Brake System Service Flashcards

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

Answer: When the brakes are applied while the vehicle is moving in reverse

Most duo-servo self-adjusters work when the brakes are applied in reverse, letting the secondary shoe move the adjuster lever.

In a duo-servo drum brake assembly, how is the primary shoe usually identified?

Answer: It faces the front of the vehicle and usually has the shorter lining

The primary (leading) shoe faces forward and typically has a shorter lining than the secondary shoe.

What does the dimension cast or stamped on a brake drum indicate?

Answer: The maximum allowable inside diameter before the drum must be discarded

The stamped discard dimension is the largest inside diameter at which the drum may still be used.

What finding most clearly indicates a leaking wheel cylinder?

Answer: Brake fluid present behind the wheel cylinder dust boots

Fluid under the boots means the piston cups are leaking and the cylinder must be rebuilt or replaced.

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

Answer: After the service brake shoes have been properly adjusted

Adjusting the parking brake before the shoes are set can hold the shoes off the anchor and cause dragging.

A brake drum is described as bell-mouthed. What does this mean?

Answer: The drum is worn larger at the open edge than at the closed edge

Bell-mouthing occurs when the open side of the drum flexes and wears to a larger diameter than the inner side.

What is a common cause of grabbing drum brakes on one wheel?

Answer: Linings contaminated with grease or brake fluid

Oil or fluid contamination changes lining friction and can make the brake grab or pull.