Contents: Checking the brake fluid level ⇓ Checking the brake system for leaks…⇓ Replacing brake fluid ⇓
This yellowish liquid, usually toxic and aggressive to paint, is neutral to metal and rubber parts. It remains quite fluid even at 40°C and maintains this fluidity up to its 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 reservoir, brake hoses and rubber cuffs. This ingress of water leads not only to corrosion of the metal parts of the system, but also to a significant decrease in the boiling temperature. With only 2.5% water content, the boiling point is already only 150°C.
This is dangerous when there is a heavy load on the brakes, as they become very hot. Near heated brakes, vapor bubbles form in the brake fluid and can be compressed. The brake pedal increases its travel and sinks deeper, and sometimes completely. In such cases, you can correct the situation by quickly pumping the pedal. This effect is especially dangerous after the car has been parked after a heavy load on the brakes. If the air flow is insufficient, the area 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 DOT 3 or DOT 4 specifications. All fluids with these designations can be safely mixed.
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. On some models, 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 tank, which moves downwards as the amount of brake fluid decreases, but you should not neglect a visual inspection.
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.
Checking the brake system for leaks and damage
To check, it is necessary to dry the bottom of the car to make it easier to identify any loose areas. Brake fluid is leaking under the dirt. Damp, dark spots or black mud may indicate the location of a leak.
Check all joints and connections, as well as the brake calipers and shield, behind which the wheel brake cylinders are located.
Brake hoses should not be wet, oily or frayed. If this occurs, the hoses need to be replaced.
The brake pipes are coated to protect against rust. If this protective layer is damaged, it can lead to the formation of rust. Therefore, the tubes cannot 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 rusty or flattened shells should be replaced.
Check that all air bleed valves have protective caps. They are located on the brake calipers or inside the brake shields.
You can perform a pressure test of the brakes yourself:
Apply full force to the brakes.
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 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 l of fresh liquid is required.
The original can be read on the resource: hyundaibook.ru
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 no more fluid comes out. Close the valves, fill the system with clean brake fluid, and then bleed the system (see below).