What Causes Rotors To Crack?

[Abo Bob]

I've cracked a rear DB4000. Using Ferrodo DS2500 pads.

I was at the track and the only thing apart from running it around there that I can think of as relevant is the fact that I left the track at some speed then sat in the kitty litter for 10 minutes.

[djr81]

I've cracked a rear DB4000. Using Ferrodo DS2500 pads.

I was at the track and the only thing apart from running it around there that I can think of as relevant is the fact that I left the track at some speed then sat in the kitty litter for 10 minutes.

Welcome to my world. My rear rotors cracked on my GT-R. I was only (At the time) using Bendix Ultimates on the rears & was always careful to let the rotors cool properly.

Did the cracks you have in your rotors start from the small return grooves on the outer circumference?

IMHO, the best bet is not to use these rotors......

[Abo Bob]

Nah mine cracked here.

[djr81]

Do you still have the rear stone guards fitted to your car?

[Abo Bob]

Yup.

[mad082]

i'd also be looking at possibly a sticky piston.

[MrStabby]

I've cracked a rear DB4000. Using Ferrodo DS2500 pads.

Here's some wild speculation that someone will probably shoot down as BS, but i read somewhere that the thermal conductivity of the pad is an important property in brake operation as it helps even out the temperature on pad and rotor. After frying my front rotors (just warped, no cracks and a blue tinge on the outer of the mating surface) with DS2500's i'm speculating that perhaps they dont conduct heat well and therefore are tougher on rotors than other pads. The outer edge of the rotor gets a lot hotter than the inside edge and the difference in thermal expansion cracks the rotor.

About 4000s - http://www.dba.com.au/DBA4000series_specs.pdf says "motorsport applications and premium street performance" for the slotted (not drilled) rotors, but in the box comes a note "warrantee of DBA product is void when used in any form or motorsport" - tossers! Since they've said motorsport applications, i can see why you cant return them based on the Fair Trading law's requirement that goods are 'fit for purpose'. That law overrules anything the manufacturer says.

Another thing about 4000s - the vane design appears to have been make to look "wikkid" rather than provide optimal cooling...but maybe i'm just bitchy.

Rgs,

Kot

[Roy]

Other then warming up and coolign them down...looks to be a metallurgy thing.

My old DBA 4000s lasted for years, in fact they are still going on a friends car. The 4000s i have now have the same slots as in djr81's photos...and i honestly dont hold out much faith that they will last as well as my old set (Old set had different slots arrangement)

[Beer Baron]

yes vane design i think is another point. I would much prefer a nice, conventional curved vanve rotor to the k-paw DBA style, but finding one for a good price is not easy.

[tacker]

Wonder if the K paw idea is causing these cracks?

If you look down the inside of the rotor you can see a straight path inbetween the K paw sections that joins both sides of the rotor together. Not sure if it would cause the problem but if you add the heat that a good track session will generate this just has to be the weakest section.

If you look at a curved vain type design the vain all over lap so there is none of these straight line oportunites, I did in the end crack my RDA k paw rotors, but only after the worse possible treatment, and they cracked in the straight line area right between any of the k paw connections.

[predator]

They generally recommend you have a cool down lap to help disipate air through the rotors, and naturally cool them.. instead, you quite *possibly* could have been slamming the hell out of the brakes at the last second and then came to a complete stop and suddenly cooler. So just metal fatigue?

[Angus Smart]

haha

my front rotors have 100000 hairline cracks in them. they going to go bang soon so i gotta do something about them

i have f50's on the front with some squeeky ass pads!

[MrStabby]

my front rotors have 100000 hairline cracks in them. they going to go bang soon so i gotta do something about them

Try getting the cracks machined out. Even though the material will be thinner, it will be stronger as the stress will be spread out across the surface rather than being concentrated at the head of the crack. That's the theory at least.. (and why slots are curved - no corners for stress to concentrate in).

Edit: Here's what DBA has to say about rotor longetivity http://www.dba.com.au/tech/major_considerations.asp

Rgs,

Kot

Edited October 23, 2006 by MrKotter

[scathing]

Good old DBA's. I know quite a few people that have cracked DBA rotors.

I did that the above at EC. I came off a pretty heavy session (playing chase car to a MX5) and forgot to do a cool-down lap before bringing it into the pits.

That said, I think it was cracked when I was driving down pit lane to my garage (had a weird pulsing coming through the brake pedal), so parking it without a cool-down lap may not be the cause.

[tacker]

Nope always do 2 cool down laps without touch brakes if i can help it, set the stop watch at the time we leave the garage and start the cool down laps at 15 minutes.

And i have 2 ducts to each front wheel so i know they are getting plenty of air to cool them, i didnt have any brake fade and i didnt feel the pulse from the crack until the next day after getting it home. Still it would have to be stronger with the curved vain design as it would have to crack the vain as well as the rotor which is not the case with the K paw design.

[r33_racer]

so no one has heard of the dont leave your car in the same spot for longer then a few mins after coming off the track after a race. Need to move the car a few inches forward or back so the heat isnt concentrating on the same spot of the rotor. Id say you came off possibly after breaking or breaking while coming off and then sat in the litter for however long with the breaks stuck on the same spot and it was too much concentrated heat.

[Roy]

Sure, leaving the caliper pistons and pad parked in the same spot of the rotor when they are glowing isnt good. It will liekly warp a rotor, but i cant see it cracking them...as its a localised thing.

Crackign a rotor suggests a metallurgical flaw, or thermal shock and cyclic loads. So it would be more likely the fact that you have stone cold rotors and you roick up to the first 6 corners standing on them rather then bringing them up to temp geradually on your warm up lap as your tyres come into their working temps/pressure.

Likewise, if you come and park it glowing red/smoking then the parked pad may cause the rotor to warp, but crack? Im not sure. Perhaps the differential expansion in the rotor cause the crack, as differential expansion/contraction are a classic for it???

[Abo Bob]

Well I do proper warm ups and proper cool downs.

I think the DS2500's seem to heat the rotors more. I've had people say my front rotors were glowing hot but with 2 track days on these pads and rotors, why aren't the front ones cracked? They would surely get a hell of a lot hotter.

[djr81]

I don't see how you can blame the pads.

Firstly, the metal in the rotor will be massively more conductive than the pad material (Any pad material).

Secondly the amount of heat input into the rotor will be defined by how hard you are braking, not by the pad characteristic.

Lastly, we are talking about rear rotors here. Mine don't usually get hot enough to flash off the high temp thermo paint (The third of the three colours). But they still crack.

And yeah, the DBA (lack of) warranty is piss week. The things are designed for track work but as soon as you get within 100 miles of a circuit the warranty is void. That is not that suprising, but it is still rubbish. I have had to bin rotors with no more than a few tenths of a mm wear. Which pisses me off no end.

Edited October 24, 2006 by djr81

[MrStabby]

I don't see how you can blame the pads.

Firstly, the metal in the rotor will be massively more conductive than the pad material (Any pad material).

Cant argue with that.

Secondly the amount of heat input into the rotor will be defined by how hard you are braking, not by the pad characteristic.

If you look at it from an energy perspective, the pad can either transfer the energy into heat or new surface area - ie by wearing out either the rotor or itself. My porsche was roughly equivant to my skyline and never had any brake issues after getting decent fluid and EBC Greens. The GTR is struggling, so next thing i'm trying is the 324mm UAS rotor kit and i'll run some ducting as well. If that doesnt work i'll try the Greens on it.

And yeah, the DBA (lack of) warranty is piss week. The things are designed for track work but as soon as you get within 100 miles of a circuit the warranty is void. That is not that suprising, but it is still rubbish. I have had to bin rotors with no more than a few tenths of a mm wear. Which pisses me off no end.

So what do you reakon is the answer? RDA? Nissan? (is nissan exy?) Upgrade?

Rgs,

Kot