Brake rotor wear
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This is a discussion on Brake rotor wear within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Hi all! I have a '02 WRX wagon with about 7500 miles on it. I am noticing an unusual amount ...

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    Brake rotor wear

    Hi all!

    I have a '02 WRX wagon with about 7500 miles on it.
    I am noticing an unusual amount of wear on the the L. side brake rotor, outside only. That one face is developing some pretty significant circumfrential grooves; I'd estimate .02 -.03 inch deep.
    Sure, I drive the car hard, but all other rotor surfaces are nice and smooth. Has anyone else noticed unusual wear patterns on their WRXes? D'ya suppose this is worth a visit to the dealership? I am tempted to insist on a new rotor and set of pads, but I thought I'd run this by "the group" first. TIA.

    ByeBye! S.
    Steve Jernigan KG0MB
    Laboratory Manager
    Microelectronics Research
    University of Colorado
    (719) 262-3101

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    Registered User PlatinumWRX's Avatar
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    Both of my front rotors are wearing with horrible grooves. I will be getting my rotors cut and installing Endless NA-S Brake pads ASAP.

    -Jim

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    Are these grooves deeper or more pronounced than the grooves on the rotors when they are new? All four of my rotors had grooves on them when I bought my car with only 3 miles on it. All other new WRXes that I looked at also had grooved rotors. This topic has also been discussed multiple times on I-Club. I'm assuming that what you are talking about are definately wear marks rather than the "normal" grooves.

    Dale

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    Hi Dale, all!

    You asked:

    >Are these grooves deeper or more pronounced than the grooves on the rotors when they are new? All four of my rotors had grooves on them when I bought my car with only 3 miles on it. All other new WRXes that I looked at also had grooved rotors. This topic has also been discussed multiple times on I-Club. I'm assuming that what you are talking about are definately wear marks rather than the "normal" grooves.

    Yours CAME with groves?!? That ain't right. When disc brakes are happy the rotors are polished relatively smooth, grooves usually indicate severely worn pads, funky pads with uneven hardness, a sticky "floating" caliper, or sometimes "hard" spots on the rotor. Never heard of "grooved" rotors being considered normal; drilled, slotted (radially), OK, but I sure can't see how circumferential grooves could do anything besides hurt brake performance. Why d'ya think they "turn" your rotors with a major brake service? To get a nice smooth surface for the new pads to seat against!
    Anyway, my car's rotors were all relatively smooth when new (11 miles on the ticker), and as mentioned, except for the one surface they still are. That left outside face is rapidly developing wear groves however; which tells me something isn't working as intended.
    I'm gonna pull the L. side caliper tomorrow and have a look at the pads and rotor. I might even get ambitious and have a friend perform a hardness test on the rotor. Then I'm going to politely request that Subaru provide me with a replacement set; if they continue wearing at the present rate, I'll be needing to buy new hardware right about the time the warranty expires. Nice feature, that.
    FWIW, I have an 84 GL wagon with ~300K miles on it that was still on the original rotors until I got it stuck (really stuck ;-) in a mud bog last summer and destroyed one side . . .
    Guess I'll go check out the discussion on i-club while I'm at it.
    Steve Jernigan KG0MB
    Laboratory Manager
    Microelectronics Research
    University of Colorado
    (719) 262-3101

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    My WRX also, like iceNine , had grooves on the rotors when I bought it. I looked at others on the lot and they all looked grooved as well. They were all very slight, so I asked the dealer what he thought about it and he told me that he hasn't seen one yet that didn't have the grooves. I do know that it has not hindered the performance during hard breaking though. In your case labman...I would definitely give your local dealer a call or show it to them.

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    Moderator GV27's Avatar
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    There's a Subaru tech bulletin on this. The grooves are normal and part of wearing the initial coating off the rotors. Can't find my link to that site right now though!

    New pads will conform to the grooved rotor just fine. The grooves don't hurt a thing. Heck, they actually increase the surface area. They turn them for two reasons: 1 - to take out slight warping, 2 - to add another item to the bill. High performance pad manufacturers actually recommend bedding new pads on old rotors and vice-versa.
    Last edited by GV27; 07-15-2002 at 11:48 AM.
    "Inasmuch as ye have done it to one of the least of these my brethren, ye have done it to me." -Jesus

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    Registered User PlatinumWRX's Avatar
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    That is correct. I will be breaking in my Endless pads on the stock rotors before switching to my DBA Slotted Rotors.

    -Jim

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    Banned dark_rex's Avatar
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    rotors are turned to create a less smooth polished surface, to create more surface area and a rougher rotor for more friction.

    wear generally smooths out the rotors, making the pad less effective, as it just heats up as it slides across the surface rather than trading it's material for stopping power.

    it's not just to take your money.

    dR

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    Moderator GV27's Avatar
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    That's the first time I've heard that. But anyway, that's the opposite of what these guys are saying. They want to turn 'em because they don't think they're smooth enough. So I guess we agree. They don't need them turned. But mechanics (not all, but a lot) will point to the grooved rotors and say "see how they're all rough? They need to be turned at a cost of $X". Rotors often get turned for the wrong reasons.
    "Inasmuch as ye have done it to one of the least of these my brethren, ye have done it to me." -Jesus

    1990 Alfa Romeo Spider Veloce
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    Registered User Nexus6's Avatar
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    This is what happens when you brake hard frequently. Especially during the 1st 1500 miles. They need to be broken in too. Mine are smooth...
    La Fee Verte
    Subaru 2002 Impreza WRX Sedan

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    Hi All!

    GV27 sez:

    >There's a Subaru tech bulletin on this. The grooves are normal and part of wearing the initial coating off the rotors. Can't find my link to that site right now though!

    Huh? I've never heard of any sort of coating on a rotor. I always go to great lengths to be sure rotors are squeaky-clean when installing new pads to avoid contaminating the pad material! Sounds like BS to me.

    >New pads will conform to the grooved rotor just fine.

    Sure they will. And the grooves on the rotor will polish down a bit too. At the expense of some percentage of the pad (and rotor) lifetime.

    >The grooves don't hurt a thing.

    Other than being an indicator of uneven wear, probably not. Not much anyway.

    >Heck, they actually increase the surface area.

    As far as "absolute" surface area, yep, a textured surface has more area than a smooth one. Of course, your pads aren't applying much pressure to the "sides" of the grooves. I'd argue that significant grooving actually DECREASES the "effective" surface area of a brake rotor.

    >They turn them for two reasons: 1 - to take out slight warping, 2 - to add another item to the bill. High performance pad manufacturers actually recommend bedding new pads on old rotors and vice-versa.

    If you break-in your pads on grooved rotors, the groove pattern will transfer to the pad. If you then replace the rotor, in all likelihood the pattern will also transfer to the new rotor. At the very least you are going to experience diminished brake performance until the pads/rotor wear enough to re-establish intimate contact. I can't imagine why you'd want to do such a thing. Sure, I've plopped new pads on a car with grooved rotors, mostly 'cause I was too lazy to pull the rotor and turn it, but that is NOT the recommended procedure. If someone is telling you that it is, I'd be pretty suspicious, ie that Subaru tech bulletin referenced above.
    In any event, grooves appearing on rotors after 50K or 70K miles would be fairly typical. Significant grooves appearing after only 7K miles, and only on the one rotor face, would seem to indicate a problem.
    And finally, someone e-mailed me suggesting that it was merely a "cosmetic" problem. Yep, it's ugly all right.
    Tell ya what; next time you go to the races, wander thru the pits and check out the brake rotors on the cars. D'ya see anyone running "grooved" rotors? NO?!? Didn't think so. If it gave even the slightest edge, tho, you can bet everyone would have them, and you could even buy "trick" pre-grooved rotors with matching pads! Ever see 'em advertised in the racing mags? Again, I don't think so.
    Or maybe there is a performance niche market no one has saturated yet . . . a real business opportunity for some enterprising soul, right up there with the electronic superchargers someone is marketing on ebay! WooHoo, gotta have me one :-P

    ByeBye! S.
    Steve Jernigan KG0MB
    Laboratory Manager
    Microelectronics Research
    University of Colorado
    (719) 262-3101

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    Moderator GV27's Avatar
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    Well alrighty then. Ummm.....the coating is a metal coating, not something that washes/disolves off. The coating keeps the rotors from discoloring while in transit and storage. The Subaru coating is called DaChromet. Its very common. Ever see rotors that are shiny gold? Coating. Here's a link to a brake product catalog. Both the Powerslot and Stillen rotors are coated.

    http://www.spswebpage.com/products/brakes.html

    The reason you don't see these at the track (and the grooving associated with these coming off) is because they hamper optimal braking. So racers use plain cast-iron. They look nice and shiny right off the track, but try leaving the car out in a hard rain. Rust city.

    Otherwise, thanks for the flame. I was simply relaying the information provided by the manufacturers of these products. Subaru does indeed have a tech bulletin for this exact discussion. Brake pad manufacturers do recomend bedding pads on used rotors. If you don't believe them, well that's your issue. I believe the bulletin was in the Fall 2001 edition of the newsletter that Subaru sends out to regional service managers. Unfortunately I can't find the link to it anymore, and I'm not a SUbaru Regional Service Manager.

    And dude, for your own benefit - I'd remove your phone number from your signature before you start flaming people. Heck, even if you aren't going to flame, it's just not a good idea. Lots of nuts on the Internet. I wouldn't put your work address there either. I frequently work on the CU campus at the Engineering Center and know right where your lab is. I'm not a nut so you don't have to worry about me coming down there because you flamed me on the Internet....but if I was you could have a problem!
    Last edited by GV27; 07-16-2002 at 12:30 PM.
    "Inasmuch as ye have done it to one of the least of these my brethren, ye have done it to me." -Jesus

    1990 Alfa Romeo Spider Veloce
    1992 Toyota 4Runner SR5 3.Slow
    1993 Honda CBR600F2
    2002 WRX SportWagon *sold*

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    Hi again, GV27, All!

    You wrote:

    >Otherwise, thanks for the flame.

    Gee. I didn't mean to inflame; sorry if I offended you . . . but this IS a discussion group after all. I did visit the web page you indicated, and sure enuf they come rite out and say they are using a coating for corrosion protection; Cadmium to be exact. A little additional research indicates that electroplated Cd is used in a manner similar to Zinc for corrosion protection. Now that I think of it, things like deck screws are also Cd plated. As Cd is (like Zn) a soft metal, I'd imagine that the coating is fairly soft, very thin, and probably disappears in the pad contact area after the first few applications of pedal, but who knows without going there?
    The real point here is that disk brake rotors aren't SUPPOSED to be grooved, they're supposed to be flat -n- smooth: if they're grooved it's because of uneven wear, period. If Subaru, or Stillen, or anyone else is putting a coating on their rotors that causes premature wear in the form of grooving, then (at the very least) they're not gonna see too many repeat customers.
    It was too damn hot last Saturday to slave over a Subaru brake, but I promise to pull that offending caliper off and have a look at the pad that is causing wear issues (remember; of 8 pad/rotor interfaces on the car, only one has issues) this weekend. Bet I find chunks of metal in the pad as a result of poor QC somewhere along the line. I'll grab some fotos and post 'em while I'm at it. As a side note to the above, care to hazard a guess as to why, if the coating is causing rotor grooving, only the one rotor face is experiencing it? Wouldn't you expect ALL rotor faces to exhibit similar wear?

    >So racers use plain cast-iron

    So, I believe, does everyone else, coated or not. Cast iron is what works.

    >Brake pad manufacturers do recomend bedding pads on used rotors. If you don't believe them, well that's your issue.

    Now, now! I didn't say that, did I? I said that if you put new pads against grooved rotors, after the dust settles you'll have matching grooves in your pads. I can't imagine that the manufacturer recommends that. Smooth used rotors, OK, but not grooved or otherwise deformed ones; that would be counterproductive.

    >And dude, for your own benefit - I'd remove your phone number from your signature before you start flaming people.

    (Shrug)
    My intent was not to flame anyone, but I am getting a bit weary of being told "Oh, don't worry 'bout those grooves, it's normal" or "You're not supposed to be able to down-shift into 1st gear on a Subaru" or whatever. Bullpoop. I've owned lotsa Subarus over the years, some with annoying little glitches it's true. Just 'cause they exist doesn't make them "right" or even "normal".
    And I prefer NOT to be anonymous. Ya wanna pick up the phone and call, feel free; I'm here 8 to 5. After that you'll have to look in the phone book, or call directory assistance for a home phone, but it's listed. You read an email or usenet post from me, you know exactly who you're talking to. GV27? Could be the FBI, CIA, ASPCA, or perhaps an SOA rep trying to sideline potential warranty claims; ya never know . . .
    And finally, bet ya DON'T know where my lab is! The Engineering Center is UC Boulder, I'm in Colorado Springs, hence uccs.edu rather than colorado.edu. And if you WERE a nut, and came around looking for trouble, I can guarantee you'd find some.
    But if you ever want to come down just to visit you're welcome to do that too; be happy to show you around.
    GV27, I've been an active internet entity almost since there was an internet to be active on, and have used the same email address for nearly that long. Haven't ever had any problems other than the typical flood of spam that my email server filters pretty efficiently. Email correspondents that I have actually met face to face have generally been good folks too. Life's too short to worry 'bout trivialities like (gasp) internet anonymity, which doesn't really exist anyway if one knows where to look and what to look for.

    Way off topic here; I'm for home. I'll post again when I have something definite to say about those pesky brakes! Again, sorry if I caused thermal runaway there GV27. Really! No offense intended.

    ByeBye! S.
    Steve Jernigan KG0MB
    Laboratory Manager
    Microelectronics Research
    University of Colorado
    (719) 262-3101

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    Registered User klancek's Avatar
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    Steve, what happened your brakes?

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    Hi klancek!

    You had asked:
    >Steve, what happened your brakes?

    Well, the car has ~17K on it now. Still some grooves on that one rotor face (left front, outside), but they do seem to be kinda smoothing out with time. This would seem to indicate to me that the original problem was some sort of contamination in/on the OEM pad . . . All of the rest of the rotors look fine.
    I just got a set of STI struts, and will be installing them in a week or two. Be a good time to pull the calipers and check things again. If I find anything odd I'll post. Other than that the rex has been just super; always a joy to drive. Actually managed a 1st place finish at one of our ice rallycross events last winter. I'm totally convinced that the T&S guys screwed up and gave me some-other-bodies times, but I wasn't about to argue the point :-)
    ByeBye! S.
    Steve Jernigan KG0MB
    Laboratory Manager
    Microelectronics Research
    University of Colorado
    (719) 262-3101

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