The disc vs drum brake debate might not be as heated as it was a few decades ago. Discs have virtually replaced drums in all new passenger cars, and drums today are reserved mainly for the rear axles in the cheapest and smallest cars and the majority of commercial trucks. But the recent resurgence of drums lining the back wheels of new EVs proves that one of the oldest automotive technologies still has something to prove. Drum brakes pair well with the high weight typical of any EV, but also function with regenerative braking where less braking power is needed. Each type of braking has its pros and cons, and different applications where they work best.
What Exactly Happens When you Press the Brake Pedal?
Both disc and drum brakes use hydraulic force and friction to bring the wheels to a safe stop. But they do this in slightly different ways and with different parts. When pressing on the pedal in a vehicle fitted with drum brakes, hydraulic wheel cylinders force two curved brake shoes against the inner surface of a rotating brake drum. The process is enabled by the piston in the master cylinder, which pushes hydraulic brake fluid through brake lines and hoses before reaching the wheel cylinders. The whole assembly of cylinders, brake drums, and brake shoes is held together by a backing plate to which the brake shoes are fastened by a series of springs. These are what bring back the shoes to their original position once you release the brake pedal.
What is the Role Of Drums?
Drums are the crucial component, along with the brake shoes in stopping the vehicle. They are hard-wearing, made of cast iron and also perform the secondary function of absorbing and dissipating high heat generated during braking. This heat-conducting property aids in better braking performance, as it considerably reduces the chances of brake fade, or the loss of braking efficiency under higher loads. To do so, the brake drum needs to be adequately sized, machined to extremely tight tolerances, and have the optimum surface hardness in the friction area. Since they rotate with the wheels, brake drums are exposed to road spray, dirt and debris, so the use of anti-corrosion coatings keeps them looking good and working flawlessly.
What are Some of the Advantages of Drum Brakes and Drums in Particular?
- The braking force in drums is higher than in discs of comparable size. That’s why drums are often smaller in diameter but provide roughly the same braking power.
- With the friction contact surface not as limited as in the case with rotors, the combination of brake drums and shoes will ultimately last longer. Durability also means less maintenance.
- The reason why drum brakes will get more safe miles is that they generate less heat. In addition, the enclosed design and drums having corrosion coatings fare better against road debris, liquids and dirt.
- Drum brakes are easier on the wallet. The drums themselves are cheaper to buy than the discs in disc brake assemblies, and reconditioning them is less costly or time-consuming than the work needed in brake calipers.
- Incorporating the parking brake into the drum brake assembly is much easier than with disc brakes.
Now, For the Cons
During heavy braking, drums can get really hot, meaning they’ll distort leading to wheel judder. There’s also some loss of brake feel in the same instances, as the drum expands, so more work is needed by the driver to reduce speed or come to a safe stop. Brake grabbing or wheel lock is more of an issue in drum brakes, as rusted, worn or dirty shoes can get jammed against the inner drake drum wall. There’s also more likelihood of stuck pistons and worn seals, reducing overall braking performance.
When to Check Your Drum Brakes?
source : thedrive.com
When you hear grinding, scraping or rattling noises, feel odd brake pedal behaviour, excessive vibrations through the wheels, and the vehicle pulling to one side with the pedal engaged, it’s time for a brake inspection. Grinding noises can mean that the friction lining in the brake drum has thinned and become worn. Rattling is also serious as it implies flaking or broken parts in the friction surface rolling around the drum. Scraping noises are often caused by worn brake shoes. This also causes a soft or spongy brake feel, as the shoes take longer to grab hold of the drums. This though can also be a sign that there’s something wrong with the master cylinder or there are leaks in the brake lines. Vehicles that pull to one side often have stuck wheel cylinder pistons. And a juddery ride will often point to warped drums getting very hot.
Replacing Drum Brakes
Drums need to be free of rust, scratches and cracks. Often, when replacing the drums, buyers are also advised to get matching brake shoes. And both brakes should be changed out at the same time to ensure proper function. Lastly, check the brake fluid. This needs to be changed every 50 thousand kilometres. Always go for reputed parts brands from reputed stores and get brakes checked and replaced at authorised shops.