Your Opinions

[Don Dada]

My rotors have been like this for a while now inside and outside

These are OEM that were slotted and i use Mintex pads strictly street driving with occasional hard breaking.

Anyone rotors doing the same? and could this be because of the pads?

Ooh... this is in a 1450kg C35 laurel with 19" chromes and R33 brakes all around.

Any feed back would be appreciated.

[2LV8ETR]

My rotors have been like this for a while now inside and outside

These are OEM that were slotted and i use Mintex pads strictly street driving with occasional hard breaking.

Anyone rotors doing the same? and could this be because of the pads?

Ooh... this is in a 1450kg C35 laurel with 19" chromes and R33 brakes all around.

Any feed back would be appreciated.

Brake rotors are usually your basic gray crummy cast iron. Rotors for production applications are almost always sand cast, and do have some built in stresses from uneven cooling- the automakers really are primarily focussed on cost, so the quality of these guys is pretty marginal. They are usually overweight to compensate. They have sand inclusions, bubbles, and porosity. They almost always exhibit quite a lot of core shift, which leads not only to balance problems but also to premature warping (due to one working surface heating more quickly than the other). This is worsened in brake designs where the pads are asymmetrical, so the heat loads differ on the two faces of the rotor.

The aftermarket rotors available for racing applications (Brembo, and other vendors) are usually a better class of materials, some of the ASTM high temperature cast irons are the norm. The best of these are usually vacuum degassed to eliminate porosity that can lead to cracking. These are also designed to run on a separate hub adapter (the hat), which eliminates one major source of stresses and also cuts the heat transfer to the hub and wheel bearings.

The best way to keep rotors alive is to keep them cool. Massive quantities of air ducted right into the rotor eye, and kept there with a blanking plate that more or less fills the eye, is the ideal. The vanes will pump the air through the rotor and help with the airflow. Wheels that help exhaust the hot air outboard help as well. Keeping the rotors cool will also pay amazing benefits in pad life. My finding has been that pad wear, even with carbon race pads, goes up exponentially once rotor temps reach about 400C.

The next best way to keep rotors alive is to heat-cycle them very gently. If you're on the street, and intend on some heavy driving, heat them gradually. An absolutely guaranteed rotor killer is to do a max-effort high speed threshold braking maneuver on cold rotors. Cast iron's thermal conductivity is really pretty poor so the surface will go up to insane temps, with the vanes between the faces still dead cold. The thermal stresses are immense, and the stock low-quality casting won't take it. Surface heat checking is the best you can hope for! I refer to this kind of stop as the rotor giving its life to save yours.

Drilled and milled rotors are great, if done right. Drilling can aid in cooling, and aids in fade control by providing a place for the high temperature gases to escape to, but can lead to warping and cracking much earlier if the car is seriously under-braked. The holes need to be drilled and chamfered in such a way as to avoid creating new stress raisers, and I have never figured out how to do that very well. Milling consists of cutting a shallow groove in the rotor face, also to provide a gas escape. I like this better, since it creates less in the way of a stress raiser if a radiused groove is used. IMHO, for an under-braked car on stock rotors, drilling or milling is a waste, you'll be throwing them away very soon, and the removal of metal is almost certain to make that sooner.

Hope this helps

[Don Dada]

Very informative read!

The thing is i don't think my rotors are warped. I don't get any pulsing on the pedal or shimming on the steering wheel when i apply the brakes.

Anyone?!?

[SkyHi_33]

As Allen explained, the stock (or OEM) rotors are made of fairly poor materials therefore by milling in to them (slotting them) you are reducing the life of the rotor and adding stress to them. When rotors stress they start cracking which is what you're experiencing here.

I would suggest you save up a bit and buy yourself a set of RDA slotted rotors or better yet higher spec slotted rotors if you got the $$ to blow.

RDA slotted rotors have been proven to work really well on skylines when matched with a decent pad and last a long time with very even wear.

Fronts for an r33 (im assuming the r33 brakes mentioned have r33 rotors?) are around $440 for a pair

Rears are somewhere around $200

So you're looking at $640ish for a good set of rotors that will last you ages with normal city driving and a bit of hard braking (hell, my old ones lasted a year and a half of track and spirited driving abuse day in day out)

I suggest you save up and replace those as I cant see them lasting too much longer, not a great feeling when they completely crack.

[Don Dada]

so u guys sayin that they WILL eventually crack? I've heard stories about R33 GTR rotors shattering, is this something i have to be aware of?

I know pads has alot to do with rotor life, are the mintex pads responsible for this?.... probably i need to use a less harsh pad?

Thanks again.

[djr81]

You need to understand the difference between small surface cracks on the faces of the rotor & more substantive cracks which are on the edges of the rotor.

The first of these are common on rotors used for track days etc. The do not necessarilly represent a problem.

The second type of cracks do represent a problem & are grounds for replacing the rotors. Any crack radiating to the outside of the rotor will, eventually, cause it to fail.

The photos aren't very clear but you definately have the former & probably the latter. The crack at about half past two looks pretty terminal.

If you have caused this sort of an issue driving on the roads you need to have a good long think about what you are doing.

The things I would question are as follows:

Are the rotors within their wear limits?

Are the stone guards still in place (I think they are) & if so are they preventing the rotor from processing cooling air and causing the outside of the rotor to cool whilst leaving the inside hot. This will show up in pad wear if the inside is well worn & the outside not then you have this problem. Differential heating/cooling from inside to outside causes cracking.

Do you allow the things to warm & cool properly ie slowly.

In anycase I would be replacing the rotors & thinking about how to get some cooling air to tthem.

Edited March 11, 2009 by djr81

[Don Dada]

Not sure the rotors are within spec but only had them skimmed once the same time i had them slotted.

Yes stone guards are still in place and strangely the outer pad is slightly more worn than the inner,and it is both the inner and outer surfaces of the rotor has the same cracks.

I have only a 15 min high way drive to work so i warm up the pads the best i can probably within the first 5 or so,but cool down time may be about 2 mins. only if i was hard on the brakes.... and hard meaning probably just one hard stop from "about" 160kms

Trust me.... a C35 is not the easiest thing to stop

Was planning on getting some slotted DBA 4000 GTR rotors and caliper extenders, as DBA is the ONLY rotor available here(Caribbean) but after what u guys went thru i'm having some serious second thoughts!!!

[badhairdave]

i think that mark at about half past 2 is just some surface staining from water or something.

Otherwise you just have some crazing.

I've been told that you are ok up to about 1/3 of the swept area, which you look to be around.

Mine are actually a bit worse than yours, or at least they were before the last track day. I really need to have a look at them before the next one...

[Don Dada]

You need to understand the difference between small surface cracks on the faces of the rotor & more substantive cracks which are on the edges of the rotor.

The first of these are common on rotors used for track days etc. The do not necessarilly represent a problem.

The second type of cracks do represent a problem & are grounds for replacing the rotors. Any crack radiating to the outside of the rotor will, eventually, cause it to fail.

The photos aren't very clear but you definately have the former & probably the latter. The crack at about half past two looks pretty terminal.

If you have caused this sort of an issue driving on the roads you need to have a good long think about what you are doing.

The things I would question are as follows:

Are the rotors within their wear limits?

Are the stone guards still in place (I think they are) & if so are they preventing the rotor from processing cooling air and causing the outside of the rotor to cool whilst leaving the inside hot. This will show up in pad wear if the inside is well worn & the outside not then you have this problem. Differential heating/cooling from inside to outside causes cracking.

Do you allow the things to warm & cool properly ie slowly.

In anycase I would be replacing the rotors & thinking about how to get some cooling air to tthem.

Definitely looks like just surface cracks just in the middle of the contact area... not radiating to the outer edge of the disc.

Checked the pads and there are some small chunks missing in the middle of the pad also

The half past 2 make is a water stain

Scoring some R33 gtr brembo so i just have to fit them up an see if they clear my rims...if not i'll have to go with standard GTR 4000 DBAs and caliper extenders.

Thanks.