What to know
- Brake rotor lateral runout, a common issue that can impact braking performance, refers to the deviation of the rotor’s surface from a true plane as it rotates.
- Attach the magnetic base of the dial indicator to the brake caliper or suspension component adjacent to the rotor.
- Lateral runout measures the deviation of the rotor surface from a true plane, while thickness variation measures the difference in thickness across the rotor surface.
Brake rotor lateral runout, a common issue that can impact braking performance, refers to the deviation of the rotor’s surface from a true plane as it rotates. Measuring brake rotor lateral runout is crucial for diagnosing this problem and ensuring optimal brake system functionality. This comprehensive guide will provide you with step-by-step instructions and insights into the importance of measuring brake rotor lateral runout.
Why Measure Brake Rotor Lateral Runout?
Brake rotor lateral runout can lead to a range of issues, including:
- Reduced braking effectiveness: The uneven surface can cause the brake pads to make inconsistent contact with the rotor, reducing braking power.
- Excessive brake noise: The uneven contact can generate vibrations that translate into squealing or grinding noises.
- Brake shudder: The varying contact between the pads and rotor can create a pulsation in the brake pedal, leading to uncomfortable shuddering.
Tools and Materials
To measure brake rotor lateral runout, you will need the following:
- Dial indicator
- Magnetic base
- Lug nuts
- Torque wrench
Step-by-Step Instructions
1. Safety First
Park the vehicle on a level surface and engage the parking brake. Allow the brakes to cool down completely before proceeding.
2. Mount the Dial Indicator
Attach the magnetic base of the dial indicator to the brake caliper or suspension component adjacent to the rotor. Position the dial indicator tip against the outer edge of the rotor surface.
3. Zero the Dial Indicator
Rotate the rotor by hand until the dial indicator reads zero. This establishes the reference point for measuring runout.
4. Measure the Runout
Slowly rotate the rotor one full turn while observing the dial indicator. The maximum deviation from the zero reading indicates the lateral runout.
5. Check the Inner Surface
If the outer surface runout is excessive, repeat the measurement on the inner surface of the rotor.
6. Compare to Specifications
Refer to the vehicle’s repair manual or brake rotor manufacturer‘s specifications for the acceptable lateral runout limit. If the measured runout exceeds the limit, the rotor may need to be replaced or resurfaced.
Interpretation of Results
- Acceptable runout: Typically within 0.002-0.005 inches (0.05-0.13 mm).
- Excessive runout: Exceeding the specified limit, indicating a need for further inspection or replacement.
Causes of Excessive Lateral Runout
- Warped rotors: Overheating due to hard braking or uneven pad wear can warp the rotor surface.
- Bent rotors: Impact from road debris or improper installation can bend the rotor.
- Hub irregularities: Misalignment or damage to the wheel hub can cause the rotor to runout.
Prevention and Maintenance
- Avoid aggressive braking: Hard braking generates excessive heat, which can warp rotors.
- Inspect brakes regularly: Check for uneven pad wear and rotor surface condition.
- Use high-quality brake components: Invest in reputable brake pads and rotors to minimize runout issues.
Importance of Accurate Measurement
Accurate measurement of brake rotor lateral runout is essential for:
- Correct diagnosis: Identifying the root cause of braking problems.
- Effective repair: Determining the appropriate repair method, such as resurfacing or replacement.
- Safety: Ensuring optimal braking performance for the safety of the driver and passengers.
Recommendations
Measuring brake rotor lateral runout is a crucial aspect of brake system maintenance and repair. By following the steps outlined in this guide, you can accurately diagnose and address this issue, ensuring smooth and effective braking performance. Remember to consult a qualified mechanic if you encounter excessive lateral runout or are unsure about the repair process.
What You Need to Learn
Q: What is the difference between lateral runout and thickness variation?
A: Lateral runout measures the deviation of the rotor surface from a true plane, while thickness variation measures the difference in thickness across the rotor surface.
Q: Can lateral runout be repaired without replacing the rotor?
A: In some cases, resurfacing the rotor can remove excessive runout. However, severe warpage or bending may require rotor replacement.
Q: How often should I check brake rotor lateral runout?
A: Regular brake inspections, including runout measurement, are recommended every 10,000-15,000 miles or as per the vehicle manufacturer‘s specifications.
