How Drum Brakes Work?- Easiest Explanation Ever

Here you can get Drum Brakes Working. Drum brakes are primarily used at the rear axle of small and compact class vehicles.

Two-wheelers such as scooters, commuter bikes, three-wheelers including auto-rickshaws widely use the Drum Brake system for braking. This type of brake system is used on the rear wheels of most hatchback cars, entry-level sedans & MUVs. It is also widely used on both front & rear wheels of trucks, buses, and other commercial vehicles in combination with hydraulic/pneumatic (either air-pressure or vacuum) brake actuating systems.

What Is Drum Brakes

A drum brake is a brake that uses friction caused by a set of shoes or pads that press outward against a rotating cylinder-shaped part called a brake drum.

The term drum brake generally approach a brake wherein footwear press at the internal surface of the drum. When shoes press on the outside of the drum, it is also referred to as a clasp brake. Where the drum is pinched among shoes, much like a conventional disc brake, it’s miles on occasion called a pinch drum brake, though such brakes are pretty rare. A related type called a band brake makes use of a bendy belt or “band” wrapping around the out of doors of a drum.

Drum Brake Working Principle

The brake shoe is allowed to expand in both the direction. As the brake lining of shoe touches the inner surface of the drum, friction is generated in between the brake shoe and drum and stops the vehicle from moving.

Working of Drum Brakes

  1. As the brake pedal is pressed, it compresses the fluid in the master cylinder and allows the piston of the wheel cylinder to expand outward.
  2. The outward movement of the piston of wheel cylinder forces the brake shoe outward towards the brake drum.
  3. As the brake shoe lining touches the inner surface of the drum, and because of the friction generated in among the brake shoe and drum, the movement of the wheel reduces and vehicle stops.
  4. As the pressure is eliminated from the brake pedal, the retracting springs attracts the brake shoe inward and the touch among the friction lining and drum ended. Now once more the brake is prepared to apply.
  5. A self adjusting screw is present at the bottom, which is used to maintain a minimum gap between the drum and brake shoe. When the lining of the brake shoe is wear out than the gap between the drum and brake shoe increases, at that time the adjuster is adjusted again to maintain the minimum gap.

Types Of Drum Brakes

There are mainly three types  – mechanical, hydraulic & pneumatic assisted brakes.

1. Mechanical:

In the mechanical system such as in two-wheeler & an auto-rickshaw, the brake shoes are actuated through a cam, that’s connected to the brake linkage & pedal. When you press the brake pedal, the cam turns. Thus, it reasons the brake shoes to increase outwards and rub in opposition to the drum.

The friction among the brake linings and the drum causes the drum to stop rotating; thereby stopping the wheel. When you release the brake pedal, the retracting springs carry the brake shoes again to their original position. This results in a gap among them and the drum and to once more spin it freely.

2. Hydraulic:

The hydraulic brake system such as in motors is a bit superior to the mechanical one. In this design, the hydraulic wheel cylinder replaces the cam. In the hydraulic system, instead of a cam, the wheel cylinder’s pistons push the brake shoes outwards.

The brake shoes fit on the anchor plate or braking plate. It holds the brakes system elements collectively and on to the car’s axle. When you press the brake pedal, the oil in the brake master cylinder multiplies the hydraulic pressure sent to the wheel cylinders. Thus, it causes its pistons to push outwards. The pistons, in turn, cause the brake shoes to expand and rub against the drum. The friction among the brake linings and the drum causes the drum to stop rotating, thereby the wheel to stop.

3. Pneumatic Assisted:

Furthermore, the third type is the pneumatic-assisted brake system. It is actuated through air-pressure which works on the same principle of that of the mechanical brake system.

It additionally includes a larger length cam or the ‘S’ shaped cam. Another name for this brake is the “S-Cam” brake system. However, high-pressure compressed air actuates a pneumatic piston that turns the cam. Mostly the medium to heavy commercial vehicles use this type of brake system.

Main Parts Of Drum Brakes

The whole assembly of the drum brake is fitted to the back plate of the wheel. The back plate remains stationary and it does not rotates with the wheel.

1. Brake Drum:

It is a round cast iron housing that is used to stop the car with the assist of brake shoe. The drum brake is bolted to the hub of the wheel. It rotates with the hub.

2. Brake Shoe:

It is the frictional a part of the drum brake, with out it the working of the brake isn’t always possible. The brake shoe has brake lining at its outer curve. It is the brake lining which makes contact with brake drum in the course of the stopping of the vehicle. It is of types

  • Primary Brake Shoe: The shoe having large lining material is known as as primary shoe.
  • Secondary brake shoe: The shoe with small lining material is known as secondary shoe.

3. Wheel Cylinder:

It is used to pressure the brake shoe outward to use the brake. The wheel cylinder is connected to the master cylinder. It contains piston which moves outward whilst brake is applied and forces the brake shoe in the direction of inner surface of the drum.

4. Return or Retracting Spring:

It is used to retract the brake shoe after brake is applied. Two go back springs are there in durm brake, one for the primary shoe and other one is for secondary shoe.

5. Self Adjuster:

It maintain the minimum gap between the brake shoe and drum so that they do not contact each other when pedal is not pressed. In the case if the brake lining wear out, and gap increases in between the shoe and drum, It can be adjusted again to maintain the gap between shoe and drum inner surface. once it is adjusted it maintains the same gab during the brake working by itself.


  1. Simple design.
  2. Fewer parts.
  3. Easy & cheaper to manufacture.
  4. Low maintenance cost.
  5. Comparatively longer life.


  1. Low braking force compared to Discs.
  2. Brakes ‘fade’ when the driver applies them for a prolonged time.
  3. The brake shoe lining made of asbestos is harmful to humans.
  4. When wet, the braking grip reduces considerably.
  5. Non-asbestos linings catch moisture; causing the brakes to grab suddenly.
  6. Heating problem: Since the friction area is totally covered by lining, so heat is developed during the friction is not allowed to go out in the atmosphere. This may reduces the braking efficiency of the vehicle.
  7. The drum brakes will not work properly if it gets wet in water. This is because water takes longer time to come out from the drum. the water reduces the friction in between the brake lining and drum.

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