Combination Valve

Combination Valve Location:

Combination Valve And Brake Warning Switch:

The brake hydraulic system in this vehicle is equipped with a combination valve. The combination valve is used for controlling and monitoring the hydraulic portion of the brake system. The combination valve serves 3 functions in the brake's hydraulic system. It directs (diverts) the brake fluid from the master cylinder to the front and rear brakes. It controls the hydraulic pressure to the rear brakes through the proportioning function of the valve and monitors for a pressure loss in the system through the pressure differential valve and warning switch. This is accomplished by combining a pressure differential valve, a warning light switch with a single proportioning valve. The combination valve is attached to the frame rail below the master cylinder.

The proportioning valve balances front to rear braking by controlling at a given ratio, the increase in rear brake system hydraulic pressure above a preset level.

The proportioning valve section operates by transmitting full input pressure to the rear brakes up to a certain point. This is called the split point. Beyond this point it reduces the amount of pressure increase to the rear brakes according to a certain ratio.

On light pedal applications equal brake pressure will be transmitted to the front and rear brakes. On heavier pedal applications the pressure transmitted to the rear will be lower than the front brakes. This will prevent premature rear wheel lock-up and skid. If hydraulic pressure is lost in one half of the front to rear split system, the operation of the remaining half of the brakes hydraulic system is not effected.

There is only one proportioning valve used on this vehicle. During any service procedures identify the combination valve used in the vehicle to the replacement combination valve by part number as well as split point (PSI) and slope.