Brakes A5 Flashcards

A technician is flushing brake fluid and finds that the fluid tests at 3.5% water content using a refractometer. The manufacturer's replacement specification is 3.0%. What are the consequences of continued operation with this fluid?

Answer: Reduced boiling point leading to vapor lock and brake fade under heavy use

Glycol-based brake fluid is hygroscopic and absorbs moisture over time. Water contamination dramatically lowers the fluid's boiling point. Above the recommendation threshold, the risk of vapor lock (fluid boiling during heavy braking and creating compressible vapor) increases significantly, leading to brake fade or failure.

When diagnosing a brake system for a vehicle that applies brakes hard when the brake pedal is pushed only slightly, what is the MOST likely cause?

Answer: Failing vacuum brake booster with a broken reaction disc allowing full boost at light input

A broken or deteriorated reaction disc in a vacuum brake booster can cause the booster to apply maximum assist with minimal pedal input. The reaction disc normally proportions boost force relative to pedal force; without it, even slight pedal pressure generates full boosted output.

During a drum brake inspection, a technician finds the brake drum inner diameter measures 9.085 inches. The drum has 9.060 stamped on the drum (discard spec), and the factory spec for inside diameter is 9.000 inches with a maximum oversize of 0.060 inches. What is the correct action?

Answer: The drum must be discarded because it exceeds the maximum oversize specification

The drum measures 9.085 inches, which exceeds the discard specification of 9.060 inches. A drum measuring beyond the discard (maximum) diameter must be replaced — it is too large to safely resurface or use in service, as it lacks the material thickness needed to absorb braking heat.

A technician is bleeding a vehicle with a diagonally split brake system (right front/left rear on one circuit; left front/right rear on the other). Starting at which wheel is MOST correct when bleeding?

Answer: Right rear, then left front, then left rear, then right front

The standard bleeding sequence for a diagonally split system is right rear, left rear, right front, left front — starting with the farthest wheel from the master cylinder and working forward. Some manufacturers may specify a different sequence; always confirm with the service manual.

A front-wheel-drive vehicle's right front brake is dragging after brake service. The caliper is new, the brake hose is new, and the brake line is clear. What is the MOST likely remaining cause?

Answer: Brake master cylinder compensating port blocked, preventing fluid return

If the brake line and hose are clear and the caliper is new and properly bled, a blocked master cylinder compensating port is the most likely cause of dragging. The compensating port allows fluid to return to the reservoir as the brake releases; if blocked, residual pressure keeps the caliper applied.

When inspecting a rear drum brake assembly, a technician finds the primary shoe has significantly less lining remaining than the secondary shoe. The brakes have been adjusted correctly. What does this indicate?

Answer: Normal wear pattern; the primary shoe always wears faster in a dual servo system

In a dual-servo (duo-servo) drum brake system, the primary shoe faces the front. During forward braking, the primary shoe has a self-energizing (servo) effect that increases its application force, causing it to wear faster than the secondary shoe. This is normal and expected behavior.