Booster & Master Cylinder
Booster
A booster is typically located between the brake pedal and the brake master cylinder, and reduces the effort required for braking.
The booster is commonly a vacuum-powered design that runs off the vacuum created by the inlet suction of the engine, or off a vacuum pump, so it only works when the engine is running. This vacuum can be checked by experts. More sophisticated servo systems are powered by hydraulic pumps, typically the power steering pump.
When your brake booster fails, the integrity of the brake system itself is not affected, but you have to step much harder on the brake pedal to bring the vehicle to a stop. In a high performance vehicle the difference can be drastic and this kind of fault should always be attended to immediately.
The most common faults on boosters are a ruptured diaphragm or faulty valve. Some boosters can be rebuilt, while others are sealed units. Certain types are also prone to corrosion of the outer casing. Boosters can also be negatively affected when a leaking master cylinder seal allows brake fluid to leak into the booster.
Visit a reliable brake expert for advice - push rod settings on boosters are critical adjustments. An error in these settings can be dangerous, and can be the cause of extensive damage to your brake system.
Master Cylinder
The master cylinder displaces hydraulic brake fluid under pressure to the rest of the brake system.
When the brake pedal is depressed, the push rod moves the primary piston forward in the cylinder. The hydraulic force so created, and the action of the primary piston spring then moves the secondary piston forward. When the forward movement of the pistons cause the seals to move past the compensating ports, hydraulic pressure starts building up in the brake lines and are transmitted to the wheel cylinders. When the brake pedal is released, the pistons can be replenished with brake fluid from the reservoir, through the compensating ports, if required.
A dual brake master cylinder splits the hydraulic system in two halves - if a leak occurs in one half, the other will still operate, but braking efficiency will be greatly reduced, and the steering may be affected under braking. Obtain immediate advice from a reliable brake expert when you sense a difference in the response of your brakes.
Sensors monitor the level of brake fluid in the reservoir, and a warning light or computer message will alert the driver when brake fluid levels drop too low.
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