Warped Brake Rotors on Jeeps and How to Prevent Them
When I picked up my new brake rotors for my Jeep the guy at the parts counter advised me to carefully clean the brake rotors of oils including oil from my fingers to prevent warping. This was new to me and got me thinking about warped brake rotors and reminded me that I have not had to deal with a warped rotor in a long time.
The first thing I learned years ago was that the pulsing sensation we called a warped brake rotor is not actually warping. You can put a dial indicator on the face of the rotor and spin it around and it will read very little run out when it is making a pounding sound when the brakes are applied. You can measure it all the way around and you will find very little difference in thickness either.
The real cause of the shudder is a chemical change in the metal of the surface of the rotor. You can sometimes see it but most of the time you can’t. Turning the rotor cuts off that surface layer making the rotor run smooth again adding to the warping myth.
The rotor surface chemically interacts with the brake pads under the heat of braking. Most of this interaction occurs during the bedding in process of the brake pads. Many high performance and racing pads have a critical bedding in process to establish the correct chemical bonding between the two materials. Usually this involves making controlled braking maneuvers at predetermined speeds to generate the heat needed for the reaction to take place. It is important not to come to a complete stop during the process so that the interface layer is kept consistent around the rotor face.
This leads to why rotors “warp” and how to avoid it. The interface layer is constantly maintained as the rotor face and the brake pad material wears away. A new layer is constantly formed with each use of the brakes.
If you come to a complete stop with the brakes hot, the reaction will continue under the pads where the heat cannot dissipate. If it is held there too long, it will create a bond that is a bit stronger or weaker than the area next to it on the rotor. As the rotor develops these uneven spots where the coefficient of friction is grater that the surrounding rotor face, the brakes will give the characteristic chatter that we call a warped rotor. The pulsing in the pedal will feel like the rotor is pushing the pads away from the surface.
I tried a lot of things before I finally got away from “warped” rotors. I tried the expensive rotors. I tried the cross drilled and slotted rotors. I tried various pad materials.
The thing that I found that helps more than anything is a simple driving technique. Some people call it the Limousine stop. I call it a creeping stop. If I suspect that my brakes are hot when coming to a stop, I will aim to stop a bit short and then just before the Jeep stops and is ready to rock back, I let off the brakes and let it creep forward about a half turn of the wheel. If I have to stay stopped like at traffic light, I will creep forward again another quarter turn of the wheel to help even out the heat buildup in the rotor.
There are times where it may not be possible to make such a stop. For example in an emergency or if you have to spot unexpectedly. You may also have to hold the brake longer than you wish thereby creating a hot spot. If this occurs, I repeat the performance pad bed in process and create a new interface layer. Depending on how bad the hot spot is, it may take several repetitions of heat cycling the pads to get them smooth again.
Since I have made this style of stop a habit, I have not had any more trouble with warped brake rotors. I can’t remember the last time I replaced rotor on one of my Jeeps due to chatter.