The top problems with classic car drum brakes often stem from their design, which is more susceptible to heat, water, and corrosion than modern disc brakes. Many issues are a result of age, lack of use, and improper maintenance, which is crucial for classic car ownership.
Heat and braking performance
- Brake fade: Drum brakes are enclosed, trapping heat and causing brake fade during heavy or prolonged braking, such as on long downhill stretches. This can result in a soft or "spongy" pedal feel and significantly reduced stopping power.
- Overheating and distortion: Excessive heat can cause the brake drum to expand, increasing its diameter. This forces the brake shoes to travel farther to make contact, diminishing braking effectiveness. Overheating can also warp the drum itself, causing vibration when braking.
- Glazed shoes: The friction material on the brake shoes can become "glazed" from high heat, developing a smooth, hard surface that reduces friction.
Hydraulic system and adjustment issues
- Fluid contamination: Brake fluid is hygroscopic, meaning it absorbs moisture over time. Water in the brake fluid can lower its boiling point and lead to vapor bubbles under high-heat braking, causing a spongy pedal feel and potential failure.
- Leaking wheel cylinders: The wheel cylinders, which push the brake shoes against the drums, are susceptible to leaks, especially after prolonged storage. A leaking wheel cylinder can contaminate the brake shoes, destroying their friction capabilities and causing the vehicle to pull to one side.
- Sticky self-adjusters: The automatic self-adjusters, which compensate for brake shoe wear, often fail due to corrosion. When they seize, the brake shoes sit too far from the drum, leading to a low brake pedal and reduced stopping power.
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Contamination and environmental factors
- Contaminants in the drum: Because drum brakes are enclosed, they can trap dirt, dust, and brake shoe material inside, which can lead to contamination and uneven braking.
- Water sensitivity: Drum brakes are highly susceptible to moisture. Driving through deep water can cause water to get trapped inside, reducing friction and braking efficiency. A light, dragging brake application can help dry them out.
- Corrosion and rust: Classic cars often sit for extended periods, allowing moisture to cause corrosion on internal components like springs, cables, and the drums themselves. This can cause the brakes to bind, drag, or fail altogether.
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Mechanical and wear-related problems
- Uneven braking and pulling: A vehicle may pull to one side when braking for several reasons, including improperly adjusted shoes, contaminated brake material on one side, or mismatched parts. Incorrectly installing the brake shoes can also cause pulling.
- Worn brake shoes: The friction material on the brake shoes can wear thin over time. This leads to reduced braking efficiency and can cause scraping or grinding noises.
- Seized hardware: Over time, the springs, levers, and cables inside the drum brake assembly can seize or break. This can prevent the brakes from properly engaging or disengaging, causing them to drag or fail
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