5 - 26 BRAKES |
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HYDRAULIC SYSTEM CONTROL VALVES
INDEX
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ABS Brake Proportioning Valve Operation . . . . . . |
. 27 |
General Information . . . . . . . . . . . . . . . . . . . . . . |
. 26 |
Hydraulic System Service Procedures . . . . . . . . . |
. 27 |
GENERAL INFORMATION
Most models not equipped with an Anti-Lock braking system have a combination hydraulic system control valve in the brake hydraulic system (Fig. 1). The valve is attached to the frame rail below the master cylinder.
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Non-ABS Proportioning Unit Operation . . . . . . . . |
. 26 |
Pressure Differential Warning Light Switch . . . . . |
. 26 |
Testing ABS Proportioning Valves . . . . . . . . . . . . |
. 29 |
rear are part of another. Both systems are routed through, but hydraulically separated by a Pressure Differential Switch. The function of the Pressure Differential Switch is to alert the driver of a malfunction in the brake system.
If hydraulic pressure is lost in one system, the warning light switch will activate a red light on the instrument panel, when the brake pedal is depressed. At this point the brakes require service. However, since the brake systems are split diagonally the vehicle will retain 50% of its stopping capability in the event of a failure in either half.
The warning light switch is the latching type. It will automatically center itself after the repair is made and the brake pedal is depressed.
The instrument panel bulb can be checked each time the ignition switch is turned to the start position or the parking brake is set.
NON-ABS PROPORTIONING UNIT OPERATION
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.
Fig. 1 Brake Combination Valve And Warning
Switch Location
The control valve assembly combines a warning switch with a dual proportioning valve (Fig. 2).
Proportioning valves balance front to rear braking by controlling at a given ratio, the increase in rear system hydraulic pressure above a preset level. Under light pedal application, the valve allows full hydraulic pressure to the rear brakes.
There is only one valve assembly in each vehicle, see Valve Application Chart. During any service procedures identify valve assemblies by part number as well as split point (PSI) and slope.
PRESSURE DIFFERENTIAL WARNING LIGHT SWITCH
The hydraulic brake system, on non-ABS vehicles, is split diagonally. The left front and right rear brakes are part of one system. And the right front and left
Fig. 2 Switch and Valve Assembly
On light pedal applications equal brake pressure will be transmitted to the front and rear brakes. On