LR3/Disco 3
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 sun wheels 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 collapsable 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 to a predetermined torque, 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 screws. 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
sun wheels and the carrier and set the correct mesh contact between the planet gears and the sun wheels. Each sun
wheel 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 sun wheel. A snap ring fitted to the splined shaft locates in the
groove the sun wheel bore and positively located the output shaft. Oil seals are pressed into each side of the pinion
housing and seal the seal the output shaft.
Differential Operation
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 sun wheels, rotating the drive halfshafts.
When the vehicle is moving in a forward direction, the torque applied through the differential to each sun wheel is equal.
In this condition both drive halfshafts rotate at the same speed. The planet gears do not rotate and effectively lock the sun
wheels 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 sun wheels. The planet gears rotate on their axes to
allow the outer wheel to rotate faster than the inner one.
SERVICE
The oil used in the open rear differential is Castrol SAF-XO. The oil contains unique additives, which enhance the
differentials operation. No other oil must be used in the open rear differential.
Open Rear Differential Serviceable Components
l
Needle roller bearing assemblies
l
Halfshaft seals
l
Chassis bush/fixings
l
Lubricant.
