310S Brake Systems 2 — Questions and Answers
Question 1: What is the function of the brake caliper?
- To store brake fluid under pressure
- To house the brake piston(s) and clamp the brake pads against the rotor when hydraulic pressure is applied (Correct answer)
- To cool the brake rotor during braking
- To convert rotary motion into linear motion
Correct answer: To house the brake piston(s) and clamp the brake pads against the rotor when hydraulic pressure is applied
The brake caliper straddles the brake rotor and contains one or more hydraulic pistons. When pressure is applied, the piston(s) push the brake pads against the rotor, creating friction to slow the wheel.
Question 2: What is the purpose of the vacuum brake booster?
- To pump brake fluid through the system
- To multiply the driver's brake pedal force using engine vacuum to reduce pedal effort (Correct answer)
- To prevent brake fade during heavy braking
- To control ABS modulator operation
Correct answer: To multiply the driver's brake pedal force using engine vacuum to reduce pedal effort
The vacuum booster uses engine intake manifold vacuum on one side of a large diaphragm and atmospheric pressure on the other to multiply the driver's pedal force, typically by a factor of 3-4, reducing the effort needed to brake.
Question 3: What is the correct procedure for bleeding a brake system?
- Start with the wheel closest to the master cylinder
- Start with the wheel farthest from the master cylinder and work toward the closest (Correct answer)
- Bleed all four wheels simultaneously
- Only bleed the wheel where work was performed
Correct answer: Start with the wheel farthest from the master cylinder and work toward the closest
The standard bleeding sequence starts at the wheel farthest from the master cylinder (usually right rear) and works toward the closest (usually left front). This ensures air is progressively pushed out of the longest lines first.
Question 4: What causes a brake caliper to stick or seize?
- Using DOT 4 brake fluid instead of DOT 3
- Corroded caliper piston, damaged piston seal, or corroded slide pins preventing proper movement (Correct answer)
- Over-tightened lug nuts
- A worn brake rotor
Correct answer: Corroded caliper piston, damaged piston seal, or corroded slide pins preventing proper movement
Caliper sticking is caused by corrosion on the piston bore, a swollen or damaged piston seal, or corroded/dry caliper slide pins (on floating calipers) that prevent the caliper from retracting or sliding freely.
Question 5: What is the purpose of DOT brake fluid ratings (DOT 3, DOT 4, DOT 5.1)?
- They indicate the fluid colour
- They specify minimum dry and wet boiling points to ensure the fluid can withstand heat generated during braking (Correct answer)
- They indicate the fluid viscosity for cold weather
- They specify the recommended change interval
Correct answer: They specify minimum dry and wet boiling points to ensure the fluid can withstand heat generated during braking
DOT ratings specify minimum boiling points — both dry (new fluid) and wet (moisture-contaminated fluid). Higher DOT numbers indicate higher boiling points, providing more resistance to vapour lock during hard braking.
Question 6: What does the ABS warning light illuminating during normal driving indicate?
- The ABS system is actively working
- A fault has been detected in the ABS system and antilock function is disabled (Correct answer)
- The brake pads need replacement
- The brake fluid level is low
Correct answer: A fault has been detected in the ABS system and antilock function is disabled
The ABS warning light indicates the ABS control module has detected a fault and has disabled antilock braking. The base brake system still functions normally, but the wheels can lock during hard braking.
310S Brake Systems 2
What is the function of the brake caliper?