Contents: Checking the brake fluid level ⤓ Checking the brake fluid level sensor ⤓ Checking the brake system for leaks…⤓
This yellowish, usually poisonous and aggressive to paint liquid is neutral to metal and rubber parts. It remains even at 40°C still quite fluid and maintains this fluidity up to the boiling point which is about 260°C.
At the same time, brake fluid has one very unpleasant property: it readily absorbs water, i.e. it is hygroscopic. And moisture can actually, for example, from the air, get into the brake fluid through microscopic leaks in the tank, brake hoses and rubber cuffs. This water that gets in not only causes corrosion of the metal parts of the system, but also significantly reduces the boiling point. With only 2.5% water content, the boiling point is already only 150°C.
This is dangerous when the brakes are heavily loaded, as they become very hot and with the heated brakes, steam bubbles form in the brake fluid, which can be compressed. The brake pedal increases its travel and falls deeper, and sometimes completely. In such cases, the situation can be corrected by quickly pumping the pedal. This effect is especially dangerous after the car has been parked after heavy load on the brakes. With insufficient air flow, the space around the brakes heats up even more, the high temperature remains for about 15 minutes after stopping and only after about 30 minutes the normal temperature of the brake fluid is restored. To prevent these effects, it is recommended to replace the brake fluid every 2 years.
Brake fluid must meet DOT3 or DOT4 specifications. All fluids with these designations can be mixed safely.
Checking the brake fluid level
The brake fluid level in the reservoir should not fall below the lower MIN mark, otherwise a leak in the hydraulic system may be suspected. Too low a fluid level in the reservoir causes the control lamp on the instrument panel to light up. The contact is closed by a float in the reservoir, which moves down as the amount of brake fluid decreases, but do not neglect a visual inspection.
Checking the brake fluid level sensor
Open the hood and wipe the brake fluid reservoir with a clean rag.
In the transparent tank, the fluid level should be between the MIN and MAX marks.
By pressing the float of the brake fluid level sensor, check the condition of the circuit between the sensor terminals.
The sensor is in good working order if the following conditions are met: when the float is above the "MIN" mark, the circuit is open, and when it is below, the circuit is closed.
Checking the brake system for leaks and damage
To check, dry the bottom of the car to make it easier to identify leaky spots. Brake fluid flows under the dirt. Wet dark spots or black dirt can indicate the leak.
Check all joints and connections, as well as the brake calipers and shield, behind which the wheel brake cylinders are located.
The brake hoses should not be wet, oily or frayed. If this is the case, the hoses must be replaced.
Brake pipes have a coating to protect against rust. If this protective layer is damaged, it can lead to rust formation. Therefore, the pipes should not be cleaned with a screwdriver, sandpaper or wire brush, but only with chemicals.
If the protective layer is damaged, it is necessary to apply a thin layer of anti-corrosion primer.
Tubes with rust spots or pinched tubes should be replaced.
Check if there are protective caps on all the bleed valves? They are located on the brake calipers or inside the brake shields.
You can perform a brake pressure test yourself.
Press the brake pedal with full force.
The pedal should not weaken after several minutes of pressing - otherwise there is a defect in the cuff of the main brake cylinder.
Loose spots on piston seals can only be detected by careful inspection in a workshop.
Replacing brake fluid.
The need to replace the brake fluid is caused not only by the already described formation of steam bubbles, but also by the possibility of corrosion in the brake cylinders and pipes due to water absorption. When changing the fluid, the operations are similar to the operation of removing air from the system. 0.6 liters of fresh fluid is required.
If possible, empty the brake fluid reservoir using a syringe or rubber bulb.
Place the tubes on all four bleed valves, lower the other ends of the tubes into suitable containers and open all four bleed valves.
Have an assistant pump the pedal until fluid stops coming out. Close the valves, fill the system with clean brake fluid, and then bleed the system (see further).