What you need to know about brake fluid
Brake fluid (TF) occupies a special position among all automotive fluids. It is literally of vital importance, since it largely determines the effectiveness of the braking system, which means that in many situations someone's life can depend on it. Like any other liquid, TZH is practically incompressible and therefore instantly transfers force from the main brake cylinder to the wheel cylinders, providing vehicle braking.
TJ classification
DOT standards developed by the US Department of Transportation have become generally accepted. They determine the main parameters of TJ - boiling point, corrosion resistance, chemical inertness with respect to rubber and other materials, the degree of moisture absorption, etc.
Fluids of classes DOT3, DOT4 and DOT5.1 are made on the basis of polyethylene glycol. The DOT3 class is already obsolete and almost never used. DOT5.1 is used primarily in sports cars with ventilated brakes. DOT4 fluids are designed for cars with disc brakes on both axles, this is the most popular class at the moment.
DOT4 and DOT5.1 fluids are quite stable and have good lubricating properties. On the other hand, they can corrode varnishes and paints and are quite hygroscopic.
They need to be changed every 1-3 years. Despite the same basis, they may have different parameters and components with unknown compatibility. Therefore, it is better not to mix them unless absolutely necessary - for example, you have a serious leak and you need to get to the garage or the nearest service station.
DOT5 class fluids have a silicone base, last 4-5 years, do not destroy rubber and plastic seals, they have reduced hygroscopicity, but their lubricating properties are much worse. They are not compatible with DOT3, DOT4 and DOT5.1 TAs. Also, DOT5 class fluid cannot be used on machines with ABS. Especially for them there is a DOT5.1 / ABS class, which is also produced on a silicone basis.
The most important properties
During operation, the TJ should not freeze or boil. It must remain in a liquid state, otherwise it will not be able to perform its functions, which will lead to brake failure. Boiling requirements are due to the fact that during braking, the liquid can become very hot and even boil. This heating is due to the friction of the brake pads on the disc. Then there will be steam in the hydraulic system, and the brake pedal may simply fail.
The temperature range in which the liquid can be used is indicated on the packaging. The boiling point of fresh TF is usually in excess of 200 °C. This is quite enough to eliminate vaporization in the brake system. However, it should be remembered that over time, TJ absorbs moisture from the air and can boil at a much lower temperature.
Just 3% water in a liquid will lower its boiling point by about 70 degrees. The boiling point of "wetted" brake fluid is also usually listed on the label.
An important parameter of TF is its viscosity and ability to maintain fluidity at low temperatures.
Another characteristic to pay attention to is the compatibility with the materials used for sealing. In other words, the brake fluid must not corrode the gaskets in the hydraulic system.
Change frequency
Gradually, TJ gains moisture from the air, and performance deteriorates. Therefore, it must be changed periodically. The standard replacement period can be found in the service documentation of the car. Usually the frequency is from one to three years. Experts recommend in the general case to focus on a mileage of 60 kilometers.
Regardless of the period of operation and mileage, the TJ should be replaced after a long period of inactivity of the car or after repair of the brake mechanisms.
There are also instruments that can measure the water content and boiling point of the brake fluid, which will help determine if it needs to be changed.
A brief brake failure followed by a return to normal is an alarm that indicates that the moisture content of the brake fluid has exceeded an acceptable limit. Due to the decrease in the boiling point of the TF, a vapor lock forms in it during braking, which disappears as it cools. In the future, the situation will only worsen. Therefore, when such a symptom appears, the brake fluid must be changed immediately!
TJ needs to be changed completely, it is impossible to be limited to topping up to the desired level.
When replacing, it is better not to experiment and fill in what the car manufacturer recommends. If you want to fill in liquid with a different base (for example, silicone instead of glycol), a thorough flushing of the system will be required. But not the fact that the result will be positive for your car.
When buying, make sure that the packaging is airtight and the foil on the neck is not torn off. Don't buy more than you need for one refill. In an opened bottle, the liquid quickly deteriorates. Be careful when handling brake fluid. Do not forget that it is extremely poisonous and flammable.
