Maintenance of the vacuum booster (servo drive) of the brakes

Removing

1. Remove the GTZ from the car.

2. Disconnect vacuum hoses from the block of the vacuum amplifier.

3. Remove the mounting clip, bend the tongues of the plastic limiter, remove the mounting pin and disconnect the pusher from the brake pedal.

4. Give nuts of fastening of the vacuum amplifier and, having moved aside a basic arm of the control valve, remove the amplifier from the car.

Installation

Installation is in the reverse order.

1. Check up correctness of adjustment of a pusher of the vacuum amplifier, in case of need make adjustment. Check the setting of the height of the position and the amount of free play of the brake pedal, if necessary, adjust the listed parameters.

2. Tighten the fixing nuts to the required torque.

Function test

1. With the engine off, depress the brake pedal several times to release the vacuum from the vacuum booster.

2. Lightly depress the pedal and hold it in this position.



3. Start the engine. The pedal should drop noticeably down. Otherwise, you should check the serviceability of the vacuum supply to the block (see accompanying illustration):

• Check the vacuum hoses for signs of material aging and other damage. Replace defective ones.
• Disconnect the vacuum hose from the vacuum booster unit and with the engine running at idle, check for vacuum by plugging the end of the hose with your thumb.
• Disconnect vacuum hoses, release a fixing collar and remove the control valve from the block of the vacuum amplifier.
• Blow into the valve from the side of the vacuum booster. Air must pass freely.
• Try to suck air through the same valve hole. This time the valve should be closed. Replace check valve if abnormal.

Pusher adjustment

1. Remove the block of the vacuum amplifier from the car.

2. Connect a hand vacuum pump equipped with a vacuum gauge to the hose fitting on the unit.

3. Create a negative pressure of 500 mm Hg in the vacuum tube of the amplifier. Art. and measure the protrusion of pusher A above the seating surface of the GTZ (see accompanying illustration). The nominal value is A = 10.275÷10.525 mm.



4. If necessary, adjust the length of the pusher, achieving the required protrusion.