Drilled disk cracks - when to change

[PositronicRay]

tapkaJohnD said:

FunMeterAMG,
, if you can find the right toad to do it on.

John

[GreenV8S]

tapkaJohnD said:

Plus holes filled with disc dust/mud, so inoperative.

Yes, if they're being used hard enough for overheating to be a concern, any surface machining should be kept clean as a matter of course.

tapkaJohnD said:

If they operate anyway. They are supposed to "vent gases heated by the pads" but as the pads cover both ends of the drilling, how?

The drillings don't actually need to lead to open space to be effective - they just need to provide a void that can be filled with gas and carry it away from the braking interface. There's a common alternative to drilling called dimpling which avoids most of the added stress of full drilling and is almost as effective.

tapkaJohnD said:

And bedding-in to conform the pads to disc scoring is a minor effect. Far more important is to condition the pads by heating them, to the highest temperature they will encounter in use, but progressively braking from higher speeds until you reach the highest you will use them at. takes minutes only, if you can find the right toad to do it on.

My experience is the opposite. Getting new pads to bed into scored discs is a miserable experience and liable to leave rings that have been overheated and rings that haven't bedded in. Also note that different types of pad have different bedding-in procedures and it's important to use the correct procedure for the pads being used.

[Clevercurves]

discs still on 20% of original pad wear. cracks appeared. is this normal or a concern?
car is a 2006 cls55 amg with the performance pack brakes. used once at vmax (180mph+)

[Clevercurves]

discs still on 20% of original pad wear. cracks appeared. is this normal or a concern?
car is a 2006 cls55 amg with the performance pack brakes. used once at vmax (180mph+)

[stevieturbo]

Wouldn't be too worried about them yet unless you're about to do some heavy track use.

For daily use, still a lot left in them

[E-bmw]

^^^^ Wot 'e said.

For normal driving they will be fine, if maybe slightly noisier.

Just keep an eye on them as under heavy use they may get a lot worse quite quickly.

[GreenV8S]

That just shows they've been used hard at least once.

More cracks equals weaker disks and they will eventually fail if left long enough, but if you keep an eye on them I expect you'll get scared enough to replace them before that happens.

Do yourself a favour and get plain / grooved disks next time. They don't look as motorsporty but work better and are far less prone to stress cracks.

[E-bmw]

GreenV8S said:

Do yourself a favour and get plain / grooved disks next time. They don't look as motorsporty but work better and are far less prone to stress cracks.

^^^^Wot 'e said.

[The Wookie]

Any cracks from the outer diameter replace immediately

Any cracks on the inner diameter, keep an eye on them for growth, replace if they’re longer than 5 or 6mm

Any cracks from the holes, keep an eye on them and replace when they start joining up with cracks from adjacent holes

As said, if you’re going to use them hard regularly then make sure to replace with grooved discs

[TonyRPH]

I zoomed in on the disc posted above and there seems to be a fair amount of cracking around the middle/inner holes?

Is that really ok? (just for my own info)

[bmwmike]

Those discs look well past it to me, i'd be changing them with new pads.

[stevieturbo]

TonyRPH said:

I zoomed in on the disc posted above and there seems to be a fair amount of cracking around the middle/inner holes?

Is that really ok? (just for my own info)

They'll have been like it for a few thousand miles, and for another few thousand miles.

If you drive like a normal person, they are fine for another few thousand miles