Brake System Service Flashcards

What is a typical maximum allowable lateral runout for a disc brake rotor measured with a dial indicator?

Answer: 0.002 in (0.05 mm)

Most manufacturers limit rotor lateral runout to about 0.002 in, since more causes thickness variation and pedal pulsation.

Which condition is most likely to cause a vehicle to pull to one side only when the brakes are applied?

Answer: Grease-contaminated pads on one front wheel

Contaminated linings on one side reduce friction there, creating unequal braking force side to side.

Which brake fluid type is silicone-based and must not be mixed with glycol-based fluids?

Answer: DOT 5

DOT 5 is silicone-based, while DOT 3, DOT 4, and DOT 5.1 are glycol-ether based.

A customer complains of a soft, spongy brake pedal that improves slightly when pumped. What is the most likely cause?

Answer: Air in the hydraulic system

Air compresses under pressure, producing a spongy pedal that firms up somewhat with pumping.

When testing a vacuum brake booster, the engine is off, the pedal is pumped to deplete reserve, and then held while the engine is started. What should the pedal do?

Answer: Drop slightly toward the floor

A working booster applies assist as vacuum builds, so the pedal moves down slightly under steady foot pressure.

What is the primary purpose of a proportioning valve in a conventional brake system?

Answer: Limit rear brake pressure during hard stops to prevent rear wheel lockup

The proportioning valve reduces pressure increase to the rear brakes during heavy braking as weight shifts forward.

What is the most common cause of a pulsating brake pedal on a vehicle with front disc brakes when ABS is not active?

Answer: Excessive rotor thickness variation

Thickness variation, often from runout-induced uneven wear, pushes caliper pistons back and forth and pulses the pedal.