How a vacuum brake servo/booster works.
A Vacuum Servo also known as a power booster or power brake unit uses a vacuum to multiply the drivers pedal effort and apply that effort to the master cylinder.
The Servo unit is situated between the brake pedal and the master cylinder, and is failsafe. If the source of vacuum is lost or the unit fails for any other reason, there is a physical connection between the pedal and the master cylinder allowing the brakes to be applied, however, without assistance the braking force is reduced and the stopping distance will in turn increase.
How to test a Vacuum Brake Servo/Booster.
There are a couple of simple tests that can be carried out to determine the operation and serviceability of the vacuum servo unit.
These tests can be carried out while sitting in the drivers seat and will show the vacuum servo's ability to boost the drivers efforts and retain vacuum in the event of a vacuum pump failure.
Questions answered. How much assistance does a Vacuum Brake Servo/Booster give?
This video looks at where the vacuum comes from in both normally aspirated and super/turbocharged engines, and tests how much assistance we actually get from a brake booster / vacuum servo unit. Which in turn shows how much of your braking effort will be lost if your vacuum boosted servo system fails.
Drum Brakes Explained
So what's better? Disc or drum brakes?
Well, the answer isn't that straightforward as they both have their merits. In this video we take a look at drum brakes and how they work. One advantage of drums over discs is the effort required by the driver or the system to apply the brakes for the same amount of braking force is far less than a disc brake system. Where a disc system usually needs a way of boosting the drivers pedal effort with a vacuum servo / brake booster, drum brakes have a self wrapping / self servo action as the rotation of the drum against the leading edge of the leading shoe actually pulls the brake shoe into the drum.
This same self wrapping action make drum brakes ideal for use as parking brakes as when the vehicle is stationary, there is unlikely to be a boosted effort, and the self wrapping action helps to keep the force applied if the vehicle tried to move.
Of course, there are disadvantages to having drum brakes, the main one being that they aren't great at getting rid of the heat they generate and contamination isn't easy to get rid of once it's in the drum.
What do you think is best? Discs or drums?
ABS - an explanantion by Bosch
ABS (Anti Lock Braking) is sometimes referred to as an anti-skid system. The system is designed to prevent the locking of a vehicles wheels while braking., especially on slippery road surfaces.
The main advantage of and ABS system is that it can optimise the available braking efficiency on most surfaces and bring the vehicle to a safe and controlled stop in the shortest distance.
Disc Brakes - An explanation of a disc brake system including floating and fixed caliper.
A look at brake discs and calipers
Split/Divided Hydraulic braking systems on modern cars
A look at split and divided braking hydraulic braking systems.