Of all the various mechanical mishaps that can strike a vehicle, problems with the brakes are among the most dangerous, and even the slightest change in the way your brakes 'feel' as they are applied can signify mechanical trouble. A powerful vibration shooting up your leg every time you apply the brakes can be a particularly disturbing phenomenon, and a number of issues with your vehicle's braking system can cause the brake pedal to vibrate alarmingly when it is used.
If your brake pedal starts vibrating noticeably when in use, the safest and fastest solution is to take your vehicle to a professional brake repair service; these services possess all the tools and accumulated knowledge required to swiftly determine what is causing your brake pedal to vibrate, and repair the problem to professional standards. However, you can diagnose some of the simpler causes of brake pedal vibration yourself by inspecting the following key components in your braking system:
The brake pads make up the business end of your vehicle's braking system, applying the friction to your vehicle's brake rotors that slow the turning of your wheels and bring it to a safe stop. As you can imagine, this creates an enormous amount of wear and tear, and aging brake pads that are starting to show the strain will often cause your brake pedal to vibrate when used.
This vibration is caused by the pad wearing unevenly, sending vibrations through the entire disc brake which can be felt through the pedal. If your brake pad has become 'glazed' from excessive use and heat, the vibration can be particularly pronounced, and you may find braking function is dangerously diminished. Consequently, inspecting your brake pads should be your first port of call if yo feel brake pedal vibration, and the pads should be replaced if any signs of wear or visible damage are present.
If you check your brake pads for damage and find none that could be causing the vibration, the problem may lie in the rotors that your brake pads are applied to. These rotors should ideally be perfectly vertically aligned, and very slight imperfections in the alignment of your brake rotors can cause noticeable and disconcerting pedal vibration. If your rotors have become rusty, or a piece of stone or solid matter has dented one of the rotor surfaces, these problems can also cause pedal vibration.
You should therefore check your brake rotors for damage immediately after checking your brake pads. Superficial surface rust and other minor problems with your rotor can be dealt with yourself, but a misaligned rotor is a more complicated problem that generally required specialised alignment equipment to fix properly.
If you can rule out issues with your brake pads and rotors, your brake system may not be the source of the vibration problem at all. Old, worn-out wheel bearings can cause your wheels and brakes to vibrate during driving, and may cause your brake pedal to vibrate even before you apply it. If a worn wheel bearing is the source of the problem, this vibration will frequently become worse when you apply the brakes and place added strain on the failing bearing.
Wheel bearings are fairly easy to remove and replace with modest mechanical skill, so you should take the time to inspect your existing bearings for any rust or damage which may be causing the problem. Be sure to check the bearings of all your wheels, as they will often wear out at different speeds when fitted to different wheels (especially in vehicles that lack all-wheel braking).