Differential Assembly: Description and Operation

DESCRIPTION

Cross-section Of The Limited Slip Rear Axle:

The standard transmission unit is a Salisbury 4HU final drive. incorporating a 'Powr-Lok' differential when specified; this is identified by the letters 'PL' on a tab under a cover bolt. A Powr-Lok differential differs from a conventional bevel gear unit by the addition of plate clutches loaded by input torque to oppose rotations of the output shafts relative to the differential cage. Clutch plates are splined to the cage. and their mating discs to the output bevels, the loading between plates and disc increases with input torque due partly to the separating forces of bevels and also to the bevel pinion cross-shafts being carried on ramps instead of being positively located in the cage. Increase in output torque causes the cross-shafts to move 'up' the ramps and, by pressing plates and discs together, to 'lock' the differential; this gives the effect of a differential-less axle at maximum torque without increasing the disadvantages of this type of axle in low-torque conditions. Some low-torque stiffness, to reduce one-wheel spin on ice, is provided by forming the outer plates as Belleville washers to produce compression between plates and discs; if one wheel is held and the propeller shaft is disconnected, a torque of between 5.6 and 9.6 kgf/m (40 to 70 lbf/ft) is required to turn the other wheel.

The final drive unit it rigidly attached to a fabricated sheet steel cross-beam which is flexibly mounted to the body structure by four rubber and metal sandwich mountings. Noises coming from the vicinity of the final drive unit usually originate from incorrect meshing of drive gear and pinion, or from bearings on differential or pinion shafts developing play. Operation procedures for the correction of these noise sources are fully covered in disassembly/assembly of final drive unit, but a noise occurring at low speeds only, under braking, could be caused by loss of pre-load in the output shaft bearings. Bearing inspection involves the removal and renewal of an oil seal before resetting pre-load, and is covered in Differential Output Shaft Seal, while if inspection indicates that bearing renewal is advisable this it detailed in Differential Output Shaft Bearing.