Test pressures for front brakes are 100 kg/cm2. These pressures are given for the 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.
The normal pressure in the hydraulic system when the brakes are not working is negligible. When the brakes are applied, the pressure rises rapidly and remains in the system until the pedal is released. Each driver will imagine how quickly the pressure rises by equating the rate of its rise to the rate of his own reaction during emergency braking.
Recent studies have shown that corrosion of brake pipes can lead to brake failure after as little as 80 days of exposure to the salt used to thaw ice and snow on the roads. This actually gives grounds to automatically suspect the presence of defects in the brake pipes on a four-year-old car. As a replacement, you can use tubes made of copper alloy.
All of the above points to the need for regular inspection of the tubes. Obviously, the inspection should be carried out in the autumn before the onset of winter and in the spring - to assess the extent of damage caused by corrosion.
Trace all the hard tubes and wash or brush off the dirt. If you see that the tubes are covered with some kind of anti-corrosion bottom compound, do not touch them. Inspect the tubes for dents that may have been caused by rocks flying off the wheels. If you find any of these, replace the defective tubing section, but read the rest of this section before doing so. Any unprotected section showing signs of corrosion or pitting on the outer surface may need to be replaced.
Flexible hoses going to each of the front wheels from under the bottom to each rear wheel should not have scuffs or cracks. Bend them and see if cracks appear on the surface. If the hoses are stiff and inflexible or kinked, it 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 spare parts if you do not want to be without a car for a long time. When removing the tube is often damaged.
Support brackets are installed where rigid tubing meets flexible hoses, and the flexible tubing is held in place by a U-clamp that fits into a groove in the fitting. Before using a wrench, soak the fittings with brake fluid, since there is always a slight corrosion in the fitting, which will prevent unscrewing. While the fittings are soaking, place a piece of plastic wrap under the brake fluid reservoir cap and wrap the cap. This is necessary to minimize fluid leakage from the disconnected tubes. Hold the hex on the flexible hose coupling while unscrewing the union on the rigid tube. Then pull out the clip to release both tubes from the bracket. In order to remove the flexible hose, you will need to perform this operation at both ends. For a rigid tube at the other end, you only need to unscrew the fitting from the cylinder or connector. When replacing a flexible hose, be careful not to damage the fittings of the tubes attached to it. If the fitting is particularly stubborn, be prepared to replace the hard tube as well. This happens quite often when using open end wrenches. It might make sense to spend some money on a special wrench for fittings, which looks like a box wrench with a cutout for the passage of the tube.
If you order a new tube from the workshop, take the old tube with you as a sample so that the fittings and sockets on the ends are identical.
Replacing hoses or tubes is carried out in reverse order. Appropriate care must be taken to ensure that the fittings are aligned when screwing in so as not to damage the threads. This means that it may be necessary to slightly bend the tube 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 the fittings are finally tightened if you do not hold the end of the flexible hose with a wrench.
If a stiff tube is removed or the fitting is loosened enough to allow air to enter the system, the system must be bled.