When checking the tightness of the vacuum brake booster, make sure the joint between the vacuum booster and the master brake cylinder is tight. If a leak is found, replace O-ring A.
Checking the tightness of the vacuum brake booster is carried out on a car with a working hydraulic brake drive.
Connect a vacuum pump between the vacuum booster and vacuum source (intake manifold) using a tee and the shortest possible tube.
Let the engine idle for one minute.
Pinch the tube (clip Mot. 453-01) in the area between the tee and the vacuum source.
Stop the engine.
If the vacuum drops by more than 33 mbar within 15 s, then there is a leak through:
- check valve (replace it);
- piston diaphragm (replace vacuum booster).
With a faulty vacuum booster, the brake system remains operational, but the force applied to the brake pedal for effective braking will be much greater than with a working booster.