Most modern brake systems use synthetic brake fluids to transfer the hydraulic pressure generated in the master cylinder to the calipers and brake cylinders. Fluid properties are therefore of great importance for the entire braking system.
Avoid using the word "brake oil" in connection with brake fluids, as even the slightest contamination with oil can damage the rubber components of the brake system and thus lead to its failure. The physico-chemical properties of brake fluids are established in the SAE J 1703 (Society of Automotive Engineers) regulations in force in many countries. These regulations specify criteria in terms of boiling point, chemical inertness, miscibility with water, rubber swelling, corrosion and lubricity that must be maintained. A very important point of the SAE regulations is the possibility of mixing individual brake fluids with each other. The safety standard FMVSS No. 116 developed by the US Department of Transportation for DOT 3 and DOT 4 glycol-based brake fluids based on SAE J1703 regulations, is even more important. DOT 5 requirements apply to silicone-based brake fluids.
The DOT 5.1 standard also covers traditional brake fluids that meet these conditions and have been developed for particularly high requirements. Since DOT 5.1 brake fluids are silicone-free, they can be mixed with fluids of the same specification (DOT 3, DOT 4 and DOT 5.1) without any problems.
1.BF standards
2. Explanation of standards
| SAE J 1703 | DOT 3 | DOT 4 | DOT 5 | DOT 5.1 | |||
| FMVSS 116 | FMVSS 116 | FMVSS 116 | Silicone base | FMVSS 116 | |||
| ISO 4925 Class 3 | SAE J 1704 | ISO 4925 Class 4 | ISO 4925 Class 6 | ISO 4925 Class 5-1 | |||
| JIS K 2233 Class 3 | JIS K 2233 Class 4 | ||||||
| Boiling point temperature equilibrium | ≥ 205oC | ≥ 205oC | ≥ 230oC | ≥ 230oC | ≥ 250oC | ≥ 260oC | > 260 o C |
| Wet boiling point | ≥ 140oC | ≥ 140oC | ≥155oC | ≥155oC | ≥165oC | ≥180oC | ≥180oC |
| Viscosity at -40o (cSt) | ≤ 1,800 | ≤ 1500 | ≤ 1800 | ≤ 1500 | ≤ 750 | ≤ 900 | ≤ 900 |
Brake fluid specifications may be used depending on the vehicle and brakes, as prescribed and approved by the vehicle or brake system manufacturer. To avoid misuse, consult the vehicle manufacturer. The ISO 4925 Class 6 classification corresponds to newly developed fluids that have low viscosity even at the lowest temperatures. They allow for greater safety and faster response of vehicles with ABS, ASR and ESP/DSC systems.
Glycol-based brake fluids are hygroscopic and become increasingly enriched with water when combined with the atmosphere. This property ensures the distribution of the water content in the fluid. At the same time, there can be no isolated water that can freeze at 0 °C and boil at 100 °C. But even the smallest amount of water can lower the boiling point of brake fluid. Replacing the brake fluid Therefore, it is recommended to replace the brake fluid every year, necessarily no later than after two years of use of the vehicle, regardless of the kilometers travelled. Observe the health hazards of brake fluid. Brake fluid is highly corrosive. Therefore, varnished surfaces, shoes and clothing should be rinsed immediately with plenty of water.
