• Lachlan Palmer

Why Does My Car Shudder When I Brake?



Shuddering brakes are a super common issue on many cars but, can be concerning and extremely annoying over time. So why does a car shake or shudder when braking?

Brakes are an extremely important part of any vehicle and have greatly improved over the last 100 years with the introduction of disc brakes, ABS and more. However, the basic principle of all brakes has not changed since the very first car.

The braking system relies, really simply, on a pad or shoe pressing into the rotor or drum and forcing it to slow down. This is the exact same principle as skaters sliding their foot along the ground to slow down. As the pad (the skater’s foot) stays stationary while the disc moves past it, a large amount of friction is present making car and the skater both slow down.

While the principle is really simple, there is a lot of energy spent which causes the brakes to become extremely hot. The need to monitor and deal with the heat and high friction caused by the friction is also part of the reason that brakes shudder.

Brakes today are made of many organic and metallic compounds, with most rotors being made out of metal. While these rotors come out of the factory perfectly flat, the constant cycle of heating up and cooling down can cause waves to form in the metal, which is called run-out. This is often made worse by wet weather, as driving through a puddle causes the brakes to cool down even faster.

Excessive waves in the material is most often the cause of shuddering in the brakes as the waves in the material cause the pad to move back and forth as it passes by. This is normally solved by simply machining or replacing the rotors or drums to ensure they are perfectly flat again.

The good thing about this is that these vibrations also make it incredibly easy to find out whether the front or rear brakes are causing the shudder. If the shudder is mainly felt in the pedal, then it is likely the rear brakes as the rear of the vehicle doesn’t normally steer. If the steering wheel is shaking and shuddering when braking, then there is potentially a problem with the front brakes, as the front of the vehicle steers the car.

Check out our recent post on what ABS/anti-lock braking is and how it has probably saved your life.

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