A lot of owners think this "Brake Judder" is the results of "warped rotors" However, Its not. It's a condition where the friction faces are not the same thickness anymore. Now your asking "... how can this happen?" "How on earth could the both friction faces of a brake disc not be parallel, even after many miles?" Good question right? Well, Here's how;

There are two basic types of brake pad friction mechanisms: abrasive friction and adherent friction. In general, all pads display a bit of each, with abrasive mechanisms dominating the lower temperature ranges while adherent mechanisms come more into play as pad temperature increases. Both mechanisms allow for friction or the conversion of kinetic energy to thermal energy, which is the function of a brake system, by the breaking of the molecular bonds in vastly different ways.

The abrasive mechanism generates friction or energy conversion by the mechanical rubbing of the brake pad material directly on the rotor disc. In a crystalline sense, the weaker of the bonds in the two different materials is broken. This obviously results in mechanical wear of both the pad and the rotor. Consequently, both pads and rotors are replaced when they are physically worn to their limit and are too thin to endure further service.

The adherent mechanism is altogether different. In an adherent system, a thin layer of brake pad material actually transfers and sticks (adheres) on to the rotor face. The layer of pad material, once evenly established on the rotor, is what actually rubs on the brake pad. The bonds that are broken, for the conversion of kinetic to thermal energy are formed instantaneously before being broken again. It is this brake pad-on-transferred brake pad material interaction at the molecular level that yields the conversion process. This is the mechanism we what to use in a street applications. The abrasive mechanism is used in racing applications.

With the adherent mechanism there is much reduced rotor wear as compared to abrasive mechanism, but it’s not a free pass – pads now become the primary wear element in the braking system. And even though rotors are not mechanically worn down with adherent systems, they still will need to be replaced on a regular basis due to cracking reaching a point of failure if they are exposed to intense, repetitive thermal cycling. This is why race teams throw out rotors that are actually as thick as or thicker than when they were brand new. It’s due to the adherent brake pad transfer layer!

Imagine the following scenario. You’re driving your truck a little too aggressively and the light changes on you. Dam! I’ve got to get this thing to stop before I reach the intersection…. You start applying heavy pressure to stop, right? You know what I’m talking about we’ve all been there before…

Well you've got the hard part accomplished. Now, what's the first thing owners trend to do or, don't do while waiting on the light?


1) Roll down the window;
2) Change the radio station;
3) Ease up on the brakes and let the rig move slowly so as to avoid the brakes pads from resting in one place on these "hotter the hell rotors" in an effort to prevent pad imprinting.


Pad imprinting? Correct. This is where most adherent friction or street brake problems start. What happens is the pad faces can bond to the friction faces of the rotors after this type of stop and when driven off, an uneven deposit of pad martial results. What's worse under braking now when the pad(s) encounter this un-even build-up of pad martial, local temperatures can reach 1200F to 1300F degrees. If this continues, iron which contains inclusions of silicon-iron carbides and high percentages of carbon can develop deposits of "Cementite" (Fe3C) in the rotor's iron matrix.

Let’s use a metaphor here and say that the inclusion of silicon iron-carbides and the high content of carbon (30%-40%) in cast-iron is simply a recipe for the development of cementite. All we have to do for its development is locating a heat source and when working with brakes, this will not be a problem...

Any guesses as to what the dark spots are? That right, cementite. Cementite is very hard, very brittle and a poor heat-sink. Because of this, the softer iron areas wear at a deferent rate than the harder cementite deposits. It is these deposits that cause peaks and valleys in the rotors friction faces that the brake pad(s) encounter(s) that cause this classic "judder" under breaking that vehicle owners believe is "warped rotors".

To combat the onset of cementite in iron takes the knowledge of a controlled stable state of "Martensite" or a "Metastability" of a "Martensitic Transformation" from "Austenite".

Austenite is a metallic, non-magnetic solid solution of carbon and iron than exist in metals. Above critical temperatures Austenite's face centered cubic. (FCC) structure allows it to hold a high proportion of carbon in solution. As it cools, this structure either breaks down into a mixture of ferrite and cementite, or undergoes a slight pattern distortion.

At ART we employ a process where-by we manage a "Martensitic Transformation". Martensite is a class of tough plate-shaped crystals. These crystals are face-centered tetragonal (FCT) and result from cooling of austenite. The rate of cooling determines the relative proportions of these materials and therefore the mechanical properties of the metal.

ART has spend a lot of time in the research of cryo-treating and heat tempering of martensite in iron to induce a martensitic transformations from retained austenite. It is these processes where we believe the durability of our products have such a big following on internet truck forums.

What does all this mean to you? Well, depending on the time frame of when you started to experience this "Brake Judder" you may be able to head it off.

I would like you to consider the following:

1) You can remove the rotors and check the friction faces for signs of pad imprinting then using "Garnet paper" not sand paper, rough up both surfaces of the rotors. During the re-installation you may want to consider replacing the pads with new pads. It all depends on how much of the pads are still usable. After re-installing re-bed the brake pads again using our bedding procedure. I have enclosed a copy of our bedding procedure herein. Review it closely before heading out to re-bed your brake pads.

2) If the above fails or you just opt for having the rotors refaced, see if you can be present when the shop machines them. Note the tone that the cutter(s) makes during the cut(s). What you're listening for is a consentience sounding cut or does the cutter(s) seem to encounter harder deposits randomly. If so, you will hear this change in the tone of the cut. If you do discern this it is the onset of cementite development and you might want to consider a new set of brake discs. But, on the other hand, you and the shop hear nothing re-install the rotors and then re-bed the pads. You should be good to go.

 

Would have been nice if u posted this when I did my front brakes... Good Stuff...