12.7. Removal and installation of the main brake cylinder

Brake fluid is poisonous. It also strongly dissolves paint. See the Prevention in the Section Pumping of Hydraulic System of Brakes.

Though for the majority of models there are spare parts and set for repair of the main cylinder, all of us recommend its full replacement on new or capitally repaired. You will need much more time for repair of the main cylinder, than for its replacement, besides you will not be able to define whether your main cylinder is subject to capital repairs until you remove it. And after that it can turn out that it cannot just be repaired.



  1. The main cylinder is connected to the vacuum amplifier of the brake system, and both of them fasten on a partition in the left part of a motive compartment. To remove the main cylinder, disconnect the electric socket (the top arrow), the union of the hydraulic brake line (the lower right arrow, other union is not visible on this photo) and give two nuts of fastening of the main cylinder (the lower left arrow, other nut is not visible on this photo).
  1. By means of the syringe pump out as much as possible liquid from the tank.
  2. Place pieces of rags under nipple connections of the line and prepare covers or plastic packages to stop up the ends of tubes after their detachment.

Brake fluid damages paint. Cover all parts of a body and try not to spill liquid during this procedure.

  1. Release connecting nuts on the ends of brake tubes where they unite to the main cylinder. To prevent breaking лысок on these nuts, it is necessary to use a special cutting cap ("brake") wrench which covers all nut.
  2. Accurately pull out brake tubes from the main cylinder and stop up their ends to prevent hit of dirt and leak of liquid.
  1. Disconnect all electric sockets from the main cylinder, then give nuts of fastening of the main cylinder to the vacuum amplifier of brakes. Pull together the cylinder from hairpins and pull out it from a motive compartment. And again be careful not to spill liquid. You will throw out a sealing ring between the main cylinder and the vacuum amplifier.

This sealing ring always should be replaced. The defective ring can serve as a vacuum cause of infringement that will reduce overall performance of brake mechanisms and will lead to their periodic failure.

Procedure of pumping


  1. Before installation of the new or capitally repaired main cylinder it should be blown on a workbench. It is recommended to install the main cylinder in a vice since it is necessary to give pressure upon its piston, and at the same time to operate a stream from exhaust outlets of brake tubes. Use a vice with the protected sponges and do not tighten them too strongly, otherwise the case of the main cylinder can burst.
  2. Insert caps with a carving into exhaust outlets of the brake line. Tighten them so that them air, but that they were easy to be released did not get.
  3. Fill the tank with brake fluid of the recommended type (see the Head Routine maintenance of the car).
  4. Pull out one cap and push assembly of the piston in a mirror of the main cylinder to remove air from the cylinder. Use for this purpose the big crosswise screw-driver.
  5. To prevent air hit back in the main cylinder, it is necessary to establish and tighten a cap before release of pressure on assembly of the piston.
  6. Repeat the procedure until from an exhaust outlet of the brake line brake fluid without vials of air does not go. Repeat the procedure for other exhaust outlet of the brake line with a cap. You watch the level of brake fluid in the tank to prevent hit of air in system.
  7. In the procedure of pumping on a workbench the high pressure therefore the caps described above it is not obligatory to establish every time at a piston otpuskaniye is not used. Instead, before releasing the piston, densely close an opening a finger that air did not get back to the cylinder. Wait several seconds that brake fluid got from the tank to the piston cylinder, then again squeeze out the piston, having taken away a finger at a liquid effluence. Do not forget to close an opening a finger every time before a piston otpuskaniye, and when the procedure for this opening is finished, establish a cap and tighten it before passing to other opening.



  1. Install the main cylinder (together with a new sealing ring) on hairpins of the vacuum amplifier and tighten fastening nuts fingers so far.
  2. Attach unions of the brake line to the main cylinder. As the main cylinder is not absolutely well fixed yet, it can be moved slightly that it was easier to attach unions. Do not strip a thread at delay in nipple connections.
  3. Delay nipple connections of the brake system and fixing nuts with the required effort.
  4. Fill the tank of the main cylinder with brake fluid, then pump over the main cylinder (only if it was not pumped over any more) and the brake system as it is described in the Section Pumping of Hydraulic System of Brakes.
  5. To pump over the cylinder directly on the car ask the assistant to squeeze out several times a pedal of a brake and then to hold it completely squeezed out. Release a nut of nipple connection to allow air and liquid to leave, then tighten a nut. Repeat this procedure until liquid without vials of air begins to come out. Carefully check work of brakes before normal operation of the car.