A dream featuring the brakes of a vehicle symbolizes your ability to be in control in some aspect of your life.
If the breaks don't work properly then this suggests that you lack control or stability in some part of your waking life, you feel powerless or helpless in some situation, or you're afraid of failing at something. The dream can also imply that you are moving too quickly and may mess up and so you need to take it easy or slow down in some part of your business or personal life.
If you use the brakes to successfully stop a vehicle in a dream then it suggests that you need to remove yourself from a potential disastrous situation or stop what you are doing in some part of your waking life.