To measure disc thickness variation, you primarily use a micrometer to take precise measurements at multiple points across the rotor's face.
Disc thickness variation (DTV) is a critical measurement for ensuring smooth braking performance. It refers to the difference in thickness around the circumference of a brake rotor. Excessive variation can lead to pedal pulsation or vibration.
Tools Needed
- Micrometer: A precision tool specifically designed for accurately measuring thickness.
Step-by-Step Measurement Process
Measuring disc thickness variation involves taking careful readings at several locations:
- Prepare the Rotor: Ensure the rotor surface is clean and free from rust, debris, or grease that could affect the measurement.
- Use a Micrometer: As specified, use a micrometer to measure the thickness of the rotor.
- Measure at Multiple Points: Take measurements around the rotor's face. It is crucial to measure at least 6 areas of the rotor's face. For accuracy, measure at equal intervals around the circumference (e.g., every 60 degrees if measuring at 6 points).
- Record Measurements: Note down each measurement taken at the different locations.
Calculating Disc Thickness Variation
Once you have recorded all the measurements:
- Identify the largest thickness measurement among all points.
- Identify the smallest thickness measurement among all points.
- Subtract the smallest value from the largest value. This difference is the disc thickness variation.
Example:
Let's say you took 6 measurements (in inches):
| Measurement Point | Thickness (in) |
|---|---|
| 1 | 0.985 |
| 2 | 0.986 |
| 3 | 0.985 |
| 4 | 0.987 |
| 5 | 0.986 |
| 6 | 0.985 |
- Largest Measurement: 0.987 inches
- Smallest Measurement: 0.985 inches
- Disc Thickness Variation: 0.987 - 0.985 = 0.002 inches
What to Look For (Tolerance)
The acceptable amount of disc thickness variation is very small. According to the reference, The measurements should not vary larger than . 001 inch (0.025 mm).
If your calculated DTV exceeds this maximum limit, the rotor is likely causing braking issues and may need to be machined (resurfaced) or replaced.
By following these steps and using a precise micrometer to measure at multiple points, you can accurately determine the disc thickness variation of a rotor.
