Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Standardized Brake Squeal Testing for Vehicles: An Overview of SAE J2625-2017
Brake squeal is a common NVH (Noise, Vibration, and Harshness) concern that affects vehicle comfort and perceived quality. To help engineers consistently evaluate brake squeal noise under vehicle-level conditions, SAE International published J2625-2017, a recommended practice for automotive vehicle brake squeal testing. This article explains the purpose, key procedures, and current status of this standard, offering practical insights for NVH professionals.
⚠️ Stabilization Notice: SAE J2625 has been stabilized since July 2017. This means it is no longer actively reviewed, and users should verify references and consider newer technologies. However, it remains a useful baseline for vehicle squeal test methods.
🛠️ Purpose and Scope
The primary goal of SAE J2625 is to establish a common, universally recognized method for performing screening test sequences that identify a brake assembly’s propensity to generate squeal noise under a variety of conditions. It is applicable to squeal type noise occurrences for passenger cars and light trucks under conventional operating conditions. The standard defines squeal as noise occurring between 900 and 18,000 Hz.
According to the document’s foreword, the procedure was created to provide a vehicle test definition that can be used on its own or as part of a larger noise test protocol. It also aims to help correlate dynamometer squeal noise tests with full vehicle measurements.
🔍 Key Test Procedures and Measurement Requirements
J2625 outlines a structured test matrix that includes preconditioning, parking lot maneuvers, and initial brake temperature (IBT) sequences at low, moderate, and high temperatures. These sequences are designed to capture squeal occurrences across typical operating conditions.
Essential measurement requirements include:
- Governing temperature: Accurate measurement of brake temperature using thermocouples per SAE J79.
- Accelerometer location: Specific placements on brake calipers, knuckles, or other suspension components to capture vibration data.
- Interior microphone: Positioned near the driver’s head to record sound levels, as specified in SAE J1477.
- Driver subjective evaluation: Recording subjective noise ratings alongside objective measurements.
The following table summarizes the main test sequences defined in the standard:
| Test Sequence | Temperature Condition | Key Features |
|---|---|---|
| Optional Winter Parking Lot Maneuver | Cold ambient (e.g., below 0°C) | Simulates cold weather brake applications. |
| Parking Lot Maneuver – Low Temperature | Low brake temperature | Controlled series of stops from low initial speeds. |
| IBT Matrix – Increasing Temperature | From cold to hot during test | Sequential stops at increasing initial brake temperatures. |
| Parking Lot Maneuver – High Temperature | High brake temperature | Stops after aggressive driving to heat brakes. |
| IBT Matrix – Decreasing Temperature | From hot to cold after heat soak | Sequential stops as brakes cool down. |
| Parking Lot Maneuver – Moderate Temperature | Intermediate brake temperature | Stops at a moderate temperature range. |
For each test, occurrence of squeal is defined as the percentage of brake applications where the peak interior sound level exceeds 50 dB(A), unless an alternative threshold is defined. The standard provides templates for summarizing results, including occurrence versus temperature, brake line pressure, and initial speed.
🔬 Engineering Design Insight: The standard’s emphasis on varying temperature conditions and specific parking lot maneuvers helps uncover squeal that might only appear under certain thermal and driving profiles. Proper accelerometer and microphone placement is critical to ensure repeatable and comparable results across different vehicles and test facilities.
Stabilization and Current Relevance
SAE J2625 was stabilized in 2017 because the technical committee found limited users for the report. While this means the standard is no longer revised, NVH engineers can still use it as a foundational reference for building a vehicle squeal test procedure. It is important to check for updated references and consider newer technologies, such as advanced data acquisition systems or more refined test matrices.
For dynamometer correlation, J2625 is complementary to SAE J2521 (Disc and Drum Brake Dynamometer Squeal Noise Matrix). Establishing a vehicle-level test method helps validate dynamometer results under real-world conditions.
Frequently Asked Questions
Q: What is the frequency range for brake squeal according to J2625?
A: The standard defines squeal as occurring between 900 Hz and 18,000 Hz.
Q: Why was J2625 stabilized?
A: The SAE Brake NVH Standards Committee determined that there were limited users for the technical report, leading to its stabilization in July 2017. Users are responsible for verifying references and considering newer technologies.
Q: Can I still use J2625 for brake squeal testing?
A: Yes, it remains a useful baseline for vehicle squeal testing. However, ensure that all referenced standards are up to date and consider integrating modern measurement tools and analysis methods.
Q: How does J2625 relate to dynamometer squeal testing?
A: J2625 provides a vehicle-level test definition that can be used to correlate with dynamometer tests like SAE J2521. Having a consistent vehicle test procedure helps validate that squeal observed on the dynamometer also occurs in the vehicle under controlled conditions.
By adhering to a standardized procedure like SAE J2625, NVH engineers can improve the consistency and comparability of brake squeal evaluations across different vehicle programs and test facilities.
