drilled disk question

[s2avant95M]

while doing my stud conversion on friday, i noticed that the holes on my porsche drilled discs were blocked with brake dust, is this a common problem? just wondered as i dont think it can be helping the brake performance. i unblocked them with a small screw driver, and i will check next week whether they block again. the calipers are mov-it big reds, with standard porsche pads (textar?)

thanks.

[Greg_S]

From what ive read of the years the drilled discs were more for style than performance and grooved or grooved and dimpled discs were better.

[s2avant95M]

greg, yes i'm aware of the thinking regarding drilled discs, next time i will go grooved if possible, but they came as part of the mov-it kit so it was'nt a conscious decision to go "drilled". i was just wondering whether the holes bloking up was a common symptom?

[Greg_S]

I have fitted grooved and dimpled discs on the back and havent seen any build up yet and same goes for the grooved discs on the front

[WabTheKing]

i was told the idea of drilled discs was to help releve gas given off the pad at very hot temp so it could vent through the centre of the disc

and grooves to de-glaze the face of the pad

all helping reduce brake fade

not to sure bout the first one but second one makes sense in my mind - think drilling may assist cooling time. think if you heated a drilled disc and a non drilled disc you would find the heat disipated quicker through the drilled one

i drill/groove my own discs anyway so im not exactly paying extra for the privalige, heavy road use dosent incur any noticable brake fade - car never runs long enough to get to a track day to try them under very heavy use!!

[Mark Halligan]

Tim,

I have the Movit kit too and I have had to clean them out a couple of times. Seems that they get blocked up with crud that sets quite hard and takes some removing if left for a long time.

[s2avant95M]

mark, do you know what causes it, is it the pads?

[Jas11n]

The discs I took off mine recently albeit the standard S2 size discs, were black diamond cross drilled and grooved. I noticed when I took em off that all the drilled holes were totally bunged up with rubbish.

[Mark Halligan]

mark, do you know what causes it, is it the pads?

Tim,

I think its a combination of different kinds of crap, rust, dirt and pad dust. It just seems to lodge in there and hardens up blocking the holes.

Mark.

[dan_b]

it's a nasty amalgam of melted disc, melted pad, dirt, tar, water, bird sh*t and what else gets on the disc surfaces.
As you can tell, it hardens over time and effectively renders any theoretical benefit of having x-drilled discs redundant as the holes get properly plugged.

By reducing the actual mass of the disc, in theory putting x-drilled holes in it could actually serve to increase brake fade as you have made a net reduction in the maximum thermal capacity of the disc itself - there's less of it to absorb heat, and a smaller face to then release that heat back off later on.

Not to mention the fractures you get round the edges of the holes...

[Keeper of The Kitten]

I'm totally with you Dan on the cross drilling thing, it's not the way to go.

I think it's also feasible that the drillings are reducing the effective swept area of the pad/disc more than grooved only discs. Maybe this reduces brake effiency in itself?

The main reason for drilling is probably weight saving on racing discs, hence road versions have less holes (only present for the bling factor), but they still present problems - like the cracking issue.

In fairness Dan, I think the surface area may be larger on a drilled disc because you have all those little cylindrical surfaces in the holes - but when they fill up that doesn't help! The comments about reduced mass and heat build up sound entirely likely.

Wab: grooves are in fact intended to remove heat - the angle of grooves is intended to throw the hot gases outwards on the disc faces (the gases will get in the grooves when that area passes under the pad), they also serve the recognised de-glazing purpose. I don't think the drilling makes much difference, I was told by AP that they don't drill for cooling reasons, they drill for weight reasons - and that only matters on discs intended to have a short lifespan.

Solution? Go for grooved-only discs!

__MDC__

[s2avant95M]

Thanks for all the replies, i feel a bit better that it is a known problem with cross drilled disks. i guess i will have to check more often and make sure they dont get bunged up. the porsche discs came as part of a kit with movit big reds. when the discs are worn out i will see what other options are available.

[Jamo]

Here's an article that i used to show to friend and foes alike.

Interesting reading.

[s2avant95M]

interesting, but as i said before ive seen all the arguments for and against drilled disks. it was not a choice i made to go drilled, the movit kit came with the porsche discs so thats what i fitted. i hope i can get grooved versions of this disc when i come to replace them.

[Jeffer]

The holes are blocked in no time. I take a small drill and drill them through every couple of weeks. Can't tell exactly what would be better: drilled / grooved / non of both....
To me drilled will let it cool quicker because of air flow through (if holes are not blocked)????