Brake Proportioning/Combination Valve: Description and Operation

Fig 41 Type 4 Proportioning Valve. Less ABS:

This valve assembly on non-ABS models, is of a dual proportioning valve design.

The proportioning valve on non-ABS models transfers full braking force to the rear brakes until a preset ratio called the split point is achieved. At this point the pressure increase is routed away from the rear brake system to prevent rear wheel lock-up.

Fig 42 Type 4 Proportioning Valve. With ABS:

On models with ABS, two screw in proportioning valves are used. These proportioning valves are attached to the rear brake outlets of the hydraulic control unit (HCU).

The brake warning light will come on when the parking brake is applied with the ignition turned On. The same light will also come on when one of the two service brake systems fail.