I was learning about the working of drum brakes, and I came to know, that each of the two brake linings of drum brake apply horizontal force in opposite directions.

That confused me, because, if somewhat equal forces are being put on opposite horizontal directions on the wheel, then how is it stopping the vehicle, that is bringing it instantly to rest. Considering, the wheel is rotating in anti-clockwise direction, how are the forces' directions working on the wheels, I mean how are the components/vector components of the forces applied by brake linings affecting the components of the kinetic motion of the wheels. Can anybody clarify?


... then how is it stopping the vehicle's car, that is bringing it instantly to rest.

It's probably an error in your writing but brakes don't bring a vehicle instantly to rest. They decelerate the vehicle in a more-or-less controlled manner over a period of time or distance.

I mean how are the components/vector components of the forces applied by brake linings affecting the components of the kinetic motion of the wheels?

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Figure 1. The friction force is at right-angles to the applied braking force.

It's as simple as shown in Figure 1. With no force applied to the brake shoe the friction force is very low. When force is applied the friction force increases.

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*Figure 2. In the case of the drum brake the situation is the same. The friction is perpendicular to the force applied on the drum by the brake shoes and opposes the direction of rotation.


Brakes using drums and shoes come in two varieties:

Single leading shoe and twin leading shoe

The single leading shoe has a single brake cylinder and opposed pistons, one for each shoe. This means one shoe gets « pulled » into the brake drum as it is applied, while the orher gets « pushed » off all due to the direction of rotation.

The shoe « pulled » into the drum provides more braking force and, as a result, wears faster.

The twin leading shoe has two separate cylinders one for each shoe and so provides more braking force overall.

On both types there is usually some type of rotating cam for adjustment.

  • $\begingroup$ Helpful, but my main doubt was concerning vector directions of forces into play. $\endgroup$ – peaceHoper May 16 '20 at 14:04
  • $\begingroup$ @peaceHoper same comment twice? It’s that good? Some research will show you the force diagrams and the equations for braking forces - this technology is very old and well covered. $\endgroup$ – Solar Mike May 16 '20 at 14:05
  • $\begingroup$ I mistakely did it, poor net connection. But I deleted it. $\endgroup$ – peaceHoper May 16 '20 at 14:06
  • $\begingroup$ can u site some sources of those technologies(only if possible) ? $\endgroup$ – peaceHoper May 16 '20 at 14:08
  • $\begingroup$ Fundamentals of Vehicle Technology by Hillier & Pittuck also a useful reference is Technical Formulae by Gieck $\endgroup$ – Solar Mike May 16 '20 at 14:15

In a drum brake when you force the pads out you create a friction force which is gradually increases and creates a torque opposing the rotation of the wheel.

This torque is transfered to the tire and starts to decellerate the car.

In the old brakes you could apply so much breaking power as to lock up the wheel and make it skid and burn the tire. But not anymore, After ABS (antilock brake assistance).

How ever no matter how strong the grip of the brake and the degree if torque it causes, nothing can bring a car to a sudden stop.

Even if it collides into a concrete wall it will still keep going untill it crashes the structure of the car enough to dissipate the kinetic energy.


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