Volvo 850 AWD General Description Manual

850 AWD

General

Modified transmission (M58)

Bevel gear

The 850 AWD with manual transmission M58,
has permanent four-wheel drive with variable
power distribution to the wheels.
Distribution of driving power to the wheels
depends on the condition of the road surface
and driving conditions. Distribution changes to
provide the best possible grip and traction.
The system includes the TRACS system for
the front wheels and a differential lock for the
rear wheels.
Note! Cars with AWD are not designed or built
for off-road driving!

The 850 AWD will initially be available:

as a station wagon
with engine B5254T
with manual transmission M58
in Europe, Canada and certain Overseas

markets.
For further information about the 850 AWD,
see VCC

-049156 (IE not found) , Service

Manual All-wheel drive (AWD), 850 1997-.

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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.

The power is transferred between the
transmission's differential housing and bevel
gear's tubular shaft via a splined joint. The
bevel gear 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 1:3.31 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

1

Rear drive unit

Viscous coupling

Freewheel unit

Final drive

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.

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

The viscous coupling allows power to be
transferred via the internal friction of a fluid
(oil).
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 protects itself from
overheating due to prolonged and intensive
slipping by automatically locking-up.

A freewheel unit is connected to the viscous
coupling. It automatically provides complete
braking stability. This is achieved by the
freewheel unit disconnecting the rear wheels
during braking so that the rear wheels cannot
transfer power to the front wheels. This means
that the car's stability is not reduced.
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.

The 850 AWD has a final drive type 1165. This
final drive is in principle the same as the 1055
used in the 1995 model year 960. 1165 differs
only in the castings and machining on the

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