Examination
The vacuum brake booster increases the force applied to the brake pedal, thereby making driving easier. The principle of operation of the vacuum brake booster is based on the use of vacuum in the intake manifold. When the vacuum booster fails, the brake system does not work, but it is necessary to apply much more effort to press the brake pedal.
Press the brake pedal several times with the engine off to create the same pressure in the cavities of the vacuum booster, close to atmospheric. At the same time, by the force applied to the pedal, determine if the valve body is sticking. Stop the brake pedal in the middle of its travel and start the engine. With a working vacuum booster, the brake pedal should go down after starting the engine. If the pedal does not go away, check the fastening of the vacuum hose tip, the connection of the tip flange in the amplifier, the condition of the hose and fitting.
Wait two minutes and turn off the engine. Press the brake pedahp each successive pressing, the pedal should become harder, and the pedal travel should decrease.
Removing
Disconnect the vacuum hose connecting the intake manifold and the vacuum brake booster. Be careful not to damage the vacuum hose when removing the vacuum booster valve from the fitting.
Remove the master brake cylinder. On models prior to 2001, remove the air intake duct and fuse/relay box.
Remove the lower trim panel from the left side of the instrument panel.
Remove the brake pedal return spring.
Pic. 11.39. Vacuum brake booster mounting: A - pin; B - nuts
Disconnect the brake booster pushrod from the top of the brake pedal by removing the cotter pin and removing the pin (pic. 11.39).
From inside the car, unscrew the four nuts securing the vacuum brake booster to the bulkhead of the engine compartment and remove the vacuum brake booster from the engine compartment.
Installation
Install in the reverse order of removal, taking into account the following.
If a new vacuum booster is installed, then check the pusher clearance as follows:
Pic. 11.40. Measuring the protrusion of the push rod of the vacuum brake booster (size A)
- measure the distance that the push rod of the vacuum brake booster protrudes from the mating surface of the master brake cylinder (pic. 11.40), and write it down as dimension A;
- measure the distance from the end of the flange to the mating surface of the main brake cylinder and write it down as dimension B;
- measure the distance from the flange to the piston of the master cylinder and write it down as dimension C;
Pic. 11.41. Gap between pusher (2) brake booster and piston (1) master brake cylinder: X = 0 mm
- subtract size B from size A, then from the resulting value (A - B) Subtract dimension C to get clearance X (pic. 11.41) pusher 2, which should be equal to 0. If the gap is negative, i.e. the pusher of the vacuum booster presses the piston 1 of the main brake cylinder, then the wheels will be constantly braked. If there is a gap, then when braking, the brake pedal travel will increase.
If the clearance does not correspond to the required value, then adjust it by changing the length of the pusher. Use pliers to hold the pusher of the vacuum brake booster from turning and screw or unscrew the head of the pusher with a wrench.
After installing the brake master cylinder and connecting the brake pipes to it, adjust the brake pedal height and bleed the air from the hydraulic brake system.