Merc W205 Front Break Discs

kitkat9933 · 25 Jun 2016 at 17:41

After getting back from shopping today, I noticed on my front break discs, loads of tiny little holes/marks all around them. Now I can't say they weren't here before, but I've never noticed them before and my back discs don't have them on.

Now I believe some cars have vented break discs, but the holes on mine don't look very well drilled and some are just marks and not even holes!

Should these be here ? It's worrying me!

Six6siX · 25 Jun 2016 at 17:58

They look uniformly drilled so probably meant to be there

Could just be brake dust clogging up some of the holes.

What car is it specifically?

kitkat9933 · 25 Jun 2016 at 17:59

C220D AMG Sport PP

Frozennova · 25 Jun 2016 at 18:00

Dimpled discs are fairly normal.

I have some aftermarket ones instead of just plain discs

slick rick · 25 Jun 2016 at 18:10

My old Merc had crossed drilled discs up front but plain on the back. The ones that look like marks as you put it are just plugged with brake dust and road dirt, you can probably clean them out by poking a screwdriver through the holes.

Dis86 · 25 Jun 2016 at 18:15

Looks to me like they're just plugged with crud.

Diddums · 25 Jun 2016 at 19:30

Frozennova said:
Dimpled discs are fairly normal.

I have some aftermarket ones instead of just plain discs

What's the point of this if you don't mind me asking? I undertand the want to create extra surface area for extra cooling but surely drilled would've been better for that? I mean you lose the surface for braking purposes but don't have the full benefit of the extra surface for cooling purposes.

Or am I being a prat again?

Janesy B · 25 Jun 2016 at 19:37

They're for cooling. You don't really lose out on much surface area and cooler brakes are more effective than overheated ones.

Diddums · 25 Jun 2016 at 19:37

Agreed, but why not drill them through then? Shirley that'd make more sense? I'm confused.

sovietspybob · 25 Jun 2016 at 19:48

drilled discs are far more prone to cracking when used heavily which is why everyone on trackdays runs either dimpled or grooved discs and not drilled.

Diddums · 25 Jun 2016 at 19:49

Very good answer and that makes perfect sense, thank you

Frozennova · 25 Jun 2016 at 20:14

Diddums said:
Agreed, but why not drill them through then? Shirley that'd make more sense? I'm confused.

As others have said, drilled discs are far more prone to cracking with not much benefit over dimpled, and to be honest I could have gone for plain blanks and never known the difference as I'd gone upgrade to YellowStuff pads and larger discs

Six6siX · 25 Jun 2016 at 20:31

I'm not sure that cracking is particularly a problem on a road car is it? The OEM disks on my car are drilled front and back and they weren't showing signs of cracking or anything when I replaced them last year.

Dis86 · 25 Jun 2016 at 20:47

Six6siX said:
I'm not sure that cracking is particularly a problem on a road car is it? The OEM disks on my car are drilled front and back and they weren't showing signs of cracking or anything when I replaced them last year.

It's not. Nor is overheating though. They're pretty much pointless on a 2l diesel and only for aesthetic purposes.