Checking drum brakes is more involved than inspecting disc brakes. Here is how to check drum brakes safely and what to look for.
How to Check Drum Brakes: Visual Inspection
Remove the wheel and drum. Look for visible cracks, deep grooves, or scoring on the brake drum surface. Hairline cracks called martensite spots mean the drum was overheated. Blue discoloration means the same thing: overheated drums are structurally weaker. Check for rust or grease stains on the brake drum and surrounding parts.
Measuring Brake Shoes and Lining Thickness
The brake shoes should have friction material at least 1/8 inch thick. If the lining thickness is less than that, the shoes need replacement. When the lining wears down to the metal backing plate, it will damage the drum and create grinding noise. Replace shoes on both sides to prevent uneven braking.
Inspecting the Wheel Cylinder
Check the wheel cylinder for fluid leaks. Dampness around the rubber boot indicates a failing seal. A leaking wheel cylinder can contaminate the brake shoes and reduce braking performance.
When to Call a Professional
Drum brakes contain tension-loaded springs that require experience to handle safely. If the drum is rusted in place, the shoes are glazed, or the drum is out of round, professional service is recommended. A mechanic can measure the drum’s inner diameter and determine if resurfacing or replacement is needed.
