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In the original article 'way-up in the thread, Carroll Smith (an engineer with the Shelby program... now deceased) speaks of (in extreme situations, presumably) the cast iron of the brake rotors being metallurgically-changed to cementite - which is harder than the surrounding matrix of cast iron. Unless the layer of cementite is removed (by the special grinding-process Smith talks about) - well, the pulsation comes back - I think - 'real soon. So it is NOT just the differential deposition of brake lining material that is the issue, but the varyining / differential surface hardness that is ALSO causing an issue...
 

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In the original article 'way-up in the thread, Carroll Smith (an engineer with the Shelby program... now deceased) speaks of (in extreme situations, presumably) the cast iron of the brake rotors being metallurgically-changed to cementite - which is harder than the surrounding matrix of cast iron. Unless the layer of cementite is removed (by the special grinding-process Smith talks about) - well, the pulsation comes back - I think - 'real soon. So it is NOT just the differential deposition of brake lining material that is the issue, but the varyining / differential surface hardness that is ALSO causing an issue...
Extreme cases to be sure, mostly in racing applications. You would have to heat the rotor to at least 1300°F to begin the transformation to cementite. That would destroy most street car pads.....
The usual culprit here is run-out caused by poor installation. If the mating surfaces are not clean the rotor will have axial run-out, it will wobble side-to-side. Excessive run-out causes the rotor to come into contact with the pad at the spot where the run-out is at its maximum even when not using the brakes. Most common street car pads have pad material that is adhesive, that is it transfers to the rotor forming a layer of friction material on the rotor surface. Normally when the rotor is installed properly the pad transfers a nice even layer (proper bedding). However, if the pad is rubbing on one single spot on the rotor all the time due to run-out, that spot will develop an ever increasing layer of pad material and sooner or later you'll start to feel the brakes start to vibrate.
 

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Extreme cases to be sure, mostly in racing applications. You would have to heat the rotor to at least 1300°F to begin the transformation to cementite. That would destroy most street car pads.....
The usual culprit here is run-out caused by poor installation. If the mating surfaces are not clean the rotor will have axial run-out, it will wobble side-to-side. Excessive run-out causes the rotor to come into contact with the pad at the spot where the run-out is at its maximum even when not using the brakes. Most common street car pads have pad material that is adhesive, that is it transfers to the rotor forming a layer of friction material on the rotor surface. Normally when the rotor is installed properly the pad transfers a nice even layer (proper bedding). However, if the pad is rubbing on one single spot on the rotor all the time due to run-out, that spot will develop an ever increasing layer of pad material and sooner or later you'll start to feel the brakes start to vibrate.
While I grant you that dirty (and differentially-dirty) seating of the rotor onto the hub would do it, Smith indicates that failure to bed the pads properly tends to differentially deposit pad material (sometimes visible, sometimes not) onto the rotor... and therefore it is rotor thickness, not TIR (Total Indicating Run-out) that causes the pulsations. Of course, a variation in rotor overall thickness WILL produce a TIR value of above zero... but that is not disk distortion (or "wobble) per se.

A number of purveyors of high performance disk brake pads talk about how proper bedding of the pads is done, as does Carroll Smith. The key is that after the sustained number of stops from speed (to 5mph) the car has to be operated to the point where the rotors are fully cooled, again.
 

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While I grant you that dirty (and differentially-dirty) seating of the rotor onto the hub would do it, Smith indicates that failure to bed the pads properly tends to differentially deposit pad material (sometimes visible, sometimes not) onto the rotor... and therefore it is rotor thickness, not TIR (Total Indicating Run-out) that causes the pulsations. Of course, a variation in rotor overall thickness WILL produce a TIR value of above zero... but that is not disk distortion (or "wobble) per se.

A number of purveyors of high performance disk brake pads talk about how proper bedding of the pads is done, as does Carroll Smith. The key is that after the sustained number of stops from speed (to 5mph) the car has to be operated to the point where the rotors are fully cooled, again.
Yes, proper bedding is important as I indicated in the post on the first page, and yes, been there done that many times...
 

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Discussion Starter #25
Wasn't expecting so many replies. Thank you all.
I showed it to two mechanics both said it's due to warped rotors. I took it to a third local mechanic and he replaced all four pads and front rotors.
I got Riley's Premium Rotors. ~$120. I drive normally and brake from a far away distance. Let's see how many miles these rotors are useful I drive 120mi a day.
 
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