The vacuum booster is provided with reduced pressure from the intake manifold through a suitable hose. When braking, due to the difference between atmospheric pressure and air pressure from the intake manifold, a large elastic membrane is displaced, which additionally acts on the piston of the brake master cylinder. When the engine is off, the vacuum booster does not provide additional assistance when applied to the brake pedal. If the engine suddenly stalls, then the created reserve of reduced pressure is enough for a few more braking.
Vehicles with a diesel engine are equipped with a pump that provides reduced pressure to the vacuum booster, due to the absence of one in the intake manifold (see illustration 8.0).
To improve the functioning of the vacuum booster, cars with a five-cylinder gasoline engine are additionally equipped with an appropriate pump. This pump is camshaft driven and located on the left side of the cylinder head (see illustration 8.0a).
Examination
1. Stop the engine.
2. Depress the brake pedal 10 times.
3. Leave the brake pedal depressed and start the engine. If the vacuum brake booster is normal, then the brake pedal will move down a little more when the engine is running. If this does not happen, then the vacuum booster is faulty. The most likely cause of the defect is a leak in the low pressure air supply hose from the intake manifold, a malfunction of the check valve on the low pressure hose, wear of the rubber sealing ring between the main brake cylinder and the vacuum booster or the vacuum booster cuff.
4. Disconnect the low pressure air supply hose from the vacuum booster to check the check valve. When purging, the valve must freely pass air, blocking its access during suction. The check valve is supplied with the hose.
5. Dismantle the main brake cylinder if the O-ring between the cylinder and the amplifier turned out to be the reason for the failure of the vacuum booster.
6. Replace the vacuum brake booster if it is out of order. Repair of the vacuum booster is not possible (see illustration).
Withdrawal
7. Remove the main brake cylinder.
8. Disconnect the low air pressure hose.
9. Remove an overlay under the panel of devices in space for legs of the driver's side.
10. Remove, acting in the footwell, the swivel shaft from the fork of the drive rod of the vacuum booster.
11. Turn away from salon self-locking nuts of fastening of the vacuum amplifier on a dividing wall.
12. Turn away two nuts over the vacuum amplifier in a motor compartment.
13. Remove the vacuum booster.
When installing a new vacuum booster, it is necessary to adjust the length of its drive rod. Adjustments are made before a new amplifier is installed. The distance between the middle of the fork and the mounting surface on the four thrust pins must be 271 mm (tolerance - 0.5 mm).
14. Tighten the jam nut after adjusting the traction.
15. Lubricate the fork shaft with a thin layer of grease. Replace the old self-locking nuts and roller mounting brackets with new ones.
16. Do not forget to install a new sealing ring between the main brake cylinder and the vacuum booster.
Visitor comments