Occasionally we come across the scenario where a vehicle has no visible sign of brake shudder when the brakes are cold but develops brake shudder when the brakes warm up. This technical article covers one of the common causes of this problem with hat type disc rotors.
The mounting faces of the disc rotor and hub are precision machined so as to accurately position the disc rotor in relation to the brake caliper. If these 2 faces a not clean and flat it will be impossible for the rotor to be mounted accurately in respect to runout and support.
Often the use of removal screws is required when removing stubborn disc rotors. During the cleaning of the hub face it is important to check for any burrs or damage that may have been caused during this process. If there is a scale found on the face of the hub it should be removed before the re-fitment or replacement of the disc rotor. If the disc rotor is mounted with this scale not lined up with the removal holes it will cause the rotor to be mounted in a stressed state.
As the disc rotor heats up with use the rotor will distort slightly due to the stress applied from the uneven mounting surface. This slight distortion will cause brake shudder and over a period of time will cause noticeable DTV (Disc Thickness Variation) in the disc rotor.
If a disc rotor has been mounted without the scale removed it will leave a noticeable impression mark on the mounting face. The pictures below show the signs of the scale and the impression marks.
Disc Brakes Australia