| Description and Operation As of '97 MY the Galaxy is also available with four‐wheel drive. This is a permanently engaged four‐wheel drive with slip‐sensing torque power distribution. The 4x4 variant will only be available with the 2,8i CD V6 engine and the AG4 automatic transmission. During normal conditions the front axle receives 100% of the available torque. When starting off on loose or slippery surfaces (with wheel spin), the torque is distributed between the front and rear axles according to grip by a viscous coupling and a locking freewheeling clutch. When reversing, the freewheeling clutch is electro‐pneumatically locked, so that the four‐wheel drive is available under the same conditions as when driving forwards. On overrun, the rear wheel drive is disconnected from the powertrain by the freewheeling clutch; in this way premature locking of the rear wheels during braking is avoided. Because the drive is separated between front and rear, the Ford Galaxy 4x4 can be equipped with a conventional ABS system. Rear differential assembly with viscous coupling and freewheeling clutch | 1 | Rear axle driveshaft | | 2 | Rear differential | | 3 | Viscous coupling | | 4 | Driveshaft | The torque is transferred from the viscous coupling through the input shaft of the rear differential assembly. From there it passes to the freewheeling clutch which is attached to the differential housing and then through the differential to the rear wheels. | 1 | Inner plates | | 2 | Outer plates | | 3 | Housing (driving) | | 4 | Hub (driven) | The viscous coupling is a wear and maintenance free hydraulic shear coupling, which cannot be repaired. The basic components of the viscous coupling are inner and outer plates which run in a silicone based fluid. This silicone based fluid has the property that it is thin when cold and thickens when it is warmed. When the coupling plates turn at different speeds the viscous coupling warms up and the amount of torque transferred increases. Rear differential assembly with viscous coupling and the freewheeling clutch components | 1 | Viscous coupling | | 2 | Freewheeling clutch | | 3 | Shift dog | | 4 | Sliding sleeve | | 5 | Differential | | 6 | Actuator ‐ freewheeling clutch lock | | 7 | Diaphragm rod | The freewheeling clutch is locked by the freewheeling clutch lock actuator. The freewheeling clutch lock actuator consists basically of a solenoid valve and a diaphragm rod. A vacuum in the rear chamber of the diaphragm canister causes the diaphragm to pull the diaphragm rod and the quadrant lever, moving the sliding sleeve and disengaging the shift dog from the driver pins on the freewheeling clutch, thereby making it able to operate. When reverse gear is selected the solenoid is operated by the reversing light switch and vacuum is applied to the front chamber of the diaphragm canister. The membrane pushes the diaphragm rod and quadrant lever and presses the shift dog onto the driver pins, thus locking the freewheeling clutch. The system also includes a vacuum reservoir and a non‐return valve. Check the operation of the viscous coupling | |  | WARNING: Keep the space in front of the vehicle clear. | 1. Drive the vehicle onto a power testing bed. • Engage "D" and drive on slowly. |  | NOTE: When the front wheels are driven and the rear wheels are stationary the viscous coupling will lock, thereby transmitting power to the rear wheels as well. | | | NOTE: The viscous coupling can only take up the revolution speed difference briefly without locking when the engine speed is slightly above idle speed and the selector lever is in position "1". | • If the vehicle moves out of the test bed when the engine is running at between 1500 rev/min ‐ 2500 rev/min, then the viscous coupling is working properly. | Check the operation of the freewheel. | 2. Release the handbrake, move the selector lever to the "N" position and raise the vehicle. • Turn the rear wheels in the forward direction: It must be possible to turn the wheels without any resistance. The driveshafts must not turn with the wheels. • Turn the wheels in the reverse direction: The front wheels must also turn in the reverse direction, driven by the driveshaft. | Check the operation of the freewheeling clutch lock. | 3. Raise the vehicle and let the engine run for about 30 seconds so that vacuum is created for the freewheeling clutch lock actuator. • Engage reverse gear and switch off the ignition. | | NOTE: The freewheeling clutch lock actuator must be heard to engage when the ignition is switched on. | • Switch on the ignition again and turn the rear wheels forwards and backwards. | | NOTE: When the wheels are turned forwards the freewheeling clutch lock must be heard to engage immediately. | • In both cases the front wheels must turn in the same direction as the rear wheels, being driven by the driveshaft. • If the rear wheels can be turned in the forward direction without any resistance then there may be a fault in the pneumatic system or in the electrical system. | Check the vacuum system for leaks. | | 4. Check the diaphragm in the freewheeling clutch lock actuator, the check valve and the vacuum reservoir (in the engine compartment) for leaks. 1. Actuator ‐ freewheeling clutch lock 2. Disconnect the vacuum hose. • Connect the manual pump to the freewheeling clutch lock actuator and check the membrane in the freewheeling clutch lock actuator for leaks. • Connect the manual pump to the vacuum reservoir in the engine compartment and test for leaks, then test the check valve. | | 
