Grand Voyager V6-3.3L VIN G Flex Fuel (1999)
Brake Proportioning/Combination Valve: Description and Operation
Fixed Proportioning Valve
The hydraulic brake system on all vehicles is diagonally split. This means that the left front and right rear brakes are on one hydraulic circuit with the
right front and left rear brakes on the other hydraulic circuit.
On vehicles equipped with ABS brakes, the brake systems Hydraulic Control Unit (HCU) is mounted to the front suspension crossmember on the
driver's side of the vehicle. The (HCU) acts as the hydraulic system junction block, diagonally splitting the brakes hydraulic system.
Fixed Proportioning Valve Location
All vehicles equipped with ABS brakes use 2 fixed proportioning valves. The fixed proportioning valves are mounted in a common bracket on the left
frame rail at the rear of the vehicle.
FIXED PROPORTIONING VALVE OPERATION
The fixed proportioning valve is made out of aluminum and has an integral mounting bracket. The fixed proportioning valve is non-serviceable
component and must be replaced as an assembly if found to be functioning improperly.
The fixed proportioning valve is mounted to the bottom of the left rear frame rail, just forward of the rear shock absorber to frame rail mounting
location. The proportioning valve has 2 inlet ports for brake fluid coming from the ABS modulator, and 2 outlet ports for brake fluid going to the rear
wheel brakes.
The fixed proportioning valve operates by allowing full hydraulic pressure to the rear brakes up to a set point, called the valve's split point. Beyond
this split point the proportioning valve reduces the amount of hydraulic pressure to the rear brakes according to a certain ratio.
Thus, on light brake pedal applications the proportioning valve allows approximately equal brake hydraulic pressure to be supplied to both the front
and rear brakes. On heavier brake pedal applications though, the proportioning valve will control hydraulic pressure to the rear brakes, so that
hydraulic pressure at the rear brakes will be lower than that at the front brakes. This controlled hydraulic pressure to the rear brakes prevents excessive
rear wheel ABS cycling during moderate stops.
