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[FMTRVT]

Matt, no one is ever wasting my time. Well, unless your trying to sell me something ….

“I have been told that the pulsating we sometime feel is warping. And, I had a regular problem of this pulsating on my Ex. With factory pads and "OEM" A/M pads. Each time I replaced the pads the rotors were turned and there would be no problem until the next time I used the brakes at the high end of use. Not a panic stop. Not where I activated the ABS. But when I would have to go from, for example, 70 to 50 under a controlled, but quick, firm, slowing. Or, as I am traveling down a hill at 40 and have to slow under a quick, firm, slow to a stop. Usually w/in the first 1000 miles of use. It did not happen sooner because, knowing of the condition, I would baby the braking system so as not to cause this "warping" to happen. Which, I believe, is not how the system should work, BTW. Then, once done, it is there until the next time I change the pads and, at that time, I have the rotors turned. Because I know that the warping will happen again and I do not have the time, nor inclination, to remove the rotors, have them turned, and reinstall them each time the "warping" occurs. Only to have them "warp" again.”


I know you said you went back and read more, but this is such an example of the classic case I want to go over it. Go get another bag of Popcorn. And I told my wife my days of long answers was over ……

Each time of a change you’ve had the rotor’s turned, until below when you replaced the rotors.

In the last few years of supplying the “aftermarket” friction to dealerships, we’ve gotten back pads where the mechanics stated they would not stop the vehicle. Sometimes they would state the “second” set of pads stopped fine after awhile. Every time we put those “non-stopping” pads on an exemplar vehicle with new OE rotors and they’d stop fine. We started to ask for the rotors back as well and when using a surface profilometer to measure the surface roughness it usually exceeded 100 uin. OE rotors from all manufacturers are in the 50-60uin range, which is where they should be. The manufacturer then started a study at its dealerships asking for rotors to be returned to Detroit. There were a lot of rotors that exceeded normal roughness measurements because the cutting bits were not changed often enough. I’ve known that auto supply stores are even worse due to our normal aftermarket business. So the deal is often rotors are turned with excessive roughness and rarely are the surfaces smoothed even a little by someone using sandpaper to polish the peaks of the turned surface. This reduces stopping effectiveness.

When a rotor develops thickness variation, in short order it develops a hard spot. (Reference A. Anderson noted in messages above). The hard region ends up being the thickest width of the rotor due to the fact it is hard to wear. When the rotor is turned, the lathe cutting bit cannot cut deeply into the hard region, leaving it slightly proud, and with a less rough surface finish. The softer region has a rougher finish. If one is very diligent, you can see this area has a little more shine to it. If the operator of the lathe put sandpaper or abrasive cloth to the rotor to polish off the peaks, they fell a slight stick-slip as the rotor turns. This is no different then taking a file to hardened steel, it won’t bite.

When a turned or new machined factory (aftermarket or OE) rotor is first on the vehicle, the brakes do not achieve full stopping ability. Both the pads and the rotor’s surfaces have to polish out smoothly, and some material transfer to the rotor has to happen. With the used rotor that has a hard region, during this time the coefficient of friction delta between the hard region and softer region is not that high. But as the softer area wears (polishes) down, both the friction differential and the thickness variation become more prevalent and pulsing is felt. This can take as short as 50 miles or as long as a few thousand miles, depending on the energy dissipation (braking), the roughness of the surfaces, the abrasiveness of the friction material l……..


You can turn the rotors again, but the situation just repeats until the rotors with the hard spots are replaced. If you also changed to a more abrasive friction material, the brand new rotor will wear in as to not having runout, and the problem is solved.


”One more question..... How does one know the different quality of the products we are considering purchasing beyond the purchase price. I have learned in my life that purchase price does not necessarily guaranty quality. Without going to the local auto store and dragging the rotors, one by one, onto the floor and checking them for size and fit. Without taking the pads to a belt sander to see how long they will last or if they will squeal.”

Unless you have a surface profilometer, a Brinell hardness tester, and a Coordinate Measuring Machine, dragging those parts out isn’t going to do you any good. Nor are there any wear life standards for friction. And part of the reason for the wear is the differential in operating conditions. As an example, in Los Angeles City Traffic tests, it’s typical for most vehicles to project about 25,000 mile pad life, the Superduties included. I’m running the exact same vehicle we used in those tests and my pad life is projecting out to over 200,000 miles. It’s been decades that the aftermarket has debated how to come up with a meaningful test for performance that we can all agree on, but it hasn’t happened yet. I’ll be dead before there is one for wear life. Like mechanics, you find a brand that works well for you and stick with it.

“I have taken my vehicles to dealerships only to have a problem because an apprentice did the work and the work was done worse than I did. I have purchased various products from various sources in my life. I have even had an account- at one point- where the auto shops purchased the products they used. But I would still be purchasing products on a hope and a prayer that I was making the proper decision(s).”

Brakes by the most part are pretty mechanically simple to work on, but little details and procedure can easily be overlooked. Because of this simplicity, there are mechanics like you mentioned, and some owners who really should not be working on what I consider the most important safety device on the vehicle. But at the same time, it one of the most hammered parts of a vehicle for parts price. We have all been indoctrinated with a brake job for $49.95, and quality pads are hard to come at that price, much less the mechanic’s time to install them at the discount auto repair shop.

”In regards to brakes rotors and pads, and keeping in mind that OEM from the dealer did not resolve my "warping" problem, how do we know that we are buying the product that we need for our application and use?”

As stated above, no pads would have solved a hardened rotor issue. Hang out in forums like this and read what some people have to say, and hash through the good and bad. The rotor warp story is one that honestly is an upward battle, one that most people in my industry think I’m nuts for even trying to talk about because 1) what is a solution on the SD is not necessarily the same solution on another vehicle platform, and 2) you can still have issues if the hubs, wheel balance, and other vehicle aspects are not considered with problem children. For example, within the Superduty product line, the Excursion is probably the most sensitive vehicle for pulsation due to it’s softer suspension and full cabin.

“I have read "5 years" in regards to the brake life. I have had my Ex for almost 90k miles and have had new pads and turned rotors right around 20K each. 20k to 25K seems to be the life of my pads regardless of which ones I use. Which, BTW, is a lot better than the life of about 18K out of my 2 previous Suburbans. Now, when I buy pads I always ask for OEM compatible products. I tried some longer life pads once and got a lot of squeal and, since the Ex is my wife's car, so I changed the for the OEM spec. pads.”

Think I kind of addressed that above.

“01 mentions ceramic/carbon. Is this a "better" pad? How is the squealing?”

For noise, with any aftermarket pad, depends on the work that the manufacturer put into it. No aftermarket manufacturer can invest the full range of development in noise abatement aspects. But there are a fair amount of aftermarket products out there that are noise free. Other will have some noise, but are a compromise for the other benefits they provide. But the best source for an answer is to see what other people find, like 01.