DIY Drum Brake Inspection: A UK Guide

Your vehicle's braking system is paramount to your safety and the safety of others on the road. While disc brakes are prevalent on front axles, many vehicles, especially older models or those with lighter loads, still rely on drum brakes on the rear. Understanding how to inspect these crucial components can save you from costly repairs and, more importantly, prevent dangerous situations. This guide will walk you through the process of checking your drum brakes, from initial system checks to detailed component inspection.

Safety First: Preparing for Brake Work

Before you begin any work on your vehicle's braking system, safety must be your top priority. Brake dust, especially from older vehicles, can contain asbestos fibres, which are hazardous if inhaled. Always work in a well-ventilated area.

• Wear an inexpensive but protective paper mask to prevent inhaling brake dust.
• Wear eye protection to shield your eyes from debris.
• Never use compressed air to clean brake parts. This will only aerosolise the dangerous dust. Instead, use a dedicated brake parts cleaner spray, saturating the dust completely before wiping it away with a rag. Dispose of contaminated rags immediately in a sealed plastic bag.
• Park your vehicle on a flat, dry surface.
• Chock the wheels that will remain on the ground to prevent any movement.
• Ensure the parking brake is not engaged if you're inspecting the rear wheels, as this will lock the shoes against the drum.
• For automatic transmissions, select 'Park'; for manual transmissions, select 'Neutral'.
• When jacking the vehicle, ensure your jack is rated for the vehicle's weight and use the manufacturer's specified lift points, usually found in your owner's manual.
• Once lifted, always support the vehicle on sturdy jack stands, never rely solely on the jack.

Initial Brake System Assessment

Before even touching a spanner, a quick assessment of your overall braking system can provide clues about potential drum brake issues:

• Brake Pedal Feel: Start the vehicle and press the brake pedal. Does it feel 'mushy' or does it travel too close to the floor? This could indicate air in the system, a fluid leak, or brake fluid that has absorbed too much moisture.
• Dashboard Warning Lights: Check for illuminated brake warning lights, ABS lights, or even the 'check engine' light, as these can signal brake system problems.
• Master Cylinder Inspection: With the engine off and bonnet open, visually inspect the master cylinder. Look for signs of leaking fluid around fittings or a low fluid level in the reservoir. A low level often points to a leak. If the fluid is cloudy or dark, it likely needs replacing. Many manufacturers recommend changing brake fluid every 24 months or 24,000 miles, as it absorbs moisture over time, leading to corrosion and reduced performance.

Accessing the Drum Brake Assembly

Once your vehicle is safely secured, you can proceed to remove a wheel to gain access to the drum brake. Remember to loosen the wheel nuts slightly before jacking the vehicle fully.

1. Remove the Wheel: Fully remove the wheel nuts and carefully take off the wheel.
2. Identify Drum Type: Brake drums are broadly classified as either 'hubbed' or 'floating' (hubless).
• Hubbed Drums: These have wheel bearings inside them, meaning the drum itself incorporates the wheel hub.
• Floating Drums: These simply slide over the lug nut studs that hold the wheels on the vehicle, without integrated bearings.
3. Removing a Hubbed Drum (Skip to Step 8 for Floating Drums):
• Pry off the Grease Cap: Using a pair of combination slip-joint pliers, carefully pry the grease cap off the end of the hub.
• Examine the Cotter Pin: You'll see a cotter pin sticking out of the side of the castellated nut (or nut-lock-and-nut combination). Pay close attention to its direction, how its legs are bent, and how it fits through the nut. A sketch can be helpful.
• Remove the Cotter Pin: Using needle-nose pliers, straighten the cotter pin and carefully pull it out. Place it on a clean rag, oriented as it was.
• Slide Off the Nut/Lock: Carefully slide the castellated nut or nut-lock-and-nut combination off the spindle. If it's greasy, wipe it clean with a lint-free rag and place it next to the cotter pin.
• Partially Pull Drum: Grab the brake drum and pull it gently towards you, but don't slide it completely off the spindle yet. Just push it back into place. This action will expose the outer wheel bearings and washer on the spindle.
• Remove Outer Bearing and Washer: Carefully slide the outer bearing, with the washer in front of it, off the spindle. This is a good opportunity to check these bearings for any signs of wear or damage.
4. Removing the Drum (Both Types): Carefully slide the entire drum off the spindle. If you have a floating drum, you might need to strike it with a hammer to break it loose from the hub.
5. Brake Dust Protocol: Once the drum is off, you'll likely see a build-up of brake dust. Remember: never blow this away with compressed air. Put your mask on, saturate the dust completely by spraying the drum with brake parts cleaner according to the instructions on the can. Wipe the drum clean with a rag, then immediately place the rag in a plastic bag and dispose of it responsibly.

Inspecting the Brake Drum Itself

With the drum removed and cleaned, it's time for a thorough inspection.

Visual Inspection:

• Inner Walls: Look closely at the inner walls of the drum. It's common to see some light grooves from normal wear. However, if these grooves appear unusually deep, or if you spot hard spots, burned places, or discolouration (often blueish or dark areas indicating excessive heat), these are signs of significant wear or damage.
• Outer Lip: Check for an outer lip that may have formed at the drum's open edge. This indicates wear and means the brake shoes have worn a deeper path into the drum's friction surface.
• Cracks: Any cracks in the drum surface or body necessitate immediate replacement.

Measuring Drum Thickness:

The most critical aspect of drum inspection is measuring its thickness to ensure it's within safe operating tolerances. This is where a brake drum micrometer comes into play. Most drums have the minimum thickness specification stamped directly onto them, usually near the mounting hub. If the drum has worn down below this stamped minimum thickness, it must be replaced. Driving with drums thinner than the specified minimum can lead to brake fade, cracking, or even complete brake failure.

Even if the friction surface appears smooth, minor peaks or valleys can exist that would cause new shoes to ride on high spots, reducing their effectiveness. For best braking performance, it's always recommended to resurface or replace drums when replacing brake shoes.

Inspecting Internal Drum Brake Components

With the drum removed, you can now inspect the various components still attached to the brake backing plate.

• Wheel Cylinders: These are crucial for pushing the brake shoes against the drum. Inspect them thoroughly for any signs of leaking brake fluid. Leaking fluid will contaminate the brake shoe lining, causing the drum brake to 'grab' unevenly and make noise. Any leakage means the wheel cylinder needs replacement.
• Brake Shoes and Linings:
• Wear: The brake shoes should show even wear across their entire surface. Look for any bald spots, thin places, or areas where the lining appears to be crumbling.
• Thickness: The brake lining should be at least 1/16-inch (approximately 1.6mm) from the steel part of the brake shoe or 1/16-inch from any rivets (if present). More thickness is always better.
• Bonding/Riveting: Ensure the linings are firmly bonded or riveted to the brake shoes. Any separation is a serious issue.
• Glazing: Glazed brake shoes (a shiny, hardened surface) can result from excessive heat or brake drag, leading to reduced braking performance and squealing or grinding noises.
• Return Springs: These springs pull the brake shoes away from the drum when the pedal is released. Over time, or under extreme use, they can lose tension strength. Weak springs can cause brake drag, where the shoes don't fully retract, leading to excessive wear, heat build-up, and glazed shoes. Check if they appear stretched or discoloured from heat.
• Hold-Down Springs: These springs keep the brake shoes in their proper position against the backing plate. If weakened by heat or age, they can cause the brake shoes to vibrate and rattle. If they become too loose or break, they can cause more serious problems, including damage to the brake drum or even a brake system lock-up. It's good practice to replace all springs and hold-down hardware whenever you replace brake shoes, as their weakness isn't always visually obvious.
• Self-Adjusting Mechanism: This mechanism ensures your shoes maintain their proper position relative to the drums as they wear down, preventing excessive pedal travel. Inspect the adjusting cables, levers, and springs for wear, rust, or weakening by heat. If compromised, they cannot maintain correct shoe-to-drum clearance, resulting in delayed or reduced braking effort.
• Brake Lines and Hoses: Take time to inspect all rubber brake hoses for cracking, chafing, swelling, or leaking. Also, check all steel brake lines for leaks, kinks, corrosion, or damage. These are critical for fluid transfer.

Frequently Asked Questions (FAQs)

How often should drum brakes be checked?

It's generally recommended to have your brakes inspected at least once a year or every 12,000 miles (20,000 km), whichever comes first. However, if you notice any of the warning signs discussed, an immediate inspection is necessary.

What are the common signs of worn drum brakes?

Common signs include:

• A 'mushy' brake pedal or a pedal that travels too far before engaging.
• Squealing, grinding, or scraping noises when braking.
• Vibration in the brake pedal or steering wheel.
• The car pulling to one side when braking.
• Reduced stopping power or increased braking distances.
• A dragging sensation from the rear wheels.

Can I drive with worn drum brakes?

No, it is extremely dangerous to drive with worn or faulty brakes. Worn brakes significantly reduce your vehicle's stopping capability, increasing the risk of an accident. Address any brake issues immediately.

What is 'brake drag'?

Brake drag occurs when the brake shoes do not fully retract from the drum when the brake pedal is released. This can be caused by weakened return springs, a faulty wheel cylinder, or an incorrectly adjusted self-adjusting mechanism. Brake drag leads to excessive heat, premature wear of components, reduced fuel efficiency, and a burning smell.

Can drum brakes be resurfaced?

Yes, if the drum is not excessively worn beyond its minimum thickness specification and does not have severe damage like cracks or deep hot spots, it can often be resurfaced (also known as 'turning' or 'machining'). This process removes a thin layer of material to create a smooth, true friction surface. However, if the drum is too thin, it must be replaced.

Conclusion

Inspecting your drum brakes is a vital part of vehicle maintenance that contributes significantly to your safety on the road. While the drum brake system is complex, understanding its components and knowing how to identify issues can help you perform basic troubleshooting and determine when professional intervention is required. Regular checks and timely maintenance will ensure your vehicle's stopping power remains reliable, giving you peace of mind on every journey.

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