Brake shoes should not have which substance on them?

• A. Oil, grease, or brake fluid
• B. Water and rust
• C. Dust and dirt
• D. Soap residue

Answer: (A)

Contaminants on the brake lining ruin the friction needed to stop smoothly. Oil, grease, or brake fluid on the friction surface creates a slippery film that prevents the shoes from gripping the drum, which dramatically reduces braking effectiveness and can lead to brake fade or failure. Drum brakes rely on clean, dry contact between the shoe material and the drum, so any of these substances must not be present; if contaminated, the shoes often need replacement and the braking system should be cleaned or serviced to restore proper function.

Water and rust, dust and dirt, or soap residue can affect braking in various ways, but they don’t pose the same immediate, severe risk as oil, grease, or brake fluid on the friction surface. Water may evaporate, rust is more a metal issue than a contamination of the lining, dust and dirt can cause some wear or roughness, and soap would reduce friction too, but the classic, most dangerous contaminant to the brake lining is oil, grease, or brake fluid.