Brake Metering Valve
The metering valve is a used by front disc rear drum type brake systems to delay the front calipers enough to overcome the rear brake springs and linkage. This valve is usually used along with the proportioning valve to help achieve balanced braking. These valves are often integrated together along with the brake warning switch inside of the combination valve.
It is located in-line of the front brakes and holds back pressure to the fronts until enough pressure builds in the system. As the rear brakes apply pressure builds to a point (75-125 psi) that forces the valve open allowing pressurized brake fluid to flow to the calipers and then applying the front brakes.
The metering valve has an inlet port from the master cylinder and a port for each of the front calipers. A spring maintains pressure on a sealed port blocking fluid pressure to the front brakes. As pressure builds in the system the spring pressure is overcome and the valve stem moves until it reaches a hold-off point. At this hold off point the brake fluid is allowed to flow freely.
This valve is usually combined with a proportioning valve. A proportioning valve is a height sensing valve located in-line to the rear brake system. This valve is used to prevent rear wheel lock-up during sudden and hard braking situations.
It is commonly found on trucks and reduces pressure to the rear brakes as the rear end lifts during hard braking. It is located between the rear axle and the vehicles frame. As the distance increases between the axle and the frame the proportioning valve reduces pressure preventing the rear tires from locking up resulting in a loss of traction.
