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Discussion Starter #1
Hey Folks -

I got the drilled and slotted rotors from irotor.com a couple of years ago and they're great. It looks like I may have finally warped the front ones and need to ask this before I order and install new ones:

Which way are the slots supposed to point?

In my current installation, if you look at the top of the rotor, the slots point toward the front of the car like this: \. However, I have seen pictures with the slots toward the back of the car like this: /. Which is right? Does it matter?

Thanks!
 

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The vanes on a rotor act like a centrifugal air fan, drawing air from the inside of the rotor and flowing it to the outside. The vanes of a directional rotor should arch back like arms on a pinwheel. On the top side of the rotor, the vanes should curve toward the back of the car.

As far as I know every brake MFG recommends the slotting like this

 

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Discussion Starter #4 (Edited)

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In reading stop tech's explanaition it sounds like it depends on the direction of the internal cooling vanes of the rotor and not the slots or cross drillings. Should be fairly easy to see which direction the cooling vanes point.
 

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We debated this on the 300M site for a while.

Eventually we decided it doesn't matter

Also don't be so certain they are warped. Uneven filming is more likely the culprit.
 

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Discussion Starter #8
DScruggs said:
Also don't be so certain they are warped. Uneven filming is more likely the culprit.
Is this possible even though I have at least 20,000 miles on the rotors? If so, what should be done instead of new rotors? As I understand it, these rotors cannot be turned since the bit would go into the cross-drill holes and snap off.
 

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What I would do if they were mine is to remove them and chuck them up it a lathe and deglaze them. Not easy to do if you don't have access to a lathe.

They certainly could be warped but I wouldn't assume it for certain.
 

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2001RT said:
As I understand it, these rotors cannot be turned since the bit would go into the cross-drill holes and snap off.
I don't know about those machines they put on your hub and turn your caliper, but from a machinist standpoint, you can turn drilled rotors on a lathe without breaking the cutting tool.

If you think there is some glazing on the rotors and can't get at a lathe as dscruggs suggests you might try a scotchbrite pad.
 

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I thought the slots cut on the surface of the rotor are for cleaning water off the rotor? The slots give the water someplace to get channeled out from under the brake pads, rather than getting compressed between the pad and the rotor. The cooling vanes are in the center between the two rotor surfaces. Just my understanding of how things work.
 

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Nope

The slots are to allow the boundary gases that build up under a heavy stop to escape thereby avoiding the phenomenon known as brake fade.
 

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Shouldn't be an issue. Carbide generally doesn't like interupted cuts. But the material used in casting rotors doesn't create much tip loading and shouldn't chip the bit. Of course the slots will lose depth, and their cooling effect.
 

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The slots are to allow the boundary gases that build up under a heavy stop to escape thereby avoiding the phenomenon known as brake fade.
Brake fade is caused by overheating of the pads and glazing them not gas traped between the pad and rotor. The slots are only there for cooling
 

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95trep3.3 said:
Brake fade is caused by overheating of the pads and glazing them not gas traped between the pad and rotor. The slots are only there for cooling
It is the overheating of the pads that increases boundary gas generation and therefore brake fade. The pressure of the trapped gases create a buffer between the pads and the rotor similar to the way a hovercraft rides above the water. The slots are there to release these boundary gases. They do NOT aid cooling in any way.
 

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95trep3.3 said:
Brake fade is caused by overheating of the pads and glazing them not gas traped between the pad and rotor. The slots are only there for cooling
It is true that overheating can cause glazing, and that overheating leads to brake fade, but as DScrugs said, brake fade is the build up of gases between the pad and the rotor. With no where to go, the gas acts as a buffer. So instead of the pad contacting the rotor, the pad is contacting the gas. Glazing is another issue.
 
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