It is common that after long use, the car will eventually break down or at least has some problems. Some of the problems can cause symptoms of the car shake when you are braking. It can be a serious problem that potentially causes a dangerous situation. Therefore, if you find that your car shows this sign, you need to make sure to get it repaired as soon as possible since it tends to get worse over time.
There is some common problem that causes the shaking car, here are some of them.
Problem with Your Brake Pad

One of the problems that cause shaking cars when you are braking is the oil, dirt, or other grimes that contaminate your brake pads. This contamination will grip the rotor, which causes vibration—that is when you feel the shake when braking. Another problem is the pads that get damaged warped or worn out. If the problem is indeed in your brake pads, usually you are going to hear a whining noise as well when you hit the brake pedal.
Problem with Your Brake Rotor & Disc

When the surface rotors start to wear down, the brake pads will grab unevenly. Sometimes, it will also make the steering wheel or your brake pedal to shake. This shake is especially felt when you are braking during high speeds. This problem is easily fixed by replacing or resurfacing your car rotors.
Your Car is Not Well Aligned

The next problem is when your car is not well-aligned, which may cause the shake when you hit the brake pedal. Not only making your car shake, but this problem can also make your tire wear down faster and make your suspension components damaged faster as well. If you notice that the steering wheel tries to turn right or left by itself when you are steering straight, that the problem is likely due to these alignment issues.
Worn Out Components of Suspension

When parts or component of your car, especially in the suspension starts to wear out, it can also cause the shake during braking. To find out if the problem is in the suspension, try to feel whether your car shakes when you turn your suspension. If it does, then the problem is probably in the suspension components. But if it is only felt when you hit the brake, then it is probably the braking pads or rotors.
Those are some problems that likely cause your car to shake when you hit the brake pedal. It is important to keep your car maintained and in its prime condition by routinely take it to the mechanic. When you see that there is a problem with the car, you should immediately get it repaired to make sure you can always drive safely.