# strange scoring/cracks on rear rotors



## flat6turboGT1 (Sep 11, 2004)

I checked out the rear brakes on the 20th today because I've been hearing this "sh-sh-sh-sh" noise from the rear that I suspected to be warped rotors brushing the pads. When I got the wheels off though I noticed these strange cracks/scoring in the rotors that are all in trapezoidal orientation. If I scrape across them with my fingernail I i can feel it snag, so I'm assuming this is what is causing the noise (I don't see any visible warpage when I turn the rotor and watch it in relation to the pad). Below are some pics. Any idea what would cause this? I'm wondering if it has anything to do with the parking brake, but i'm pretty sure the contact patch of the pad on the rotor is actually square since the edges are tapered up so who knows. Any ideas/suggestions would be greatly appreciated. Obviously everything needs to be replaced but I'm more interested in what would cause this so it doesn't happen again.
This is already the second set of rear rotors that have been on the car. When I bought the car there was crazy radial scoring on all four rotors (you can see the same thing going on in these pics in addition to what I am talking about) so I replaced all rotors and pads after bringing it home. Then about a year later the rears were scored like crazy already, so again replaced rotors and pads and also cleaned and lubricated the slide on both rear calipers. And now we're at about a year since I did that and am having this issue. 
Anyway, here are the pics:
























_Modified by flat6turboGT1 at 2:20 PM 10-11-2008_


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## germancarnut51 (Mar 23, 2008)

*Re: strange scoring/cracks on rear rotors (flat6turboGT1)*

Where are you buying your rotors? What brand are they? What brand of brake pads are you buying?
The economical/cheap brake rotors are MIM (powdered metal injection molded) A metal powder is poured into a mold, and subjected to heat and pressure to metal the metal into the finished object. I have serious doubts about the use of this type of material for some purposes.
The rotor in the photos show severe wear damage, and I never recommend turning rotors any more. Modern rotors are only spec'd with a few mm of wear thickness, and turning will take them below spec. 
I would guess that you have been getting cheap MIM rotors, and the rotors are failing because heat from the brake pads being transferred to the rotors when they are hot is causing metal fatigue.
The marks on your rotor are from the brake pads. Looks like you have been parking the car with the brakes still hot. You could try driving around easy for 5 minutes without using the brakes before parking to cool the brakes down.
Some brake pads hold heat more than others, and some brake brakes seem to generate more heat than others, and the way that some people drive is harder on brakes than other drivers.
Could be the combination of the rotors you are buying, with the brake pads you are using, and your driving style are not compatible.


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## flat6turboGT1 (Sep 11, 2004)

*Re: strange scoring/cracks on rear rotors (germancarnut51)*

Each time I've bought Zimmermann rotors, under the impression that they were a nice variation of the OEM rotor. Pads were Pagids each time. I've had a few people suggest that the pads might be too aggressive for that particular rotor, but I didn't have the angular scoring the first time around with this combo. 
I wouldn't have considered turning the rotors, for the very reasons you specified. Just trying to decide which direction to go so this doesn't happen again. Would it be safe to assume that ordering "OEM" rotors and pads from the stealership would guarantee me a better match between the pads/rotors? ...or anyone have any recommendations?


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## HilF (Jan 10, 2004)

*Re: strange scoring/cracks on rear rotors (flat6turboGT1)*

as posted by gcn51, you're probably parking with hot rotors and pads.
i've used zimermans without issues like this, so either pads (which pagids are they?) or heat.


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## flat6turboGT1 (Sep 11, 2004)

*Re: strange scoring/cracks on rear rotors (white_r!ce)*


_Quote, originally posted by *white_r!ce* »_as posted by gcn51, you're probably parking with hot rotors and pads.
i've used zimermans without issues like this, so either pads (which pagids are they?) or heat.

don't know the specifics of the pad. It's supposed to be just an OEM replacement pad, as I didn't have any desire to go with anything more aggressive at the time.


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## VWn00b (Mar 4, 2005)

*Re: strange scoring/cracks on rear rotors (flat6turboGT1)*

Those don't look like cracks at all, and with the way pads are shaped, I'm betting it has to do something related to that.
They look more like a digging mark, that is into the rotor face.


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## walkingfool (Mar 24, 2008)

*Re: strange scoring/cracks on rear rotors (flat6turboGT1)*

This is an interesting issue. Here's my two cents worth.
The radial scoring is normal wear on a rotor. I personally don't consider it a problem unless the rotors are not running true. You might try OEM pads and see if that helps.
The trapezoidal marks, I agree with others, and as you suspected, are due to clamping on the parking brake while everything is hot. As it cools unevenly, it warps slightly. I have three suggestions (and they all seem a little stupid in the first place, if you can't just drive and park, but ...here goes)
Can you finish a drive with a cooldown period? 
Or can you park in a place where you can leave the parking brake off until the brakes cool down? 
Or maybe you can put some ducting in place to get more cool air on the brakes while you're still in motion. That way, they can withstand putting on the parking brake.
And, let us all know how things turn out.


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