping them cool is keeping them clean, blow the junk out of the air gap and holes

Bill,
Speaking strictly of aftermarket drilled rotors; does a pronounced chamfer on the drilled holes reduce the tendecy to this cracking phenomena, or not really help at all? I know this subject comes up ALL THE TIME here, and regardless of how many times we are all told NOT to do this to standard rotors, it seems to be here to stay...?
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Old 10-16-2005, 04:40 PM
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It is my understanding that the aftermarket rotors, despite chamfered holes, will still crack. The OEM rotors which have the holes cast into them and have a radius at each hole, have less of a tendency to crack.

Each design, when heated enough, will certainly crack. Keep em cool, or run carbon/carbons or ceramic pads and rotors $$$$$$$$$$$$$
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Old 10-16-2005, 04:54 PM
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I notice a crack in one of my rotors on my '85 TL and changed them just to be on the safe side.....(maybe I jumped the gun.)

Would cryogenic treatment help reduce cracking? I know it is done for wear characteristics. Just wondering.
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Old 10-16-2005, 06:35 PM
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Hi Andrew,

These are common, and are known as temperature cracks.

As Jack said, keep monitoring them, and if they grow, then you'll want to replace them.

But first, have you checked the thickness of the rotors? That's much more important, as if they are thinner than their service thickness, your caliper pistons will extend too far, with a risk of "locking" in place and not retracing.
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Old 10-17-2005, 05:41 AM
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Thanks guys for all the replies.

The rotors are Zimmerman rotors so they are not cast holes. The thinkness is 23.6mm so it looks like the cracks will be the controlling factor for end of life.

It looks like some cooling ducts are in my future. The last couple of DE's have been fun and fast ("speed will come" is very true, and a beautiful thing when it does), so the stock brakes have been getting a good workout on this slightly overweight "fat pig" Carrera Cab.

Andrew
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Old 10-17-2005, 07:38 AM
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I had Zimmerman's that cracked also on my race car. I swapped them out for the ATE units that have the two "Saturn" ring slots cut out of them. They work very well without any problems.

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Old 10-17-2005, 08:42 AM
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