Brake fluid is critical to the function and performance of your brake system. Choosing the right brake fluid will insure trouble free functioning for many years. Conversely, the wrong brake fluid will damage seals and cause the failure of your brake system. There are two predominant “families” of brake fluid in use worldwide:
A. The first family is polyethylene-glycol based and is compatible with only EPDM seals.
These fluids have been developed for the hydraulic brakes of motor vehicles and are called DOT3, DOT4, DOT5 or DOT5.1
DOT3 has lower performance and has been replaced by DOT4. DOT4 is the most commonly used fluid in motor vehicles. DOT5 is usually silicone-based, but is not commonly used, and is not miscible (“mixable”) with DOT3 or DOT4. DOT5.1 is not miscible with DOT5 and may also be not miscible with DOT3 or DOT4.
The primary objection to DOT 3 and 4 fluids was that they are hygroscopic (they absorb water). However, in a sealed reservoir, in a corrosion-resistant brake system, DOT4 fluids will remain usable for minimum 10 years. Additionally DOT3 and 4 brake fluids are aggressive with paint. Continent systems and care in handling remove this negative.
In the “DOT” family, we recommend using DOT4 and only DOT4 because the performance is adequate, and all DOT4 brands are miscible with each other.
DOT4 is used on many ultralight aircraft. You can purchase DOT4 almost everywhere around the globe as it is used on all recent cars and most motorcycles.
B. The second family is mineral-oil based and compatible with only* NBR (Nitrile) seals.
The hydraulic fluid MIL-H-5606 has been commonly used in general aviation for many years.
The major deficiencies of MIL-H-5606 are its high flammability and a relatively low boiling point.
In the ”mineral” or “MIL” family we recommend using the MIL-PRF-87257 as a replacement of the MIL-H-5606. These 2 fluids are compatible and miscible each other. MIL-PRF-87257 is fire resistant and synthetic-hydrocarbon based, it has also a higher boiling point than MIL-H-5606.
NBR (Nitrile) seals >>> mineral fluid >>> red color >>> MIL-PRF-87257 recommended
EPDM seals >>> DOT4 brake fluid >>> colorless to amber color >>> DOT4 only
EPDM seals are very sensitive to petroleum based solvent: few minutes of contact can completely damage the EPDM seals. That is why we recommend cleaning the parts only with a dry cloth or soap and water.
* These fluids may be compatible with other seal materials (contact us for more information)