The test pressures for the front brakes are 100 kg/cm². These pressures are given for a cold state of the brake system. The temperature of the drums and discs during emergency braking from a speed of 90 km/h reaches 80°C, and during a long descent on the brakes it can reach 400°C. The pressure must be increased even more as the temperature of the brake fluid in the cylinder increases.
Normal pressure in the hydraulic system when the brakes are not working is negligible. When the brakes are applied, pressure builds up quickly and remains in the system until the pedal is released. Every driver will imagine how quickly the pressure increases, equating the speed of its rise to the speed of his own reaction during emergency braking.
Recent studies have shown that corrosion of brake lines can lead to brake system failure after just 80 days of exposure to salt used to melt ice and snow on roads. This effectively gives grounds to automatically suspect the presence of defects in the brake pipes on a four-year-old car. Tubes made of copper alloy can be used as a replacement.
All of the above indicates the need for regular inspection of the tubes. Obviously, inspection should be carried out in the fall before winter sets in and in the spring to assess the extent of damage caused by corrosion.
Trace the routes of all hard pipes and wash or brush away any dirt. If the tubes appear to be coated with any kind of anti-corrosion underbody compound, do not touch them. Inspect the tubes for dents that may have been caused by stones flying from the wheels. If you find any of these, replace the defective section of tube, but read the rest of this section before doing so. Any exposed section that shows signs of corrosion or pitting on the outer surface may need to be replaced.
The flexible hoses running to each of the front wheels, from under the bottom to each rear wheel should not have any abrasions or cracks. Bend them and see if any cracks appear on the surface. If the hoses are stiff and inflexible or kinked, this means they are nearing the end of their service life. If in doubt, replace the hoses. Also make sure that they do not rub against the body.
Before attempting to remove the tube for replacement, it is important to be sure that you have the necessary replacement parts if you do not want to be without your car for a long time. When removing the tubes they often get damaged.
Where the rigid tubes meet the flexible hoses, support brackets are installed and the flexible tube is held in place with a U-shaped clamp that fits into a groove in the fitting. Before using a wrench, soak the nipples in brake fluid, as there is always a small amount of corrosion in the nipple that will prevent it from being loosened. While the fittings are soaking, place a piece of plastic film under the lid of the brake fluid reservoir and screw the lid on. This is necessary to minimize fluid leakage from disconnected tubes. Hold the hex key on the flexible hose coupling while loosening the nipple on the rigid tube. Then pull the clamp out to release both tubes from the bracket. To remove the flexible hose, you will need to perform this operation on both ends. For a rigid tube on the other end, you only need to unscrew the nipple from the cylinder or connector. When replacing the flexible hose, be careful not to damage the fittings of the tubes connected to it. If the nipple is particularly stubborn, be prepared to replace the rigid tube as well. This happens quite often when using open-end wrenches. It might be worth spending a little money on a special nipple wrench, which is like a box wrench with a notch for the tube to fit through.
If you order a new tube from a repair shop, take the old one with you as a sample so that the nipples and sockets at the ends are identical.
Replacing hoses or tubes is done in reverse order. Appropriate care must be taken to ensure that the fittings are aligned when tightening to avoid damaging the threads. This means that you may have to bend the tube a little where it enters the connection, but this bend should never be too sharp.
When installing flexible hoses, be careful not to twist them. This can happen when final tightening of the fittings if the end of the flexible hose is not held with a wrench.
If a rigid tube is removed or a fitting is loosened to the point that air can enter the system, the system should be bled.