310S Brake Systems 4 — Questions and Answers
Question 1: What is the purpose of the electronic brake force distribution (EBD) system?
- To apply the parking brake automatically on hills
- To electronically adjust brake pressure between front and rear axles based on vehicle load, replacing the mechanical proportioning valve (Correct answer)
- To provide automatic emergency braking
- To control brake pad wear rate
Correct answer: To electronically adjust brake pressure between front and rear axles based on vehicle load, replacing the mechanical proportioning valve
EBD uses the ABS wheel speed sensors and hydraulic modulator to electronically distribute braking force between the front and rear axles based on real-time load conditions, replacing the fixed-ratio mechanical proportioning valve.
Question 2: What causes brake noise (squeal) during light braking?
- Low brake fluid level
- High-frequency vibration between the brake pad and rotor surface (Correct answer)
- A failing wheel bearing
- Worn tire tread
Correct answer: High-frequency vibration between the brake pad and rotor surface
Brake squeal is caused by high-frequency vibration of the brake pad against the rotor. Factors include pad material composition, lack of anti-squeal shims or compound, glazed pad/rotor surfaces, and the absence of chamfers on pad edges.
Question 3: A technician notices that one rear drum brake has brake fluid on the backing plate. What is the most likely cause?
- A cracked brake drum
- A leaking wheel cylinder seal (Correct answer)
- Condensation from temperature changes
- Overfilled master cylinder
Correct answer: A leaking wheel cylinder seal
Brake fluid on the backing plate indicates a leaking wheel cylinder. The internal seals (cups) deteriorate over time, allowing hydraulic fluid to leak past the pistons and onto the backing plate and brake shoes.
Question 4: What is the function of the brake drum self-adjuster mechanism?
- To compensate for brake fade during heavy use
- To automatically take up the clearance between the shoes and drum as the linings wear, maintaining proper pedal height (Correct answer)
- To apply the parking brake
- To balance braking force between front and rear
Correct answer: To automatically take up the clearance between the shoes and drum as the linings wear, maintaining proper pedal height
The self-adjuster mechanism uses a star wheel or strut that incrementally takes up the increased clearance as brake shoe linings wear. This maintains the shoes close to the drum, keeping pedal travel consistent.
Question 5: What is the correct procedure after replacing brake pads and rotors?
- Drive immediately at highway speed to bed in the pads
- Pump the brake pedal to seat the caliper pistons against the pads, then perform a proper bed-in procedure (Correct answer)
- No special procedure is needed
- Bleed the entire brake system
Correct answer: Pump the brake pedal to seat the caliper pistons against the pads, then perform a proper bed-in procedure
After pad and rotor replacement, the brake pedal must be pumped to extend the caliper pistons to contact the pads. Then a proper bed-in (burnishing) procedure of gradual stops is performed to transfer an even layer of pad material to the rotors.
Question 6: What does brake rotor discard thickness mean?
- The thickness of a new replacement rotor
- The minimum safe thickness below which the rotor must be replaced because it cannot safely absorb and dissipate braking heat (Correct answer)
- The thickness at which the rotor should be machined
- The maximum thickness allowed for a rotor
Correct answer: The minimum safe thickness below which the rotor must be replaced because it cannot safely absorb and dissipate braking heat
Discard (minimum) thickness is the thinnest the rotor can safely be. Below this thickness, the rotor cannot absorb and dissipate braking heat adequately, risking brake fade, cracking, or catastrophic failure.
310S Brake Systems 4
What is the purpose of the electronic brake force distribution (EBD) system?