Why does my car shudder when I brake?

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A shuddering car under braking can be a particularly scary experience – the last thing you want is a crucial element of your car failing.

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There are several different reasons why your car may be shaking or shuddering when you hit the brakes, but for the most part, it’s a sign that it’s time to book your ride in with a local mechanic for some maintenance.

James Boer, a mechanic for Bentley and Rolls-Royce cars, recommends not ignoring a shudder in your brake system.

“When your brakes shudder, it could mean something as simple as fixing warped brake rotors or worn pads. But it also could mean a jammed piston in your caliper or worn-out suspension components. Regardless, it should not be ignored if you feel the car shake when you hit the brakes.”

How do brakes work in a car?

To understand why your brakes are shuddering, you must first understand how brakes work in a car. Some systems are slightly different, but here’s the gist.

A braking system is comprised of seven main components: the pedal, the booster, the master cylinder, the ABS block, calipers, discs and pads.
When you press the brake pedal, it forces the braking rod into what’s called a brake booster. This is a vacuum-operated component that uses the vacuum to multiply the force of pressing the brake pedal.

The booster then pushes into what’s called a master cylinder, this component sends brake fluid down the lines to the respective corners of the car.
If your car has ABS, which is now a requirement for passenger cars, the fluid will travel down into an ABS block.

A wheel speed sensor is located on each wheel, which senses when the brakes are locking up. It sends this information to the ABS block, which then intermittently releases the brakes to allow for wheel traction if it feels that you are going to lock up the brakes.

After the ABS block, the fluid will make its way to a caliper. The fluid is used to push out a piston in the caliper that squeezes a brake pad onto the disc (or rotor), using a clamping motion to add resistance and slow the car down.

With all things considered, here’s what may be causing your shuddering brakes.

Why does my car shudder when I brake?

Stuck brake caliper

A stuck brake caliper/piston requires an urgent fix. It can cause brake failure, often caused by poor maintenance or leaving the car sitting for extended periods of time without driving it.

At best, it will warp your rotor, causing you to lose some brake performance. At worst, it can cause complete brake failure if it gets so hot that it boils the brake fluid.

You can tell if you have a stuck caliper as your car will veer to one side under braking, and excessive heat will come off one of your brakes after driving.

Caliper rebuilds can cost between $250 and $1000 in parts and labour.

Worn brake pads

Worn brake pads can often cause excessive heat and vague braking. As your brake pad begins to wear down, it loses some of its heat dissipation properties, which can cause a shudder, loud metal-on-metal noises, and warped brake rotors.

The quicker you get to changing the pads, the cheaper the job will be. If you change your brake pads when they’re starting to get low, you can get away with just changing the pads.

However, if you wear them down to the point where they are unusable, you can eat into the rotor beyond getting it machined, which will leave you needing to buy new pads and rotors.

A brake pad change will cost between $150 and $400, while adding new rotors can double or triple the cost.

Warped brake rotors

Warped brake rotors or discs are one of the most common issues with brake shuddering. They are caused by poor maintenance, heavy brake useage, and excessive heat.

Because the pad no longer has a flat surface to run over when it clamps onto the rotor, the pedal will shudder.

It all comes back to excessive heat, which can occur if you’re travelling down a long, steep gradient each day and riding the brakes, your brake pads are worn and can’t dissipate the heat well enough, or your brake caliper is stuck on slightly.

You’ll be able to tell if your rotor is warped because you will be able to feel intermittent force back through the pedal.

If you feel like your rotors are warped, you should book your vehicle into the mechanic as soon as possible. It’s possible that it could be as simple as machining the disc and replacing the pads on that axle, which will cost around $400 to $1000 depending on the car. But it can mean a brake caliper rebuild, which will cost a few hundred dollars more on top of the rotor and replacement.

Worn suspension components

Worn suspension components can cause the wheel to move under braking, which in turn causes a shudder through your car.

The usual culprits are swaybar bushings, lower control arms and tie rods. Because these are used to hold your wheel in place while allowing for movement when you turn the steering wheel, the rubber can become worn and allow the entire hub assembly to move excessively under braking.

Most suspension components aren’t going to break the bank when being replaced. They can be easily diagnosed by jacking the front or rear of the car up and checking for movement by trying to move the wheel from side to side.

Low tyre pressures

Low tyre pressures can often cause a shudder in the brake as it causes the car to be unstable.

It’s an easy check: head to a petrol station, check your tyre-pressure placard and ensure that all four tyres are inflated to the manufacturer’s recommendation.

ABS module

If your car is shuddering only under hard braking, then your ABS module could be kicking in.

As mentioned previously, it works by modulating your brakes to maintain traction and prevent the wheels from locking up. When activated, it causes the brakes to shudder.

If you feel like this is happening unnecessarily, it could actually mean you need new tyres and are losing traction under braking.

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