Automotive Service Excellence
Automobile And Light Truck
Certification Examination A5 – Brakes
Question And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A
Instant Download Pdf
1. A technician finds brake fluid leaking from the rear of the master cylinder
into the brake booster. What is the most likely cause?
A. Warped rotor
B. Failed master cylinder rear seal
C. Plugged brake hose
D. Seized caliper piston
Answer: B. Failed master cylinder rear seal
The rear seal inside the master cylinder prevents brake fluid from escaping into
the brake booster. When this seal fails, fluid leaks directly into the booster
housing. This condition can reduce hydraulic pressure, contaminate the booster
diaphragm, and eventually lead to brake failure if not repaired promptly.
2. A brake pedal slowly sinks to the floor while steady pressure is applied.
What is the most likely cause?
A. Air in the brake lines
B. Weak return springs
C. Internal master cylinder bypassing
D. Excessive rotor runout
,Answer: C. Internal master cylinder bypassing
When the brake pedal slowly sinks during constant pressure, brake fluid is
bypassing internally around worn master cylinder seals. Unlike air in the system,
which usually creates a spongy pedal, internal bypassing allows pressure to leak
past the piston cups, causing gradual pedal drop without external leakage.
3. Which tool is commonly used to measure rotor lateral runout?
A. Micrometer
B. Vernier caliper
C. Dial indicator
D. Torque wrench
Answer: C. Dial indicator
A dial indicator precisely measures rotor runout by detecting side-to-side
movement as the rotor rotates. Excessive runout can cause brake pulsation,
uneven pad wear, and steering vibration. Accurate measurement helps
determine whether machining or rotor replacement is necessary.
4. Brake fluid contaminated with petroleum products will usually cause:
A. Brake fade
B. Swollen rubber components
C. Warped rotors
D. Glazed pads
Answer: B. Swollen rubber components
Petroleum products such as engine oil or transmission fluid attack rubber seals
and hoses in hydraulic brake systems. The rubber swells, softens, and
deteriorates, leading to sticking pistons, blocked passages, and hydraulic failure.
In most cases, major hydraulic components must be replaced after
contamination.
5. What is the main purpose of a proportioning valve?
,A. Increase pedal height
B. Reduce front brake pressure
C. Prevent rear wheel lockup
D. Eliminate brake noise
Answer: C. Prevent rear wheel lockup
The proportioning valve limits hydraulic pressure to the rear brakes during hard
braking. Since vehicle weight shifts forward under braking, rear wheels can lock
prematurely if pressure is not controlled. The valve improves stability and
reduces the risk of skidding.
6. Excessive brake pedal free play may be caused by:
A. Loose wheel bearings
B. Air in the system
C. Improper pushrod adjustment
D. Warped drums
Answer: C. Improper pushrod adjustment
The pushrod between the brake pedal or booster and master cylinder must have
proper clearance. Excessive clearance creates extra pedal travel before hydraulic
pressure builds. This condition results in excessive free play and delayed brake
response.
7. A technician measures rotor thickness below minimum specification. What
should be done?
A. Machine the rotor
B. Replace the rotor
C. Install softer pads
D. Adjust the caliper
Answer: B. Replace the rotor
, Rotors below minimum thickness cannot safely dissipate heat and may crack or
warp under braking loads. Machining would further reduce thickness, making
the rotor unsafe. Replacement is the only proper repair.
8. Brake fade is usually caused by:
A. Low tire pressure
B. Excessive heat buildup
C. Weak wheel bearings
D. Loose suspension parts
Answer: B. Excessive heat buildup
Brake fade occurs when excessive heat reduces friction between pads and rotors
or causes brake fluid to boil. This results in reduced stopping power and longer
stopping distances. Overloaded vehicles, aggressive braking, or dragging brakes
commonly contribute to fade.
9. Which brake fluid type is silicone-based?
A. DOT 3
B. DOT 4
C. DOT 5
D. DOT 5.1
Answer: C. DOT 5
DOT 5 brake fluid is silicone-based and does not absorb moisture like glycol-
based fluids. It is commonly used in specialty or military vehicles but should not
be mixed with DOT 3, DOT 4, or DOT 5.1 fluids because incompatibility can
damage the system.
10.A pulsating brake pedal during stopping is commonly caused by:
A. Worn wheel studs
B. Rotor thickness variation
C. Weak booster spring
D. Excessive tire pressure
Automobile And Light Truck
Certification Examination A5 – Brakes
Question And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A
Instant Download Pdf
1. A technician finds brake fluid leaking from the rear of the master cylinder
into the brake booster. What is the most likely cause?
A. Warped rotor
B. Failed master cylinder rear seal
C. Plugged brake hose
D. Seized caliper piston
Answer: B. Failed master cylinder rear seal
The rear seal inside the master cylinder prevents brake fluid from escaping into
the brake booster. When this seal fails, fluid leaks directly into the booster
housing. This condition can reduce hydraulic pressure, contaminate the booster
diaphragm, and eventually lead to brake failure if not repaired promptly.
2. A brake pedal slowly sinks to the floor while steady pressure is applied.
What is the most likely cause?
A. Air in the brake lines
B. Weak return springs
C. Internal master cylinder bypassing
D. Excessive rotor runout
,Answer: C. Internal master cylinder bypassing
When the brake pedal slowly sinks during constant pressure, brake fluid is
bypassing internally around worn master cylinder seals. Unlike air in the system,
which usually creates a spongy pedal, internal bypassing allows pressure to leak
past the piston cups, causing gradual pedal drop without external leakage.
3. Which tool is commonly used to measure rotor lateral runout?
A. Micrometer
B. Vernier caliper
C. Dial indicator
D. Torque wrench
Answer: C. Dial indicator
A dial indicator precisely measures rotor runout by detecting side-to-side
movement as the rotor rotates. Excessive runout can cause brake pulsation,
uneven pad wear, and steering vibration. Accurate measurement helps
determine whether machining or rotor replacement is necessary.
4. Brake fluid contaminated with petroleum products will usually cause:
A. Brake fade
B. Swollen rubber components
C. Warped rotors
D. Glazed pads
Answer: B. Swollen rubber components
Petroleum products such as engine oil or transmission fluid attack rubber seals
and hoses in hydraulic brake systems. The rubber swells, softens, and
deteriorates, leading to sticking pistons, blocked passages, and hydraulic failure.
In most cases, major hydraulic components must be replaced after
contamination.
5. What is the main purpose of a proportioning valve?
,A. Increase pedal height
B. Reduce front brake pressure
C. Prevent rear wheel lockup
D. Eliminate brake noise
Answer: C. Prevent rear wheel lockup
The proportioning valve limits hydraulic pressure to the rear brakes during hard
braking. Since vehicle weight shifts forward under braking, rear wheels can lock
prematurely if pressure is not controlled. The valve improves stability and
reduces the risk of skidding.
6. Excessive brake pedal free play may be caused by:
A. Loose wheel bearings
B. Air in the system
C. Improper pushrod adjustment
D. Warped drums
Answer: C. Improper pushrod adjustment
The pushrod between the brake pedal or booster and master cylinder must have
proper clearance. Excessive clearance creates extra pedal travel before hydraulic
pressure builds. This condition results in excessive free play and delayed brake
response.
7. A technician measures rotor thickness below minimum specification. What
should be done?
A. Machine the rotor
B. Replace the rotor
C. Install softer pads
D. Adjust the caliper
Answer: B. Replace the rotor
, Rotors below minimum thickness cannot safely dissipate heat and may crack or
warp under braking loads. Machining would further reduce thickness, making
the rotor unsafe. Replacement is the only proper repair.
8. Brake fade is usually caused by:
A. Low tire pressure
B. Excessive heat buildup
C. Weak wheel bearings
D. Loose suspension parts
Answer: B. Excessive heat buildup
Brake fade occurs when excessive heat reduces friction between pads and rotors
or causes brake fluid to boil. This results in reduced stopping power and longer
stopping distances. Overloaded vehicles, aggressive braking, or dragging brakes
commonly contribute to fade.
9. Which brake fluid type is silicone-based?
A. DOT 3
B. DOT 4
C. DOT 5
D. DOT 5.1
Answer: C. DOT 5
DOT 5 brake fluid is silicone-based and does not absorb moisture like glycol-
based fluids. It is commonly used in specialty or military vehicles but should not
be mixed with DOT 3, DOT 4, or DOT 5.1 fluids because incompatibility can
damage the system.
10.A pulsating brake pedal during stopping is commonly caused by:
A. Worn wheel studs
B. Rotor thickness variation
C. Weak booster spring
D. Excessive tire pressure
