Drilled & Slotted Brake Rotor Rotation

[freds]

Is this rotor, from Ff gallery on the wrong side?

16319

[apexanimal]

The rotation direction is based on the internal cooling vanes, not the slot direction...

[freds]

The rotation direction is based on the internal cooling vanes, not the slot direction...

It your point that it is mounted correctly?.......or not? ......Which was the question. (I asked, in case I am missing some obscure reason for mounting it that way...and not just a quick "throw it on for a photo shoot".

The internal "cooling vanes" are straight-radial, on Subaru rotors (and all that I have seen), so they are neutral as far as rotation is concerned.{There may be some exotics out there that are not, I don't know of any.}

Check this link for info <http://reviews.ebay.com/What-is-the-direction-of-rotation-for-my-new-rotors?ugid=10000000016687378>

[fateo66]

The rotation direction is based on the internal cooling vanes, not the slot direction...

Like Apexanimal stated first and foremost the internal vanes dictate the direction. IMO 90% of the kids out there that I run into at different car meets and events put their slotted rotors on backwards!

Slotted rotors should be installed so that the end of the slot on the outer edge of the rotor enters the brake pad first. Pulling threw in a perpendicular manner, if the slots enters the brake pad parallel to the caliper you will experience pedal vibration and diminished pad life due to the pad diving into the slot.

So yes without being able to verify the vanes I would say that these rotors are facing the correct way.

https://www.cquence.net/media/wysiwyg/disc_rotation.jpg

http://www.camaro5.com/forums/attachment.php?attachmentid=86785&d=1263688400

http://zeckhausen.com/images/Rotors/how_to2.jpg

http://www.timskelton.com/lightning/race_prep/brakes/images/disc_direction.jpg

[bigAl]

That rotation scheme makes sense from a ventilation standpoint. On the otherhand, I have been reading that slotted rotors really aren't such a good thing after all, because of increased disc failures and reduced area.

[freds]

According to BRAKE MOTIVE in answer to a FAQ, they say the following:






"Hello,
Another frequently asked question is, "Which direction do the slots on my rotors face?". We machine different drill/slot patterns on our rotors for uniformity from the left side to right side of the vehicle. The easiest way to describe it is if the rotor is mounted correctly on your vehicle, the top-most slot will point up and toward the back of the vehicle. Below is a picture to illustrate the difference in machining between the right (passenger) side and the left (driver) side rotors."16320


I guess that explains why I asked the original question....now I'm still not sure, especially since the Subaru vanes are straight radial.

Any more help anyone?

[freds]

Quoted from<http://answers.yahoo.com/question/index?qid=20110420175851AAiaVsF>

"You are right that if the outside edge (farthest from the hub) contacts the pad first, the slot does as it is engineered to do -- deglaze the pad by shaving off the pad. The slot is actually designed more for pad maintenance than for off-gassing. Drilled rotors allow the gasses to escape into the internal fins decreasing pad float and effectively increasing braking torque. Slotted rotors provide a channel for the gasses to escape, but racing rotors are usually drilled for off-gassing and slotted for pad maintenance.

In street driving slotted rotors are NOT recommended for exactly the reason you pointed out -- they shave the pads reducing pad life. But you already have them in hand. Now to find the best solution.

You already know more than most of the people in this thread. Almost all the answers so far say to run them so the hub end of the slot touches the pad first. There is even a guy claiming to be a brake repair shop expert that has never read the brembo page that says exactly what you already know. If the outer edge contacts the pad first it helps deglaze; just like sharpening a knife you need to push the knife toward the stone. If you drag a knife away from the stone you end up with more curling, less material removal, and a bad edge.

So, yes if the brake manufacturer did not include directionality on the rotors, then running them in the "wrong" direction will reduce how much bite the slots have on the pads. Less bite = less dust and more pad life.

On the noise side, I don't know if it will make a difference. The logical thought is that the regular direction would force air under the pads toward the hub. That might make the helicopter noise louder by having the hub to reverberate against. So, by that logic running the rotors the wrong direction would reduce the air pressure against the hub. Sound is vibrations in air pressure. Or am I just grasping a straws here?

The reference to cracking of drilled rotors only happens when the rotors are not heat cycled correctly during break-in. Or failing to bring the rotors slowly to temperature before track time. Or bad drilling process. Remember that thermal shock will crack solid rotors, so set the rotors with 30 gentle stops during break-in and then heating them gently before track time or aggressive driving.

Last word of advice: do NOT use semi-metallic pads on drilled rotors. The idea behind semi-metallic pads is that the the metal conducts the heat away from the face of the pad to the backing plate where the backing plate can radiate the heat. With drilled or slotted rotors, the heat is dissipated by removing the hot gases from the front of the pad. Using semi-met pads actually will increase the surface temperature of the rotors. Heating the surface faster than the rest of the rotor will cause heat checking. In a drilled rotor the heat checking focuses on the drilled holes and often causes the splitting that another person pointed out. Instead use ceramic.
Source(s):
I have a 97 E38. Replaced the OE rotors with drilled.
Never noticed the buzzing except at 10-15 MPH beside a concrete wall."


and


"I'd be willing to give you a little ''primer" if you won't take offense. Don't buy drilled brake rotors. Six months from now you will see heat cracks around the drilled holes. Your best bet is EBC slotted and dimpled rotors. The slots must rotate from the inside out otherwise you'd be scooping heat and brake dust back toward center of the wheel bearing. Right and left side slotted rotors have different part numbers. The "airplane propeller" noise slotted rotors make is less noticeable after the first 500 miles of EASY use. If your windows are rolled up you'll never hear the slotted EBC rotors.
Source(s):
Alignment, suspension and brake shop."




Anyone with any personal experience out there?

Are the OEM Subaru WRX slotted and drilled? and if yes what is the stock mounting?

[JeromeS13]

OEM units are not slotted or drilled, so they are not directional or side dependent.

[freds]

Thanks everyone! I knew I was ignorrant, thats why I asked in the first post. Now, after the responses here and reading a few long...long threads on NASIOC on this topic, I have a lot more information on the subject.

With the many conflicting opinions interspersed with some good solid information, I'm now "informed-ignorant" (ha-ha)