Part 1

Four-Wheel Drive Systems - 4.2L/4.4L (Part 1)

Transfer Box Component Location (Part 1):

Transfer Box Component Location (Part 2):

Transfer Box Exploded View (Part 1):

Transfer Box Exploded View (Part 2):

Transfer Box Exploded View (Part 3):

Transfer Box Exploded View (Part 4):

GENERAL
The DD295 transfer box is full time, permanent four-wheel-drive unit, with 50/50 torque distribution to the front and rear driveshafts. Magna Steyr Powertrain manufactures the unit, which is identical for all engine derivatives and supports these features:
^ Permanent four-wheel-drive with a bevel gear center differential, providing a 50:50 torque split
^ Selectable high and low range for optimum on-road and off-road performance
^ Two-speed, fully synchronized 'shift-on-the-move' system allows the driver to change the range without having to stop the vehicle
^ Electronically controlled multi-plate clutch providing a center differential lock and torque biasing function to give improved traction performance and vehicle dynamic stability.

A strategy, to electronically control the center differential multi plate clutch assembly, has been developed to provide:
^ a pre-loading function, increasing locking torque with increased driving torque
^ a slip controller to increase locking torque under off-road conditions and decrease locking torque for optimum comfort, e.g. parking.

The unit is located under the vehicle and is mounted on the cross-member, behind the transmission.

The transfer box receives a torque input from the transmission output shaft, which is passed through the unit to two outputs for the front and rear drive shafts.

The input torque is equally distributed via a bevel gear type differential. In order to provide an optimal torque distribution to each wheel in all driving conditions, the unit is equipped with an electronically controlled locking and torque-biasing device. This device detects wheel slip via various vehicle system inputs to the transfer box control module and locks the differential accordingly. The locking torque is applied through a multi-plate clutch assembly.

A planetary gear set, located in the differential assembly, allows the driver to select high or low range whilst driving, this is known as 'shift on the move'. When in low range, the planetary gear set provides a ratio of 2.93:1, which gives the vehicle an extremely low crawl speed for off road driving and trailer towing. High range is a direct drive from the transmission output shaft and provides a 1:1 ratio.

Both the center differential locking and biasing and the 'shift on the move' features are actuated via a DC transfer box motor, which is controlled by the transfer box control module, via a Pulse Width Modulation (PWM) signal.

Transfer Box - Sectional View (Part 1):

Transfer Box - Sectional View (Part 2):

Transfer Box Power Flow

Transfer Box Power Flow:

Input torque from the transmission is transferred to the input shaft of the transfer box and then onto the planetary sun gear and planetary pinion gears. The planetary pinion gears are held in place by the planet pinion shafts, which are connected to the differential carrier, and drive the differential pinion gears. The torque is then distributed to both the front and rear carriers, which are connected to the outputs of the transfer box. The rear carrier is connected directly to the rear output flange; the front carrier is connected to the sprocket and therefore to the chain drive, which provides front output flange rotation.

TRANSFER BOX CASINGS
The front and rear casing assemblies are manufactured from cast aluminum.

Front Casing Assembly
The front casing assembly provides the location for the input shaft bearing, the front output flange bearing and the oil pump. It is also equipped with threaded holes to mount the chassis mounting bush, two lifting eyes and a breather cartridge for the transfer box breather pipe. The breather pipe allows an equalization between atmospheric and internal transfer box pressure.

Rear Casing Assembly
The rear casing assembly provides the location for the rear output flange bearing, the transfer box motor and the oil fill and drain plug. Fins are cast into the rear casing assembly to improve heat dissipation. The unit number is also stamped into the rear housing.

OIL PUMP
An oil pump assembly is located in the front casing to provide lubrication for the bearings and rotary components through cross-drillings in the input shaft. A flat-sectioned coupling on the input shaft drives the rotor of the pump; the stator is fixed to the front housing assembly. A tube is attached to the pump, which leads into a calm suction area at the bottom of the two casing assemblies. The collector magnet in the suction area of the pump collects any metallic debris.

CHAIN DRIVE
The chain-drive transfers drive from the center differential to the front output flange. A 3/8" pitch chain connects the sprocket on the transfer box input shaft with the sprocket on the front output flange. As both sprockets have the same number of teeth, the rotational speed of both sprockets is identical.