How it works: Disc vs. drum brake

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Drum brake

• Drum brake is a small drum which rotates with the wheel in case of automobile and has a pair of shoes known as brake shoes inside it. When the brake paddle is pressed then the brake shoes are forced against the side of the walls of the drum and apply brake by means of friction.
• Drum brakes are pure mechanically operated.
• In drum brake water is collected inside the drum when vehicle runs in water or at washing time. This water accumulating affects the efficiency of the braking.
• Drum brakes are not effective at high speed because at high speed when brake is applied then due to friction lager amount of heat generates due to this over heating occurs. As temperature increases the coefficient of friction decreases due to this friction lining fade away and loss of torque transmitting capacity of friction lining at higher temperature.
• Drum brakes has less torque transmitting capacity.
• Its response time is high as compare to disc brakes
• This may be self locking
• Drum brakes are used in heavy vehicles due to the self actuating properties i.e. when the corner edges of the brake pad comes in contact with outer cover then the rest of brake pad is comes in contact itself so less effect is required by the driver.
• Less effective in different applications and heavy in weight as compare to disc brakes
• Here is no fluid is used so it is not require any kind of maintenance when vehicle is used after long time.
• In case of drum brakes for inspections and service of brake; wheel and drum are dissemble first because brake parts like pad brake shoes etc are attached inside the drum.
• Drum brakes are not completely self adjusting and less efficient than disc brakes.

The maintenance of drum brake is cheaper than disc brake

DISC BRAKE

• Disc brake has a disc shaped metal plate and a caliper which is attached to the wheel and disc is rotates with the wheel of automobile. The caliper is used to exert force on the pads. The friction lining of the caliper comes in contact with a small portion of the disc. The reaming portion of disc helps in dissipation of the heat to the surrounding. Two pads on either side of the disc are used and the friction lining is attached to the both pad. Caliper is attached to the non rotating member and exerts force on both the pads. When brake paddle is pressed then pads are also pressed against the rotating disc then the friction between the disc and pads retards the speed and stop the disc.
• Disc brakes are mechanically operated but they can also be linked with ABS system and some other advance technologies.
• They work efficiently in adverse conditions like in heavy rains and there is no such effect of water in case of disc brakes.
• In case of disc brakes no overheating occurs because only a small portion of the disc is come in contact with the friction pads and rest area of disc helps in better dissipation of heat. So they can be used in high speed applications. The coefficient of friction is not change very easily and the friction lining not fade away easily.
• Disc brakes have high torque transmitting capacity in small volume.
• Disc brakes as easy to control and has fast response time as compare to drum brake.
• Disc brakes never be self locking
• Disc brakes generally used in medium and low vehicles because there is no self actuating property.
• More effective in different applications and light in weight.
• When vehicle is not in use for long time then the chances of damage of brake fluid pipe increases which causes failure in braking and require maintenance and braking fluid may loss its viscosity which should be replaced.
• Disc brakes are easily inspected without removal of the wheel because it is mounted with the wheel so the defaults in the brake visually inspected very easily.
• Disc brakes are better stopping power than drum brake and completely self adjusting, so overall performance of the disc brake is better than the drum brake.
• Maintenance cost is high if we used disc brakes.

COMPARISON

1. Constructional Difference

DRUM

In drum brakes instead of disc a drum is used whose outer part having drum lines is coupled with the wheel’s hub and rotates with the wheel.

In drum brakes a drum is used inside which the brake shoes along with the actuating mechanism (cylinder or spring) are mounted in such a way that when the brakes are applied the outward motion of the brake shoes makes frictional contact with the rotating drum lines and the vehicle decelerate or stops.

In drum brake instead of the brake pads, large brake shoes made up of frictional material glued over a metallic shoe like component are used for making frictional contact with the rotating drum lines and the outward of these brake shoes is governed by the hydraulic cylinder mounted inside the drum.

The overall arrangement of the drum brake system is quite large as compared to the disc brake system.

DISC

In disc brakes a circular metallic plate is used which is coupled with the wheel’s hub and rotates with the wheel.

In disc brakes a calliper is used which mounted over the disc in such a way that when the brakes are applied the movement of the brake pads try to clamp the rotating disc(making frictional contact) which in turn causes vehicle to decelerate or stop.

In disc brake small brake pads made up of frictional material (having rough surface) are used for making frictional contact with the rotating disc, the clamping movement of these brake pads is governed by the small hydraulic cylinders called wheels cylinders mounted inside the callipers.

Overall arrangement of the disc brakes system is quite small as compare to the drum brakes.

2. Working Difference

DRUM

The initial working of the drum brakes is same as the disc brake but after the brake oil leaves the master cylinder the working of drum brake is as follows.
The brake oil from the master cylinder having high pressure enters the brake drum and applies pressure on the wheel cylinder pistons of the drum brakes due to which the piston moves.

Due to this movement of piston the brake shoes inside the brake drum moves outward and makes contact with the rotating drum lines.

Due to this frictional contact between brake shoes and drum line the vehicle decelerates or stops.

DISC

The working principle of the disc brake is same as the drum brake but the movement of components is different.
In disc brake system when the brake pedal is pressed the piston of the master cylinder pushes the highly compressed brake oil (hydraulic fluid) through the brake lines to the brake calliper.

This brake oil having high pressure enters the brake calliper and due to this high pressures the pistons of the wheel cylinders of both sides i.e. right pad side and left pad side moves.

Due to these movement of the wheel cylinder piston the brake pads moves in inward direction and try to clamp the rotating disc. Due to this contact between brake pads and rotating disc frictional force is generated which in turn finally decelerate or stops the vehicle.

3. Efficiency or Brake Force Difference

DRUM

The brake force applied by the drum brakes over the rotating wheel is moderate or less as the frictional force generated due to the contact between the brake shoes and the rotating drum line is moderate or low but is enough to decelerate or stop the vehicle. Due to this reason drum brakes are used in heavy vehicles

As they can be expand to any size so the use of drum brakes in heavy vehicle is quite efficient.

DISC

The brake force applied by the disc brakes over the rotating wheel is quite high as the frictional force generated due to the contact between the brake pads and the rotating disc is quite high, due to this reason the disc brakes are good for others on the road, but are sometimes dangerous for the driver.

Due to the limitations of increase or maximum in size disc brakes are usually not used in heavy vehicles.

4. Difference in Application.

As they can be expand to any size so the use of drum brakes in heavy vehicle likes trucks and buses is very common.

As the disc brakes can be made as small as required the use of disc brakes in 2-wheelers like scooters and bikes, become very common.