Brake It Down: A Guide to Disc and Drum Car Brakes

No matter how many safety systems your car has, stopping and maneuvering to avoid obstacles is still done the old-fashioned way – with brakes. Braking systems, like all vehicle components, have evolved over the years to keep up with increasing engine power and to provide better stopping performance in larger and faster vehicles. For passenger cars, this has meant the gradual shift from older drum brake systems to more effective disc brakes. 

Car Brake Basics and How They Work

Brakes do more than just slow down your car. Yes, reducing speed and bringing the vehicle to a controlled stop is their main purpose, but a decent set of car brakes helps navigate bends, avoid obstacles, safely descend hills, and adjust for changing road or weather conditions. They are also essential in emergency stops, avoiding collisions with pedestrians and other vehicles, and in general safety. 

Pressing the brake pedal activates more than a few parts. Since most cars rely on hydraulic systems, compressed hydraulic fluid from the master cylinder (typically located near the firewall, in front of the brake pedal) travels through sealed brake lines and creates the necessary pressure in wheel cylinders, consisting either of disc brake or drum brake components. 

Both types activate auxiliary parts (shoes in drums and pads in disc brakes). The friction of pads and discs or shoes and brake drums is what slows the vehicle down. Releasing the pedal activates springs and other parts, with pads and shoes returning to their normal position, ready for the next stop. 

Disc Brake Components 

More common in recent vehicles, disc brakes get their name from the metal disc attached to the wheel hub. Discs rotate and move (or stop) with the wheels. Hovering above the disc is a calliper, fitted with one or more pistons. This is actuated by hydraulic pressure when pressing the pedal to push pads within the callipers to press against the surface of the discs, and slow down or stop the vehicle. Taking your foot off the pedal engages a return mechanism, so the calliper pistons and pads are pulled back. The drop in pressure draws the brake fluid back into the brake lines and into the master cylinder.

Braking is simplified with additional parts. For instance, brake boosters between the pedal and master cylinder amplify the pressure in the hydraulic fluid when pressing the pedal, ensuring safe stopping with minimal effort. And modern safety systems, such as anti-locking brakes (ABS), wheel speed and autonomous braking sensors (among others), line each wheel for more controlled braking, preventing wheel lock or slippage. 

Parts in Drum Brakes 

Drum brakes are an older design, typically fitted on the rear axle of entry-level cars, as well as on larger, heavier trucks and buses. They consist of a backing plate that holds the other components, including a cylindrical cast-iron drum attached to the wheel (thus the name), twin-piston cylinders and brake shoes. Braking occurs when the shoes are forced against the drums, again with the help of hydraulic fluid from master brake cylinders. 

The Disc vs. Drum Brake Debate 

Each type of brake design has its intended application and set of pros and cons. Disc brakes are preferred in lighter vehicles for their immediate braking response, reduced instances of brake fade (a temporary reduction in braking power), shorter stopping distances and overall higher consistency and predictability. Parts are also easier to access and maintain. With numerous designs and careful material choices, they’re also more durable, requiring fewer replacements. 

Drums can generate higher brake force (necessary in stopping heavier vehicles), are enclosed designs so suffer less environmental wear, often at the expense of longer braking distances and reduced brake feel through the pedals. Their main advantage is the lower production and purchasing costs, considering they require more frequent replacements. 

Common Brake Component Issues 

Brake pads are the most common brake replacement item, lasting between 48,000 and 80,000 kilometres, depending on the vehicle and driving conditions. Similar intervals apply to drum shoes, though shoes on rear axles (with discs up front) tend to last longer due to higher brake force (and accompanying wear) generated by the front brake assembly. Replacing pads and shoes is a good opportunity to check the overall condition of the brakes, including wear or damage to the discs, callipers, and cylinders.

Parts can fail earlier than recommended replacement times, with common signs being: 

• Longer stopping distances: Worn rotors, pads and shoes are the main reason vehicles take longer to slow down or stop. This is largely due to the reduced friction area. Fluid leaks, ruptured brake lines or issues with master cylinders and boosters can also lead to reduced braking performance. 
• Screeching and grinding noises when applying the pedal: Pads that have worn out to the metal backing plates produce a screeching or grinding noise when coming into contact with the rotors. Grinding noises are also caused by stuck calliper pistons or warped and uneven discs. 
• Vibrations and the vehicle pulling left or right: Uneven pad and shoe wear means uneven brake force between the left and right wheels, causing vibrations and, in many instances, the car pulling to either side. The same issue can be caused by varying tire pressure. 
• Spongy or soft brake feel: Check brake fluid levels, the condition of master cylinders and leaks in the brake lines. 
• Burning smells: Worn parts generate more heat, often leading to overheating and burning smells. 
• Brake warning light(s): Vehicles equipped with multiple sensors notify drivers of dangerously low pad thickness, issues with the parking brake or problems with related safety systems, such as the ABS. Again, if a yellow or red brake warning light comes up in the dashboard, have your car checked promptly by a qualified mechanic. 

To ensure safety, have brakes regularly inspected and serviced. Conduct periodic visual inspections for pad wear (brake pad dust accumulated on the wheels is a common sign), wear, scraping and discoloration in the discs and rust in drum assemblies. Replace faulty parts as per manufacturer recommendations, or if you’re tuning your car, consider aftermarket car brakes for improved braking performance.