Caravan FWD L4-2.4L VIN X (1997)
Brake Proportioning/Combination Valve: Description and Operation
Fixed Proportioning Valve Location
GENERAL INFORMATION
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 drivers side of the vehicle. The HCU acts as the hydraulic system junction block,
diagonally splitting the brakes hydraulic system. 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. 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.
OPERATION
The fixed proportioning valve operates by allowing full hydraulic pressure to the rear brakes up to a set point, called the valves 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.
Proportioning Valve Mounting Location
MOUNTING
One assembly containing two proportioning valves are used in the system, one for each rear brake hydraulic circuit. The proportioning valve is
located on the frame rail next to the fuel tank, forward of the right rear shock absorber. Be sure replacement proportioning valve assemblies have
the same split point and slope as the proportioning valve being replaced.
