Most people like predictability in their lives so they know what to expect in any given situation. This allows them to cope with everyday pressures and retain a sense of calm in an otherwise stressful world. So, when they encounter something unusual in a typically predictable situation, the alarm bells can start to ring. You may be in that situation today, as you've noticed some very strange behaviour from your car. Instead of decelerating smoothly and efficiently when you press the pedal, you get a jolting sensation instead. What could this be and what should you do?
Is It Your ABS?
Firstly, you need to satisfy yourself that this is not normal. You may wonder how something like that could possibly be normal in any circumstances, but if you were driving in wet or slippery conditions when this happened it might be the anti-lock braking system in operation. If you're not familiar with ABS, it is a fail-safe added to the vehicle by manufacturers to protect you in difficult driving conditions.
ABS will account for any additional pressure that you might put on the brake pedal and will vary the energy that's actually transferred to the road wheels. By doing so, it helps to avoid a lock-up, where too much pressure causes the wheel to slide across the slippery surface, rather than seeking traction. It does so by opening and closing a valve in rapid succession instead of applying constant pressure and this can translate into the jolting or pulsing sensation you feel through your foot.
Could the Discs Be Warped?
However, if you are noticing this strange behaviour in a variety of different (and not potentially dangerous) situations, then your car may be suffering from warped brake discs. When you attempt to decelerate, friction pads adhere to the discs, which in turn slow down the road wheels.
Typically, these discs are small and uniform but, in some situations, can warp. This could happen if you were to drive through a lot of standing water when the discs were very hot, for example. In this scenario the discs might cool very quickly, and this could warp the surface.
Is It Safe?
Usually, this won't markedly affect your ability to stop the vehicle, although the pulsing sensation is not very pleasant.
You will need to take the vehicle to an auto mechanic for them to assess everything, as the discs may need to be machined or replaced.