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What's the deal with "quiet" rotors (gray iron, etc) and zinc-plating?

Discussion in 'Performance' started by MoPar~Man, Feb 20, 2017.

  1. MoPar~Man

    MoPar~Man Member

    I've noticed on sites like rockauto there are rotors for sale that are
    described as quiet.

    Supposedly there is a type of iron (called "Gray" iron) that has a
    different microstructure that is less prone to high-frequency
    brake-squeel noise, but this type of iron is supposedly what most or all
    rotors are already made with.

    So is this true?

    That you can count on your standard white-box, no-name brand of rotors
    that might cost you $20 - $30 a rotor is already made using the most
    appropriate type of iron, this so-called "Gray" iron, and that anything
    labelled as "low-noise" rotors are just throwing that term in to extract
    a few more bucks from the price?

    (This is not about whether or not a rotor is cross-drilled or slotted,
    so let's not take this thread on that tangent).

    Also, I've noticed that there are some rotors that appear to be black in
    color - not just the edges but the entire rotor. I think these are
    described as being zinc plated - presumably the plating gets worn away
    on the rotor surface in contact with the pads. Anyone have any
    experience with these? Do the areas of the rotor that are black *stay
    black* over time and hence they don't rust?
  2. Doug D

    Doug D Virginia Gentleman

    This the first I've heard of "Gray Iron". Whether they are "better", I have no idea.

    As far as the coating, I only see the coating applied to the non brake surface to help prevent rust and corrosion.

    Additionally, I see some rotors have Cryogenic Treatment.

    Cryogenic treatment is a one-time stress relief process that involves both cold and heat cycling of the brake rotor. Using a proprietary computer-controlled process over a 24-hour period, the cryo machine gradually cools the rotors down to -300 º F, then gradually brings them up to over +300º F, and finally back to room temperature. This conditioning of the rotor improves its service life, especially in fleet and emergency vehicle applications.

    Again, I have no idea whether this treatment enhances the service life or not.
  3. MoPar~Man

    MoPar~Man Member

    Put this into a google search:

    "Noise Dampening Iron" rotors

    You'll find an assortment of online vendors describing rotors with the term "Noise Dampening Iron".

    If there really was a different class of iron that had unique noise-dampening properties that cost a little more (or maybe a lot more) than "regular" rotors, I'd love to know about that.

    Yes, there are several different types of brake pads, but there really doesn't seem to be different metalurgy when it comes to the rotors. I think this "Noise Dampening Iron" is a marketing gimic.

    There might be stainless-steel rotors (which presumably won't rust) but the thermal properties of stainless steel are not optimal compared to cast iron (based on what I've read).

    I believe the squeel that I'm getting is happening at the contact point where the pad backing plate rests and slides against the bracket or arm that is part of the wheel hub or knuckle. This arm/bracket is what keeps the pads from being rotated when they grab the rotor. So the full braking force is applied to this contact point, and over time as the pads wear and get thinner, the backing plate moves laterally to a different contact point on the bracket, and over time you'll get a groove forming on that bracket. When you apply the brakes while in reverse and then again when in drive, you'll hear the pads clunk because of the play caused by the groove in the bracket.

    This is why there are pads sold with small shims that make up for the bracket wear. But I think even with shims if there is a brake squeelthat won't go away, it's happening because of something going on at the contact point of the bracket. If there is some special product designed for that application, I'd like to know. Brake lube doesn't help.
  4. pt006

    pt006 Member

    Gray cast iron has been around a long time. Most machinery was/is made from it. It was a finer grained cast iron that was more stable than regular cast iron. It may soften the vibration a little.

    Zinc plating is silvery colored, so it may be a zinc compound they are talking about. Likely for slowing down the rusting process. And looks.

    Doug mentioned the cryogenic treatment. I read that one or more USA companies buy rough machined rotors from china, cryo treat them, then finish machine them. This will result in a more stable/accurate rotor.

    Some of the older pad sets came with a tube of anti-squeal paste/glue. A little on the backside of the pads and its mating surface seemed to help. Pad material makes the biggest difference for a squeal problem. [opinion]. Hard pad material wears rotors faster.
  5. MoPar~Man

    MoPar~Man Member

    Put this in google search and select "images":
    black zinc plated rotors

    Yes, there are zinc-plated rotors that are black. What makes them black? I don't know. The black part will wear off the rotor surface by the brake pads, but otherwise it looks like all other surfaces will remain black.
  6. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES" Level 2 Supporter

    Centric advertises themselves as the only company in the US that does the heat treatment and final finishing of rotors. They claim that all other brands are entirely processed overseas.
  7. Rick Anderson

    Rick Anderson Active Member

    There are different types of cast iron, made from different recipes and different process's. I've always taken the "Gray" or "Noise Dampening Iron" to be just one of the types of Cast Iron that is used for rotors. I've also heard its a softer iron than most and helps dampen the noise. I've always took it as there might be some advantage to making rotors with a harder cast iron, but all the OEM's have selected the Gray iron for its better ability to dampen noise and vibration.

    Zinc plating? I've never seen rotors claimed to be zinc plated, I have seen all sorts of different coating advertised as being used on rotors, that can resist the heat and road chemicals that make rotors rust really bad, most are somewhat effective, just never seen them advertised zinc plating, no do they look like zinc plating to me either. I've heard of cadmium plating for rotors, which is a gold color and there is black cadmium plating as well. But most of the coated rotors I have purchased seem to have a black coating that appears like a tough paint (according to the advertising its a special coating, not simply paint).

    Cryogenic Treatment. Its stress relieving the metal, there are different process's but this one stabilizes the molecular structure of the rotor which makes it stronger. I have splurged on the Cryogenic Treated rotor once for my Neon R/T that I was using EBC GreenStuff Brake Pads. The pads were awesome but were chewing up the rotors something awful, the rotors didn't last any longer than the pads did. The Cryogenic treated rotors faired much better, and lasted much longer and more trouble free than other rotors with these pads.
  8. Rick Anderson

    Rick Anderson Active Member

    They introduce impurities in the process that can change the color of the coating. That is how they make black chrome, its just chrome that they intentionally screw up the process to produce the wrong, but desired color.

    The rotors I see on google images look like cadmium plated, but they claim to be zinc plated. Perhaps like chrome plating, its really a mix of materials and they refer to the finish in marketing terms as too what sounds best to sell to consumers. i.e. a mix of zinc and cadmium and more materials that is plated on the rotor.

    The plating or coating is not invincible, the heat, road salt and road chemicals will eat away at the coating and rust can start to form. In my experience, the coatings/platings work, but don't expect to much, they will eventually get rusty, just not as fast nor nearly as bad as uncoated/unplated rotors.
  9. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES" Level 2 Supporter

    Cadmium can be other colors. Same for other materials. When the RoHS initiative was introduced, some people mistakenly thought that any blue chromate coating was compliant, which was not true. You cannot distinguish trivalent from hexavalent chromate by color.
  10. pt006

    pt006 Member

    There was a black coating on Chrysler cars ~2003 that was used on their brake lines. It worked very well as an anti-rusting coating. I think it is no longer allowed.
  11. gwilliams2076

    gwilliams2076 New Member

    Rotors are not plated. They are all painted with coatings pigmented with zinc, aluminum or a blend of both Zn/Al to provide corrosion to the rotors other than obviously the brake plates.

    FCA uses zinc and the Zn/Al blend but is converting 100% to the latter as new programs are released.

    Ford and GM use the Zn/Al blend, Mercedes uses zinc and BMW/Volkswagen/Honda, aluminum coatings.

    Black paint is old technology and is basically obsolete other than for brake drum applications

    They all serve the same purpose as sacrificial corrosion inhibitors but the Zn/Al blend is the the most cost efficient of all the products.