Rear Differential
REAR DIFFERENTIAL - 4.2L AND 4.4LComponent Location - 4.2L and 4.4L (Part 1):
Component Location - 4.2L and 4.4L (Part 2):
The rear differential converts the "angle of drive" through 90° and distributes drive, via the rear drive halfshafts, to the rear wheels.
The rear differential for the 4.2L and 4.4L V8 gasoline variants utilize the same output ratio and is located centrally in the rear of the chassis.
The unit is mounted to the chassis via rubber bushes and bolts; two mounting points at the rear of the unit and one at the front.
Rear Differential Exploded View - 4.2L and 4.4L (Part 1):
Rear Differential Exploded View - 4.2L and 4.4L (Part 2):
Rear Differential Exploded View - 4.2L and 4.4L (Part 3):
The cast iron casing comprises two parts; a cover and a carrier. The carrier provides locations for all the internal components. The carrier is sealed to the cover via an O-ring seal and secured with twelve bolts. The cover and carrier have cast fins, which assist mobility. A breather tube is fitted to the top of the carrier. This allows a plastic tube to be fitted and routed to a high point under the vehicle body, preventing the ingress of water when the vehicle is wading.
The carrier contains an oil drain plug. The differential unit contains approximately 1.16 liters of oil from a dry fill. If oil is being replaced, a smaller quantity of oil will be required due to residual oil retained in the pinion housing.
The differential is a conventional design using a hypoid gear layout, similar to the front differential and has a final drive ratio of 3.73:1.
The differential comprises a pinion shaft and hypoid pinion gear and a crown wheel drive gear with an integral cage, which houses two planet gears. Two sunwheels are also located in the cage and pass the rotational drive to the drive shafts.
The pinion shaft is mounted on two opposed taper roller bearings, with a collapsible spacer located between them. The spacer is used to hold the bearings in alignment and also collapses under the pressure applied to the pinion-flanged nut. This allows the flanged nut to be tightened by measuring the torque-to-turn, which collapses the spacer, setting the correct bearing preload.
The pinion shaft has an externally splined outer end, which accepts and locates the input flange, which is retained by the pinion nut and retainer. The input flange has four threaded holes and mates with the rear drive shaft. Four bolts secure the rear drive shaft to the input flange. An oil seal is pressed into the pinion housing and seals the input flange to the pinion housing. The pinion shaft has a hypoid gear at its inner end, which mates with the crown wheel drive gear.
The crown wheel drive gear is located on the differential case and secured with ten bolts. The differential case is mounted on taper roller bearings located in machined bores on each side of the pinion housing. Shims are retained in the casing behind the bearing cups, the shim thickness is selected to apply the correct bearing preload and hypoid backlash.
The differential carrier has a through hole, which provides location for the shaft. The shaft is supported by a sun gear and a needle roller bearing. The shaft is fitted with a snap ring at one end, which locates in a machined groove in the sun gear, locking the shaft in position.
The sun gears are located in pockets in the carrier cage and mesh with the planet gears. Spacers are fitted between the sunwheels and the carrier and set the correct mesh contact between the planet gears and the sunwheels. Each sunwheel has a machined bore with internal splines and machined groove near the splined end. The groove provides positive location for a snap ring fitted to the end of each output flange.
Each output shaft has a spline, which locates in each sunwheel. A snap ring fitted to the splined shaft locates in the groove of the sunwheel bore and positively locates the output shaft. Oil seals are pressed into each side of the pinion housing and seals the output shaft.
Rear Differential Operation - 4.2L and 4.4L
The operating principles of the front and rear differentials are the same. Rotational input from the drive shaft is passed via the input flange to the pinion shaft and pinion gear. The angles of the pinion gear to the crown wheel drive gear moves the rotational direction through 90°.
The transferred rotational motion is now passed to the crown wheel drive gear, which in turn rotates the differential casing. The shaft, which is secured to the casing, also rotates at the same speed as the casing. The planet gears, which are mounted on the shaft, also rotate with the casing. In turn, the planet gears transfer their rotational motion to the left and right hand sunwheels, rotating the drive halfshafts.
When the vehicle is moving in a forward direction, the torque applied through the differential to each sunwheel is equal. In this condition both drive halfshafts rotate at the same speed. The planet gears do not rotate and effectively lock the sunwheels to the differential casing.
If the vehicle is turning, the outer wheel will be forced to rotate faster than the inner wheel by having a greater distance to travel. The differential senses the torque difference between the sunwheels. The planet gears rotate on their axes to allow the outer wheel to rotate faster than the inner one.