What regulates pressure to the front and rear brakes?

The metering and proportioning valve plays a crucial role in regulating the pressure to the front and rear brakes, particularly in vehicles with disc brakes at the front and drum brakes at the rear. This valve ensures that the brake system applies the appropriate amount of pressure to each set of brakes under various driving conditions.

When braking is initiated, the metering valve initially delays pressure to the rear brakes until a certain level of pressure is reached at the front brakes. This action helps to prevent the rear brakes from locking up before the front ones can engage properly, enhancing stability during braking.

Once the front brakes have generated enough pressure, the proportioning valve takes over to adjust and balance the brake pressure between the front and rear systems, ensuring that both sets of brakes contribute effectively to the vehicle's stopping power without causing skidding or loss of control.

Other components, while they play significant roles in the braking system, do not directly regulate brake pressure in the same way. Brake fluid is essential for transmitting force within the brake lines, piston pumps generate hydraulic pressure, and brake shoes are part of the braking mechanism but do not control pressure distribution. Therefore, the metering and proportioning valve is the correct answer for this question.