Front Drive Axle And Differential
Front Drive Axle and Differential
OVERVIEW
The front differential converts the 'angle of drive' through 90 degrees and distributes drive, via the drive halfshafts, to the front wheels.
The front 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 halfshaft 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 casing 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 12 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 plug.
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 above 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 output ratio of the front differential varies depending on the engine variant. For additional information, refer to Specifications Front Drive Axle/Differential
The ratio is changed by changing the amount of teeth between the crown wheel drive gear and pinion gear. For example, with a ratio of 3.54:1, the crown wheel drive gear will have 3.54 times more teeth than the pinion gear.
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 halfshaft 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 collapses at a predetermined rate due the torque applied to the pinion nut. The remaining load is carried as preload in the bearings and is set with the pinion nut to give the desired assembly torque-to-turn. This can only be performed during first assembly when new bearings are coated with friction modifier.
An oil seal is pressed into the LH casing and seals the input flange to the differential unit. The pinion shaft has a hypoid 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 10 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 planet 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 halfshaft. A groove is machined in the bore to locate the snap ring fitted to the drive halfshaft, providing positive drive halfshaft location.
The operating principles of the front and rear differential are the same. For additional information, refer to Rear Drive Axle and Differential