Front rotor cracks

#1

I have asked this question on bf.c forum but I thought I would ask here as well.

When I crack my front rotor, it’s always the outside surface that cracks. Has anyone cracked the inside surface of their front rotor? If so, what percentage of the time do you crack the inside vs. the outside?

#2

I have cracked the inside also, not sure on the percentage its usually the outside but I have had the rotor crack on the inside towards the center of the rotor.

#3

Are you running backing plates/brake ducts?

#4

rrroadster wrote:

yes

#5

There are 3 contributors to rotor cracking.

  1. Rotor break in. From Carbotech’s site: New rotors just like new pads need to be bedded in. Brake rotors don’t require as much bedding as brake pads require. If you follow the brake pad bed-in procedure your rotors will be completely bedded. Proper bedding will increase the rotor life and make it more resistant to thermal cracking. By cleaning the disc surface you want to make sure you have completely removed any and all grease, surface residue, and debris that might contaminate or damage the brake pads.

I had a buddy lose a rotor on his Corvette a couple of weeks ago at VIR. He new why before he got back in the pits; he didn’t take enough time to break them in before going on the track with them.

  1. Uneven cooling. All ducts need to do is provide a cool air source at the center of the rotor. The spinning vanes will pull the air through and evenly cool the rotor. If your ducting is blowing air on the inside surface of the rotor, then you are experiencing uneven cooling which thermally stresses the rotor to crack.

  2. Drilled rotors. Stay away from them. The holes are just crack initiators.

#6

rrroadster wrote:

[quote]There are 3 contributors to rotor cracking.

  1. Rotor break in. From Carbotech’s site: Proper bedding will increase the rotor life and make it more resistant to thermal cracking.

  2. Uneven cooling. All ducts need to do is provide a cool air source at the center of the rotor. The spinning vanes will pull the air through and evenly cool the rotor. If your ducting is blowing air on the inside surface of the rotor, then you are experiencing uneven cooling which thermally stresses the rotor to crack.
    [/quote]

Proper bedding makes rotors more resistant to thermal cracking how?

If our lives depended on it we couldn’t cool a complex shape like a rotor homogenously. Getting air flow into the center of the rotor is a step in the right direction because the interior surfaces of the 2 rotors would get about the same amount of air, but that’s lightyears from genuinely even cooling. It’s also useful because the cool air flow is hitting a fair amount of surface area. But nothing about it is even.

It’s a complex shape in a crazy turbulent air stream. Cooling will never be even.

The list of things that I don’t know shit about is miles long. But after 4 semesters of thermo and heat transfer, even I came away with something.

#7

I live and race in the desert, and I have only seen a thinner than hair crack at the edge of the outside face going towards the center of one of my front rotors in my MZ3 roadster once. I didn’t change the rotor and kept tracking/autoxing the car all summer following the advice of a fellow racer and race car mechanic in town. Nothing happened, but it was always in the back of my mind, so I ended up changing the rotors anyway, and for $150 I was able to brake with more confidence, just brake :wink:

#8

Chi, just change your rotors before this turns into a 5 page discussion on brake rotor venting/cooling/bedding/etc.

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#9

Ranger wrote:

Don’t feel bad that you had to repeat the class. I had to take English in summer school in Tennessee.:stuck_out_tongue:

Steve D.

#10

Which is the quicker way to end it all?

  1. bullet to the head
  2. kicking the car out of gear and letting it run over you
  3. carbon monoxide poisioning
  4. reading a Ranger post
#11

Gasman wrote:

[quote]Which is the quicker way to end it all?

  1. bullet to the head
  2. kicking the car out of gear and letting it run over you
  3. carbon monoxide poisioning
  4. reading a Ranger post[/quote]

Technically, given a list containing four items, you would be looking for the quickest way to end it all. If you had two choices, then you could pick the quicker.:stuck_out_tongue:

I learned something in summer school.

Steve D.

PS - So I shouldn’t ask Ranger what he thinks of cryogenically treated rotors?:S

#12

Gasman wrote:

[quote]Which is the quicker way to end it all?

  1. bullet to the head
  2. kicking the car out of gear and letting it run over you
  3. carbon monoxide poisioning
  4. reading a Ranger post[/quote]

My wife’s been out of town for a couple days. Thanks to you ragging my ass I didn’t hardly miss her.

#13

Steve D wrote:
So I shouldn’t ask Ranger what he thinks of cryogenically treated rotors?:S[/quote]

You can if you want, I just won’t look.

#14

Gasman wrote:

I don’t think you can resist. It’s like watching bugs fly into a zapper. You know what’s coming. You know it’s not pretty. But with an anticipation, you have to look for that zapping flash and get a tiny thrill from the sizzling sound.