DFFT Brakes and Braking Systems 2 — Questions and Answers
Question 1: A brake pedal slowly sinks to the floor when held under constant pressure. What is this condition called?
- Brake pedal creep caused by a faulty master cylinder (Correct answer)
- Brake fade from overheated rotors
- Hydraulic lock caused by a seized caliper
- Vapor lock in the brake lines
Correct answer: Brake pedal creep caused by a faulty master cylinder
A worn or damaged master cylinder internal seal allows fluid to bypass under sustained pressure, causing the pedal to slowly sink.
Question 2: During a DFFT inspection, you find one brake rotor has a blue discoloration. What does this indicate?
- The rotor has been subjected to excessive heat (Correct answer)
- The rotor has surface rust from prolonged storage
- The rotor has been machined incorrectly
- The rotor is made from a different alloy
Correct answer: The rotor has been subjected to excessive heat
Blue discoloration on a brake rotor is a sign of overheating, which can alter the metal's hardness and cause the rotor to warp or crack.
Question 3: A vehicle's parking brake fails to hold the car on a moderate hill. What is the most likely cause on a rear-drum brake vehicle?
- Stretched or corroded parking brake cable (Correct answer)
- Low brake fluid in the reservoir
- Worn front disc brake pads
- A faulty ABS wheel speed sensor
Correct answer: Stretched or corroded parking brake cable
A stretched or corroded cable prevents the parking brake mechanism from applying sufficient force to hold the rear drum shoes against the drum.
Question 4: After a brake job, a customer returns complaining the brake pedal is very hard to press. What was likely the fault in the repair?
- The brake booster vacuum hose was not reconnected (Correct answer)
- The brake fluid was overfilled in the reservoir
- New pads were installed without lubricating the slides
- The calipers were not properly bled after installation
Correct answer: The brake booster vacuum hose was not reconnected
The brake booster uses engine vacuum to multiply pedal force; without vacuum supply, the driver must overcome hydraulic resistance unassisted, making the pedal feel very hard.
Question 5: A customer reports the brake pedal vibrates when stopping at highway speed. What is the most likely cause?
- Warped or uneven brake rotors (Correct answer)
- Air trapped in the brake caliper
- Worn brake pad friction material
- A cracked brake drum on the rear axle
Correct answer: Warped or uneven brake rotors
Warped rotors cause the caliper piston to rapidly advance and retract as the high and low spots pass, creating a pulsating vibration felt through the pedal.
Question 6: You notice brake fluid is leaking from behind a front wheel. What is the most probable source?
- A leaking brake caliper piston seal (Correct answer)
- A cracked brake rotor
- A loose wheel speed sensor
- A worn wheel bearing seal
Correct answer: A leaking brake caliper piston seal
When the caliper piston seal deteriorates, brake fluid bypasses the seal and leaks out, which also reduces hydraulic pressure and braking effectiveness.
DFFT Brakes and Braking Systems 2
A brake pedal slowly sinks to the floor when held under constant pressure.
What is this condition called?