Disc Thickness Variations (DTV): measuring disc, rotor run-outs, causes and preventions
If your brake pedal feels like it’s pulsing or vibrating, you might have brake disc thickness variation (DTV). This is a small variation in the thickness of the friction surface of the rotor(s). This is usually caused by the rotors receiving uneven wear.
What is disc thickness variation?
Brake disc thickness variation means variation in the thickest and the thinnest parts of the rotor. This causes the rotors to have an uneven wear. This is a rotor condition that one of the rotor surface is thicker than other.
How disc thickness variation occurs?
-The force of uneven clamping and rotating
-Rotors not installed correctly
-Improper positioned calipers
-Irregular brake friction patterns
-Rust and dirt deposits
Disc thickness variation causes:
-Pedal pulsation, which occurs when the rotor rotates through the brake pads and calipers (more noticeable with heavy brakes)
-Steering wheel oscillation (feels like it’s pulsing or vibrating)
-Vibration, the thin and thick sections of the rotor slip in between brake rotors
How to measure rotor run-outs?
-Measure at least 6 areas of the rotor’s face
-Use a micrometer to measure the thickness of the rotor
-The measurements should not vary larger than .001 inch (0.025 mm)
-Start measuring a quarter inch from the edge of the rotor
-Measurements larger than .006 inch (0.15mm) is an indication of DTV and might need replacement
What is lateral run-outs?
Lateral run-outs (LRO) means the rotor thickness stays the same but the rotor plates are wobblily or moving up and down.
How to fix lateral run-outs?
-The rotors can be re-surfaced to the same as other rotor surfaces
-Shimming the rotors will change the run-outs in the rotor
How to prevent DTV?
-Install brake system properly, especially brake rotors, pads, and calipers
-Clean the wheels and rotors thoroughly
-Use a wrench to tighten the lug nuts to ensure lug nut torque
-Follow the break-in procedure correctly
*disc resurfacing may be required to correct the disc thickness variations, run-outs, and scorings.
Typical run-out value
Most of the rotors in the market today are range between 0.0005 to 0.001 inches
|Small Cars||.01mm (0.0003 in)|
|Medium Cars||.08mm (0.03 in)|
|Luxury Cars||.50mm (0.019 in)|