I've seen quite a few others like this. Is it bad? Dangerous? Normal?

From my very limited knowledge of mechanics/materials, stress fractures are quite bad. It can very easily lead to destroyed disc. Im sure a more informed person will come along and explain more

cracks dont look that bad but your pads must be harsh as the discs are badly scored..

This is why a lot of people don't recommend drilled discs.

Drilling weakens the structure of the metal, giving a much higher probability of a crack forming, especially when driven hard.

Better of with grooved as drilled crack.

Just get a decent flat disc and some better pads, no need for drilled groved for road use.

Look at how the pad dust has filled in the drill holes, defeats the object of drilling them

I've got cheap mtec drilled and grooved discs on the front and ebc drilled and grooved on the back both with ferrodo pads and neither have cracked at all.

i know plenty been said negative wise bout drilled discs but mercedes use them on a lot of their hi performance cars.

i know plenty been said negative wise bout drilled discs but mercedes use them on a lot of their hi performance cars.

This is very true War, but it is merc and they will use higher quality metals and the higer perfomance cars are designed for the drilled discs.... are they not?

Just as Rossy does not say what brand the discs are

Edited 13 July, 201114 yr by vRSsunroof

i know plenty been said negative wise bout drilled discs but mercedes use them on a lot of their hi performance cars.

Are they drilled, or cast with the holes though?

not sure...porsche use drilled as do others..

ive got the mtec drilled ones as well no probs so far been on about a year (look cool as ****)

Those cracks are absolutely nothing to worry about, keep an eye on them however for signs of the cracks enlarging, if you have any cracks which look like they might meet another adjacent crack you should renew the discs and pads as a set.

Warwick, yes, Porsche and Mercedes do you use drilled discs, but they are ceramic composite discs rather than cast iron, check out the cost of replacement parts for some idea of the difference between a Skoda with cosmetically enhanced (drilled) discs and real high performance equipment.

Personally I only use grooved discs on a road car since the grooves genuinely enhance braking performance, drilling a few holes in an otherwise standard disc isn't going to affect unsprung weight enough (which is the only reason for drilling) to improve anything.

If you are changing your discs, then these are the ones you want.

http://briskoda.net/forums/topic/8303-ebc-brakes/

I know the thread is from 2004, but I don't think the disc design has changed since then. Those ones are grooved and dimpled, not drilled.

Those cracks are absolutely nothing to worry about, keep an eye on them however for signs of the cracks enlarging, if you have any cracks which look like they might meet another adjacent crack you should renew the discs and pads as a set.

Ah, you again. Care to enlighten us with awesome links again to make your point? Make sure to read the material you post this time though.

Those cracks are absolutely nothing to worry about, keep an eye on them however for signs of the cracks enlarging, if you have any cracks which look like they might meet another adjacent crack you should renew the discs and pads as a set.

Warwick, yes, Porsche and Mercedes do you use drilled discs, but they are ceramic composite discs rather than cast iron, check out the cost of replacement parts for some idea of the difference between a Skoda with cosmetically enhanced (drilled) discs and real high performance equipment.

Personally I only use grooved discs on a road car since the grooves genuinely enhance braking performance, drilling a few holes in an otherwise standard disc isn't going to affect unsprung weight enough (which is the only reason for drilling) to improve anything.

fairly sure my boss' C180 K had drilled discs on the front, doubt they were any kind of ceramic composite and it was a company car so only ever got serviced at a main dealer - unlikely it got anything other than OEM parts fitted

Are they drilled, or cast with the holes though?

This is the key question.

:peek: :think: :wonder:

This is why a lot of people don't recommend drilled discs.

Drilling weakens the structure of the metal, giving a much higher probability of a crack forming, especially when driven hard.

+1

Metal also often don't given any warning of failure. It will simply snap. Not something you want at 70 as the shattering disc may take out suspension or your alloy.

I've had a disc shatter on a van on the m25 on rush hour on a 4 lane section. It but the brake line and broke the steel wheel. A brown trousers moment I can assure you, and the van was serviced only days before.

Any signs of stress fractures in a disc, means they should be replaced. Top end cars excluded, drilled and grooved discs were initially designed for pro track use, were the discs get replaced every few races. Any drilled or machined hole in a component that gets as hot as brakes, is just inviting stress fractures.

Are they drilled, or cast with the holes though?

Cast. They're really drilled effect as the act of drilling is likely to create fatigue and couldnt be done on a commercial scale to meet global demand.

*Ding*

The cheapest is taking a solid or slotted rotor and cross drilling holes in it. Some drawbacks to this are the fact that the heat from drilling process changes the hardness of the metal right at the hole and makes the rotor harder and more brittle inside of the hole. The holes can develop stress fractures around the holes due to the different temperatures and hardness of the rotor face and the surface of the hole. (the face heats up, and the hole doesn’t because there is no pad contact). This can cause the metal to expand and contract at different rates, resulting in stress fractures and cracked rotors.

A way to minimize this is to chamfer the holes. This is similar to “countersinking” a screw hole. The edge of each hole is expanded right at the face of the rotor, creating a “ring” of non-contact area on the face of the rotor. This is a sort of temperature transition zone that transitions the higher heat of the face to the lower temperature of the surface inside the hole.

The ideal way to make a “drilled” rotor is the way Porsche does it. The expensive way. Cast the holes in when the rotor is made. This eliminates the hardness/brittle problem because the rotor is created using a single process, resulting in a uniform hardness consistency throughout the metal. These of course can cost up to $500+ per rotor.

Source - http://www.xtpusa.com/faqs/brakes

Doesn't sound too far-fetched..

*Ding*

The cheapest is taking a solid or slotted rotor and cross drilling holes in it. Some drawbacks to this are the fact that the heat from drilling process changes the hardness of the metal right at the hole and makes the rotor harder and more brittle inside of the hole. The holes can develop stress fractures around the holes due to the different temperatures and hardness of the rotor face and the surface of the hole. (the face heats up, and the hole doesn’t because there is no pad contact). This can cause the metal to expand and contract at different rates, resulting in stress fractures and cracked rotors.

A way to minimize this is to chamfer the holes. This is similar to “countersinking” a screw hole. The edge of each hole is expanded right at the face of the rotor, creating a “ring” of non-contact area on the face of the rotor. This is a sort of temperature transition zone that transitions the higher heat of the face to the lower temperature of the surface inside the hole.

The ideal way to make a “drilled” rotor is the way Porsche does it. The expensive way. Cast the holes in when the rotor is made. This eliminates the hardness/brittle problem because the rotor is created using a single process, resulting in a uniform hardness consistency throughout the metal. These of course can cost up to $500+ per rotor.

Source - http://www.xtpusa.com/faqs/brakes

Doesn't sound too far-fetched..

Sounds about right...but the main reason that I heard (could also be as well as the above) was that on expensive discs that are drilled after casting was that the holes are drilled and spaced correctly with the internal vanes on vented discs...on cheaper drilled and vented discs the spacing is to close to the internal vanes..thus causing even more problems.

If you read mags like EVO etc. you will find that even Lambo's, Porsche etc with drilled discs have this problem. Evo mag run very expensive cars in their fleet and some of the contributing writers own "dream car" hire companies....drilled steel/iron discs are their worst nightmare!!!! New carbon/ceramic types are much better!

The way around this is to only partally drill the hole eg "dimple" it as per EBC 3G discs which I have (also grooved)...no problem!!!!

Sorry if this thread is inappropriate like all the rest of my life is...

Sorry if this thread is inappropriate like all the rest of my life is...

Lol