Brake Systems Flashcards

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

Answer: When the brakes are applied while backing up

Most duo-servo self-adjusters work when the brakes are applied in reverse and the secondary shoe moves enough to turn the star wheel.

On a duo-servo drum brake, where is the primary shoe (usually the one with the shorter lining) installed?

Answer: Toward the front of the vehicle

The primary shoe faces the front, and the secondary shoe with the longer lining faces the rear.

What does the maximum diameter dimension stamped on a brake drum mean?

Answer: The diameter at which the drum must be discarded

The stamped maximum diameter is the discard limit, so a drum worn to that size must be replaced.

While inspecting a drum brake, a technician finds fluid behind the wheel cylinder dust boot. What should be done?

Answer: Rebuild or replace the wheel cylinder

Fluid behind the boot shows the wheel cylinder cups are leaking, so the cylinder must be rebuilt or replaced.

An out-of-round brake drum will most likely cause what?

Answer: Pedal pulsation or a grabbing feel during braking

An out-of-round drum makes the shoes move in and out as the drum turns, so the driver feels pulsation.

When should the parking brake cable be adjusted during a rear drum brake job?

Answer: After the service brake shoes are adjusted

The service shoes must be adjusted first, or a tight cable can keep the shoes from seating and cause drag.

Both rear drums are hot after a test drive, and the rear brakes drag. Which cause is most likely?

Answer: An over-adjusted parking brake cable

An over-tightened parking brake cable keeps both rear shoes partly applied and makes the brakes drag and overheat.