What are the reasons for the poor braking performance of motorcycle drum brakes?
3 Answers
Motorcycle drum brakes may fail to provide adequate braking for the following reasons: 1. The brake pedal may bend due to a fall or collision, shortening the effective length of the lever arm and reducing the amplification of braking force. 2. Incorrect installation can lead to diminished secondary amplification of braking force. 3. Worn brake shoes can cause the brake cam to rotate at a larger angle, altering the direction of braking force transmission and reducing the lift effect, thereby failing to effectively transfer braking force to the shoes, further weakening braking performance. 4. An uneven surface inside the brake drum can result in insufficient contact area with the brake shoes. 5. Misalignment between the brake shoes and the drum, either due to excessive clearance or improper assembly, can cause eccentricity.
I've been riding motorcycles for over ten years and frequently encounter issues with ineffective braking. The most common problem is excessive wear of the brake linings—once the friction surface is worn smooth, there's no stopping power at all. During the rainy season, water can seep into the drum, making the brakes as slippery as if they were oiled. Another major factor is oil contamination, such as transmission fluid leakage or dust buildup, which can reduce braking efficiency by 30%. Once, riding home in the rain, water entered the drum and completely disabled the brakes, forcing me to slow down and pull over. Improper adjustment of the brake arm is also common, where excessive travel means pressing the pedal has no effect. Heat fade becomes more noticeable after long-distance rides, with continuous downhill braking causing the linings to soften. Regular maintenance is advised: use calipers to check lining thickness every 500 km and replace immediately if it's below 3 mm; clean the drum interior promptly after rides; carry spare brake linings during the rainy season. Safety first—if the brakes fail, don't force the ride; head straight to a repair shop.
From a mechanical perspective, there are multiple factors causing motorcycle drum brakes to fail. The friction coefficient decreases as the brake lining wears out, and material aging accelerates, especially in high-temperature environments. A smooth friction surface, such as rust on the drum or oil contamination, can eliminate contact force. Having disassembled many old bikes, I found 80% of failures stem from oil or water infiltration. A loose brake cable extends the travel distance, making the pressing action half as effective. System contamination, like water erosion, worsens performance in wet and cold weather. Thermal fade occurs when descending slopes—the lining heats up and deforms, reducing braking force by two-thirds. Though drum brakes have a simple structure, maintenance is crucial: clean the drum chamber every 1,000 km, wipe off oil residue; check lever responsiveness; add protective covers when riding in rain. Keeping them dry and properly adjusted significantly enhances safety.
