Iveco cars equipped with vacuum booster, which allows the car even at low speeds, light brake pedal, it will have a higher braking effect, which will lead to the front brake system is too sensitive, easy to lock Slip, reduce driving stability. To avoid these drawbacks, a hysteresis valve was installed in the front brake circuit of the car. Only when the pressure reaches 0.14MPa, this valve allows the brake fluid to pass, this pressure just can make the brake shoe begin to open. The brake master cylinder pressure reaches 1.26MPa before the pressure remains unchanged, the pressure exceeds this value, the hysteresis valve opens, the brake fluid normally sparse to the front brake circuit, if the brake pedal has stepped on at this time, It can reach the maximum allowable braking system pressure, to achieve the role of braking.