Forester F4-2.5L SOHC (2004)
Brake Proportioning/Combination Valve: Description and Operation
Proportioning Valve (Models with Rear Drum Brake)
The proportioning valve prevents the rear wheels from locking and resultant skidding that would occur during hard braking due to transfer of vehicle
weight toward the front wheels. The valve distributes a reduced pressure to the rear wheel brakes as compared with the pressure to the front wheel
brakes when a specified master cylinder fluid pressure (called "split point") is exceeded as shown in the diagrams below.
OPERATION
1) Operation before the split point
The piston is held pressed toward the left by the spring so that the piston is kept away from its lip seal.
Under this condition, fluid pressure "P3" to the rear wheel cylinders is equal to fluid pressure "P2" from the master cylinder.
