What is the Difference between Disc and Drum Brakes
The modern brake drum system was invented in 1902 and used widely on cars starting in the 1930s. The disc brakes were actually conceptualized years earlier before the brake drums and were successfully used in the same year the brake drum was invented.
Brake drums were widely used on cars earlier as there were no real design problems compared to disc brake designs. Brake drums are made of cast iron that usually has holes on its closed end that pass through the stud bolts of the wheels and axle hub. It settles in good fit on the wheel axle hub with the back plate covering the open end. The slave cylinders are bolted on the back plate, which in turn is bolted on a flange fixed on the axle housing. It is also on the back plate where the brake shoes are attached with a series of springs.
The braking action of the brake shoes against the brake drum is done either by a single-acting or double acting slave cylinder. Brake shoes have brake pads either riveted or glued on them that contact the inner surface of the brake drums. Single-acting would have only one piston while a double-acting one would have two pistons acting in opposite directions on both ends of the cylinder. There are also two designs of braking actions one would be “Leading and trailing shoes” operated by a double-acting cylinder. The other design is the “Twin (or two) Leading shoes” operated by two single-acting cylinders one each end of the brake shoes and acting on opposite directions. This design is better as the braking action is equally applied at the same time at the top and bottom of the brake drum. The other design involves the “leading shoe” exerting more effort than the trailing shoe.
Adjusting the brake shoes can be done manually or automatically. There are two common ways to adjust the brake shoes: One is to step on the brakes while backing the car for a few feet and the other is to jerk the handbrake abruptly while backing. To know which way to use them, refer to the car’s owner manual or dealer.
The disc brakes are totally different in design and construction. As it implies, it is a disc where brake pads apply “pinching” pressure to slow down or stop a car. The brake pads are held by what is called the Brake Caliper, where the brake pistons are contained. The brake pistons are much larger than those of brake drums and are self adjusting. Brake pads travel on pins where they are inserted into. As there are no springs involved in disc brake pads to hold them still, anti-rattle clips and anti-squeal devices are employed for each brake pad.
Disc brakes would have more designs compared to brake drums. The most common is the single-acting Lockheed caliper. This type applies pressure to both cylinder and caliper thus equalizing pressure on both brake pads on opposite sides of the disc. Most late model cars have the calipers installed in front of the discs. The cast metal discs are also bolted on to the hub of axles that also has a back plate for protection.
Other differences of brake drums and disc brakes are:
- Disc brakes cool faster because most of the disc is exposed to rushing air. The discs could also be slotted or ribbed for better cooling.
- It is easier to check and maintain disc brakes compared to brake drums that has a series of return springs often difficult to remove and install.
- Stopping efficiency of disc brakes is better and does not fade.
- Disc brakes hardly retain any dirt or water that makes it clean and more efficient even under wet or flood conditions.
The only advantage of brake drums over disc brakes is incorporating handbrake mechanisms with it. That is the reason why many cars still have brake drums on rear wheels and disc brakes in front. The final comparison and difference will be: An all-disc brake car will have shorter braking distance and better stopping performance compared to an all-brake drum car.
