Brake Rotors Solid vs Cross drilled

[Keith]

Hey folks, I've been needing to machine my front rotors about every six months or so. If I change over to cross drilled rotors. do you still have to machine them twice a year?

 

[tlong]

Rotors

Whoa!! Is this is a race car? Have you checked minimum thickness lately? I don't believe in ever turning them; Hib will agree.

Something ain't right here. I was told you can't turn drilled rotors anyway. If you are really doing this they are warping because they are the thickness of a paper plate.

Welcome to the place of knowledge (opinion?) and send in 5 bucks.

Tim

 

[grapeknutz]

I have come to the conclusion turning rotors is a bad idea, Most brake lathes are not very well maintained and have significant run out. The best thing you can do is to check for runout while the rotor is in the vehicle, if warped dont cut the rotor replace it as it will continue to warp as the rotor is thinner, not good!
As for the cross drilled rotors make shure that the holes are counter sunk so the sharp edges are gone, as the first place a crack will develop will be at a sharp corner.

 

[Tom Bryant]

If your rotors are needing turned because they are pulsing due to warping you can usually do it once or maybe even twice. This depends on if you reached the minimum thickness the first time or not. Once they are under specs they are not going to stay straight, period. I don't see anything wrong with turning rotors on a mildly driven daily driver. Most of us can't afford to buy rotors every few months.

If your rotors are grooving due to excessive wear you may have a problem with your system holding too much residual pressure and the brakes are dagging all the time. Then again, maybe you drive hard or do a lot of track time. Some people have these problems because they use the brake pedal for a foot rest.

This brings up another point. There is a big difference in quality of rotors from various manufacturers. Some are poor quality iron and will begin to pulse in just a short time after you put them on. Others are will go a long time before they cause any problems. If you buy the bargain priced ones and drive them aggressively you better get them by the pallet. Don't bother to turn them because the next high speed hard braking manuver will warp them again.

As for drilled rotors. I have been thinking of getting some for a while myself. I doubt that a regular brake lathe could be used to resurface a drilled rotor because the tool would catch in the holes and break. I don't think I would throw them away if they started to show some minor wear or grooving though. I would take them to a good machine shop and have them Blanchard ground like you would a flywheel. Then re-chamfer the holes. I'm not a machinist but I can't see why that wouldn't work. Plus you would be sure that the 2 sides were perfectly parrellel.

If you drive hard drilled or drilled and gas grooved rotors might just be what you need.

Tom

 

[Keith]

This is my daily driver and I don't pound it at the track. I can't remember making any emergency stops, but plenty of short triple digit runs whenever the CHP aint watching. The rotors have a lot of meat on em, but the pulling and machining is getting to be a drag. But the drilled rotors sound like an expensive machine job. I'll have to check with my machinist.

Thanks for the info.

KC

 

[tlong]

May I ask why you are pulling them? The sympton yields the cause. Fix the cause instead. Mine have 50K and are working great. This is a curious situation that will be answered here with more info if you care to add. The truth is out there.

 

[Tuna]

Yes, please tell us why you keep pulling them and turning them!

I got over 90K out of my rotors and never pulled them or turned them and I changed the pads twice on them. That included many triple digits runs, 3 years of autocrossing and daily driving use. I put a new set of stock rotors back on the car.

 

[c4cruiser]

There should be no need to resurface stock rotors. Sound like you have some problems. Are the calipers mounted tightly and are the bolts for the calipers and front mounting brackets torqued correctly? Do the pads have a taper?

I jst use auto parts store rotors for track days and in-between. I buy the ones with a lifetime warranty and just take them back after a couple of events to get them replaced for free!!

Drilled rotors are OK for street use, but I would not consider the low-end or cheapie ones for any sort of high performance use. The cheap drilled rotors are drilled after the rotor is cast and machined. The drilling will cause cracking when the rotor is exposed to exterme heat such as that encountered in track use or high-speed autocross events. This can result in a rotor coming apart. Not a good thing at warp speed!

The high end rotors such as Brembo and Wildwood use a casting process that puts the holes in at the time the molten metal is poured into the mold. This method keeps crack from forming around the holes. Some rotors are also cyrogenically treated to insure the metal will not crack.

 

[militant_x]

Everything I have read about drilled rotors has been negative. They crack very easily, the cracks then destroy the brake pads. Slotted is the best in my opinion.

-chris