Final Drive - Description
DescriptionGeneral
The front and rear differentials convert the "angle of drive" through 90° and distribute drive, via the drive shafts, to the front and rear wheels.
The front and rear differentials have different output ratios for the V8 and Td6 variants and, although visually similar, can the identified try part numbed
The front differential is mounted on the LH side of the engine sump. The rear differential is mounted on the rear subframe.
Front Differential
Part 1:
Part 2:
Front Differential - Exploded View
The differential is mounted on the LH side of the vehicle sump. The sump has a cast tube through it, which allows for the fitment of the RH drive shaft and separates the engine oil from the differential oil. The differential unit is secured to the engine sump with 4 bolts. The bolts pass through lugs in the differential casing and are secured into threaded holes in the sump. An O-ring seal is fitted to the easing and locates in the sump to provide a seal between the casing and the sump.
The casing comprises two halves with machined mating faces. When assembled, the iron casing halves are sealed with a thin film of Loctite 574 sealant and secured together with twelve bolts. The LH casing is the carrier for all the rotating parts and the RH casing is a cover to close the unit and a support for the RH carrier bearing. A breather tube is fitted to the casings. This allows a plastic tube to be fitted and routed to a high point in the engine compartment, preventing the ingress of water when the vehicle is wading.
The LH casing is fitted with a drain plug and a filler/level plug. The level plug allows the unit to be filled with oil until it leaks from the filler hole, ensuring the correct quantity of oil is added. The differential unit contains approximately 0.8 litre of oil for a dry fill and requires approximately 0.75 litre if oil is changed due to residual oil retained in the casings.
The differential is a conventional design using a hypoid gear layout. This employs a hypoid bevel pinion gear and crown wheel, with the pinion offset below the center line of the crown wheel. This design allows for a larger pinion gear to be used which has the advantages of increased gear strength and reduced operating noise.
The front differential is available in two ratios. V8 engine vehicles use a differential with a final drive ratio of 3.73:1 and Td6 engine vehicles use a final drive ratio of 4.10:1. The ratio is changed by changing the amount of teeth between the crown wheel drive gear and pinion gear. Therefore for a ratio of 4.10:1, the crown wheel drive gear will have 4.10 times more teeth than the pinion gear. This equates to the crown wheel drive gear having 41 teeth and the pinion gear having 10 teeth.
Front Differential - Sectional View
The differential comprises a pinion shaft and hypoid bevel gear, 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 shaft 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 nut. This allows the 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. The opposite end of the output flange has an internal spline which provides positive location for the front propeller shaft. The flange has an external O-ring seal which seals against the front propeller shaft shroud preventing the ingress of dirt and moisture into the splines. An oil seal is pressed into the LH casing and seals the input flange to the differential unit. The pinion shaft has a hypoid level gear at its inner end which mates with the crown wheel drive gear.
The crown wheel drive gear is located on the carrier and secured with ten screws. The carrier is mounted on taper roller bearings located in each casing half. The bearings are press fitted into the casing and a spacer is located on the outside face to apply preload to the bearing.
The carrier is fitted with a shaft onto which the two planes gears are mounted. The shaft is secured in the carrier with a roll pin. The sun wheels are located in pockets within the carrier and mesh with the planet gears. Curved plates are located between the carrier and the sun wheels and hold the sun wheels in mesh with the planet gears. Each sun wheel has a machined, splined. bore to accept the drive shaft. A groove is machined in the bore to locate the snap ring fitted to the drive shaft, providing positive drive shaft location.
Rear Differential
The rear differential is located centrally in the rear subframe. The front of the differential is attached to the subframe via rubber bushes and bolts. The rear of the differential is mounted to the subframe via a single, offset rubber bush and a bolt.
The casing comprises two parts. The pinion housing is made from cast iron and provides locations for all the internal components. The pinion housing is sealed at the rear by an aluminum casting which is secured to the pinion housing with eight bolts and spring washers. A gasket between the two casings seals the unit. The rear cover has cast fins which assist heat dissipation. A breather tube is fitted to the rear cover. 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 rear cover contains en oil level plug which allows for oil filling and level checking, with the differential installed in the vehicle. The level plug allows the unit to be filled with oil until it leaks from the filler hole, ensuring the correct quantity of oil is added. The differential unit contains approximately 1.2 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 The rear differential is available in two ratios. V8 engine vehicles use a differential with a final drive ratio of 3.73:1 and Td6 engine vehicles use a final drive ratio of 4.10:1. The ratio is changed by changing the amount of teeth between the crown wheel drive year end pinion gear. Therefore for a ratio of 4.10:1, the crown wheel drive gear will have 4.10 times more teeth than the pinion gear. This equates to the crown wheel drive gear having 41 teeth and the pinion gear having 10 teeth.
Rear Differential - Sectional View
The differential comprises a pinion shaft and spiral bevel 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 hearings, 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 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. The output flange has six threaded holes and mates with the rear propeller shaft. Six bolts secure the rear propeller 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 spiral bevel gear at its inner end which mates with the crown wheel drive gear.
The crown wheel drive gear is located on the carrier and secured with ten screws. The carrier is mounted on taper roller bearings located in machined bores on each side of the pinion housing. The bearings are retained in the casing by a circlip, the thickness of which is selected to apply the correct bearing preload.
The carrier has a through hole which provides location for the shaft. The shaft provides the mounting for the planet gears in the carrier cage. The shaft is fitted with a snap ring at one end which locates in a machined groove in the carrier, locking the shaft in position.
The sun wheels 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 flange has a splined shaft which located 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 flange. Oil seals are pressed into each side of the pinion housing and seal the output flange to the housing. Each output flange has six threaded holes which provide for the attachment of the rear drive shafts.
The rear cover is located on the rear of the pinion housing and is sealed to the housing with a gasket and secured with eight bolts.