Addtional Information, AWD Version

System Overview

General
- The 850 AWD (All-wheel drive) with manual transmission M58, has permanent four wheel drive with variable distribution of power to the wheels.
- Initially the car will be available:
- as a station wagon
- with engine B5254T
- with manual transmission M58
- in Europe, Canada and certain Overseas markets.
- Distribution of driving power to the wheels depends on the condition of the road surface and driving conditions and changes to provide the best possible grip and traction.





Modified Transmission (M58)
- To provide the car with four-wheel drive, transmission M56 has been modified (and given the designation M58) so that power can be taken off to a bevel gear.





Bevel Gear
- The power is transferred between the transmission's differential housing and bevel gear's tubular shaft via a splined joint. The bevel gear's crown wheel is pressed and bonded to a tubular shaft. The bevel gear's crown wheel and pinion have a ratio of 1:3.31. As the final drive has a ratio of 3.31:1 the ratio between the front and rear wheels is the same.
- The bevel gear transmits power to the final drive via a propeller shaft. The propeller shaft is of the conventional type and has a support bearing mounted in a cross member. The propeller shaft has CV joints front and rear and a traditional joint in the middle by the support bearing. The propeller shaft runs along the tunnel in the floor of the car.





Rear Drive Unit
- A short torque tube is mounted on the final drive. The torque tube contains a viscous coupling and a freewheel unit. Together with the final drive and drive shafts these make up the rear drive unit.

1. Propeller shaft
2. Torque tube
3. Viscous coupling and freewheel unit
4. Final drive
5. Drive shaft





Viscous Coupling
- The viscous coupling transmits driving power to the rear wheels when necessary. In normal driving conditions on dry asphalt only a small proportion of driving power is transmitted to the rear wheels via the viscous coupling. However, the slightest difference in speed between the front and rear wheels causes power to be transmitted to the rear wheels to ensure good grip.
- The viscous coupling consists of plates alternately connected to the input and output shafts. These plates are encased in a housing filled with silicone oil. The oil, because of its viscosity and the difference in speed between the plates, transmits power to the rear wheels. The viscous coupling is protected from overheating due to prolonged and intensive slipping by automatically locking-up.





Freewheel Unit
A freewheel unit is connected to the viscous coupling. It is located after the viscous coupling an has two functions:
- Disconnecting rear-wheel drive during braking.
- Enabling four-wheel drive when reversing.
- The freewheel unit has an input and an output shaft.
- These shafts can be connected via a freewheel and via a centrifugal roller lock-up mechanism.
- The freewheel unit, which has a centrifugal roller lock-up mechanism, also makes it possible to reverse with four- wheel drive at up to 50 km/h (31.2 mph).

Freewheel
- When driving forward power can be transmitted from the input shaft to the output shaft (rear wheels) via the freewheel.
- During braking the rear wheels may rotate faster than the front wheels. In this case the freewheel is driven in the "wrong" direction by the output shaft. No power can be transmitted this way because the freewheel is free. The rear wheels can never drive the front wheels and negatively affect braking stability.
- When reversing the freewheel is driven by the input shaft in the "wrong" direction. The freewheel is free and cannot transmit power. In certain cases power can instead be transmitted via the centrifugal lock-up mechanism.

Centrifugal Lock-up Mechanism

The Centrifugal Lock-up Mechanism Consists Of:
- Centrifugal weights in the form of ball bearings
- A spring-loaded cage with a ball race. The ball race has ramps and six small ball bearings
- Internal cut-outs in the input shaft.
- At low speeds the small ball bearings are forced out of the ramps and engage with the cut-outs in the input shaft. Power is then transmitted from the input shaft via the ball bearings.
- When speed increases the centrifugal weights are thrown outward. At approx. 50 km/h (31.2 mph) the centrifugal weights press back the spring-loaded cage and ball race. The ball bearings are freed from the input shaft and power can no longer be transmitted via the roller lock-up.





Anti-spin Control For Front And Rear Wheels
- To provide the best possible grip and maximum traction when moving off and driving at low speed the car is equipped with an anti-spin control system for the front and rear wheels.
- The front wheels have the Volvo TRACS system. This electronic anti-spin system is integrated with the car's ABS brake system. For further information see Page 29 in Service Manual Section 5 Brakes (including. ABS and TRACS) 850 1992- TP 5001031.
- The rear wheels, driven from the final drive, have an automatic mechanical differential lock system. If a rear wheel slips when moving off the differential lock locks- up and automatically transfers power to the wheel with the best grip. The differential lock is disengaged at 40 km/h (25 mph).





Final Drive
- The 850 AWD has a final drive type 1165. This final drive is in principle the same as the 1055 in the 960 model year 1995-The 1165 has some external differences - in its castings and details on its housing and rear cover.
- The 1165 final drive has automatic differential lock.





Rear Drive Shaft
- Drive shafts do not have flanges and screwed joints. They are a single unit attached to the differential gears by snap rings.
- CV joints cannot be replaced separately, drive shafts must be replaced as a unit.





Multi-link Rear Suspension
- This version of the 850 has multi-link rear suspension. This consists of a rear axle member made up of an upper and lower section. These are joined to each other with screwed joints. The upper and lower sections of the
- rear axle member are in cast aluminum. The final drive is mounted between the members. The member is mounted on the side-members of the car body.