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Understanding SAE J866-2019: Brake Lining Friction and Environmental Marking System
SAE J866-2019 provides a uniform identification system for brake linings, combining friction coefficient classification (based on SAE J661 tests) with environmental markings for regulated materials like copper and heavy metals (per SAE J2975). This standard does not establish performance requirements but ensures consistent edge coding across the industry.
Friction Coefficient Coding: The Two-Letter Code
Based on test data from SAE J661, manufacturers assign a two-letter code. The first letter represents the normal friction coefficient, averaged from four temperatures on the second fade curve. The second letter corresponds to the hot friction coefficient, averaged from ten specific points during the fade and recovery cycles.
Table 1 defines the letter ranges:
| Code Letter | Friction Coefficient Range |
|---|---|
| C | Not over 0.15 |
| D | Over 0.15 but not over 0.25 |
| E | Over 0.25 but not over 0.35 |
| F | Over 0.35 but not over 0.45 |
| G | Over 0.45 but not over 0.55 |
| H | Over 0.55 |
| Z | Unclassified |
🛠️ Engineering Design Insight: The friction coefficient code is derived from precise temperature points specified in SAE J661, not averaging the entire test. The normal friction uses four points on the second fade curve (93 °C, 121 °C, 149 °C, 204 °C), while the hot friction uses ten points from recovery and fade cycles. This specificity ensures consistent classification but does not predict real-world brake performance, which is influenced by system design and operating environment.
Environmental Markings and Edge Code Application
Environmental markings indicate compliance with state regulations (e.g., California and Washington laws) regarding copper content and other heavy metals. The marking consists of a letter (A, B, or N) followed by the two-digit year of manufacture. Table 2 summarizes the material limits as measured by SAE J2975.
| Designation | Copper Content (% by weight) | Other Heavy Metals Limits |
|---|---|---|
| A | Not applicable (n.a.) | Cadmium ≤0.01%, Chromium (VI) ≤0.1%, Lead ≤0.1%, Mercury ≤0.1%, Asbestiform fibers ≤0.1% |
| B | >0.5 to 5.0 | Same as A limits |
| N | 0.5 or lower | Same as A limits |
For example, “B16” indicates a material meeting the B copper range (greater than 0.5% up to 5%) and manufactured in 2016. The environmental marking must be the last characters in the edge code string.
⚠️ Critical Note: The environmental marking must appear at the end of the edge code, with no additional alpha or numeric characters after it. This requirement ensures unambiguous identification of compliance status.
Edge Code Placement and Example
Markings must be applied to an external non-contacting surface. For brake linings with thickness of 3.2 mm or greater, the minimum letter height is 2.8 mm; for thinner linings, the height can be up to 0.4 mm less than the lining thickness.
A complete edge code might look like: SCB 115 FF 1660 B16
- SCB – Company assigned ID (at least 2 characters)
- 115 – Formulation identification
- FF – Friction coefficient code (normal = F, hot = F)
- 1660 – Batch code (optional, here meaning 60th day of 2016)
- B16 – Environmental marking (material designated B, year 2016)
Frequently Asked Questions
How are the normal and hot friction coefficients calculated?
Normal friction coefficient is the average of four points from the second fade curve at 93 °C, 121 °C, 149 °C, and 204 °C. Hot friction coefficient is the average of ten points: 204 °C and 149 °C on the first recovery; 232 °C, 260 °C, 288 °C, 316 °C, and 343 °C on the second fade; and 260 °C, 204 °C, and 149 °C on the second recovery. If a temperature is not reached in the prescribed time, the value at 10 minutes is used.
What does the environmental marking “N21” mean?
“N21” indicates a material that meets the “N” designation: it passes the heavy metal limits for cadmium, chromium (VI), lead, mercury, and asbestiform fibers, and contains 0.5% or lower copper content by weight. The “21” denotes manufacture in 2021.
Can the friction coefficient code predict brake system performance?
No. SAE J866 explicitly states that the friction code does not establish performance requirements and cannot reliably be used to predict overall brake performance. Brake system design, operating conditions, and environmental factors play major roles.
Where must the edge code be placed on the brake lining?
The code must be marked on an external non-contacting surface. The minimum letter height is 2.8 mm for linings 3.2 mm or thicker; for thinner linings, the letter height can be up to 0.4 mm less than the lining thickness.
