Brakes A5 Flashcards

After brake service, the brake pedal is low and spongy. The technician bled the brakes repeatedly but the pedal condition persists. What should be suspected next?

Answer: A defective master cylinder that bypasses internally under pedal pressure

A spongy pedal that persists after thorough bleeding indicates the master cylinder is bypassing internally. The piston cup seals are worn, allowing fluid to pass back past them under pressure rather than building pressure in the system. The pedal compresses without building resistance.

A disc brake caliper slides freely on its mounting bolts when tested by hand, but the customer reports a pulling sensation to the right during braking. What is the MOST likely cause?

Answer: A collapsed brake hose on the left front that restricts fluid flow back to the master cylinder

A collapsed brake hose on one side can allow fluid pressure in but restrict return flow. The left brake remains partially applied after the pedal is released while the right releases normally, creating greater braking force on the left and pulling the vehicle to the right (toward the less-braking side... wait — actually this would pull left). Let me reconsider: the question states pulling RIGHT means the RIGHT has MORE braking force — so a collapsed hose on the RIGHT restricts release.

A customer states that the brake pedal pulsates during normal stops but not during ABS activation. What is the MOST likely cause?

Answer: Warped or thickness-variation (DTV) brake rotors

Pedal pulsation during normal stops that is NOT associated with ABS activation is caused by warped or thickness-varying rotors. As the rotor's high and low spots pass the brake pads during stops, they alternately push and release the pads, transmitting pulsation back through the caliper to the brake pedal.

The parking brake on a rear disc brake vehicle does not hold the car on a slope. The service brakes work normally. What is the MOST likely cause?

Answer: Out of adjustment parking brake cable or seized rear caliper parking brake mechanism

Rear disc brake calipers use a separate mechanical mechanism (screw or lever actuated) for parking brake function, independent of the hydraulic circuit. If this mechanism seizes or the cable stretches/goes out of adjustment, the parking brake loses effectiveness while service brakes remain normal.

A technician is measuring brake rotor thickness and finds it measures 0.870 inches. The minimum thickness cast into the rotor hat is 0.810 inches, and the discard thickness specification in the service manual is 0.803 inches. What is the correct action?

Answer: The rotor can be resurfaced if there is enough material above the discard spec

At 0.870 inches, the rotor is above both the minimum cast thickness (0.810 in.) and the discard thickness (0.803 in.). The rotor can be resurfaced as long as it will remain above 0.810 inches after machining. The technician must verify that sufficient material exists for resurfacing.

A vehicle equipped with ABS stops normally in most situations, but the ABS activates prematurely during normal stops on dry pavement. A scan tool shows no ABS codes. What is the MOST likely cause?

Answer: A wheel speed sensor with excessive air gap or metallic debris on the reluctor ring

Premature ABS activation without fault codes is commonly caused by a wheel speed sensor with excessive air gap or debris on the tone ring (reluctor ring). This causes false speed fluctuations that the ABS module interprets as wheel lockup, triggering ABS unnecessarily on dry pavement.