For 1990-2009 cars

### Differential Lock System

The differential lock system is an air operated system with an electrical circuit used to control the differential lock indicator. The main components of the system are air pressure operated and not affected by the circuit. Problems with the electrical circuit will only affect differential lock indicator operation. Voltage is supplied from the IGN SW circuit breaker through the ignition 1 voltage circuit to the differential lock indicator. When the ignition switch is in the START position, current will travel through the bulb test signal circuit to the ignition switch grounding internally causing the differential lock indicator to illuminate. This lets the driver know that the indicator is functioning properly.

When the differential lock control valve is placed in the ON position this allows air pressure to build up in the system. The air pressure is used to lock the left and right side axle shafts so no inter-axle differential takes place and torque is transmitted equally to both wheels. When air pressure builds up to about 35 kPa (5 psi.) in the system, the differential lock switch closes providing ground for the differential lock switch signal circuit. This completes the indicator circuit illuminating the differential lock indicator.

When the differential lock control valve is placed in the OFF position, air pressure is released from the system disengaging the differential lock. The differential lock switch opens and the differential lock indicator turns off.

View the list of major components that make up the differential lock system below.

### Differential Lock Switch

The differential lock switch is mounted to the dash panel.

When the differential lock control valve lever is placed in the ON position, air pressure builds in the system closing the differential lock switch. This condition completes the indicator circuit illuminating the differential lock indicator lamp.

When the differential lock control valve lever is placed in the OFF position, air pressure is released and the differential lock switch opens. This opens the indicator circuit causing the differential lock indicator lamp to turn off.

### Differential Lock Control Valve

The Bendix® TW-1 differential lock control valve is mounted in the instrument panel.

When the differential lock control valve lever is moved to the ON position, air pressure in the system causes a mechanical clutch to engage and lock the differential. This condition allows equal torque to be transmitted to the rear axle without differential action.

When the differential lock control valve lever is moved to the OFF position, the differential lock disengages. This condition allows torque to be transmitted to the rear axle through differential action.

### Differential Lock Relay Valve

The Bendix® SV-1 differential lock relay valve is mounted to the right side frame side rail behind the rear axle housing. It controls air pressure delivery to the driver controlled differential lock shift cylinder.

### Differential Lock Pressure Protection Valve

The differential lock pressure protection valve is mounted to the brake pedal bracket. The valve is a normally closed pressure sensitive type control valve. It protects the vehicle's air system if a failure occurs in the differential lock air system.