A car that lunges forward when braking is not only scary but potentially very dangerous. It can signal that your brakes are wearing out or that you have a problem with your transmission. The good news is that there are many possible reasons for this issue, some of which can be easily fixed while others require the attention of a professional mechanic.
The most common reason for this type of jerking is that the front brake pads are worn out and not gripping the rotors. This is especially common in older cars. Typically you will hear a squeal or a grinding sound when this is the case. Often the steering wheel will also shake or vibrate in response to this issue.
Another reason for this is that the rear brakes are worn out or not absorbing enough pressure. The rear brakes absorb most of the weight of the vehicle while braking, so it is important that they are in good condition. This is the most likely reason if the steering wheel also shakes or vibrates during braking.
Some transmissions, particularly the ZF 8 speeds, gear down when you apply the brakes and then engage a lower gear to slow the engine down as well. This lurch you feel is the additional engine speed that needs to be slowed down by the brakes as that gear engages. You may also hear a clunking noise that sounds like fingernails on a chalkboard when this is the case.