Braking Systems and Vehicle Control
This domain tests hydraulic braking, brake components, bleeding, brake fade, ABS and stopping distance.
Hydraulic braking
- Pascal's law states that pressure applied to a confined fluid is transmitted equally in all directions.
- The master cylinder creates pressure; wheel cylinders or calipers apply the brakes.
- Brake fluid is hygroscopic, so it absorbs water and should be replaced at the maker's interval.
- Air in the system makes the pedal spongy; bleeding removes it.
- Disc brakes use a caliper and pads; drum brakes use wheel cylinders and shoes.
Vehicle control
- Stopping distance = thinking distance + braking distance.
- Brake fade is loss of braking caused by heat, common with prolonged hard use.
- ABS prevents wheel lock and keeps steering control; it does not shorten every stopping distance.
- The parking brake acts on the rear wheels and is separate from the hydraulic service brake.
Worked example
A master-cylinder piston has an area of 4 cm² and receives a force of 200 N. Pressure = force ÷ area = 200 ÷ 4 = 50 N/cm². A wheel cylinder has an area of 16 cm², so force there = 50 × 16 = 800 N. The reasoning is that pressure is the same throughout, while force rises with piston area.
Traps
- Saying ABS always shortens stopping distance; on loose gravel it may lengthen it.
- Confusing brake fade with air in the lines.
- Opening the reservoir or bleeding without following the correct sequence.
- Using the parking brake as a normal service brake.