Brake Proportioning/Combination Valve: Description and Operation

Fig 35 Type 3 Proportioning Valve Identification:

Master Cylinder For ABS Equipped Vehicles:

Fig 4 Type 3 Master Cylinder. Less ABS:

GENERAL INFORMATION
This vehicle uses screw-in proportioning valves at the Master Cylinder or Hydraulic Control Unit (HCU) instead of the combination valve used in prior designs. With this new design, the chassis brake tubes connect directly from the master cylinder or HCU to the brake flex hose. The non-ABS master cylinders are a four outlet design with two screw-in proportioning valves attached directly to the inboard side of the master cylinder housing. The ABS Master Cylinders are a two outlet design with the screw-in proportioning valves attached directly to the HCU.

PURPOSE
Proportioning valves balance front to rear braking by controlling at a given ratio, the increase in rear brake system hydraulic pressure above a preset level (split point). Under light pedal application, the proportioning valve allows full hydraulic pressure to be applied to the rear brakes.

IDENTIFICATION
There are two proportioning valve assemblies used in each vehicle. Due to differences in thread sizes, each proportioning valve has a different part number. During any service procedures identify valve assemblies by supplier part number and or the color identification band.