SOS MECHANIC CERTIFICATION -
BRAKES EXAM QUESTIONS AMD
ANSWERS 2027
1. What is the primary function of a proportioning valve in a hydraulic brake system?
A. To increase overall system pressure during emergency stops
B. To bleed air automatically from the master cylinder
C. To prevent rear wheel lock-up by limiting pressure to the rear brakes during heavy
braking
D. To distribute equal hydraulic pressure to all four wheels simultaneously
Answer: C
Conceptual Explanation: A proportioning valve regulates hydraulic pressure to the rear
brakes under heavy braking conditions to prevent the rear wheels from locking up
prematurely due to weight transfer to the front.
2. Which type of brake fluid absorbs moisture from the atmosphere the most easily?
A. DOT 5.1 synthetic
B. DOT 5 (Silicone)
C. Mineral oil based fluid
,D. DOT 3
Answer: D
Conceptual Explanation: DOT 3 and DOT 4 are glycol-based fluids that are hygroscopic,
meaning they readily absorb moisture, which lowers their boiling point over time.
3. When diagnosing a brake pedal that slowly sinks to the floor under constant pressure, the
most likely cause is:
A. Air trapped in the brake lines
B. Internal master cylinder bypass (leaking piston seals)
C. Glazed brake pads
D. A restricted brake hose
Answer: B
Conceptual Explanation: A sinking pedal under steady pressure indicates that fluid is
leaking past the primary piston seals inside the master cylinder, rather than being pushed
to the calipers.
4. What is the correct procedure for measuring brake rotor thickness variation (parallelism)?
A. Using a dial indicator attached to the steering knuckle
B. Using a micrometer at four or more equally spaced points around the friction surface
C. Using a vernier caliper across the outer diameter only
D. Measuring the runout with a feeler gauge
, Answer: B
Conceptual Explanation: Rotor thickness variation should be checked using an outside
micrometer at multiple equidistant points around the rotor to detect any uneven wear.
5. In an ABS (Antilock Braking System) equipped vehicle, what component modulates
hydraulic pressure to individual wheels during an event?
A. Master cylinder pushrod
B. Hydraulic control unit (HCU) solenoid valves
C. Vacuum brake booster
D. Proportioning valve
Answer: B
Conceptual Explanation: The HCU contains solenoid valves and a pump that rapidly
apply, hold, and release hydraulic pressure to individual wheel circuits during ABS
activation.
6. What is the primary purpose of a low drag brake caliper design?
A. To increase brake pad life by maximizing friction
B. To prevent brake squeal at high speeds
C. To eliminate the need for a brake fluid flush
D. To reduce rolling resistance and improve fuel economy by retracting pads slightly from
the rotor
BRAKES EXAM QUESTIONS AMD
ANSWERS 2027
1. What is the primary function of a proportioning valve in a hydraulic brake system?
A. To increase overall system pressure during emergency stops
B. To bleed air automatically from the master cylinder
C. To prevent rear wheel lock-up by limiting pressure to the rear brakes during heavy
braking
D. To distribute equal hydraulic pressure to all four wheels simultaneously
Answer: C
Conceptual Explanation: A proportioning valve regulates hydraulic pressure to the rear
brakes under heavy braking conditions to prevent the rear wheels from locking up
prematurely due to weight transfer to the front.
2. Which type of brake fluid absorbs moisture from the atmosphere the most easily?
A. DOT 5.1 synthetic
B. DOT 5 (Silicone)
C. Mineral oil based fluid
,D. DOT 3
Answer: D
Conceptual Explanation: DOT 3 and DOT 4 are glycol-based fluids that are hygroscopic,
meaning they readily absorb moisture, which lowers their boiling point over time.
3. When diagnosing a brake pedal that slowly sinks to the floor under constant pressure, the
most likely cause is:
A. Air trapped in the brake lines
B. Internal master cylinder bypass (leaking piston seals)
C. Glazed brake pads
D. A restricted brake hose
Answer: B
Conceptual Explanation: A sinking pedal under steady pressure indicates that fluid is
leaking past the primary piston seals inside the master cylinder, rather than being pushed
to the calipers.
4. What is the correct procedure for measuring brake rotor thickness variation (parallelism)?
A. Using a dial indicator attached to the steering knuckle
B. Using a micrometer at four or more equally spaced points around the friction surface
C. Using a vernier caliper across the outer diameter only
D. Measuring the runout with a feeler gauge
, Answer: B
Conceptual Explanation: Rotor thickness variation should be checked using an outside
micrometer at multiple equidistant points around the rotor to detect any uneven wear.
5. In an ABS (Antilock Braking System) equipped vehicle, what component modulates
hydraulic pressure to individual wheels during an event?
A. Master cylinder pushrod
B. Hydraulic control unit (HCU) solenoid valves
C. Vacuum brake booster
D. Proportioning valve
Answer: B
Conceptual Explanation: The HCU contains solenoid valves and a pump that rapidly
apply, hold, and release hydraulic pressure to individual wheel circuits during ABS
activation.
6. What is the primary purpose of a low drag brake caliper design?
A. To increase brake pad life by maximizing friction
B. To prevent brake squeal at high speeds
C. To eliminate the need for a brake fluid flush
D. To reduce rolling resistance and improve fuel economy by retracting pads slightly from
the rotor
