Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/730290
52 | September - October 2016 | www.machinerylubrication.com BACK PAGE BASICS uncommon to experience caliper temperatures of 400 to 500 degrees F. Even with these higher than normal tempera- tures, the brake fluid still must perform. A fluid that reaches its boiling point will vaporize inside the line. This causes the fluid to become compressible and provide inadequate hydraulic transfer of the braking force. Boiling point can be broken into two cate- gories: dry and wet. The dry boiling point applies to the fluid straight from the container. The wet boiling point is measured based on a 3.7-percent water absorption. Another essential property of a brake fluid is its viscosity. Fluids must meet SAE specifica- tions at minus 40 degrees C and 100 degrees C. For the different classifications, the minimum and maximum viscosity ranges will vary. Packaging The packaging in which a brake fluid is shipped and stored is also important. Before purchasing, always ensure the foil cap is intact. A damaged bottle or cap will expose the fluid to moisture contamination. According to FMVSS No. 116, there are stan- dards for packaging and labeling by which all manufacturers must abide. Purchase only the amount of brake fluid you need, as opposed to buying a larger bottle just because it is a better deal. Any leftover fluid should be disposed of once it has been opened, since any humidity will be sucked into the fluid, degrading the performance of the braking system when you perform a top-off or refill the system. Final Thoughts When deciding which brake fluid to purchase, the best advice is to stick with what's in your system. Just because a fluid falls within a certain classification doesn't mean it won't provide equal or better performance than a fluid with a higher classification. Depending on the composition, a DOT 3 fluid may have a better boiling point than a DOT 4 fluid. In addi - tion, vehicles with an anti-lock braking system (ABS) are designed to work within the viscosity range of the specified classification. Keep in mind that even though all fluids meeting DOT specifications must be compat - ible, mixing is not recommended. DOT 5 fluids should never be mixed with other classifica- tions. The different boiling points and standards can result in decreased performance. A vehicle specified to use a DOT 3 fluid was designed and tested for the compatibility of the DOT 3 fluid's chemical composition. Changing classifications will alter the chemical composition, and the compatibility of components will be unknown. Therefore, when switching fluids, a full system cleanse should be performed. Unless you are a professional racecar driver, a change in brake fluid will likely be unnotice - able. When replacing your fluid, it's more important to properly bleed your system and seal everything. Also, don't use brake fluid that has been sitting around for an extended period of time. As mentioned previously, brake fluids are hygroscopic, so any humidity will end up inside the bottle. By changing your brake fluid every one to two years, you should enjoy many years of reliable braking. About the Author Garrett Bapp is a technical consultant with Noria Corporation, focusing on machinery lubrica- tion and maintenance in support of Noria's Lubrication Program Development (LPD). He is a certified lubrication specialist through the Society of Tribologists and Lubrication Engineers (STLE) and holds a Machine Lubrication Technician (MLT) Level II certification through the International Council for Machinery Lubrication (ICML). Contact Garrett at gbapp@noria.com. 52 | September - October 2016 | www.machinerylubrication.com Testing Brake Fluids The Federal Motor Vehicle Safety Standards (FMVSS) No. 116 stipulates the requirements for motor vehicle brake fluids. To be considered for one of the DOT classifications, a brake fluid must go through the following tests: 1. Equilibrium reflux boiling point (dry boiling point) 2. Wet equilibrium reflux boiling point (tested with 3.7 percent water) 3. Kinematic viscosities 4. pH value 5. Brake fluid stability (high-temperature and chemical stability) 6. Corrosion 7. Fluidity and appearance at low temperature 8. Reserved 9. Water tolerance (low temperature and at 60 degrees C) 10. Compatibility (low temperature and at 60 degrees C) 11. Resistance to oxidation 12. Effects on cups 13. Stroking properties 14. Fluid color