The main brake cylinder. Car brake system
The master brake cylinder on cars is of key importance, since it is with its help that the system creates the pressure needed to compress the calipers of the wheels. In order to understand how to correctly diagnose and repair this site, you need to know what it consists of, what elements are subject to the most wear and require special attention. You will also need to learn how to bleed the brake system after replacing the cylinder.
Features of the master cylinder
To create pressure in the brake system, it is necessary to transfer the force that occurs when you press the pedal to the piston of the cylinder. It is worth noting that the effort must be very large, and even when rubbing the pads on the discs, vibration arises, which is perfectly transmitted by the liquid. As a result, the pedal starts to rattle, the foot is hit, especially when driving on a rough road.
For this purpose, a vacuum brake booster is provided, which is installed between the pedal and the cylinder. It allows you to avoid shocks, and also increases the force of depression. As a result, pressing the pedal does not require good physical fitness, braking efficiency is improved. On the first cars of VAZ, for example, model 2101, there was no vacuum booster. Who went, he knows what effort must be applied to make a stop. And the sensitivity leaves much to be desired.
The basis of the cylinder is a metal case. It has three threaded holes to which the brake pipes are connected. Two are directed to the front wheels, and one - to the rear. There are also two tubes designed to be connected to the expansion tank. The brake master cylinder 2109 connects directly to it without the use of flexible hoses.
Inside the unit is divided into two chambers in which there are two pistons. They are interconnected, which ensures uniform pressure in all circuits of the system. On the pistons there are rubber cuffs.They are necessary for sealing, so that the liquid does not flow out of the housing. Fastening to the vacuum amplifier is made using studs on the latter. Replacing the master cylinder is to disconnect from the old system and install a new one.
How to diagnose faults
Damage to the brake cylinder is not very much, and more precisely, two - the formation of leaks and the destruction of metal elements (eg, springs). It is worth noting that the latter happens extremely rarely, leaks of brake fluid appear much more often. And in some cases, to notice them immediately fails, since everything goes into a vacuum amplifier.
But the main sign is noticeable immediately - the liquid leaves the expansion tank. First, carefully inspect the brake pipes and hoses, then calipers. If they do not find any leaks of brake fluid, then we can conclude that the cylinder's sealing gum has become unusable, that is, erased. Perhaps the master cylinder repair kit used in the last repair was of poor quality.
On VAZ cars, it is quite rare to remove the brake master cylinder, as it is a reliable unit, if you follow it, it will serve for many years. But if the need arose, then you will need to pay attention to when the last brake fluid change was carried out. It is recommended to do this approximately once every two years, at least. The fact is that it contains additives that evaporate under the action of high temperature (but imagine how the liquid heats up during compression). And the braking performance without additives is getting worse.
First drain the brake fluid from the system and remove the expansion tank. To unscrew the brake pipes, use a special wrench type. Pay attention to the fact that the faces of the tips of the tubes are made of soft metal, when they try to unscrew with an open-end wrench they will come together. And to conduct the removal of the node will be problematic. After disconnecting the tubes, you can safely unscrew the two nuts that secure the cylinder to the brake booster. Now the node is ready for repair.
Should I install a brake master cylinder repair kit?
It is rather difficult to answer this question, but if you go into details, it turns out that the repair kit is not able to improve the state of the brake system. And for this there are several reasons. Compare with the cylinder and piston of an internal combustion engine. They have one common parameter - repair size. In other words, in the presence of production on the surface of the cylinder of the internal combustion engine, a liner bore and the installation of pistons large in diameter are necessary. As a result, all sizes are the same, tightness at a high level.
And now pay attention to the brake cylinder. On its inner surface is also present development. But during the repair the piston remains the same, only the sealing ring changes. First, it can be made of low-grade rubber, which will collapse under the action of a liquid. Secondly, its size may not correspond to the diameter of the cylinder. And the chance to stumble on a fake is extremely high. Much more effective will be the replacement of the entire unit. However, the price of the main brake cylinder does not bite much, for VAZ 2108-21099 it varies in the range of 700-800 rubles, depending on the manufacturer and seller.
Disassembly and assembly site
To remove the pistons, springs, rod from the cylinder body, you will need to unscrew the two bolts at the bottom. They are intended for fixing so that the pistons do not fall out of the housing. It is advisable to hold the hole in the cylinder with your finger. Just because this mechanism does not understand, it must be a good reason. This is usually the appearance of a leak, so the replacement of rubber seals is carried out during disassembly. It is worth noting that the rings must be changed in any case, it does not matter at all whether they are in good condition.
Even if it is close to perfect, you need to change them to avoid problems. After the repair, the entire assembly is assembled in the reverse order; do not let dirt, dust, foreign objects get into the cylinder. This will lead to its destruction. Install the cylinder on the brake booster and connect the pipes, a surge tank to it. And then the most difficult procedure - pumping. It is unrealistic to replace the main brake cylinder of VAZ and do not pump.
Bleeding brake system
After completing the assembly, make sure that all connections are tight and tight.You will need a partner for this procedure, you only need him to squeeze the brake pedal at your command. Always start pumping from the far wheel (rear on the right side), then pump the second rear, and then the front on the right side. The left front wheel is pumped in the last turn. Type in a small jar brake fluid, take a transparent tube (for lack of a suitable one, you can use a section of the tube to which the windscreen washers are connected).
Put one end of the tube on the bleed nipple, and lower the other into a jar of liquid. This way you can observe if the system is airing. The partner makes 5-6 brake pedals, then fixes it in the squeezed state. At this time, you turn the nozzle half a turn, allowing air to escape. You spin, and the assistant again presses the pedal. And so on, as long as no air remains in the system. Just watch the level of fluid in the tank, otherwise you will need to repeat the procedure again.