Brake Systems and Safety Inspection Flashcards

An ABS wheel speed sensor has an air gap larger than specification. What is the most likely result?

Answer: A weak or erratic sensor signal and an ABS warning light

A larger air gap weakens the magnetic signal, so the ABS module sees erratic or missing wheel speed and sets a fault.

How is a passive (magnetic) wheel speed sensor's output usually checked?

Answer: Measure AC voltage while spinning the wheel

A passive sensor makes its own AC voltage that rises with wheel speed, so you check its AC output while the wheel turns.

Why should brake fluid be tested and replaced at intervals?

Answer: It is hygroscopic and absorbs moisture, which lowers its boiling point

Glycol brake fluid absorbs water over time, which lowers its boiling point and causes internal corrosion.

When should a replacement master cylinder be bench bled?

Answer: Before it is installed on the vehicle

Bench bleeding removes air from the master cylinder bores before installation, which makes bleeding the whole system much easier.

The brake pedal slowly sinks to the floor under steady foot pressure, and there are no external leaks. What is the most likely cause?

Answer: Worn primary or secondary cups inside the master cylinder

Fluid bypassing the master cylinder piston seals lets the pedal sink with no external fluid loss.

On most duo-servo drum brakes, when does the star-wheel self-adjuster work?

Answer: When the brakes are applied while backing up

Most duo-servo self-adjusters advance the star wheel when the brakes are applied while the vehicle moves in reverse.

Where is the maximum allowable brake drum diameter usually found?

Answer: Stamped or cast on the brake drum

The maximum diameter (discard) dimension is usually stamped or cast on the drum itself.