cross-drilled rotors on newer cars??? - PeachParts Mercedes-Benz Forum

JHZR2 · #1 07-27-2004, 03:31 PM

Hi,

Im curious about the cross drilled rotors seen on the newest MBs, staring with the s-class and now the c class and maybe the e as well.

There is always a lot of discussion about cross drilled rotors, and lots of people are against them. Theyre an artifact from 1950s era racing when pads off gassed too much... They thermally crack easily... there's no point to using them, a solid rotor holds more heat and will provide better performance. Even new porsches and ferraris can devellop cracks, etc with use.

So then why does MB put them on? MB typically is REALLY good at testing and engineering stuff to provide the best longevity and service life. So why would they put these old technologies on their cars? I have heard that performance-wise, slotting is much better, and as far as Ive seen, F1 and other fast race cars use either solid or slotted discs nowadays.

Is there something that I'm missing? Im considering putting x-drilled zimmermans onto my 91 BMW, but have been really turned off; I think Im going with ATE powerdiscs in front and balo in the rear. But Im still curious how a technology that so many says is useless and can degrade performance can make its way onto more and more new MB cars.

Thanks,

JMH

manny · #2 07-27-2004, 05:37 PM

In a nutshell?
Cross-drilled looks cool & lightens the rotor a little bit.
As far as cracking & warping goes, I don't see a problem yet ( I have Zimmerman's ).
The key is to CAST the rotors with the holes, not drill them as an after-thought.
As far as F 1 brakes goes, most of them are carbon or ceramic rotors, that are not expected to last more than 500 miles.

kramlavud · #3 07-27-2004, 08:34 PM

For everyday street use you do not need them, other than to show to the gawkers.

regards,
Mark

JHZR2 · #4 07-27-2004, 09:49 PM

Agreed. Im not buying them either (I am giving the ate powerslot rotors a shot on the front though). Its just curious, as there is so much negativity against them, that it really interests me as to why MB would begin putting them on the cars.

JMH

AusMBtech · #5 07-28-2004, 05:17 AM

They do look better than slotted rotors but slotted rotors give a noise at low speed braking which isn't desirable for benz's.

I've yet to see any drilled rotors show signs of cracking (the result of high heat) possibly due to the softer compound of benz pads which helps reduce heat generation

ktlimq · #6 07-28-2004, 06:45 AM

Quote:

The key is to CAST the rotors with the holes, not drill them as an after-thought.

Porsche says they are drilled.

On all 911 models, the front and rear discs are cross-drilled to improve braking in the wet. The brakes respond faster because the water vapor generated under braking can be released more efficiently. The discs are also internally vented for better heat dispersal.

© 2004 Porsche Cars North America, Inc.

Kestas · #7 07-28-2004, 08:33 AM

Quote:

Originally posted by manny
...The key is to CAST the rotors with the holes, not drill them as an after-thought.

I've designed automotive castings and even poured them. I can't imagine casting such small holes. Rule of thumb says you have to leave at least 0.060" stock on cast surface for machining, preferably 0.090". That's just too much detail for a sand casting, not even mentioning the required chamfer at the hole's edge critical to reduce cracking from thermal cyclic fatigue.

Greg in Oz · #8 07-28-2004, 09:18 PM

We had a MB club night at a local disc brake manufacturer here in Sydney. They explained to us the benefits of slotted and cross-drilled rotors. They also admitted that slotted were for those wanting serious improvements in braking performance whereas the cross-drilled rotors, whilst giving some improvements, were more for show. They do their own casting and then machine the slots or cross-drill afterwards on the rotors that require that treatment. They advised against DIY cross-drilling as they said great care must be exercised in the positioning of holes to prevent possible cracking. Slotted rotors did appear to be superior.