Perforated Disc

[zenman63]

Anyone ever noticed there disc's with cross drillings are handed?

The SLK 350 are not and we are building an AMG 6 pot big brake kit for the 639 Vito and have one new disc today form ECP and its a Pagid part number 104220988, but the other side is the same part number so is the wrong way round?

 

[Vilus]

This was a surprise to me also. I bought new genuine MB discs front and rear. Both sets were not handed, meaning the vanes on one side rotate forwards and bite into the air, and on the other side they rotate backwards. Not what you'd expect on a performance car.

 

[hotrodder]

The cross drillings are cosmetic things for the most part... For some reason people still think they look 'sporty' despite being a relic from a time when pad outgassing was a real problem and something that makes discs more prone to cracking. Rarely found on 'real' race cars these days and when they are it's usually for weight saving on the back brakes only

The internal vanes exist in various styles* some of which are directional but they aren't always handed on production cars because unless air is properly ducted to them** it ain't gonna make much difference if they're rotating 'backwards' and it's pretty much impossible to work the brakes hard enough to need that much cooling on public roads

* pillars, radial vanes and curved vanes for example. Obviously with sporty silly cross drilled brakes the vane type needs to be compatible with whatever cross drilling pattern is currently considered the "fastest" [/tongue in cheek]

** vented discs work like a centrifugal fan, air is drawn in at the centre and thrown outwards. On road cars the disc backing plate/dust shield effects things... some just have a hole in them others have an air duct built into them and less commonly it's a decent size and well thought out duct

 

[markjay]

http://www.zeckhausen.com/how_to_properly_install_rotors.htm