Excessive rotor disc thickness variation (DTV) primarily causes pedal pulsation. While it can also contribute to premature pad wear and noise, pedal pulsation is the most likely symptom. DTV, also known as parallelism, refers to variations in the rotor’s thickness. This can be measured with a micrometer at eight points around the rotor, with a typical specification of five ten-thousandths of an inch.
DTV is often caused by lateral runout—a warped rotor. This warping can result from improper lug nut torquing, incorrect lug nuts, or an unclean hub surface. A warped rotor repeatedly strikes the brake pad, which can lead to DTV, even with floating calipers, ultimately causing pedal pulsation.
To check for lateral runout, a dial indicator is used against the rotor, which is then spun. A typical specification is around three thousandths of an inch. It’s crucial to ensure the rotor is securely mounted and the hub is clean before measuring.
In summary, when diagnosing brake issues, always check specifications, including rotor minimum thickness, disc thickness variation (DTV), and lateral runout. A rotor below its discard thickness cannot dissipate heat effectively, leading to brake fade and requiring replacement. Ensuring proper installation and maintenance during brake jobs helps prevent warped rotors and DTV.
Disc Brake Diagnosis
