Checking the vacuum brake booster

The vacuum booster is designed to create additional force applied to the rod of the master brake cylinder. The vacuum in the brake booster is created by reduced pressure in the intake manifold.

The vacuum booster cannot be repaired and is replaced in the event of a malfunction. If, with the engine running, an unusual amount of pedal force is required to achieve adequate braking, have the brake booster checked.

Check vacuum booster in the following order:

• press the brake pedal 5-6 times with the engine off to create the same pressure in the vacuum and atmospheric chambers of the vacuum booster, close to atmospheric (remove the vacuum);
• keeping the brake pedal depressed, start the engine;
• with a working vacuum booster, the brake pedal after starting the engine should «go ahead» and loosen the resistance force on the leg;
• if the brake pedal is not «goes ahead», check the tightness of the connecting hose between the inlet and the booster or the vacuum booster itself.

The non-return valve may also be the cause of the malfunction of the vacuum booster. Using a screwdriver, carefully squeeze out the valve and blow it in the direction of the arrow stamped on the valve. The purge air must exit from the other side of the valve. If you blow against the arrow stamped on the valve, then the air, on the contrary, should not come out from the other side. During installation, the valve is pressed into the vacuum brake booster.

Attention! The cause of the malfunction of the vacuum brake booster should be sought at the service station.

Removing and installing a vacuum booster without an installed ABS system

Note. The description of removal and installation of the vacuum booster with the ABS system installed is presented in paragraph 15.9.1.

Withdrawal vacuum booster in the following order:

• remove the wire «–» from the output of AB;

• remove partitions of compartment AB (pic. 328);
• remove the noise insulation located in the engine compartment of the engine;
• remove AB;
• remove the expansion tank of the cooling system;
• disconnect the multi-pin connector for indicating the temperature of the coolant and unscrew the two bolts;
• unscrew two bolts and remove the right partition of the AB compartment;
• unscrew one bolt and remove the left rear bulkhead of the AB compartment. Set the expansion tank aside;
• disconnect the plug on the brake fluid reservoir cap and unscrew the reservoir cap;
• using a siphon pear, pump out the brake fluid from the reservoir and remove the master brake cylinder;
• disconnect the vacuum hose going to the vacuum brake booster;
• remove the lower casing of the instrument panel from the driver's side;

• remove spring clamp 1 (pic. 329), then remove the connecting pin 2 and disconnect the brake booster pusher rod from the brake pedal;
• unscrew the four nuts securing the vacuum brake booster and remove it.

Installation the vacuum booster, carry out in the reverse order of removal, performing the following:

• tighten the four nuts securing the vacuum booster to 40 Nm;
• install brake master cylinder (see 15.5.1);
• after installation, restore the fluid level in the tank and bleed the hydraulic drive system.