Brake Shudder - Are My Rotors Warped?
You have just changed the rotors and brake pads on your vehicle. A week or two later you start to feel a vibration when you apply the brakes. Left unchecked this gets progressively worse and is very annoying. A quick call to your mechanic friend and it is determined that you have warped your rotors.
You even use a micrometer to verify that surface varies in thickness. Of course this confirms your diagnosis. The choices usually are exchange the rotors under warranty or have them resurfaced on a brake lathe. Everything is new and true yet a week later you start to feel that shudder again.
This is when many unhappy campers start to fuss and cuss. Disparaging the manufacturer, the distributor and the installer (providing it was not themselves).
Here is the truth. The brake rotors were never warped. Every manufacturer of rotors and brake pads has had these claims and all agree that the surface of the rotor has high spots from the resins of the friction material that transfers from the brake pads. These uneven high spots are the cause of the vibration and shudder. Hence “the rotors are warped”
Prevention is simple. Recovery a little more involved.
Bedding-In the Brake Pads
Bedding-In is critical to brake performance. Your new brake pads need to establish an even layer of friction material deposited on the rotors. This initial layer of friction material must be evenly distributed to Bed-In the brake pads. First make 5 normal to aggressive stops from 40 mph down to 10 mph in quick succession. Do not let the brakes cool and do not let the rotors come to a complete stop. Next make 5 moderate stops from 35 mph to 5 mph in quick succession. Again do not let the brakes cool. You will start to smell the friction material resin as the brake pads get hot. When these steps are complete, take a five to ten minute drive, somewhere at road speeds that you will not need to use the brakes. This is the cool down step. This allows the heated resin in the brake pads to cool and cure. After this allow the brakes to cool to the outside temperature. Make sure that there is no pressure on the brake pedal or emergency cable as they cool. Your brake pads are now properly Bedded-In.
The critical aspect of this is, at no time during the initial heating process do you let the rotor come to a complete stop. This is when the resin of the new brake pads has migrated to the surface and if you stop for any extended time this is transferred unevenly to the surface of the rotor.
Now, your new disc brake rotors and pads are ready for normal use. The brake rotors have acquired a thin, even coating of friction material and resin on the rotors. The complete process of layering up the braking surface can take 150 to 300 miles depending the vehicle weight and personal driving style.
Recovery, if you are already experiencing vibration. Have the rotors resurfaced. Many shops can now do this while the brake rotors are on the on the vehicle. After resurfacing go through the Bed-In process described above.
There are other reasons for brake vibration or shudder. Rust or scale on the rotor hub mating surface, over torquing lug bolts, bad caliper bushings. These generally manifest immediately not a few hundred miles later.
I hope this has been helpful and informative. I welcome your comments
Dave @ thebrakeguys
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