Braking is an essential function of a motor vehicle, so whenever something feels off or weird under braking, it is a reason to be alarmed, and you might wonder why my car shakes when braking.
This can range from warped brakes, worn-out wheel bearings, worn-out steering joints, worn-out suspension bushes, loose wheel nuts, ABS engagement, and wheel hop.
In this article, we cover the 7 reasons that might result in your vehicle shaking when braking so you can get it correctly diagnosed.
1. Warped brake discs
Warped brake discs are one of the most common reasons why cars start shaking under braking. Since the disc’s surface isn’t flat anymore, the brake pads gain a loose grip on the disc’s surface.
The slower you go, the slower and more prominent you will feel this effect, and at high speed, it might be stable until a certain speed is reached and then start shaking until you reach a standstill or release the brakes.
2. Worn-out wheel bearings
Worn-out wheel bearings can cause shaking under braking but not severe shaking.
The amount of free play in a worn-out (in this case, worn out at such a level that you don’t hear a grinding noise while driving) wheel bearing is very little.
It is enough, though, that you will be able to feel it through the steering wheel but not throughout the entire vehicle.
3. Worn-out steering joints
Connecting your steering wheel to the tires of the car is numerous universal and Heim joints. Over time these joints wear out usually at the same rate, so they start getting play in them.
While an individual joint can’t get enough slack to influence the car under braking, two or more can. It can be so bad that you sometimes think the whole car will fall into pieces. I have experienced it, it is not pleasant.
What is happening is under braking, the two front wheels are moving left and right independently from one another, not a vast amount, but it might be close to 1 to 3 degrees of angle, and constantly switching direction.
This gives it that violent shake feeling.
4. Worn-out suspension bushes
This is usually something to look out for on cars that are close and over ten years old. The suspension of a vehicle isn’t rigid or hard connected to the chassis of a car; they have rubber between them and the chassis.
This helps prevent unnecessary noise and vibration from the tire on the road entering the vehicle’s chassis.
Over time from regular use, these rubber bushes start to dry out and wear out; it can be so bad you can have no bushing material left.
Under braking, the entire suspension can change its geometry because the bushings are too far gone or nonexistent. This can result in the car vibrating and shaking as well.
5. Loose wheel nuts
Hopefully, shaking under braking is the only thing you experience with loose wheel nuts because the wheel can also easily break free, resulting in your car dropping to the ground on that specific side.
This is a common problem for the DIYers and even workshops, installing the wheels on the car and forgetting to fasten, hopefully only one wheel.
It isn’t apparent when you look at the wheel that it isn’t adequately secured, but once you start driving, the car might start to vibrate in most cases. Under braking, you will feel it wobbling and shaking the car. If this happens to you it can be as costly as replacing your engine.
6. ABS engagement under heavy braking or slippery conditions
Modern vehicles equipped with ABS (Anti-lock Braking Systems) can also under heavy emergency braking or slippery road surfaces, giving you the feeling of the car shaking.
This, however, is normal and not something you need to worry about.
Under these conditions, when braking, the car tries to stop the wheels from locking up, hence the meaning of Anit-lock.
Top-of-the-range vehicles like Mercedes and Rolls-Royce have high-tech and high-bit-rate ABS modules that can engage and disengage the brakes 100’s of times per second, giving it a very smooth feel and no jerkiness.
Standard budget-oriented everyday cars have much cheaper and lower bit-rate ABS modules that might only be able to disengage and reengage the brakes under 60 times a second, giving it a more violent on-off feeling and may give the feel of the car shaking.
7. Wheel hop
This phenomenon happens with older cars with no ABS systems; under emergency or heavy braking, the wheels lock up and slide, but sometimes the road surface and the tire grip are enough for the wheel to bounce violently up and down.
If you ever watched some of the older car chases in the movies, you would have heard the sound of tires chirping under braking and that is then what is happening.
The best thing to do in this situation is to release and apply the brakes just enough not to lock up or to start wheel hopping again.
Final thoughts on why a car shakes when braking
With more modern cars on the road, the biggest reason a vehicle can shake under braking is worn-out parts or poorly fastened wheels.
Hopefully, this article will help you diagnose why your car is shaking when braking or at least motivate you to take your vehicle to get inspected.