Brake Repair

Question 1

What things effect kinetic energy?

Answer 1

Kinetic energy is a mix of mass and speed squared.

Question 2

What things effect friction?

Answer 2

Pressure between two surfaces, composition of materials, and condition of surfaces.

Question 3

What is the equation of the coefficient of friction?

Answer 3

Force to move an object / weight of object.

Question 4

How does brake fade occur?

Answer 4

The brake rotor or drum absorbs heat faster than it dissipates it, the drum or rotor will reach a point where it can’t absorb anymore heat.

Question 5

What is mechanical fade?

Answer 5

When the brake drums expand so much that the shoes no longer reach the drum.

Question 6

What is lining fade?

Answer 6

When friction material overheats, its COF drops due to “thermal saturation”.

Question 7

What is hydraulic fade?

Answer 7

When brake fluid reaches boiling point, fluid starts to vaporise and bubble, the vapour compresses rather than transferring pressure.

Question 8

What is Pascal’s law?

Answer 8

It states that fluid pressure is applied in a uniform manner.

Question 9

How does Pascal’s law effect brake pistons?

Answer 9

If the master cylinder has a 10cm2 piston, and the front brakes have a 20cm2 piston. 10N on the master cylinder piston would equal 20N on the brake piston.

Question 10

What characteristics does brake fluid need?

Answer 10

Remain viscous at high/low temps, have a high boiling point, and act as a lubricant.

Question 11

What is the most common brake fluid chemical used?

Answer 11

Polyglycol.

Question 12

What are the advantages/disadvantages of silicone brake fluid, and what DOT type is it found in?

Answer 12

It is good because it is not hygroscopic, it has a high boiling point, and doesn’t ruin paint. Although it is hard to bleed air from it. It is found in DOT 5 fluid.

Question 13

What metals are in brake tubing?

Answer 13

Copper-plated steel sheets, then plated with tin and zinc for corrosion protection.

Question 14

What are the main components in a brake drum assembly?

Answer 14

Backing plate, brake shoes, return/anchor/hold-down springs, wheel cylinder, and adjuster.

Question 15

What happens when a leading edge shoe is pressed against the brake drum?

Answer 15

Friction is increased through a reactive force known as self-energising or servo action.

Question 16

How does a duo-servo drum setup work?

Answer 16

Both shoes are anchored at the top, the primary shoe gets wedged into the drum, then the motion is transferred to the secondary shoe through the shoe-adjusting screw assembly.

Question 17

How does a leading-trailing drum setup work?

Answer 17

When the leading shoe is pressed against the drum, the drum pushes the shoe into the anchor which wedges the top of the shoe harder into the drum.

Question 18

What does the compression spring do in a wheel cylinder?

Answer 18

When the master cylinder draws fluid back from the wheel cylinder, the inertia could cause a vacuum and allow air to enter through the system past the piston cup, the compression spring holds the piston cups in contact with the cylinder wall.

Question 19

What is a brake drum normally made of?

Answer 19

Cast iron with a mild steel centre.

Question 20

How high can friction heat reach in a brake drum?

Answer 20

Up to 315 degrees.

Question 21

What characteristics does a brake drum need?

Answer 21

Accurately balanced, sufficiently rigid, resistant to wear, highly heat conductive, lightweight, correct COF.

Question 22

How does the brake pad move back after the brake pedal has been pressed?

Answer 22

The seal of the caliper piston flexes when the piston pushes out, when the pedal is released the seal flexes back to the original position which brings the pad back.

Question 23

What are the main components of the brake booster?

Answer 23

The body, booster piston and diaphragm, piston return spring, and control valve assembly.

Question 24

What are the two vacuum booster designs?

Answer 24

Single diaphragm and tandem diaphragm.

Question 25

What is the importance of a reservoir cap on a master cylinder?

Answer 25

It is vented to atmosphere so that if fluid drops it doesn’t create a vacuum.

Question 26

How does a proportioning valve work?

Answer 26

Up to the “split point”, fluid passes the p.valve’s cylinder cup, as pressure from the rear brakes increases, it pushes the p.valve’s piston to the left, closing off the gap in the cylinder cup and stopping flow to the brakes.

Question 27

How does the vacuum booster work?

Answer 27

There are two pressure chambers, one with vacuum and one that can have vacuum or atmospheric pressure, when the brake are pressed, the valve which allows atmospheric pressure to enter the variable chamber opens and the atmospheric pressure pushes against a diaphragm between the two chambers, assisting in brake force.

Question 28

How does a master cylinder work?

Answer 28

There are two pistons in the cylinder, when the brakes are pressed, the first piston is activated, when it pushes out far enough, it pushes against the second piston which opens up the second brake circuit.

Question 29

What are the main types of proportioning valves?

Answer 29

Single p.valve, p and bypass valve, dual p.valve, load sensing p.valve, load sensing and bypass valve.

Question 30

What does the bypass circuit do in a proportioning valve?

Answer 30

If the front wheel circuit fails, it stops the function on the proportioning valve, allowing full pressure to the rear wheels.

Question 31

What does a dual p.valve do?

Answer 31

They are in FF cars, as there are two circuits which run to the rear wheels, as FF cars have front and rear brakes activated on each circuit, there is no need for a bypass function.

Question 32

What does a LSPV do?

Answer 32

It senses how much weight is over the rear tyres and adjusts what the “split point” would be, varying at what point the proportioning valve starts to operate.

Question 33

What is slip ratio, and what is the ideal level of slip?

Answer 33

Slip ratio is the difference between vehicle speed and the speed of the wheels. Ideal ratio is between 10-30%

Question 34

What components does the ABS system include?

Answer 34

Skid control ECU, brake actuator, wheel speed sensor, combination meter, stop light switch, and deceleration sensor.

Question 35

What does a typical ABS brake actuator generally consist of?

Answer 35

Pressure holding solenoid valve, pressure reduction solenoid valve, pump motor, and resevoir.

Question 36

What is the initial check function on an ABS module?

Answer 36

Each time the vehicle is turned on and travelling faster than 6km/h, the skid control ECU operates the solenoid valves in sequence in order to check the electrical system of the ABS.

Question 37

What is the diagnostic function on an ABS module?

Answer 37

If a fault is found in the ABS system, the ABS light will come on the combination meter and a DTC will be stored.

Question 38

What is the fail-safe function on an ABS module?

Answer 38

If the skid control ECU detects a fault in the system electrical current from the ECU to the actuator is turned off, making the car act as if there is no ABS, but still functioning.

Question 39

How does EBD work when travelling in a straight line?

Answer 39

The skid control ECU senses wheel speeds between front and rear wheels, which can vary depending on loads, and will distribute brake force accordingly.

Question 40

How does EBD work when cornering?

Answer 40

When cornering, the inside wheels have less load than the outside wheels, the skid control ECU receives signals from speed sensors and applies more brake force to the to the wheels with more traction.

Question 41

What does brake assist do?

Answer 41

In emergency braking situations, a driver may not press hard enough on the pedal for the full braking force to be achieved. The BA system uses a pressure sensor in the ABS actuator to detect the speed and force of the pedal being depressed.

Question 42

What does TRC do?

Answer 42

If too much throttle is applied during take off or while driving on slippery surfaces and the wheels start to slip, the ABS actuator will apply brake force to the drive wheels and the motor output will be reduced.

Question 43

What does VSC do?

Answer 43

The vehicle stability control system is used to help stabilise the car through cornering, the system detects steering slip and applies brake force according to each wheel to help stabilise the vehicle.

Question 44

How does a hydraulic brake booster work?

Answer 44

The booster uses a pump, pump motor, pressure relief valve, accumulator pressure sensor, and accumulator to build pressure inside the accumulator and uses that pressurised fluid to assist in brake force.