Rotor Type question

[z34Phoenix]

which is best for my planned setup?

 

I already have drilled & slotted rotors on rear. (the front ones warped by a blown wheel bearing)

Pads: Not sure if Im going to use ceramic again or go to hawk pads

Steel lines: rubber lines to be replaced by steel braided lines.

 

Drilled: (I am leaning toward Drilled rotors)

research says these are prone to cracking. IMO i believe this is due to improper drilling methods IE non CNC and having holes drilled and not cast into the rotor. but they are good at cooling the rotor faster if it is also a vented disk, which the front is.

 

Slotted:

I have done some searches and found that a good number of reviews say that the powerslot rotors are very prone to warping. IMO i atribute that to the thining of the rotor at the slot area.

 

Drilled and Slotted:

I know in theory they are the best. they would wear pads the fastest (even though i had good pad wear with the ones i had) These rotors have the least surface area of the group the slots might weaken the rotor just like the standard slotted.

 

well tell me what you all think.

if anyone has or had drilled rotors please let me know what you think

[bartonmd]

1. do not, repeat DO NOT use Hawk pads on non-vented rotors (like the rear of the W cars)!!! If used hard enough, repeated times, they WILL crack your rotors! Using them on vented rotors seems to be OK though (Like the front rotors). Has to do with the pad material having a VERY high specific heat, so they don't let the heat get to the fluid/calipers, BUT that heat has to go somewhere, so it stays in the rotors... warping and fragging insues. Have seen this on the rear of DSM cars... at least 2-3 at every rally race. BTW, I know guys have NOT had problems with EBC Green Stuff pads, although I haven't tried them myself... car got totalled before we trashed rear pads on it (factory replacement)

 

2. Drilled rotors are OK IF they are MEANT to be drilled into those rotors (like NOT drilling factory rotors)... The reason some of the drilled rotors crack is the sharp edge (trailing edge to be exact) of the holes get hotter than the rest of the rotor, which is why they can crack. This probability is taken down a BUNCH if the holes are radiused so the pad isn't rubbing on a sharp, 90 degree corner, but more of a 45 degree edge.

Edit: Also, it helps with the cracking if the rotor material is something like stainless steel instead of cast iron, because cast iron is very brittle, which is why the heating of the trailing edges of the holes (and that material expanding as a result) can cause stress on the rest of the rotor that's not as hot, sometimes cracking it. But running stainless rotors (stainless has a VERY low coeficient of friction compared to cast iron because of the porosity of cast iron compared to the smooth surface of stainless steel), you get into using Sintered, high friction pads that you wouldn't normally use on a street car.

 

3. Common misconception: drilled/slotted rotors keep your brakes cool. This is only partly true. Pads work better when they are up to the operating temperature they are meant to work at. Drilled/slotted rotors first, get them up to temperature faster because of the edges of the holes/slots the pads go over. You're basically trading swept area for heat generation. The holes/slots also keep better contact between the pads and rotors by allowing the gas that is created by heating the pads (and carbonizing pad material) to escape instead of the pads riding on that gas instead of the rotor. As it happens, the holes/slots also give the rotors more surface area (think "heat sink" with all the fins giving a set size of material a much larger surface area) so they do cool a bit better than standard rotors, but that is more of an "also" than a primary reason.

 

4. I have not tried them, but have heard good things about the Brembo slotted/dimpled rotors that Tirerack sells... I think you can get them both front and rear for the Lumina anyway, I assume all the W-bodies in the same era have the same rotors??

 

Just my $0.02 on the subject of braking...

 

Mike

[DaveFromColorado]

if you're getting drilled or slotted rotors, or having your rotors drilled/slotted, it's always a good idea to have them chryo-treated first - usually the drilling has to be done when the rotors are glowing red hot to prevent any cracking, and the rest of the chryo-treatment will prevent the rotors from warping - I used chryo-treated non-drilled/slotted rotors and drums on my Mustang, and have not had any problems with warpage - and I push my brakes till they fade to almost nothing when on the road-courses ...

 

--Dave.